helium

ヘリウム

関

He

　 　

WordNet

1. a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas) (同)He, atomic number 2

PrepTutorEJDIC

1. ヘリウム(希ガス類元素;化学記号は『He』)
2. heliumの化学記号

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/09/05 04:07:40」(JST)

wiki ja

[Wiki ja表示]

水素 ← ヘリウム → リチウム - ↑ He ↓ Ne 2He 周期表
外見
無色の気体 高電圧をかけると紫色に発光する ヘリウムのスペクトル
一般特性
名称, 記号, 番号	ヘリウム, He, 2
分類	希ガス
族, 周期, ブロック	18, 1, s
原子量	4.002602(2)
電子配置	1s2
電子殻	2（画像）
物理特性
相	気体
密度	(0 °C, 101.325 kPa) 0.1786 g/L
融点での液体密度	0.145 g/cm3
融点	(at 2.5 MPa) 0.95 K, −272.20 °C, −457.96 °F
沸点	4.22 K, −268.93 °C, −452.07 °F
臨界点	5.19 K, 0.227 MPa
融解熱	0.0138 kJ/mol
蒸発熱	0.0829 kJ/mol
熱容量	(25 °C) 20.786 J/(mol·K)
蒸気圧(defined by ITS-90)
圧力 (Pa) 1 10 100 1 k 10 k 100 k 温度 (K) 1.23 1.67 2.48 4.21
原子特性
イオン化エネルギー	第1： 2372.3 kJ/mol
	第2： 5250.5 kJ/mol
共有結合半径	28 pm
ファンデルワールス半径	140 pm
その他
結晶構造	六方晶系
磁性	反磁性
熱伝導率	(300 K) 0.1513 W/(m·K)
音の伝わる速さ	972 m/s
CAS登録番号	7440-59-7
最安定同位体
詳細はヘリウムの同位体を参照
同位体 NA 半減期 DM DE (MeV) DP 3He 0.000137%* 中性子1個で安定 4He 99.999863%* 中性子2個で安定 *Atmospheric value, abundance may differ elsewhere.

ヘリウム （新ラテン語: helium）は、原子番号 2、原子量 4.00260、元素記号 He の元素である。

無色、無臭、無味、無毒で最も軽い希ガス元素である。すべての元素の中で最も沸点が低く、加圧下でしか固体にならない。ヘリウムは不活性の単原子ガスとして存在する。また、存在量は水素に次いで宇宙で2番目に多い。ヘリウムは地球の大気の0.0005%を占め、鉱物やミネラルウォーターの中にも溶け込んでいる。天然ガスと共に豊富に産出し、気球や小型飛行船の浮揚用ガスとして用いられたり、液体ヘリウムを超伝導用の低温素材としたり、大深度へ潜る際の呼吸ガスとして用いられている。 名称確定の希ガス元素としては唯一末尾が「-ium」である。（他の希ガス元素は末尾が「-on」）

特徴

標準状態において、ヘリウムは単原子ガスとして存在する。ヘリウムを固化するには非常に特殊な条件下に置かなければならない。元素の中で沸点が最も低く、標準圧力下では温度を下げて絶対零度になっても不確定性原理のため液体のままであり、固化するにはさらに高い圧力をかける必要がある。液体とガスの臨界温度の差は 5.19 K しかない。固体ヘリウムはヘリウム3とヘリウム4で必要な圧力が異なり、圧力を調節して体積の30%をコントロールすることができる。ヘリウムは比熱容量が非常に高く、密度の高い蒸気となり、部屋の温度が上昇すると素早く膨張する。

固体ヘリウムは 1.5 K、2.5-3.5 MPa という非常に低い温度と高い圧力の下でしか存在できない。だいたいこのくらいの温度以上になると、相転移を起こしてしまう。これ以下の温度ではそれぞれ立方体型の分子を作っている。

ヘリウム4の2つの液体状態、ヘリウムIとヘリウムIIは、量子力学の研究（超流動現象）において重要で、物質が超伝導を帯びるような絶対零度に近い超低温で発現する。

用途

以下に挙げるような様々な用途に使用されている。

• ヘリウムガス
  • ヘリウムは水素の92.64%もの浮揚力があり、燃えないため、水素よりも安全なガスとして風船等の浮揚用ガスとして利用され、広告用バルーンや天体観測用気球、軍事用偵察気球などに使用されている。また、ヘリウム中では音速が空気中よりずっと速い（純粋ヘリウム中では約1000m/s）ため、ヘリウムを吸入してから発声すると、甲高い音色の奇妙な声が出る（ドナルドダック効果）。これに着目して、いわゆるパーティグッズとしても利用される。このような市販の「変声」用ガスには、酸欠等になるのを防ぐために酸素が20%ほど含まれているが、風船用ガスとの誤用による事故や吸い過ぎによって嘔吐や意識を失う事故が度々発生しており、その大半は12歳以下の子供によるものである。ヘリウムに薬理作用はないが、酸素を混合していないガスの吸引による自殺に使用された例も報告されている。
• 低温工学
  • ヘリウムは沸点、融点ともに最も低い元素であり、液体ヘリウムは他の超低温物質よりも低温となり、超伝導や低温学など、絶対零度に近い環境での研究が必要な分野で冷媒として使用されている。また、ヘリウム3とヘリウム4を使った希釈冷凍法がある。
• 労働産業
  • ヘリウムと酸素等との混合ガスはテクニカルダイビングなど、大深度潜水用の呼吸ガスとして用いられる。ヘリウムは窒素よりも麻酔作用が少ないため、窒素中毒などの中毒症状を起こしにくい。さらにヘリウムは粘度が低いため、高圧下でも呼吸抵抗が小さく、身体からの排泄速度が速いとされている。しかし、特定の条件下では気泡が生じやすく一旦血管内に気泡が生じた場合は消失しにくいとの報告がある。欠点として熱伝導率が高いため、体温調節が難しくなり低体温症になる危険があること、また空気と比較してはるかに高価であることがある。ヘリウムと酸素の混合ガスであるヘリオックスと、ヘリウム、酸素、窒素を混合したトライミックスがある。
• 医療
  • また液体に溶けやすく人体に無害と言う特性もあり、血管内で素早く膨らませたり縮めたりすることで心臓の機能を補助するIABPのバルーンに吹き込む気体として採用されている。
  • 液体ヘリウムはNMRやMRIの測定装置で超伝導電磁石の冷却に使われている。
• その他
  • 能美防災の民生用蓄圧式消火器には、窒素の代わりに圧力源として使われている。
  • ガスクロマトグラフィーなどのキャリヤーガスとしても使用される。
  • 液体ヘリウムはロケットの噴射口を守る冷却剤、シリコンやゲルマニウム結晶の保護材、あるいは原子炉の冷却材、超音速風洞実験での充満ガス、タンデム加速器の超伝導ブースターなどに用いられている。
  • 同位体であるヘリウム3は核融合発電の燃料としての利用が考えられている。しかし、現在熱核融合炉で想定されている温度の領域では、トリチウム燃料の場合に比べて核融合反応が起こりにくい上、地球上で天然に採取する事はほとんど不可能である。太陽から噴出した太陽風が月面に堆積した物を採取する、木星などの木星型惑星で採取する等の方法が検討されている。
  • ヘリウムは分子が小さく、きわめて微小な孔にも浸入可能であるため（ヘリウムを詰めた風船が時間が経つと小さくしぼみ、浮力が落ちるのはこのためである）、配管のリーク（漏れ）を高精度で非破壊検査するのに用いられることがある（配管に気体のヘリウムを流してヘリウムリークディテクタで漏れを検知する）。前述の特徴のほか、化学的に安定で人畜に無害、また大気中にほとんど存在しないため誤検出の心配がないなど、この用途には理想的な物質であるとされている。しかしわずかな隙間にも侵入するため、潜水艦や減圧室などヘリウムの混合ガスを使用する状態において、防水として設計された時計などの隙間にも侵入し、圧力変化によって腕時計のガラスを吹き飛ばしてしまうことがある。このため、一部のダイバーズ・ウォッチにはヘリウム・エスケープ・バルブが付いており、この機構で内部のヘリウムを自動的に外へ逃がすことができる。水素に次いで軽い気体であるため、ポンプなどを使って移動させる時に少ないエネルギーで素早く移動させる事ができる。

