放射化学第九讲放射防护.ppt
2023/10/26,放射化学,Radiochemistry,2023/10/26,第九讲 放射防护,放射防护中使用的量及单位射线防护概念放射防护标准射线的防护X、射线的防护；中子的防护。剂量监督废物处理、处置应用辐射管理,2023/10/26,9-1放射防护中使用的量及单位,吸收剂量；当量剂量有效剂量待积当量剂量；集体当量剂量集体有效剂量相对生物效应确定性效应随机效应,2023/10/26,放射防护Radiological Protection,目标：在不过分限制有益的、产生辐射的实践的前提下，为人们提供一个适宜的防护标准To provide an appropriate standard of protection for man without unduly limiting the beneficial practices giving rise to radiation exposure,2023/10/26,辐射，Radiation,Where does radiation come from?A large contribution of the radiation on earth is from the sun(solar)or from radioactive isotopes of the elements(terrestrial).Radiation is going through you at this very moment!,2023/10/26,日常照射,Radon is a highly radioactive element that can have serious adverse effects if it gathers in large quantities.,Your annual dose of radiation from natural sources is about 0.003 Sv or 3 mSv,2023/10/26,细胞的损伤及其对辐射的修复能力,All living cells have enzymes designed to repair radiation damage to DNAIn some cases,radiation-damaged DNA will produce cancer cellsOnly estimates of the risk of low-level radiation exist,2023/10/26,天然辐射与寿命损失,2023/10/26,照射量（Radiation exposure）,一束X或射线穿过空气时与空气发生相互作用使空气电离而产生次级电子，这些次级电子继续使空气电离而产生带电粒子，最后全部损失了自身的能量。,dQ：在空气中所形成的一种符号的离子总电荷的绝对值。,2023/10/26,照射量（Radiation exposure）,Exposure(X,照射量)based on the ionizing effect in air of X-and g-radiation。Unit:rntgen(R，伦琴):1R=2.58 x 10-4 C/kgThe unit“Roentgen”(R)is a measurement of the specific ionization of air molecules by photons.It only applies to gamma or x-ray radiation in air.,2023/10/26,Unit:J/kg;,gray(Gy，戈瑞)或 rad（拉德）1Gy=1J/kg=100rad,吸收剂量(Absorbed Dose),单位质量的物质所吸收的辐射的能量；辐射防护中最基本的量；适用于任何能量、任何种类的电离辐射及任何受照射物质,电离辐射授予某一体积元中物质的平均能量，焦尔（J),该体积元中物质的质量，千克(kg),2023/10/26,吸收剂量率（Absorbed Dose rate）,吸收剂量对时间的导数：,dD：dt时间间隔内吸收剂量的增量；单位：Jkg-1 S-1(戈瑞/小时，Gy/h,拉德/小时，rad/h）,2023/10/26,器官或组织的平均吸收剂量,T:电离辐射授予某器官或组织的总能量（Total energy imparted in a tissue or organ）mT:器官或组织的质量（The mass of that tissue(from 10g,ovaries to 70 kg,the whole body)；单位：戈瑞，Gy,或拉德,rad,2023/10/26,当量剂量（Equivalent Dose,HT.R）,2023/10/26,当量剂量（Equivalent Dose,HT.R）,辐射引起的某一生物效应的发生率，不仅与物质的吸收剂量有关，而且与辐射的种类和能量有关；全身照射条件下，当吸收剂量为1mGy时，能量为4.5MeV的快中子诱发某种生物效应的概率比能量为250keV的X射线诱发同样生物效应的概率大10倍；,2023/10/26,当量剂量,根据放射生物学资料，根据外部辐射场的类型或体内沉积的放射性核素发射的辐射的类型和能量，确定一个辐射权重因子WR；器官或组织的当量剂量定义为WR与DT.R的乘积。,2023/10/26,当量剂量（Equivalent Dose,HT.R）,DT.R:辐射R在器官或组织T中产生的平均吸收剂量（Absorbed dose averaged over the tissue or organ T,due to Radiation R）;WR:辐射R的辐射权重因子（Radiation weighting factor）Unit of HT.R:J/Kg,sievert(Sv，希沃特，与吸收剂量单位戈瑞区别)1J/kg=1Sv=100rem（雷姆）,2023/10/26,当量剂量（Equivalent Dose,HT.R）,如果辐射场为混合辐射场，如中子和辐射场，内照射的、和辐射场；这时的当量剂量为各辐射的当量剂量之和。