輻射的單位.docx

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1、幅射的军位有那些?幅射的罩位分卷放射性活度罩位和幅射剜量罩位雨大类肌均由n除幅射罩位及度量委具曾(ICRU)所公布，耦作1除制罩位(SI罩位)。以下曾述襄低1重要的幅射罩位：活度(activity)一放射性核槿於每罩位内羟生自彝性蜕燮的次数，耦卷活度。活度的罩位卷宾克，曾嘉成Bq,它的定羲卷1宾克(Bq) =1蜕燮/秒宾克是用来表示一他I幅射源，如to的强度(蜕燮率)。另外一他常用的单位卷居里：1 居里(Ci) =3. 7X10阳克(Bq)活度吸收剜量(absorbed dose)， D每罩位量的物(公斤)，平均吸收的幅射能量(焦耳)，耦悬吸收剜量。吸收剜量罩位是戈雷，Gy,它的定羲卷1戈雷(

2、Gy) =1焦耳/公斤每小畤平均所接受的吸收剜量耦卷吸收剜量率，罩位卷戈雷/小畤,它的千分之一卷毫戈雷/小畴(mGy/h),百离分之一卷微戈雷/小畤(pGy/h) o等效翅I量(dose equivalent)， HT不同槿类直的幅射(Q 、B 、丫 、n)照射人醴的幺且或器官，虽隹使人醴留且有相同的吸收剜量，但谷13曾造成不同程度的害现象。卷此,金十封不同槿的乾i射言丁出射因数(Q),代表不同鞭;射量寸人醴幺且造成不同程度的生物害，它的值列於下表：幅射槿X射名泉、Y射名泉、具他粒子和霜子中子、子和静止量大於1彳固原子量罩位的罩甯荷粒子粒子及多重荷粒子20资料来源:ICRP-26 (1977)

3、等效狸J量即卷人的吸收理J量和射因数的乘稹，它已含有幅射封幺且幺散器官彳募害的意羲了。它的军位是西弗，曾嘉成Sv,定羲卷:Ht （西弗）=D （戈雷）XQ千分之一西弗卷毫西弗（mSv），百离分之一西弗卷微西弗（pSv） o我仍号拍一张胸部X光片，胸部疑大区勺接收0. 1毫西弗剜量。彳强射因数Q值也可知，&粒子雎然穿透力很弱但健康效朦谷艮大,如把剑235、226等放射a粒子的同位素吃迤醴内，刖曾封醴内系且器官造成敕大的害。单位畤内平均所接受的等效剜量耦卷等效剜量率，例如毫西弗/年（mSv/y）,微西弗/小日寺（|JSv/h）都是等效剜量率的军位。.有效等效来)量(effective dose e

4、quivalent), He由於人醴各幺且器官封幅射的敏感度不同，所以员隹各接受相同的等效剜量，但是造成健康损失（罹患致死癌或不良遗傅）的 （械率）郤不同，也就是不同的器官照射相同的幅射量所照成的害不同。因此又JT出能加槿因数（Wr）来代表各幺目器官接受幅射封健康损失的檄率。如下表，可知性腺抵抗幅射的能力敕其他器官来的低。若把各幺且器官的等效剜量（Hr）,奥其加槿因数的乘再加以2息和,即成卷有效等效杳J量（He）。He代表全身的幅射剜量,用来言平估幅射可能造成我凭健康效鹰的单位也是西弗（Sv）。例如台湾地g的民冢，平均每年接受天然背景幅射剜量（He）幺勺2毫西弗（mSv）,典全世界的平均值（2

5、. 4mSv）差不多。器官的加因数（Wt）器官或WtICRP-26ICRP-60性腺（生殖腺）0. 250. 20缸骨髓0.120.12结踢（大踢直踢）0.12月市0.120. 12田0. 12膀胱0. 05乳腺0.150. 05肝朦0. 05食道0. 05甲状腺0. 030. 05皮唐0.01骨骼表面0. 030.01其绘部分0. 300. 05资料来源:ICRP-26(1977)及 ICRP-60(1991)UNITS OF RADIATION MEASUREMENTThe curie is the number of particles per second from 1 gram of

6、Radium = 3.7 x 10 E10 counts/second = 37 billion cps. = 37 billionBecquerel.1 Becquerel (Bq) = 1 count per second = 1 event per second1 microcurie = 1 uCi = 37,000 Bq = 37,000 cps.1 microcurie = 2.22 x 10E6 disintegrations / minute = 2,220,000 cpm.1 nanocurie = 1 billionth of a curie = 2,220 disinte

7、grations / minute.1 picocurie = 2.2 disintegrations / min.Dosage units:Gray (Gy) = 1 Joule/kgSievert (Sv) = Gray x QF, where QF is a quality factor based onthe type of particle.QF for electrons, positrons, and xrays = 1 QF = 3 to 10 for neutrons,protons dependent upon the energy transferred by these

8、 heavierparticles.QF = 20 for alpha particles and fission fragments.The Sievert is a measure of biological effect.Converting older units:1 rad = 1 centigray = 10 milligrays ( 1 rad = lcGy = 10 mGy )1 rem = 1 centisievert = 10 millisieverts ( 1 rem = IcSv = 10 mSv )1 mrad = 10 uGyNominal background r

9、adiation absorbed dose of 100 mrad/year = 1mGy/yr.Nominal background radiation dose biological equivalent oflOOmrem/year = lmSv/yr.Occupational whole body limit is 5 rem/yr = 50 mSv/yr. ( Recentlyproposed that levels be reduced to 2 rem/yr.)2.5 mrem/hr or 25 uSv/hr is maximum average working level i

10、nindustry.Exposure rate from Naturally Occurring Radioactive Material(NORM) ; an empirically derived conversion factor for Ra-226decay series: L82 microR/ hour = 1 picoCurie/gram.Radiation Quantities and UnitsPerry Sprawls, Ph. D.Introduction and OverviewSeveral forms of ionizing radiation are used

11、in medical imaging.HOW MUCH RADIATIONDID THE PATIENT RECEIVE?Even though the risk is low, if there is a risk at all, it isappropriate to manage the radiation delivered to patients beingimaged and to use only sufficient radiation to produce thenecessary image quality. The question we begin with is: H

12、ow muchradiation is delivered to apatients body? As we areabout to see, that is notalways an easy question toanswer. There are severalfactors contributing to thecomplexity. They include the many quantities that can be used toexpress the amount of radiation, the different units that are used,and the

13、generally uneven distribution of the radiation within thepatients body.Also, some medical imaging procedures expose the staff toradiation. It is necessary to determine their exposure so thatthe risk can be managed in the context of ALARA programs.STAFF EXPOSUREDetermining and expressingthe radiation

14、 to the staff andother persons in an imagingfacility is also somewhatcomplex because of the reasons mentioned above.Radiation QuantitiesAs we see below, there are many different physical quantities thatcan be used to express the amount of radiation delivered to a humanbody. Generally, there are both

15、 advantages and applications aswell as disadvantages andlimitations for each of thequantities. There are twotypes of radiation quantitiesthose that express theconcentration of radiation atRADIATION QUANTITIESCONCENTRATION ITOTALPHOTON FLUENCEENERGY FLUENCEEXPOSUREDOSEDOSE EQUIVALENTTOTAL PHOTONSTOTAL ENERGYINTEGRAL EXPOSUREINTEGRAL DOSEEFFECTIVE DOSE EQquantities in much mo