歴史

発見

ヘリウム原子の存在を示す最初の証拠は、1868年8月18日に太陽の彩層部分の光を発光分光分析(en)した際に見つかった、波長587.49ナノメートルの黄色い輝線だった。これを発見したのは、インドのグントゥールで皆既日食を観察していたフランス人天文学者のピエール・ジャンサンだった。彼は当初、この線はナトリウムを示すと考えたが、同年10月20日にイギリス人天文学者ノーマン・ロッキャーがやはり太陽光を分析して黄線を観測し、ナトリウムのフラウンホーファー線記号D₁やD₂に近かったことから、D₃と名づけた。ロッキャーは、この元素が太陽を構成する地球では知られていない元素だと結論づけ、彼とイギリスの化学者エドワード・フランクランドは、ギリシア語で太陽（ἥλιος）を意味する「ヘリウム」と名づけた。

ヘリウムのスペクトル

1882年、イタリアの物理学者ルイージ・パルミエーリ(en)は、ヴェスヴィオ山の溶岩を分析していた際に、スペクトルD₃線を見つけた。これが地球上で初めてヘリウムの存在を示唆する証拠となった。

1895年3月26日、イギリスの化学者ウィリアム・ラムゼー卿がクレーベ石(en)（10%以上の希土類元素を含む閃ウラン鉱）と無機酸を反応させる実験を通じてヘリウムの分離に成功し、地球上で初めて生成した。ラムゼーはアルゴンを探していたが、硫酸で発生させたガスから窒素や酸素を取り除いた残りをスペクトル分光して調べたところ、太陽光と同じD₃線を発見した。そしてこれが、ロッキャーやウィリアム・クルックスが名づけた「ヘリウム」であると同定した。実はアメリカの地球科学者ウィリアム・フランシス・ヒレブランド(en)がラムゼーに先立ち閃ウラン鉱標本の試験を行っている際に変わったスペクトルを見つけていたが、彼はこれを窒素のスペクトルと思い込んでいた。ヒレブランドはラムゼーに祝辞の手紙を送っている。

原子量を計測できる程度の量は、スウェーデンウプサラ市でペール・テオドール・クレーベとアブラハム・ラングレ(en)が抽出に成功した。

1907年（1903年?）にアーネスト・ラザフォードとトーマス・ロイズは、新しく見つかったガスをガラス管に詰めてスペクトルを調べようとした際に、粒子が薄いガラス壁を通り抜けることを見つけ、アルファ粒子がヘリウムの原子核であることを突き止めた。1908年にはオランダのヘイケ・カメルリング・オネスがガスを1K以下まで冷却し、液化に初めて成功した。彼はさらに温度を下げて固体を得ようとしたが、常圧のヘリウムは三重点を持たないため、これには失敗した。しかし、1926年に、オネスの教えを受けたウィレム・ヘンドリック・ケーソンが1cm³のヘリウム固体化に初めて成功した。

1938年、ロシアのピョートル・カピッツァは絶対零度近くまで冷却したヘリウム4がほとんど粘性を持っていないことを発見し、これは超流動と呼ばれた。1972年には、アメリカのダグラス・D・オシェロフ、デビッド・リー、ロバート・リチャードソンによって、絶対零度に近い温度域でヘリウム3でも同じ現象が発見された。

産出と利用

1903年、アメリカ・カンザス州デクスター(en)で石油掘削のボーリングが行われたところ、不燃性のガスが湧き出た。カンザス在住の地質学者エラスムス・ハワース(en)がこれを収集し、ローレンス市のカンザス大学で化学者ハミルトン・キャディ(en)とデイヴィッド・マクファーランドの協力を得て成分解析を行った。その結果、ガスは質量比で窒素72%、メタン15%（酸素がなかったため燃焼しなかった）、水素1%と、残り12%の成分は解明できなかった。さらに解析を進めた結果キャディとマクファーランドは、1.84%はヘリウムであることを突き止めた。これによって、地球全体では希少であるヘリウムがアメリカのグレートプレーンズ地下に大量に存在しており、天然ガスの副産物として入手可能だということが判明した。アメリカの主なヘリウム含有ガス田は、ほとんどがカンザス州、オクラホマ州、テキサス州西部の地域にある。

この発見によって、アメリカ合衆国は一大ヘリウム供給国となった。第一次世界大戦時、リチャード・スレルホール卿(en)の助言を受けて、アメリカ海軍は3基の実験的な小規模ヘリウム製造設備に投資をした。これは、空気よりも軽く不燃性のガスを阻塞気球に使う目的があった。これ以前、ヘリウムガスは通算で1m³も得られていなかったのだが、この計画で生産されたガスは純度92%で5,700m³にのぼり、1921年12月1日に処女航行を行った世界初のヘリウム飛行船C-7（アメリカ海軍）にも使われた。

第一次世界大戦中、抽出方法は低温によるガスの液化法からそれほど改良されなかったが、生産は続けられた。当初は飛行船などの揚力ガス(en)需要が中心だったが、第二次世界大戦中にはそれに加えアーク溶接用の需要が拡大した。ヘリウム質量分析計(en)も原子爆弾を製造するマンハッタン計画で用いられた。

ヘリウムモニュメント。1968年、ヘリウム発見100周年を記念してテキサス州アマリロに造られた。

1925年、テキサス州アマリロでアメリカ合衆国連邦政府は「ヘリウム国家備蓄」を開始した。これは、民間の商用や戦時の軍用目的の飛行船へ供給体制を備えることを目的とした「連邦によるヘリウムの国家戦略的備蓄」である。アメリカ軍はドイツへのヘリウム輸出を制限したが、これが水素を用いざるをえなくなったヒンデンブルク号の爆発事故の遠因となった。大戦後にヘリウム需要は縮小したが、1950年代に入ると、宇宙開発競争や冷戦を背景としたロケットエンジンの推進剤用などへ酸素や水素の冷却用として、ヘリウムの用途は広がった。1965年、アメリカのヘリウム消費量は戦時中の最大量の8倍にもなった。「ヘリウム条例1960修正条項」（Public Law 86–777）発布後、アメリカ合衆国鉱山局（USBM）は、カンザス州ブシュトン市(en)にある複数の民間所有ガス精製工場から天然ガス中のヘリウム回収を始め、これを延長684kmのパイプラインでテキサス州アマリロ近郊のクリフサイドにある国家備蓄基地へ集約した。これらのヘリウム-窒素混合ガスはクリフサイド周辺のガス田に再注入され、純度向上と貯蔵を両立させた。

1995年段階で、アメリカのヘリウム備蓄量は10億m³（14億ドル相当）に達し、翌年に議会は貯蔵増の停止と、「ヘリウム民営化条例1996」(Public Law 104–273)を採決して、2005年までに備蓄ヘリウムをすべて販売することを内務省に命じた。ただし、備蓄分の売り切りは2015年と予想される。

1930年から1945年にかけて生産され、飛行船に使われたヘリウムの純度は98.3%であった。1945年には純度99.9%ヘリウムが溶接用に少々製造された。1949年までにヘリウムはグレードA（99.95%）まで商用生産が実現した。

工業用ヘリウムの需要は急増している。

長い間、アメリカは全世界の商用ヘリウム生産量90%以上を担って来た。その他にはカナダ、ポーランド、ロシア等でも生産された。1990年代中頃、アルジェリアのアルゼウ(en)にて、全ヨーロッパの需要量を賄う1,700万m³の新工場が稼動を開始した。2000年までにアメリカのヘリウム総需要は年間1500万kgまで増加したが、2004年から2006年にかけてカタールのラス・ラファンとアルジェリアのスキクダ(en)でそれぞれ新工場の建設が行われた。2007年段階で、ラス・ラファンは稼動率50%、スキクダは未稼働の状態にある。しかし、アルジェリアはスキクダでの生産が始まれば、世界2位の供給国となる。その一方で、世界的なヘリウム需要は価格とともに上昇し、2007年の消費量は2002年比倍増となった。需給バランスの変動により、将来は深刻なヘリウム不足と価格高騰が予測される。

2012年には、世界的なヘリウム供給不足が発生した。原因は、アメリカでの設備トラブル、新興国での需要増などが考えられている。このため、東京ディズニーリゾートでは2012年11月21日からパーク内でのヘリウム風船の販売を休止した。

