half-value layer

半価層

WordNet

1. prepare or position for action or operation; "lay a fire"; "lay the foundation for a new health care plan"
2. put in a horizontal position; "lay the books on the table"; "lay the patient carefully onto the bed" (同)put down, repose
3. impose as a duty, burden, or punishment; "lay a responsibility on someone"
4. lay eggs; "This hen doesnt lay"
5. not of or from a profession; "a lay opinion as to the cause of the disease"
6. fix or determine the value of; assign a value to; "value the jewelry and art work in the estate"
7. the amount (of money or goods or services) that is considered to be a fair equivalent for something else; "he tried to estimate the value of the produce at normal prices" (同)economic value
8. (music) the relative duration of a musical note (同)time value, note value
9. relative darkness or lightness of a color; "I establish the colors and principal values by organizing the painting into three values--dark, medium...and light"-Joe Hing Lowe
10. the quality (positive or negative) that renders something desirable or valuable; "the Shakespearean Shylock is of dubious value in the modern world"
11. a numerical quantity measured or assigned or computed; "the value assigned was 16 milliseconds"
12. an ideal accepted by some individual or group; "he has old-fashioned values"
13. partially or to the extent of a half; "he was half hidden by the bushes"
14. one of two divisions into which some games or performances are divided: the two divisions are separated by an interval
15. (of siblings) related through one parent only; "a half brother"; "half sister"
16. consisting of one of two equivalent parts in value or quantity; "a half chicken"; "lasted a half hour"
17. partial; "gave me a half smile"; "he did only a half job"
18. make or form a layer; "layer the different colored sands"
19. single thickness of usually some homogeneous substance; "slices of hard-boiled egg on a bed of spinach" (同)bed
20. a hen that lays eggs
21. thin structure composed of a single thickness of cells
22. a relatively thin sheetlike expanse or region lying over or under another
23. (usually used in combination) having value of a specified kind; "triple-valued"
24. held in great esteem for admirable qualities especially of an intrinsic nature; "a valued friend"; "precious memories" (同)precious

PrepTutorEJDIC

1. 《場所の副詞[句]を伴って》‘を'『置く』,横たえる / ‘を'『きちんと置く』(並べる),〈土台など〉‘を'すえる,〈鉄道など〉‘を'敷設する / …‘を'『用意する』,準備する / (…に)〈身体の一部〉‘を'置く,つける《+『名』+『on』(『to』)+『名』》 / (…に)〈信頼・愛情〉‘を'置く,寄せる,託す;〈強調・重要性など〉‘を'置く《+『名』+『on』+『名』》 / 〈ほこり・波・風など〉‘を'押さえる,〈恐れ亡霊など〉‘を'静める,なだめる / 〈卵〉‘を'産む / 〈かけ〉‘を'する;(…に)〈金〉‘を'かける《+『名』+『on』+『名』》 / (…に)〈税・罰金・義務など〉‘を'課する,〈重荷・責任など〉‘を'負わせる《+『名』+『on』(『upon』)+『名』》 / 〈悪事など〉‘を'(…の)せいにする《+『名』+『against』(『to』)+『名』》 / 《状態を表す副詩[句]を伴って》(特によくない状態に)…‘を'『置く』,する / (…に)〈権利の主張・報告など〉‘を'提出する,申し出る《+『名』+『before』(『to』)+『名』》 / (…で)…‘の'表面をおおう《+『名』+『with』+『名』》;(…に)…‘を'広げる《+『名』+『on』+『名』》 / 卵を産む / 位置,配置,地形,地勢
2. lieの過去形
3. (歌うために書かれた)短い物語詩 / 《詩》(一般に)歌,調べ
4. (僧職にある人に対して)俗人の / (専門家に対して)しろうとの,門外漢の
5. 〈U〉(…の)『価値』,値打ち,有用性,重要性《+of+名》 / 〈U〉〈C〉(…の)『価格』,値段《+of+名》 / 〈U〉〈C〉《米》《修飾語句を伴って》(払った金銭に対する)正当な値打ち / 〈C〉(単語の)意味,意義 / 〈C〉値,数値 / 〈C〉音の長短 / 〈C〉色価,(色の)明暗の度 / 〈C〉《複数形で》(道義・倫理などの)価値基準,価値観 / (ある金額に)…‘を'『評価する』,見積もる《+名+at+名〈金額〉》 / …‘を'『高く評価する』,尊重する,重んじる
6. 〈C〉〈U〉『半分』,2分の1;約半分 / 〈U〉《時刻を表す数詞と共に用いて》『半』,30分 / 〈C〉《おもに英》(2学期制の学校での)前(後)期 / 〈C〉(競技などの)前(後)半;(野球で1イニングの)表(裏) / 〈C〉=halfback / 『半分の』 / 不十分な,中途はんぱな / 『半ば』,半分[だけ] / 半時間だけ,30分だけ / 不完全に / かなり,ほとんど
7. 《複合語を作って》(物を)積む人(物),置く人(物) / 卵を産む鶏・層;(ペンキなどの)一塗り;一皮 / (園芸で)取り木 / …‘を'層にする / 〈植物〉‘を'取り木する
8. 貴重な,高く評価される,大切な

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/06/24 20:35:48」(JST)

wiki en

[Wiki en表示]

A material's half-value layer (HVL), or half-value thickness, is the thickness of the material at which the intensity of radiation entering it is reduced by one half. HVL can also be expressed in terms of air kerma rate (AKR), rather than intensity: the half-value layer is the thickness of specified material that, "attenuates the beam of radiation to an extent such that the AKR is reduced to one-half of its original value. In this definition the contribution of all scattered radiation, other than any [...] present initially in the beam concerned, is deemed to be excluded." Rather than AKR, measurements of air kerma, exposure, or exposure rate can be used to determine half value layer, as long as it is given in the description.