,2023/10/26,辐射权重因子（Radiation weighting factors）,2023/10/26,辐射权重因子（中子）,2023/10/26,例 题,In 1 year,a worker received a g dose of 0.02 Gy,a thermal neutron(Ns)dose of 0.002 Gy,and a fast neutron dose(Nf)of 0.001 Gy.What is his total equivalent dose？(Take wR for fast neutrons as 20.)Equivalent dose=absorbed dose x radiation weighting factorEquivalent dose,g=0.02 x 1=0.02 SvEquivalent dose,Ns=0.002 x 5=0.01 SvEquivalent dose,Nf=0.001 x 20=0.02 SvTotal equivalent dose=0.05 Sv,2023/10/26,有效剂量 E(Effective dose),2023/10/26,有效剂量 E(Effective dose),人体是一个统一的生命体，一个器官受照，影响人的整体，多个器官同时受照，将带来更大危险；辐射所诱发的随机性效应发生的概率，不仅与当量剂量有关，而且与受照的组织和器官有关；不同的组织或器官在相同的均匀照射条件下，即使受到相同的当量剂量的照射，所诱发的随机性效应的发生率也不尽相同；,2023/10/26,有效剂量,为使单个器官或组织受照所致的随机性效应的发生率与全身均匀照射所致的随机性效应联系起来，分别给各个器官或组织的当量剂量一个权重因子WT；所有组织的权重因子之和为1,2023/10/26,有效剂量 E(Effective dose),HT:组织或器官的当量剂量（Equivalent dose in tissue or organ T）WT:组织权重因子（Weighting factor for tissue T）,有效剂量：人体所有组织的当量剂量的加权值,2023/10/26,组织权重因子,2023/10/26,待积当量剂量HT()（Committed equivalent dose）,2023/10/26,9.1.4 待积当量剂量HT(),放射性核素进入人体后对组织或器官的照射剂量，将随着放射性核素的衰变和时间的推移而逐步积累；针对单次摄入某种放射性核素对人体所产生的照射，采用待积剂量当量来描述；待积当量剂量是人体在单次摄入放射性物质之后，某一特定组织接受的当量剂量率在时间内的积分。,2023/10/26,待积当量剂量HT(),:50 years for adults,From intake to 70 years for children,Following an intake to the body of a radioactive material,there is a period during which the material gives rise to equivalent dose in the tissue of the body in varying rates.,2023/10/26,待积有效剂量E()Committed effective dose,2023/10/26,9.1.5 待积有效剂量E(),单次摄入放射性物质后，产生的待积组织或器官当量剂量乘以相应的组织权重因子WT，然后求和，即为待积有效剂量；待积有效剂量用于评价单次摄入某一活度的放射性核素对组织或器官所造成的危害；,积分时间的单位为年,2023/10/26,集体当量剂量 ST;Collective equivalent dose,2023/10/26,集体当量剂量 ST,集体当量剂量用来评价某一人群某指定的组织或器官所受到的总的照射情况；当评价某一辐射事件对特定人群所造成的危害以及进行辐射防护的最优化设计时，使用集体当量剂量。,2023/10/26,集体当量剂量,2023/10/26,集体有效剂量）S Collective effective dose,2023/10/26,9.1.7 集体有效剂量）S,集体有效剂量用来评价某一人群所受到的辐射照射：,2023/10/26,辐 射 量,2023/10/26,传能线密度LET Linear Energy Transfer,2023/10/26,传能线密度LET,传能线密度：一个致电离粒子沿其径迹的电离密度的一种量度：A measure of the density of ionization along the tract of an ionizing radiation,2023/10/26,相对生物效应 Relative Biological effects of radiation,2023/10/26,9.1.8 相对生物效应,一种辐射对于另一种辐射的相对生物效应，是产生同样程度的某一规定的生物学终点所需要的这两种辐射的吸收剂量的反比值。