2013年12月、カタールのRasGasが世界最大級の年産3,680万立方メートルの生産設備を稼動させた。

日本は全量を輸入に頼っているが、財務省の貿易統計では近年の日本の輸入量は年間2,000トン前後。2012年、2013年にはアメリカの生産減で品不足となったが、これを補うためにカタールほかからの輸入が増えている。2013年は全輸入量1,902トン中、米国からが1,747トン（シェア91.8%）、カタールからが121トン（6.4%）、その他からが34トン（2.8%）であったが、2014年に入りカタールのシェアが急増している。

同位体

詳細は「ヘリウムの同位体」を参照

ヘリウム原子の原子核は 2つの陽子と2つの中性子からなり、周りを2つの電子が回って構成される（ヘリウム4）。同位体にヘリウム3（陽子 2、中性子 1、電子 2）がある。

ヘリウム3は、天然には非常に僅かしか存在しないので、原子炉で生成したものが利用される。原子炉内で、リチウム6に中性子を当てると、三重水素とヘリウム4ができ、この三重水素がベータ崩壊して（半減期12.5年）、ヘリウム3となる。

そのほか、人工的に作られた同位体としては、ヘリウム6、ヘリウム8、ヘリウム10などがある。

ヘリウムの同位体を用いた地球化学的な応用は大きく分けて2つある。まず、ヘリウム3をトレーサーとした地球物質の循環を探ることができる。もうひとつは岩石中に天然に存在する放射性同位体であるウランやトリウムの放射壊変（アルファ崩壊）に伴って放出されるヘリウム4の蓄積量から、その岩石の生成年代を求めることができる（U, Th/He 放射年代測定）。

脚注

注釈

出典

関連項目

• 超流動
• 反ヘリウム
• ヘリウムフラッシュ
• 液体ヘリウム
• 水素爆弾
• 核融合

外部リンク

• 国際化学物質安全性カード ヘリウム - 国立医薬品食品衛生研究所

wiki en

[Wiki en表示]

This article is about the chemical element. For other uses, see Helium (disambiguation).

Helium,  ₂He

Spectral lines of helium
General properties
Name, symbol	helium, He
Appearance	colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
Pronunciation	/ˈhiːliəm/ HEE-lee-əm
Helium in the periodic table
– ↑ He ↓ Ne hydrogen ← helium → lithium
Atomic number	2
Standard atomic weight (±) (Ar)	4.002602(2)
Element category	noble gas
Group, block	group 18 (noble gases), s-block
Period	period 1
Electron configuration	1s2
per shell	2
Physical properties
Phase	gas
Melting point	0.95 K ​(−272.20 °C, ​−457.96 °F) (at 2.5 MPa)
Boiling point	4.222 K ​(−268.928 °C, ​−452.070 °F)
Density at stp (0 °C and 101.325 kPa)	0.1786 g/L
when liquid, at m.p.	0.145 g/cm3
when liquid, at b.p.	0.125 g/cm3
Triple point	2.177 K, ​5.043 kPa
Critical point	5.1953 K, 0.22746 MPa
Heat of fusion	0.0138 kJ/mol
Heat of vaporization	0.0829 kJ/mol
Molar heat capacity	20.78 J/(mol·K)
vapor pressure (defined by ITS-90) P (Pa) 1 10 100 1 k 10 k 100 k at T (K)     1.23 1.67 2.48 4.21
Atomic properties
Oxidation states	0
Electronegativity	Pauling scale: no data
Ionization energies	1st: 2372.3 kJ/mol 2nd: 5250.5 kJ/mol
Covalent radius	28 pm
Van der Waals radius	140 pm
Miscellanea
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound	972 m/s
Thermal conductivity	0.1513 W/(m·K)
Magnetic ordering	diamagnetic
CAS Registry Number	7440-59-7
History
Naming	after Helios, Greek god of the Sun
Discovery	Pierre Janssen, Norman Lockyer (1868)
First isolation	William Ramsay, Per Teodor Cleve, Abraham Langlet (1895)
Most stable isotopes
iso NA half-life DM DE (MeV) DP 3He 0.000137%* 3He is stable with 1 neutron 4He 99.999863%* 4He is stable with 2 neutrons
* Atmospheric value, abundance may differ elsewhere

Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.

Helium is the second lightest element and is the second most abundant element in the observable universe, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this figure in the Sun and in Jupiter. This is due to the very high nuclear binding energy (per nucleon) of helium-4 with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and is believed to have been formed during the Big Bang. Large amounts of new helium are being created by nuclear fusion of hydrogen in stars.

Helium is named for the Greek god of the Sun, Helios. It was first detected as an unknown yellow spectral line signature in sunlight during a solar eclipse in 1868 by French astronomer Jules Janssen. Janssen is jointly credited with detecting the element along with Norman Lockyer. Jannsen observed during the solar eclipse of 1868 while Lockyer observed from Britain. Lockyer was the first to propose that the line was due to a new element, which he named. The formal discovery of the element was made in 1895 by two Swedish chemists, Per Teodor Cleve and Nils Abraham Langlet, who found helium emanating from the uranium ore cleveite. In 1903, large reserves of helium were found in natural gas fields in parts of the United States, which is by far the largest supplier of the gas today.

Liquid helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners. Helium's other industrial uses—as a pressurizing and purge gas, as a protective atmosphere for arc welding and in processes such as growing crystals to make silicon wafers—account for half of the gas produced. A well-known but minor use is as a lifting gas in balloons and airships. As with any gas whose density differs from that of air, inhaling a small volume of helium temporarily changes the timbre and quality of the human voice. In scientific research, the behavior of the two fluid phases of helium-4 (helium I and helium II) is important to researchers studying quantum mechanics (in particular the property of superfluidity) and to those looking at the phenomena, such as superconductivity, produced in matter near absolute zero.

On Earth it is relatively rare — 5.2 ppm by volume in the atmosphere. Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations up to 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Helium is a finite resource, and once released into the atmosphere, it readily escapes into space.

History

Scientific discoveries

The first evidence of helium was observed on August 18, 1868 as a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India. This line was initially assumed to be sodium. On October 20 of the same year, English astronomer Norman Lockyer observed a yellow line in the solar spectrum, which he named the D₃ Fraunhofer line because it was near the known D₁ and D₂ lines of sodium. He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist Edward Frankland named the element with the Greek word for the Sun, ἥλιος (helios).

Spectral lines of helium

In 1882, Italian physicist Luigi Palmieri detected helium on Earth, for the first time, through its D₃ spectral line, when he analyzed the lava of Mount Vesuvius.

Sir William Ramsay, the discoverer of terrestrial helium

On March 26, 1895, Scottish chemist Sir William Ramsay isolated helium on Earth by treating the mineral cleveite (a variety of uraninite with at least 10% rare earth elements) with mineral acids. Ramsay was looking for argon but, after separating nitrogen and oxygen from the gas liberated by sulfuric acid, he noticed a bright yellow line that matched the D₃ line observed in the spectrum of the Sun. These samples were identified as helium by Lockyer and British physicist William Crookes. It was independently isolated from cleveite in the same year by chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, who collected enough of the gas to accurately determine its atomic weight. Helium was also isolated by the American geochemist William Francis Hillebrand prior to Ramsay's discovery when he noticed unusual spectral lines while testing a sample of the mineral uraninite. Hillebrand, however, attributed the lines to nitrogen. His letter of congratulations to Ramsay offers an interesting case of discovery and near-discovery in science.

In 1907, Ernest Rutherford and Thomas Royds demonstrated that alpha particles are helium nuclei by allowing the particles to penetrate the thin glass wall of an evacuated tube, then creating a discharge in the tube to study the spectra of the new gas inside. In 1908, helium was first liquefied by Dutch physicist Heike Kamerlingh Onnes by cooling the gas to less than one kelvin. He tried to solidify it by further reducing the temperature but failed because helium does not solidify at atmospheric pressure. Onnes' student Willem Hendrik Keesom was eventually able to solidify 1 cm³ of helium in 1926 by applying additional external pressure.

In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that helium-4 has almost no viscosity at temperatures near absolute zero, a phenomenon now called superfluidity. This phenomenon is related to Bose–Einstein condensation. In 1972, the same phenomenon was observed in helium-3, but at temperatures much closer to absolute zero, by American physicists Douglas D. Osheroff, David M. Lee, and Robert C. Richardson. The phenomenon in helium-3 is thought to be related to pairing of helium-3 fermions to make bosons, in analogy to Cooper pairs of electrons producing superconductivity.