Half-value layer refers to the first half-value layer, where subsequent (i.e. second) half-value layers refer to the amount of specified material that will reduce the air kerma rate by one-half after material has been inserted into the beam that is equal to the sum of all previous half-value layers.

Quarter-value layer is the amount of specified material that reduces the air kerma rate (or exposure rate, exposure, air kerma, etc...) to one fourth of the value obtained without any test filters. The quarter-value layer is equal to the sum of the first and second half-value layers.

The homogeneity factor (HF) describes the polychromatic nature of the beam and is given by:

The HF will always be less than or equal to one (it is only equal to one in the case of a monoenergetic beam). In case of a polychromatic beam, the HF is less than one because of beam hardening.

HVL is related to Mean free path, however the mean free path is the average distance a unit of radiation can travel in the material before being absorbed, whereas HVL is the average amount of material needed to absorb 50% of all radiation (i.e., to reduce the intensity of the incident radiation by half).

In the case of sound waves, HVL is the distance that it takes for the intensity of a sound wave to be reduced to one-half of its original value. The HVL of sound waves is determined by both the medium through which it travels, and the frequency of the beam. A "thin" half-value layer (or a quick drop of -3dB) results from a high frequency sound wave and a medium with a high rate of attenuation, such as bone. HVL is measured in units of length.

See also

• Attenuation coefficient
• Radiation protection

References

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• Energy dependent calibration of XR-QA2 radiochromic film with monochromatic and polychromatic x-ray beams.

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Japanese Journal

• マンモグラフィにおける半価層測定の精度

• 石井 里枝,吉田 彰,石井 美枝 [他],藤元 志保,逸見 典子
• 日本放射線技術學會雜誌 67(12), 1533-1539, 2011-12-20
• … The half-value layer (HVL) is an important index of the image quality or radiation risk in mammography. … We investigated the influence of multiple factors that affect HVL value, such as thickness or purity of the aluminum attenuator, detector material of dosimeter, fluctuation of X-ray output, detector location in X-ray field and so on, for accurate average glandular dose computations. …
• NAID 10030042544

• 診断領域X線の線質表現法として用いられる実効エネルギーの問題点

• 加藤 秀起,林 直樹,鈴木 昇一 [他],安藤 翔,宮本 まみ,若杉 奈央,鈴木 志津馬
• 日本放射線技術學會雜誌 67(10), 1320-1326, 2011-10-20
• … The effective energy has been generally used as a method of handily expressing an X-ray quality by one numerical value. … The effective energy is a concept derived from "Half Value Layer (HVL)" that is the expressing parameter of beam quality based on the attenuation of the primary X-ray by a material. … However, recently feelings are that the effective energy should be handled like an absolute numerical value to physical characteristics of X-rays. …
• NAID 10030042205

• 銅製パイプ型吸収体を用いた新しい実効エネルギー測定法

• 飯田 泰治,能登 公也,三井 渉 [他],高田 忠徳,山本 友行,松原 孝祐
• 日本放射線技術學會雜誌 67(9), 1183-1191, 2011-09-20
• … The general method of measuring the half-value layer (HVL) for X-ray computed tomography (CT) using square aluminum-sheet filters is inconvenient in that the X-ray tube has to be set to stationary mode. …
• NAID 10029482113

Related Links

• Half-Value Layer

Half-Value Layer The thickness of any given material where 50% of the incident energy has been attenuated is know as the half-value layer (HVL). The HVL is expressed in units of distance (mm or cm). Like the attenuation ...

• Half-Value Layer - definition of Half-Value Layer by The Free ...

Half-Value Layer synonyms, Half-Value Layer antonyms. Information about Half-Value Layer in the free online English dictionary and encyclopedia. Printer Friendly Dictionary, Encyclopedia and Thesaurus - The Free Dictionary ...

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★リンクテーブル★

関連記事	「value」「valued」「lay」「layer」「layered」

「value」

　　[★]

• n.

• 値、価値

• v.

• 評価する

関

account、appraisal、appraise、appreciate、appreciation、assess、assessment、characterization、estimate、estimation、evaluate、evaluation、judgement、judgment、worth

　 　 　 　 　 　 　 　

「valued」

　　[★]

• adj.

• 価値ある

関

meritorious、valuable、worth、worthwhile、worthy

　 　 　

「lay」

　　[★]

• vt.

• 横たえる、横臥させる

関

lie、recumbent

　 　 　 　 　 　 　 　 　

「layer」

　　[★]

• n.

• 層

関

laminar、strata、stratum、tier

　 　 　 　 　 　

「layered」

　　[★]

• adj.

• 層状の

関

lamellar、laminar、layering、stratiform