,2023/10/26,相对生物效应,Particles with high energy loss effects cause typically greater damage.The RBE for different kinds of radiation can be expressed in terms of energy loss effects LET.,2023/10/26,These high energies are sufficient to kill more cells than actually available!,Biological effects of radiation,2023/10/26,急性照射和慢性照射,2023/10/26,急性照射和慢性照射,短时间内受到大剂量的照射为急性照射，急性照射可造成损伤或死亡;长时间内接受小剂量的照射为慢性照射，慢性照射可造成晚期癌症.Acute exposure is a large dose in a short period of time，acute exposure can result in injury or death);Chronic exposure is exposure to a small dose of radiation over a long period of time，chronic exposure can result in cancer later in life.,2023/10/26,急性照射的生物效应,2023/10/26,Acute Radiation Syndrome,前期症状,厌食，恶心呕吐腹泻,无症状,潜伏期,发病期,厌食，恶心呕吐，腹泻 组织损伤,恢复或死亡,Time,Irradiation,2023/10/26,急性照射症状的严重程度和时间分布依赖于最大的吸收剂量；前期症状一般在6小时后发生；如果全身照射剂量超过50-100拉德，前期症状出现的更早，也更严重。The severity and the timescale for the acute radiation syndrome depends on the maximum delivered dose.The first symptoms show up after 6 hours.If the whole body exposure exceeds a critical threshold rate of 50-100 rad the symptoms show up more rapidly and drastically.,Acute Radiation Syndrome,2023/10/26,确定性效应Deterministic effects,2023/10/26,确定性效应Deterministic effects,如果在一个组织或器官中有足够多的细胞被杀死或不能繁殖和发挥正常功能，则该器官将丧失其功能：这种效应称作确定性效应。If enough cells in an organ or tissue are killed or prevented from reproducing and functioning normally,there will be a loss of organ functiondeterministic effects,2023/10/26,Deterministic effects,确定性效应的发生有阈值；效应的严重程度随剂量的增加而增强；照射量与确定性效应之间有明确的因果关系。A certain minimum dose must be exceeded before the effect occursThe severity of the effect increases as dose increaseThere is a clear causal relationship between exposure and occurrence,2023/10/26,随机效应Stochastic effects,由一个改变了的细胞可能引起的躯体或遗传效应，称作随机效应。The somatic and hereditary effects,which may start from a single modified cell Stochastic effects,2023/10/26,9-2 放射防护概念The Conceptual Framework of Radiological Protection-Objective,ICRP publication 60,1990-11,2023/10/26,9.2.1 放射防护的目标,避免确定性效应的发生，采取有效措施减小随机效应的发生几率To prevent the occurrence of deterministic effects by keeping doses below the relevant thresholds,and to ensure that all reasonable steps are taken to reduce the induction of stochastic effects,2023/10/26,放射防护原则,实践的正当性防护的最优化个人剂量限值Justification of a practiceOptimisation of protectionIndividual dose limits,2023/10/26,实践的正当性原则Justification of a practice,涉及照射的实践，除非对受照个人或社会带来的利益足以补偿其辐射危害时才可实施。No practice involving exposures to radiation should be adopted unless it produces a sufficient benefit to the exposed individuals or to society to offset the radiation detriment it causes,2023/10/26,防护的最优化原则Optimisation of protection,对于一项实践中的任一特定源，个人剂量的大小、受照的人数以及潜在的照射等，在考虑了经济和社会因素后，都应当保持在可以合理达到的尽量低的程度。