Extraction and use

After an oil drilling operation in 1903 in Dexter, Kansas produced a gas geyser that would not burn, Kansas state geologist Erasmus Haworth collected samples of the escaping gas and took them back to the University of Kansas at Lawrence where, with the help of chemists Hamilton Cady and David McFarland, he discovered that the gas consisted of, by volume, 72% nitrogen, 15% methane (a combustible percentage only with sufficient oxygen), 1% hydrogen, and 12% an unidentifiable gas. With further analysis, Cady and McFarland discovered that 1.84% of the gas sample was helium. This showed that despite its overall rarity on Earth, helium was concentrated in large quantities under the American Great Plains, available for extraction as a byproduct of natural gas.

This enabled the United States to become the world's leading supplier of helium. Following a suggestion by Sir Richard Threlfall, the United States Navy sponsored three small experimental helium plants during World War I. The goal was to supply barrage balloons with the non-flammable, lighter-than-air gas. A total of 5,700 m³ (200,000 cu ft) of 92% helium was produced in the program even though less than a cubic meter of the gas had previously been obtained. Some of this gas was used in the world's first helium-filled airship, the U.S. Navy's C-7, which flew its maiden voyage from Hampton Roads, Virginia, to Bolling Field in Washington, D.C., on December 1, 1921, nearly two years before the Navy's first rigid airship to be helium-filled, the Naval Aircraft Factory-built USS Shenandoah, itself flew for the first time in September 1923.

Although the extraction process, using low-temperature gas liquefaction, was not developed in time to be significant during World War I, production continued. Helium was primarily used as a lifting gas in lighter-than-air craft. This use increased demand during World War II, as well as demands for shielded arc welding. The helium mass spectrometer was also vital in the atomic bomb Manhattan Project.

The government of the United States set up the National Helium Reserve in 1925 at Amarillo, Texas, with the goal of supplying military airships in time of war and commercial airships in peacetime. Because of the Helium Control Act (1927), which banned the export of scarce helium on which the US then had a production monopoly, together with the prohibitive cost of the gas, the Hindenburg, like all German Zeppelins, was forced to use hydrogen as the lift gas. Helium use following World War II was depressed but the reserve was expanded in the 1950s to ensure a supply of liquid helium as a coolant to create oxygen/hydrogen rocket fuel (among other uses) during the Space Race and Cold War. Helium use in the United States in 1965 was more than eight times the peak wartime consumption.

After the "Helium Acts Amendments of 1960" (Public Law 86–777), the U.S. Bureau of Mines arranged for five private plants to recover helium from natural gas. For this helium conservation program, the Bureau built a 425-mile (684 km) pipeline from Bushton, Kansas, to connect those plants with the government's partially depleted Cliffside gas field, near Amarillo, Texas. This helium-nitrogen mixture was injected and stored in the Cliffside gas field until needed, when it then was further purified.

By 1995, a billion cubic meters of the gas had been collected and the reserve was US$1.4 billion in debt, prompting the Congress of the United States in 1996 to phase out the reserve. The resulting "Helium Privatization Act of 1996" (Public Law 104–273) directed the United States Department of the Interior to empty the reserve, with sales starting by 2005.

Helium produced between 1930 and 1945 was about 98.3% pure (2% nitrogen), which was adequate for airships. In 1945, a small amount of 99.9% helium was produced for welding use. By 1949, commercial quantities of Grade A 99.95% helium were available.

For many years the United States produced over 90% of commercially usable helium in the world, while extraction plants in Canada, Poland, Russia, and other nations produced the remainder. In the mid-1990s, a new plant in Arzew, Algeria, producing 17 million cubic meters (600 million cubic feet) began operation, with enough production to cover all of Europe's demand. Meanwhile, by 2000, the consumption of helium within the U.S. had risen to above 15 million kg per year. In 2004–2006, two additional plants, one in Ras Laffan, Qatar, and the other in Skikda, Algeria, were built. Algeria quickly became the second leading producer of helium. Through this time, both helium consumption and the costs of producing helium increased. From 2002 to 2007 helium prices doubled.

As of 2012 the United States National Helium Reserve accounted for 30 percent of the world's helium. The reserve was expected to run out of helium in 2018. Despite that a proposed bill in the United States Senate would allow the reserve to continue to sell the gas. Other large reserves were in the Hugoton in Kansas, United States and nearby gas fields of Kansas and the panhandles of Texas and Oklahoma. New helium plants were scheduled to open in 2012 in Qatar, Russia and the United States state of Wyoming but they were not expected to ease the shortage.

In 2013, Qatar started up the world's largest helium unit. 2014 was widely acknowledged to be a year of over-supply in the helium business, following years of renowned shortages. Nasdaq reported (2015) that for Air Products, an international corporation that sells gases for industrial use, helium volumes remain under pressure due to feedstock supply constraints.

Characteristics

The helium atom

Main article: Helium atom

The helium atom. Depicted are the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case.

Helium in quantum mechanics

In the perspective of quantum mechanics, helium is the second simplest atom to model, following the hydrogen atom. Helium is composed of two electrons in atomic orbitals surrounding a nucleus containing two protons along with some neutrons. As in Newtonian mechanics, no system consisting of more than two particles can be solved with an exact analytical mathematical approach (see 3-body problem) and helium is no exception. Thus, numerical mathematical methods are required, even to solve the system of one nucleus and two electrons. Such computational chemistry methods have been used to create a quantum mechanical picture of helium electron binding which is accurate to within < 2% of the correct value, in a few computational steps. In such models it is found that each electron in helium partly screens the nucleus from the other, so that the effective nuclear charge Z which each electron sees, is about 1.69 units, not the 2 charges of a classic "bare" helium nucleus.

The related stability of the helium-4 nucleus and electron shell

The nucleus of the helium-4 atom is identical with an alpha particle. High-energy electron-scattering experiments show its charge to decrease exponentially from a maximum at a central point, exactly as does the charge density of helium's own electron cloud. This symmetry reflects similar underlying physics: the pair of neutrons and the pair of protons in helium's nucleus obey the same quantum mechanical rules as do helium's pair of electrons (although the nuclear particles are subject to a different nuclear binding potential), so that all these fermions fully occupy 1s orbitals in pairs, none of them possessing orbital angular momentum, and each cancelling the other's intrinsic spin. Adding another of any of these particles would require angular momentum and would release substantially less energy (in fact, no nucleus with five nucleons is stable). This arrangement is thus energetically extremely stable for all these particles, and this stability accounts for many crucial facts regarding helium in nature.

For example, the stability and low energy of the electron cloud state in helium accounts for the element's chemical inertness, and also the lack of interaction of helium atoms with each other, producing the lowest melting and boiling points of all the elements.

In a similar way, the particular energetic stability of the helium-4 nucleus, produced by similar effects, accounts for the ease of helium-4 production in atomic reactions involving both heavy-particle emission, and fusion. Some stable helium-3 is produced in fusion reactions from hydrogen, but it is a very small fraction, compared with the highly favorable helium-4.

Binding energy per nucleon of common isotopes. The binding energy per particle of helium-4 is significantly larger than all nearby nuclides.

The unusual stability of the helium-4 nucleus is also important cosmologically: it explains the fact that in the first few minutes after the Big Bang, as the "soup" of free protons and neutrons which had initially been created in about 6:1 ratio cooled to the point that nuclear binding was possible, almost all first compound atomic nuclei to form were helium-4 nuclei. So tight was helium-4 binding that helium-4 production consumed nearly all of the free neutrons in a few minutes, before they could beta-decay, and also leaving few to form heavier atoms such as lithium, beryllium, or boron. Helium-4 nuclear binding per nucleon is stronger than in any of these elements (see nucleogenesis and binding energy) and thus no energetic drive was available, once helium had been formed, to make elements 3, 4 and 5. It was barely energetically favorable for helium to fuse into the next element with a lower energy per nucleon, carbon. However, due to lack of intermediate elements, this process requires three helium nuclei striking each other nearly simultaneously (see triple alpha process). There was thus no time for significant carbon to be formed in the few minutes after the Big Bang, before the early expanding universe cooled to the temperature and pressure point where helium fusion to carbon was no longer possible. This left the early universe with a very similar ratio of hydrogen/helium as is observed today (3 parts hydrogen to 1 part helium-4 by mass), with nearly all the neutrons in the universe trapped in helium-4.

