核技术导论英文课件：Chapter 2 Radiation c

1、Chapter 2. Radiation Radioactivity2.Radiation interaction with Matter 3.Radiation Doses and hazard AssessmentOverviewTypes of Radioactive DecayEnergetics of Radioactive DecayCharacteristics of Radioactive DecayDecay DynamicsNaturally Occurring Radionuclides2.1 Radioactivity3c) Beta Decay Spectra and

2、 NeutrinoPauli: Neutrino with spin 1/2 is emitted simultaneously with beta, carrying the missing energy.?c)The mass of the neutrino is negligibly small.5d) Positron Decay Energy3）36CI decays into 36S (35.967081 u) and 36Ar. If the energy release is 1.142 MeV to 36S and 0.709 MeV to 36Ar, calculate t

3、he masses of 36CI and 36Ar. Describe the modes of decay.5) The radionuclide 41Ar decays by - emission to an excited level of 41K that is 1.293 MeV above the ground state. What is the maximum kinetic energy of the emitted - particle?Radioactive Decay Kinetics -exponential Number of radioactive nuclei

4、 decrease exponentially with time as indicated by the graph here.As a result, the radioactivity vary in the same manner. Note l N = A l No = Ao6) The activity of a radioisotope is found to decrease by 30% in one week. What are the values of its (a) decay constant, (b) half-life, and (c) mean life? b

5、) Three Component Decay ChainsDaughter Decays Faster than the ParentI 2,transient equilibrium: daughters decay rate is limited by the decay rate of the parent.I 2,The activity of the daughter approaches that of the parent. This extreme case is known as secular equilibrium(久期平衡).4）An initial number N

6、A(0) of nuclei A decay into daughter nuclei B, which are also radioactive. The respective decay probabilities areA and B. IfB = 2A , calculate the time (in terms of A)when NB is at its maximum. Calculate NB (max) in terms of NA(0)overviewPhoton InteractionsNeutron InteractionsInteraction of Heavy Ch

7、arged Particles with MatterScattering of Electrons in a Medium2.2 Radiation interaction with Matter 1) overviewI = Io ex mean-free-path lengthHalf-Thickness4) Interaction of Heavy Charged Particles with MatterFast moving protons, 4He, and other nuclei are heavy charged particles.Coulomb force domina

8、tes charge interaction.They ionize and excite (give energy to) molecules on their path.The Born-Bethe Formula for Energy Loss of Charged Particles.能量损失Range of Heavy Charged Particles in a Medium sourceShieldParticles lose all their energy at a distance called range.A material is found to have a ten

9、th-thickness of 2.3 cm for 1.25 MeV gamma rays, (a) What is the linear attenuation coefficient for this material? (b) What is the half-thickness? (c) What is the mean-free-path length for 1.25-MeV photons in this material?The specific rate of energy loss (-dE/dx) of a 5 MeV proton in silicon is 59 k

10、eV mg-1 cm2 and its range R is 50 mg cm-2 . Calculate values of (-dE/dx) and range R for deuterons, tritons, 3He and a particles, all of which have the same speed as the proton.Historical RootsDosimetric QuantitiesNatural Exposures for HumansRadiation Effects2.3 Radiation Doses and hazard Assessment

11、Early workers exposed to X-rays developed dermatitis（皮炎）.Uranium miners developed skin lesions.People working with radioactivity experienced illness.Researchers exposed to radioactivity suffered radiation sickness at advanced age.Manhattan project workers in Los Alamos, Oak Ridge, Hanford, and atomi

12、c worker in the former USSR suffered anorexia（厌食）, fatigue, headache, nausea（反胃）, vomiting, and diarrhea.Historical RootsCollective Response to Radiation RiskIn 1928, the International Committee on X-ray and Radium Protection was formed to look into the risk of radiation. It is now called Internatio

13、nal Commission on Radiological Protection, ICRP.In 1942, a group of health physicists had the responsibility to assess problems and implement safe operation procedures regarding radioactivity. After WW2, the (American) National Council of Radiation Protection (NCRP) was formed in 1946.Guidelines are