在潜在照射情况下，防护的最优化原则应当受到个人剂量或个人风险限值的约束，以便限制可能发生的、来自固有的经济和社会价值观上的不平等现象的发生。,2023/10/26,防护的最优化原则Optimisation of protection,The magnitude of individual doses,the number of people exposed,and the likelihood of incurring exposures should all be kept as low as reasonably achievable,economic and social factors being taken into account.This procedure should be constrained by restrictions on the doses to individuals,or the risks to individuals in the case of potential exposures,so as to limit the inequity likely to result from the inherent economic and social judgements.,2023/10/26,个人剂量限值Individual Dose and Risk Limits,个人受到的来自所有相关实践的照射应有剂量限。在潜在照射情况下应有一定程度的风险控制。目的在于保证在任何正常情况下，个人受到的来自这些实践的辐射危害不会达到不可接受的程度。并非所有的源都需要在源处加以控制，但是，在确定剂量限值之前，将某些源作为相关源是必要的。,2023/10/26,个人剂量限值Individual Dose and Risk Limits,The exposure of individuals resulting from the combination of all the relevant practices should be subject to dose limits,or to some control of risks in the case of potential exposures.These are aimed at ensuring that no individual is exposed to radiation risks that are judged to be unacceptable in any normal circumstances.Not all sources are susceptible to control by action at the source and it is necessary to specify the sources to be included as relevant before selecting a dose limit,2023/10/26,实施的干预措施应利大于弊；干预的形式、规模和时间长短应遵循最优化原则，即净利益最大化原则；采取干预措施时，不能应用剂量限值原则，但可以预设采取干预措施的剂量值。由于高于该剂量值将产生严重的确定性效应，因此这时采取干预措施总是正当的；,干预的基本原则General Principles for Intervention,2023/10/26,干预的基本原则General Principles for Intervention,The proposed intervention should do more good than harmThe form,scale and duration of the intervention should be optimised,i.e.the net benefit should be maximisedDose limits do not apply in intervention,but there will be some level of projected dose above which,because of serious deterministic effects,intervention will almost always be justified,2023/10/26,Lecture Complete,2023/10/26,9.2.4 职业照射Occupational Exposure,2023/10/26,9.2.4 职业照射(Occupational Exposure),5年期间的平均有效剂量20mSva-1,其中任何一年的有效剂量50mSv;有效剂量限值是可容忍的上限；对于超过个人剂量限值的个人来讲，勿需对其以后的照射设置特别限制。