All heavier elements (including those necessary for rocky planets like the Earth, and for carbon-based or other life) have thus been created since the Big Bang in stars which were hot enough to fuse helium itself. All elements other than hydrogen and helium today account for only 2% of the mass of atomic matter in the universe. Helium-4, by contrast, makes up about 23% of the universe's ordinary matter—nearly all the ordinary matter that is not hydrogen.

Gas and plasma phases

Helium discharge tube shaped like the element's atomic symbol

Helium is the second least reactive noble gas, after neon, and thus the second least reactive of all elements. It is inert and monatomic in all standard conditions. Because of helium's relatively low molar (atomic) mass, its thermal conductivity, specific heat, and sound speed in the gas phase are all greater than any other gas except hydrogen. For similar reasons, and also due to the small size of helium atoms, helium's diffusion rate through solids is three times that of air and around 65% that of hydrogen.

Helium is the least water-soluble monatomic gas, and one of the least water-soluble of any gas (CF₄, SF₆, and C₄F₈ have lower mole fraction solubilities: 0.3802, 0.4394, and 0.2372 x₂/10⁻⁵, respectively, versus helium's 0.70797 x₂/10⁻⁵), and helium's index of refraction is closer to unity than that of any other gas. Helium has a negative Joule-Thomson coefficient at normal ambient temperatures, meaning it heats up when allowed to freely expand. Only below its Joule-Thomson inversion temperature (of about 32 to 50 K at 1 atmosphere) does it cool upon free expansion. Once precooled below this temperature, helium can be liquefied through expansion cooling.

Most extraterrestrial helium is found in a plasma state, with properties quite different from those of atomic helium. In a plasma, helium's electrons are not bound to its nucleus, resulting in very high electrical conductivity, even when the gas is only partially ionized. The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind together with ionized hydrogen, the particles interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora.

Liquid helium

Liquefied helium. This helium is not only liquid, but has been cooled to the point of superfluidity. The drop of liquid at the bottom of the glass represents helium spontaneously escaping from the container over the side, to empty out of the container. The energy to drive this process is supplied by the potential energy of the falling helium.

Main article: Liquid helium

Unlike any other element, helium will remain liquid down to absolute zero at normal pressures. This is a direct effect of quantum mechanics: specifically, the zero point energy of the system is too high to allow freezing. Solid helium requires a temperature of 1–1.5 K (about −272 °C or −457 °F) and about 25 bar (2.5 MPa) of pressure. It is often hard to distinguish solid from liquid helium since the refractive index of the two phases are nearly the same. The solid has a sharp melting point and has a crystalline structure, but it is highly compressible; applying pressure in a laboratory can decrease its volume by more than 30%. With a bulk modulus of about 27 MPa it is ~100 times more compressible than water. Solid helium has a density of 0.214 ± 0.006 g/cm³ at 1.15 K and 66 atm; the projected density at 0 K and 25 bar (2.5 MPa) is 0.187 ± 0.009 g/cm³.

Helium I state

Below its boiling point of 4.22 kelvins and above the lambda point of 2.1768 kelvins, the isotope helium-4 exists in a normal colorless liquid state, called helium I. Like other cryogenic liquids, helium I boils when it is heated and contracts when its temperature is lowered. Below the lambda point, however, helium does not boil, and it expands as the temperature is lowered further.

Helium I has a gas-like index of refraction of 1.026 which makes its surface so hard to see that floats of styrofoam are often used to show where the surface is. This colorless liquid has a very low viscosity and a density of 0.145–0.125 g/mL (between about 0 and 4 K), which is only one-fourth the value expected from classical physics. Quantum mechanics is needed to explain this property and thus both types of liquid helium are called quantum fluids, meaning they display atomic properties on a macroscopic scale. This may be an effect of its boiling point being so close to absolute zero, preventing random molecular motion (thermal energy) from masking the atomic properties.

Helium II state

Main article: Superfluid helium-4

Liquid helium below its lambda point begins to exhibit very unusual characteristics, in a state called helium II. When helium II boils, due to its high thermal conductivity it does not bubble but rather evaporates directly from its surface. Helium-3 also has a superfluid phase, but only at much lower temperatures; as a result, less is known about such properties in the isotope.

Unlike ordinary liquids, helium II will creep along surfaces in order to reach an equal level; after a short while, the levels in the two containers will equalize. The Rollin film also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape.

Helium II is a superfluid, a quantum mechanical state (see: macroscopic quantum phenomena) of matter with strange properties. For example, when it flows through capillaries as thin as 10⁻⁷ to 10⁻⁸ m it has no measurable viscosity. However, when measurements were done between two moving discs, a viscosity comparable to that of gaseous helium was observed. Current theory explains this using the two-fluid model for helium II. In this model, liquid helium below the lambda point is viewed as containing a proportion of helium atoms in a ground state, which are superfluid and flow with exactly zero viscosity, and a proportion of helium atoms in an excited state, which behave more like an ordinary fluid.

In the fountain effect, a chamber is constructed which is connected to a reservoir of helium II by a sintered disc through which superfluid helium leaks easily but through which non-superfluid helium cannot pass. If the interior of the container is heated, the superfluid helium changes to non-superfluid helium. In order to maintain the equilibrium fraction of superfluid helium, superfluid helium leaks through and increases the pressure, causing liquid to fountain out of the container.

The thermal conductivity of helium II is greater than that of any other known substance, a million times that of helium I and several hundred times that of copper. This is because heat conduction occurs by an exceptional quantum mechanism. Most materials that conduct heat well have a valence band of free electrons which serve to transfer the heat. Helium II has no such valence band but nevertheless conducts heat well. The flow of heat is governed by equations that are similar to the wave equation used to characterize sound propagation in air. When heat is introduced, it moves at 20 meters per second at 1.8 K through helium II as waves in a phenomenon known as second sound.

Helium II also exhibits a creeping effect. When a surface extends past the level of helium II, the helium II moves along the surface, against the force of gravity. Helium II will escape from a vessel that is not sealed by creeping along the sides until it reaches a warmer region where it evaporates. It moves in a 30 nm-thick film regardless of surface material. This film is called a Rollin film and is named after the man who first characterized this trait, Bernard V. Rollin. As a result of this creeping behavior and helium II's ability to leak rapidly through tiny openings, it is very difficult to confine liquid helium. Unless the container is carefully constructed, the helium II will creep along the surfaces and through valves until it reaches somewhere warmer, where it will evaporate. Waves propagating across a Rollin film are governed by the same equation as gravity waves in shallow water, but rather than gravity, the restoring force is the van der Waals force. These waves are known as third sound.

Isotopes

Main article: Isotopes of helium

There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. In the Earth's atmosphere, there is one 3
He atom for every million 4
He atoms. Unlike most elements, helium's isotopic abundance varies greatly by origin, due to the different formation processes. The most common isotope, helium-4, is produced on Earth by alpha decay of heavier radioactive elements; the alpha particles that emerge are fully ionized helium-4 nuclei. Helium-4 is an unusually stable nucleus because its nucleons are arranged into complete shells. It was also formed in enormous quantities during Big Bang nucleosynthesis.

Helium-3 is present on Earth only in trace amounts; most of it since Earth's formation, though some falls to Earth trapped in cosmic dust. Trace amounts are also produced by the beta decay of tritium. Rocks from the Earth's crust have isotope ratios varying by as much as a factor of ten, and these ratios can be used to investigate the origin of rocks and the composition of the Earth's mantle. 3
He is much more abundant in stars, as a product of nuclear fusion. Thus in the interstellar medium, the proportion of 3
He to 4
He is around 100 times higher than on Earth. Extraplanetary material, such as lunar and asteroid regolith, have trace amounts of helium-3 from being bombarded by solar winds. The Moon's surface contains helium-3 at concentrations on the order of 10 ppb, much higher than the approximately 5 ppt found in the Earth's atmosphere. A number of people, starting with Gerald Kulcinski in 1986, have proposed to explore the moon, mine lunar regolith and use the helium-3 for fusion.

Liquid helium-4 can be cooled to about 1 kelvin using evaporative cooling in a 1-K pot. Similar cooling of helium-3, which has a lower boiling point, can achieve about 6999200000000000000♠0.2 kelvin in a helium-3 refrigerator. Equal mixtures of liquid 3
He and 4
He below 6999800000000000000♠0.8 K separate into two immiscible phases due to their dissimilarity (they follow different quantum statistics: helium-4 atoms are bosons while helium-3 atoms are fermions). Dilution refrigerators use this immiscibility to achieve temperatures of a few millikelvins.

It is possible to produce exotic helium isotopes, which rapidly decay into other substances. The shortest-lived heavy helium isotope is helium-5 with a half-life of 6978760000000000000♠7.6×10⁻²² s. Helium-6 decays by emitting a beta particle and has a half-life of 0.8 second. Helium-7 also emits a beta particle as well as a gamma ray. Helium-7 and helium-8 are created in certain nuclear reactions. Helium-6 and helium-8 are known to exhibit a nuclear halo.

Compounds

See also: Noble gas compound

Structure of the helium hydride ion, HHe⁺

Structure of the suspected fluoroheliate anion, OHeF⁻

Helium has a valence of zero and is chemically unreactive under all normal conditions. It is an electrical insulator unless ionized. As with the other noble gases, helium has metastable energy levels that allow it to remain ionized in an electrical discharge with a voltage below its ionization potential. Helium can form unstable compounds, known as excimers, with tungsten, iodine, fluorine, sulfur and phosphorus when it is subjected to a glow discharge, to electron bombardment, or else is a plasma for another reason. The molecular compounds HeNe, HgHe₁₀, and WHe₂, and the molecular ions He+
2, He2+
2, HeH+
, and HeD+
have been created this way. HeH⁺ is also stable in its ground state, but is extremely reactive—it is the strongest Brønsted acid known, and therefore can exist only in isolation, as it will protonate any molecule or counteranion it comes into contact with. This technique has also allowed the production of the neutral molecule He₂, which has a large number of band systems, and HgHe, which is apparently held together only by polarization forces.

Van der Waals compounds of helium can also be formed with cryogenic helium gas and atoms of a substance, such as LiHe and He₂.

Theoretically, other true compounds may also be possible, such as helium fluorohydride (HHeF) which would be analogous to HArF, discovered in 2000. Calculations show that two new compounds containing a helium-oxygen bond could be stable. Two new molecular species, predicted using theory, CsFHeO and N(CH₃)₄FHeO, are derivatives of a metastable [F– HeO] anion first theorized in 2005 by a group from Taiwan. If confirmed by experiment, the only remaining element with no known stable compounds would be neon.

Helium has been put inside the hollow carbon cage molecules (the fullerenes) by heating under high pressure. The endohedral fullerene molecules formed are stable up to high temperatures. When chemical derivatives of these fullerenes are formed, the helium stays inside. If helium-3 is used, it can be readily observed by helium nuclear magnetic resonance spectroscopy. Many fullerenes containing helium-3 have been reported. Although the helium atoms are not attached by covalent or ionic bonds, these substances have distinct properties and a definite composition, like all stoichiometric chemical compounds.

Under extremely high pressures helium can react with many elements. At 130 GPa Na₂He is thermodynamically stable with a fluorite structure.

Occurrence and production

Natural abundance

Although it is rare on Earth, helium is the second most abundant element in the known Universe (after hydrogen), constituting 23% of its baryonic mass. The vast majority of helium was formed by Big Bang nucleosynthesis one to three minutes after the Big Bang. As such, measurements of its abundance contribute to cosmological models. In stars, it is formed by the nuclear fusion of hydrogen in proton-proton chain reactions and the CNO cycle, part of stellar nucleosynthesis.

In the Earth's atmosphere, the concentration of helium by volume is only 5.2 parts per million. The concentration is low and fairly constant despite the continuous production of new helium because most helium in the Earth's atmosphere escapes into space by several processes. In the Earth's heterosphere, a part of the upper atmosphere, helium and other lighter gases are the most abundant elements.

Most helium on Earth is a result of radioactive decay. Helium is found in large amounts in minerals of uranium and thorium, including cleveite, pitchblende, carnotite and monazite, because they emit alpha particles (helium nuclei, He²⁺) to which electrons immediately combine as soon as the particle is stopped by the rock. In this way an estimated 3000 metric tons of helium are generated per year throughout the lithosphere. In the Earth's crust, the concentration of helium is 8 parts per billion. In seawater, the concentration is only 4 parts per trillion. There are also small amounts in mineral springs, volcanic gas, and meteoric iron. Because helium is trapped in the subsurface under conditions that also trap natural gas, the greatest natural concentrations of helium on the planet are found in natural gas, from which most commercial helium is extracted. The concentration varies in a broad range from a few ppm up to over 7% in a small gas field in San Juan County, New Mexico.

As of 2011 the world's helium reserves were estimated at 40 billion cubic meters, with a quarter of that being in the South Pars / North Dome Gas-Condensate field owned jointly by Qatar and Iran.

Modern extraction and distribution

For large-scale use, helium is extracted by fractional distillation from natural gas, which can contain up to 7% helium. Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly nitrogen and methane). The resulting crude helium gas is purified by successive exposures to lowering temperatures, in which almost all of the remaining nitrogen and other gases are precipitated out of the gaseous mixture. Activated charcoal is used as a final purification step, usually resulting in 99.995% pure Grade-A helium. The principal impurity in Grade-A helium is neon. In a final production step, most of the helium that is produced is liquefied via a cryogenic process. This is necessary for applications requiring liquid helium and also allows helium suppliers to reduce the cost of long distance transportation, as the largest liquid helium containers have more than five times the capacity of the largest gaseous helium tube trailers.

In 2008, approximately 169 million standard cubic meters (SCM) of helium were extracted from natural gas or withdrawn from helium reserves with approximately 78% from the United States, 10% from Algeria, and most of the remainder from Russia, Poland and Qatar. In the United States, most helium is extracted from natural gas of the Hugoton and nearby gas fields in Kansas, Oklahoma, and the Panhandle Field in Texas. Much of this gas was once sent by pipeline to the National Helium Reserve, but since 2005 this reserve is being depleted and sold off.

Diffusion of crude natural gas through special semipermeable membranes and other barriers is another method to recover and purify helium. In 1996, the U.S. had proven helium reserves, in such gas well complexes, of about 147 billion standard cubic feet (4.2 billion SCM). At rates of use at that time (72 million SCM per year in the U.S.; see pie chart below) this is enough helium for about 58 years of U.S. use, and less than this (perhaps 80% of the time) at world use rates, although factors in saving and processing impact effective reserve numbers.

Helium must be extracted from natural gas because it is present in air at only a fraction of that of neon, yet the demand for it is far higher. It is estimated that if all neon production were retooled to save helium, that 0.1% of the world's helium demands would be satisfied. Similarly, only 1% of the world's helium demands could be satisfied by re-tooling all air distillation plants. Helium can be synthesized by bombardment of lithium or boron with high-velocity protons, but this process is a completely uneconomic method of production.

Helium is commercially available in either liquid or gaseous form. As a liquid, it can be supplied in small insulated containers called dewars which hold up to 1,000 liters of helium, or in large ISO containers which have nominal capacities as large as 42 m³ (around 11,000 U.S. gallons). In gaseous form, small quantities of helium are supplied in high-pressure cylinders holding up to 8 m³ (approx. 282 standard cubic feet), while large quantities of high-pressure gas are supplied in tube trailers which have capacities of up to 4,860 m³ (approx. 172,000 standard cubic feet).

Conservation advocates

According to helium conservationists like Nobel laureate physicist Robert Coleman Richardson, the free market price of helium has contributed to "wasteful" usage (e.g. for helium balloons). Prices in the 2000s have been lowered by U.S. Congress' decision to sell off the country's large helium stockpile by 2015. According to Richardson, the current price needs to be multiplied by 20 to eliminate the excessive wasting of helium. In their book, the Future of helium as a natural resource (Routledge, 2012), Nuttall, Clarke & Glowacki (2012) also proposed to create an International Helium Agency (IHA) to build a sustainable market for this precious commodity.

Applications

The largest single use of liquid helium is to cool the superconducting magnets in modern MRI scanners.