,2023/10/26,Occupational Exposure,The recommended limit on the effective dose is 20 mSv/a,averaged over 5 years,with the further provision that the effective dose shall not exceed 50 mSv in any single yearNo special restrictions are required on the subsequent exposure of an individual who has exceeded a dose limit,2023/10/26,1cm2皮肤和眼的5年平均剂量限值分别为:500mSv/a和150mSv/a；年摄入剂量为20mSv;孕妇腹部的年剂量限值为2mSv/a，年摄入剂量限值为1mSv/a.,ICRP publication 60,1990.11,职业照射,2023/10/26,The effective dose limit is the boundary of tolerabilityDose limits for skin and lens of the eye are 500 mSv/a averaged over any 1 cm2 and 150 mSv/a,respectivelyAnnual Limits on Intake(ALIs)are based on a committed effective dose of 20 mSvOnce pregnancy is declared,the conceptus should be protected by applying a supplementary equivalent dose limit to the surface of the womans abdomen of 2 mSv/a for the remainder of pregnancy and by limiting intakes of radionuclides to about 1/20 of the ALI,Occupational Exposure),2023/10/26,9.2.5 医疗照射(Medical Exposure),由于多数医疗照射是正当的，受照者通常都是受益者，因此，与其它照射比较，医疗照射的最优化受到关注的程度不够；因此，诊断放射学还留有很大的降低剂量的空间；应尽量避免怀孕妇女的腹部照射，除非非做不可。,2023/10/26,医疗照射,美国每年有2 billion X射线检查，32 million核医学诊断，5.5 million化疗，有数百万开展医学检查的技术人员。There are about 2 billion diagnostic x-ray examinations,32 million nuclear medicine procedures and 5.5 million radiation therapy treatments annuallyThere are several million technologists giving medical examinations,2023/10/26,医疗照射,2023/10/26,公众照射(Public Exposure),公众照射（关键人群的平均剂量）应使用剂量限值和约束；剂量限值仅与特定的事件有关，与业已存在于环境中的放射性核素（天然的或人造的）无关；年剂量限值为1mSv，皮肤和眼睛分别为50mSv和15mSv.,2023/10/26,剂量限值,2023/10/26,Dose limits,2023/10/26,INDIVIDUAL-AND SOURCE-RELATED CONCEPTS,2023/10/26,9-3射线的防护,2023/10/26,9-3射线的防护,防护的一般方法：尽量缩短照射时间；尽量增大与照射源的距离；在人员和照射源之间加屏蔽。重带电粒子的防护中子的防护射线的防护X、射线的防护,2023/10/26,粒子的防护,Alpha particles can be blocked byA sheet of paperOne or two inches of airThe outer layer of the skinThus,materials that emit alpha radiation are only dangerous if inhaled or ingested(where they can be next to biological tissue),2023/10/26,射线的防护,Beta particles can be blocked byA thin aluminum plateSeveral feet of airThe first few layers of the skinThus,beta particles are dangerous if inhaled or ingested and to the cornea（角膜）,where they can cause cataracts（白内障）,2023/10/26,射线的防护,Gamma particles can be blocked byA couple inches of leadA few feet of concreteThus,care must be taken to shield oneself from gamma radiationX-rays are similar to gamma rays but do not penetrate as far-you are probably safe if separated by a normal wall,2023/10/26,放射防护的一般原则,Effects of exposure to radiation depends on the following factorsDistance from the sourceShieldingExposure timetype of radiationactivity of the sourcepart of the body exposed,2023/10/26,注量、注量率,2023/10/26,注量、注量率,辐射场中某一点的粒子注量是以该点为中心，截面积为da的小球内的粒子数dN除以da所得的商：,2023/10/26,外照射的防护及剂量计算,2023/10/26,射线的防护,射线具有一定的穿透能力，易被组织表层吸收，引起表层组织的辐射损伤。