Estimated 2013 U.S. fractional helium use by category. Total use is 47 million cubic meters.

  Cryogenics (32%)

  Pressurizing and purging (18%)

  Welding (13%)

  Controlled atmospheres (18%)

  Leak detection (4%)

  Breathing mixtures (2%)

  Other (13%)

While balloons are perhaps the best known use of helium, they are a minor part of all helium use. Helium is used for many purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness. Of the 2008 world helium total production of about 32 million kg (193 million standard cubic meters) helium per year, the largest use (about 22% of the total in 2008) is in cryogenic applications, most of which involves cooling the superconducting magnets in medical MRI scanners. Other major uses (totalling to about 60% of use in 1996) were pressurizing and purging systems, maintenance of controlled atmospheres, welding, and leak detection. Other uses by category were relatively minor fractions.

Controlled atmospheres

Helium is used as a protective gas in growing silicon and germanium crystals, in titanium and zirconium production, and in gas chromatography, because it is inert. Because of its inertness, thermally and calorically perfect nature, high speed of sound, and high value of the heat capacity ratio, it is also useful in supersonic wind tunnels and impulse facilities.

Gas tungsten arc welding

Main article: gas tungsten arc welding

Helium is used as a shielding gas in arc welding processes on materials that at welding temperatures are contaminated and weakened by air or nitrogen. A number of inert shielding gases are used in gas tungsten arc welding, but helium is used instead of cheaper argon especially for welding materials that have higher heat conductivity, like aluminium or copper.

Minor uses

Industrial leak detection

A dual chamber helium leak detection machine

One industrial application for helium is leak detection. Because helium diffuses through solids three times faster than air, it is used as a tracer gas to detect leaks in high-vacuum equipment (such as cryogenic tanks) and high-pressure containers. The tested object is placed in a chamber, which is then evacuated and filled with helium. The helium that escapes through the leaks is detected by a sensitive device (helium mass spectrometer), even at the leak rates as small as 10⁻⁹ mbar·L/s (10⁻¹⁰ Pa·m³/s). The measurement procedure is normally automatic and is called helium integral test. A simpler procedure is to fill the tested object with helium and to manually search for leaks with a hand-held device.

Helium leaks through cracks should not be confused with gas permeation through a bulk material. While helium has documented permeation constants (thus a calculable permeation rate) through glasses, ceramics, and synthetic materials, inert gases such as helium will not permeate most bulk metals.

Flight

Because of its low density and incombustibility, helium is the gas of choice to fill airships such as the Goodyear blimp.

Because it is lighter than air, airships and balloons are inflated with helium for lift. While hydrogen gas is also buoyant, helium has the advantage of being non-flammable (in addition to being fire retardant). Another minor use is in rocketry, where helium is used as an ullage medium to displace fuel and oxidizers in storage tanks and to condense hydrogen and oxygen to make rocket fuel. It is also used to purge fuel and oxidizer from ground support equipment prior to launch and to pre-cool liquid hydrogen in space vehicles. For example, the Saturn V rocket used in the Apollo program needed about 370,000 m³ (13 million cubic feet) of helium to launch.

Minor commercial and recreational uses

Helium as a breathing gas has no narcotic properties, so helium mixtures such as trimix, heliox and heliair are used for deep diving to reduce the effects of narcosis. At depths below 150 metres (490 ft) divers breathing helium–oxygen mixtures begin to experience tremors and a decrease in psychomotor function, symptoms of high-pressure nervous syndrome. This effect may be countered to some extent by adding an amount of narcotic gas such as hydrogen or nitrogen to a helium–oxygen mixture. At these depths the low density of helium is found to considerably reduce the effort of breathing.

Helium–neon lasers, a type of low-powered gas laser producing a red beam, had various practical applications which included barcode readers and laser pointers, before they were almost universally replaced by cheaper diode lasers.

For its inertness and high thermal conductivity, neutron transparency, and because it does not form radioactive isotopes under reactor conditions, helium is used as a heat-transfer medium in some gas-cooled nuclear reactors.

Helium, mixed with a heavier gas such as xenon, is useful for thermoacoustic refrigeration due to the resulting high heat capacity ratio and low Prandtl number. The inertness of helium has environmental advantages over conventional refrigeration systems which contribute to ozone depletion or global warming.

Helium is also used in some hard disk drives.

Scientific uses

The use of helium reduces the distorting effects of temperature variations in the space between lenses in some telescopes, due to its extremely low index of refraction. This method is especially used in solar telescopes where a vacuum tight telescope tube would be too heavy.

Helium is a commonly used carrier gas for gas chromatography.

The age of rocks and minerals that contain uranium and thorium can be estimated by measuring the level of helium with a process known as helium dating.

Helium at low temperatures is used in cryogenics, and in certain cryogenics applications. As examples of applications, liquid helium is used to cool certain metals to the extremely low temperatures required for superconductivity, such as in superconducting magnets for magnetic resonance imaging. The Large Hadron Collider at CERN uses 96 metric tons of liquid helium to maintain the temperature at 1.9 kelvin.

Inhalation and safety

Effects

Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood.

The speed of sound in helium is nearly three times the speed of sound in air. Because the fundamental frequency of a gas-filled cavity is proportional to the speed of sound in the gas, when helium is inhaled there is a corresponding increase in the resonant frequencies of the vocal tract. The fundamental frequency (sometimes called pitch) does not change, since this is produced by direct vibration of the vocal folds, which is unchanged. However, the higher resonant frequencies cause a change in timbre, resulting in a reedy, duck-like vocal quality. The opposite effect, lowering resonant frequencies, can be obtained by inhaling a dense gas such as sulfur hexafluoride or xenon.

Hazards

Inhaling helium can be dangerous if done to excess, since helium is a simple asphyxiant and so displaces oxygen needed for normal respiration. Fatalities have been recorded, including a youth who suffocated in Vancouver in 2003 and two adults who suffocated in South Florida in 2006. In 1998, an Australian girl (her age is not known) from Victoria fell unconscious and temporarily turned blue after inhaling the entire contents of a party balloon. Breathing pure helium continuously causes death by asphyxiation within minutes. This fact is used in the design of suicide bags.

Inhaling helium directly from pressurized cylinders is extremely dangerous, as the high flow rate can result in barotrauma, fatally rupturing lung tissue.

Death caused by helium is rare. The first media-recorded case was that of a 15-year-old girl from Texas who died in 1998 from helium inhalation at a friend's party; the exact type of helium death is unidentified.

In the United States only two fatalities were reported between 2000 and 2004, including a man who died in North Carolina of barotrauma in 2002. A youth asphyxiated in Vancouver during 2003, and a 27-year-old man in Australia had an embolism after breathing from a cylinder in 2000. Since then two adults asphyxiated in South Florida in 2006, and there were cases in 2009 and 2010, one a Californian youth who was found with a bag over his head, attached to a helium tank, and another teenager in Northern Ireland died of asphyxiation. At Eagle Point, Oregon a teenage girl died in 2012 from barotrauma at a party. A girl from Michigan died from hypoxia later in the year.

On February 4, 2015 it was revealed that during the recording of their main TV show on January 28, a 12-year-old member (name withheld) of Japanese all-girl singing group 3B Junior suffered from air embolism, losing consciousness and falling in a coma as a result of air bubbles blocking the flow of blood to the brain, after inhaling huge quantities of helium as part of a game. The incident was not made public until a week later. The staff of TV Asahi held an emergency press conference to communicate that the member had been taken to the hospital and is showing signs of rehabilitation such as moving eyes and limbs, but her consciousness has not been sufficiently recovered as of yet. Police have launched an investigation due to a neglect of safety measures.

The safety issues for cryogenic helium are similar to those of liquid nitrogen; its extremely low temperatures can result in cold burns, and the liquid-to-gas expansion ratio can cause explosions if no pressure-relief devices are installed. Containers of helium gas at 5 to 10 K should be handled as if they contain liquid helium due to the rapid and significant thermal expansion that occurs when helium gas at less than 10 K is warmed to room temperature.

At high pressures (more than about 20 atm or two MPa), a mixture of helium and oxygen (heliox) can lead to high-pressure nervous syndrome, a sort of reverse-anesthetic effect; adding a small amount of nitrogen to the mixture can alleviate the problem.