射线与物质作用的一个特点是产生韧致辐射。韧致辐射的强度与射线的能量和屏蔽材料的原子序数有关；韧致辐射的最大能量近似等于初级粒子的能量；,2023/10/26,射线的防护,射线的防护必须考虑两层屏蔽：第一层用低原子序数的材料（减弱韧致辐射）屏蔽射线（常用烯基材料、有机玻璃及铝等）第二层用高原子序数的材料屏蔽韧致辐射（常用生铁、钢板和铅板）,2023/10/26,射线剂量的计算,射线为连续谱；在物质中的衰减近似服从指数衰减规律；散射明显：散射不仅与空气成分、离源的距离有关；而且与源周围散射物的存在及几何形状、位置有关；很难用公式来描述散射的影响；至今尚无满意的理论公式来计算源的剂量；常用经验公式。,2023/10/26,点源的剂量计算,洛文格(Lovinger)总结了12种放射性核素的直接测量数据，提出了著名的经验公式；当射线的能量为0.1672.24MeV时，用公式：,2023/10/26,点源的剂量计算（续）,2023/10/26,常用核素的一些物理性质,2023/10/26,面源的剂量计算,无限平面源：所考虑的点到该平面的距离为x（g/cm2),该点的吸收剂量率为：,2023/10/26,面源的剂量计算,圆盘源：所考虑的点在圆盘的轴上，离圆盘的距离为a，圆盘的半径为R0，则圆盘源在该点的吸收剂量率为：,2023/10/26,例题1,计算活度为1Ci的32P 点源在相距30.5cm处的空气中产生的吸收剂量率。解：32P为放射性核素，其最大能量Emax=1.709MeV,平均能量为0.694MeV,空气的密度=1.29310-3g/cm3,r=30.50.001293=3.9410-2g/cm2,2023/10/26,例题1（续）,2023/10/26,例题2,假设皮肤表面被32P沾污，沾污程度为3.7104Bq/cm2，求沾污皮肤的吸收剂量率。解：从辐射防护的角度出发，估算皮肤的吸收剂量时，可取其厚度为4mg/cm2,因此，x=410-3g/cm2,=1g/cm3,分别计算得到：C=1.5,=0.298,=9.19cm2/g,CA=3.7104Bq/cm2,x=3.68 10-2;x/C=2.45 10-2;皮肤表面污染可视为无限大平面源的情况，带入相应公式得:,2023/10/26,例题2,2023/10/26,单能电子的注量率与吸收剂量的关系,单能电子束的吸收剂量可用电子在物质中的阻止本领计算；只要知道指定物质所接受的单能电子的注量率，可用下式计算指定物质的吸收剂量率。,2023/10/26,表9-2,2023/10/26,重带电粒子剂量的计算,等效质子质量法：具有相同速度的两种带电粒子在同一物质中的阻止本领之比等于他们所带电荷平方之比；Mp和MI分别代表质子和重带电粒子的质量；T和v分别代表入射重带电粒子的动能和速度,有Tp=mpTI/MI;不同能量的质子在不同材料中的质量碰撞阻止本领可查；,2023/10/26,9.3.3 辐射剂量的计算,质能吸收系数：光子在某物质中穿行单位距离时，由于各种相互作用而被该物质吸收的能量占其总能量的份额。光子注量率与吸收剂量的关系：,2023/10/26,辐射剂量的计算,对于具有非连续谱的核素，诸如60Co、226Ra等，其吸收剂量率的计算公式为：,2023/10/26,辐射剂量的计算,若已知空气中某一点的吸收剂量率，可用下式计算同一点其它物质的吸收剂量率：,2023/10/26,表9-3,2023/10/26,剂量换算因子法,剂量换算因子：fD光子在空气中单位注量的吸收剂量若知道光子在空气中某一点的注量率,便可用公式计算吸收剂量率。,2023/10/26,表9-4,2023/10/26,例题3,计算距活度为3.71010Bq的137Cs放射源1米处肌肉组织的吸收剂量率。解：E(137Cs)=0.66MeV,(en/)肌肉=0.00324m2kg-1,r=1m,2023/10/26,例题3,方法2：解：fD(137Cs)=3.0910-12Gycm2,(en/)空气=0.002931m2kg-1.,2023/10/26,9.3.4 中子剂量的计算,比释动能K：间接电离粒子与物质相互作用时，在单位质量的物质中产生的带电粒子的初始动能的总和；在带电粒子平衡条件下，若韧致辐射的能量损失可以忽略不计时，比释动能等于吸收剂量。,2023/10/26,中子剂量的计算,中子与物质相互作用过程的能量转移：中子将能量转移为带电粒子的动能；带电粒子通过电离、激发和韧致辐射损失能量；电离、激发过程中损失的能量被物质吸收。对于单能中子：,2023/10/26,中子剂量的计算,对于具有谱分布的中子：,2023/10/26,中子剂量的计算,剂量换算因子法：根据某一中子源或确定能量的中子注量率，可计算吸收剂量率：,2023/10/26,各种中子源的剂量换算因子,2023/10/26,例题,求距中子发射率为2.5106中子/s的钚-铍源1米处的当量剂量率。解：查得钚-铍中子源的fD=4.73310-15Gym-2,E(平均）=4.2MeV,WR=10,s=2.5106中子/s，r=1m,2023/10/26,作业,计算距活度为3.7109Bq的137Cs放射源2米处肌肉组织的吸收剂量率。求距中子发射率为2.5106中子/s的钚-铍源中子源30厘米处的当量剂量率。,2023/10/26,韧致辐射（bremsstrahlung）,当高速运动的带电粒子从原子核附近掠过时，它会受到原子核库仑场的作用而产生加速度。根据经典电动力学，受到加速或减速的带电粒子的部分或全部能量将转变成连续的电磁辐射。这就是韧致辐射。,