Additional images

• 3D schematic of a Helium atom

See also

• Abiogenic petroleum origin
• Helium-3 propulsion
• Leidenfrost effect
• Quantum solid
• Superfluid
• Tracer-gas leak testing method

References

Bibliography

• Bureau of Mines (1967). Minerals yearbook mineral fuels Year 1965 II. U. S. Government Printing Office. 
• Committee on the Impact of Selling the Federal Helium Reserve, Commission on Physical Sciences, Mathematics, and Applications, Commission on Engineering and Technical Systems, National Research Council (2000). The Impact of Selling the Federal Helium Reserve. The National Academies Press. ISBN 0-309-07038-4. Retrieved 2010-04-02. 
• Emsley, John (1998). The Elements (3rd ed.). New York: Oxford University Press. ISBN 978-0-19-855818-7. 
• "Mineral Information for Helium" (PDF). United States Geological Survey (usgs.gov). Retrieved 2007-01-05. 
• Vercheval, J. (2003). "The thermosphere: a part of the heterosphere". Belgian Institute for Space Aeronomy. Archived from the original on 2005-01-01. Retrieved 2008-07-12. 

External links

Listen to this article (info/dl)

This audio file was created from a revision of the "Helium" article dated 2009-07-15, and does not reflect subsequent edits to the article. (Audio help)

More spoken articles

General

• U.S. Government's Bureau of Land Management: Sources, Refinement, and Shortage. With some history of helium.
• U.S. Geological Survey publications on helium beginning 1996: Helium
• Where is all the helium? Aga website
• It's Elemental – Helium
• Chemistry in its element podcast (MP3) from the Royal Society of Chemistry's Chemistry World: Helium
• International Chemical Safety Cards – Helium; includes health and safety information regarding accidental exposures to helium

More detail

• Helium at The Periodic Table of Videos (University of Nottingham)
• Helium at the Helsinki University of Technology; includes pressure-temperature phase diagrams for helium-3 and helium-4
• Lancaster University, Ultra Low Temperature Physics – includes a summary of some low temperature techniques

Miscellaneous

• Physics in Speech with audio samples that demonstrate the unchanged voice pitch
• Article about helium and other noble gases

Helium shortage

• America’s Helium Supply: Options for Producing More Helium from Federal Land: Oversight Hearing before the Subcommittee on Energy and Mineral Resources of the Committee on Natural Resources, U.S. House Of Representatives, One Hundred Thirteenth Congress, First Session, Thursday, July 11, 2013
• Helium Program: Urgent Issues Facing BLM's Storage and Sale of Helium Reserves: Testimony before the Committee on Natural Resources, House of Representatives Government Accountability Office
• Kramer, David (May 22, 2012). "Senate bill would preserve US helium reserve: Measure would give scientists first dibs on helium should a shortage develop. Physics Today web site". 
• [1]

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

• 1. ヘリオックスの生理学および臨床での用途 physiology and clinical use of heliox
• 2. The evaluation, diagnosis, and treatment of the adult patient with acute hypercapnic respiratory failure
• 3. Assessment and management of dyspnea in palliative care
• 4. 慢性閉塞性肺疾患（COPD）患者における肺過膨張 dynamic hyperinflation in patients with copd
• 5. Croup: Pharmacologic and supportive interventions

English Journal

• Hydroxyl radical formation in batch and continuous flow ultrasonic systems.

• Juretic H1, Montalbo-Lomboy M2, van Leeuwen JH3, Cooper WJ4, Grewell D5.
• Ultrasonics sonochemistry.Ultrason Sonochem.2015 Jan;22:600-6. doi: 10.1016/j.ultsonch.2014.07.003. Epub 2014 Jul 9.
• The creation of free radicals by ultrasonic cavitation is the main mechanism that leads to chemical degradation of target pollutants and the process is considered an alternative advanced oxidation technology. The goal of this study was to compare the effects of batch and continuous flow ultrasonic s
• PMID 25088186

• Cold atmospheric plasma treatment selectively targets head and neck squamous cell carcinoma cells.

• Guerrero-Preston R1, Ogawa T1, Uemura M1, Shumulinsky G1, Valle BL1, Pirini F1, Ravi R1, Sidransky D1, Keidar M2, Trink B1.
• International journal of molecular medicine.Int J Mol Med.2014 Oct;34(4):941-6. doi: 10.3892/ijmm.2014.1849. Epub 2014 Jul 11.
• The treatment of locoregional recurrence (LRR) of head and neck squamous cell carcinoma (HNSCC) often requires a combination of surgery, radiation therapy and/or chemotherapy. Survival outcomes are poor and the treatment outcomes are morbid. Cold atmospheric plasma (CAP) is an ionized gas produce
• PMID 25050490

• Effects of Helium Implantation on the Tensile Properties and Microstructure of Ni73P27 Metallic Glass Nanostructures.

• Liontas R1, Gu XW, Fu E, Wang Y, Li N, Mara N, Greer JR.
• Nano letters.Nano Lett.2014 Sep 10;14(9):5176-83. doi: 10.1021/nl502074d. Epub 2014 Aug 6.
• We report fabrication and nanomechanical tension experiments on as-fabricated and helium-implanted ∼130 nm diameter Ni73P27 metallic glass nanocylinders. The nanocylinders were fabricated by a templated electroplating process and implanted with He(+) at energies of 50, 100, 150, and 200 keV to cre
• PMID 25084487

• Lung ventilation volumetry with same-breath acquisition of hyperpolarized gas and proton MRI.

• Horn FC1, Tahir BA, Stewart NJ, Collier GJ, Norquay G, Leung G, Ireland RH, Parra-Robles J, Marshall H, Wild JM.
• NMR in biomedicine.NMR Biomed.2014 Sep 10. doi: 10.1002/nbm.3187. [Epub ahead of print]
• The purpose of this work was to assess the reproducibility of percentage of ventilated lung volume (PV) measured from hyperpolarized (HP) 3 He and 1 H anatomical images acquired in the same breath-hold when compared with PV measured from 3 He and 1 H images from separate breath-holds. Volumetric 3 H
• PMID 25208220

Japanese Journal

• Simultaneous Measurements of Super-Radiance at Multiple Wavelengths from Helium Excited States(1)Experiment

• Nakajima Kyo,Harries James R.,Iwayama Hiroshi [他]
• Journal of the Physical Society of Japan 84(5), 054301-1-7, 2015-05
• NAID 40020461493

• Collective Excitations in a Two-Dimensional Electron System on Liquid Helium-4 under Cyclotron Resonant Condition

• Badrutdinov Alexander O.,Abdurakhimov Leonid V.,Konstantinov Denis
• Journal of the Physical Society of Japan 84(5), 053601-1-4, 2015-05
• NAID 40020461365

• Simultaneous Measurements of Super-Radiance at Multiple Wavelengths from Helium Excited States: I. Experiment

• Nakajima Kyo,Harries James R.,Iwayama Hiroshi,Kuma Susumu,Miyamoto Yuki,Nagasono Mitsuru,Ohae Chiaki,Togashi Tadashi,Yabashi Makina,Shigemasa Eiji,Sasao Noboru
• Journal of the Physical Society of Japan 84(5), 2015-04-07
• NAID 160000000703

• Collective Excitations in a Two-Dimensional Electron System on Liquid Helium-4 under Cyclotron Resonant Condition

• Badrutdinov Alexander O.,Abdurakhimov Leonid V.,Konstantinov Denis
• Journal of the Physical Society of Japan 84(5), 2015-04-02
• NAID 160000000693

Related Links

• Heliumの使い方。AndroidのアプリとアプリのデータをRoot化せ ...

非常に参考になる情報をありがとうございます。 記事にを参考にHeliumでInternal Storageにバックアップし、そのフォルダをPCにコピー。NEXUS7を初期化して、当初の目的をはたし、再びHeliumをインストールして、PCからInternal Storageで ...

• Helium - App Sync and Backup - Google Play の Android アプリ

バックアップ、復元、およびあなたのアプリケーションを同期！ ... Helium is the missing app sync and backup solution for Android. Helium does NOT require root. All Android users can use Helium to backup and sync ...

• Helium

Helium

---

★リンクテーブル★

リンク元	「He」
拡張検索	「sensory epithelium」

「He」

　　[★] ヘリウム helium 　

「sensory epithelium」

　　[★]

感覚上皮

関

neuroepithelium