14、 given for radioactive material handling and applications.Today, safety committee is set up to deal with radiation risks.Mission Statement of the ICRPThe International Commission on Radiological Protection, ICRP, is an independent Registered Charity, established to advance for the public benefit the

15、 science of radiologicalprotection, in particular by providing recommendations and guidance on all aspects of protection against ionising radiation. From check with ICRP for up-to-date guidance regarding radiationProtection standardsGB4792-84 放射卫生防护基本标准 卫生部发布GB8703-88 辐射防护规定 环保局发布GB 18871-2002 电离辐射防

16、护与辐射源安全基本标准 2002-10-08 发布 2003-04-01 实施 中华人民共和国国家质量监督检验检疫总局发布2) Dosimetric quantities a physical measure correlated with a radiation effect.When you can measure what you are speaking about, and express it in numbers, you know something about it. Lord KelvinLord Kelvin Radiation Absorption and Dosage

17、The amount of energy absorbed from exposure to radiation is called a dose. The radiation effect measured by a dosimeter reflects an equivalence of certain dosage of X-rays. The amounts are defined in certain units as shown here. typeunits RadioactivityBq, Ci Exposure dose Gy, rad (R) Quality factor

18、Q Biological dose Sv, remUnits for Radiation Source (review)The SI unit for radioactivity is Bq (1 becquerel = 1 dps). The decay is not necessary all absorbed unless its internal. 1 curie = 3.7e10 Bq.These units have nothing to do with energy, type (a, b, g, X-rays, neutrons, protons or particles),

19、and effect of radiation.Commonly used unitsmegacuriekilocuriemillicuriemicrocurienonocuriepicocuriethese modifiers are also used for other units.disintegrations per secondthe fluence is not closely enough related to most radiation effects to be a useful determinant.Dose Units - roentgen, rad, and gr

20、ay Amounts of absorbed energy are not the same as exposed.The amount of radiation energy absorbed is called a dose. A roentgen ( R) is a dose of X- or -rays that produce 1 esu charge at STP (negative and positive each or 2.1e9 ion pairs) in 1.0 L.1 R = 352.1e9 = 7.35e10 eV (*1.6x10-12 erg/eV) = 0.12

21、 erg (per 0.00123 g air) = 1 rad (100 erg per g of any substance)1 Gy = 1 J / kg (1 J per kg of any substance is a gray, Gy) = 1e7 erg / kg = 100(100 erg/g) 100 radIn air, the average energy required to produce an ion pair is 35 eV average energy1 Gy being equal to an imparted energy of 1 joule per

22、kilogram.corpuscular radiationphotonsA Dosage Evaluation ExampleA 5-MeV particle is absorbed by 1 gram of water, estimate the dosage in rad and rem. The Q factor is 10 for particle, and thus the dose is 8e-7 rem or 8e-9 Sv. If the a particle is absorbed by a of 10-9 g cell, then the dose is 109 time

23、s higher (0.8 Gy, 8 Sv), exceeded lethal (致命) dose for most living beings.Integral Dose Used in Radiation TherapyTotal energy absorbed by an organ called integral dose is gram-rad or g-rad or g-Gy total dosage received by an organ.g-Gy = dose * mass of the organAccumulated dose is the dose received

24、over a period, but g-Gy is the total dose received in a single time.The Quality Factor QF and Dosage UnitsThe factor reflecting the relative harmfulness of various types of radiation is called the quality factor (QF) or relative biological effectiveness (rbe) Biological dose = QF * exposure doseExpo

25、sure and Biological DosageSI unit cgs unitExposure unit1 Gy = 100 rad (=100 R)Biological dose1 Sv = 100 rem (= Qrad)Gy: gray, Sv: sievert, R: roentgen, rem: roentgen equivalent manSummary of Units for Radioactive DosageQuantitySymbol SI unitcgs unitConversion factorradioactivityABqCi1 Ci = 3.7e10 Bq

26、exposure doseXC/kgR1 C/kg = 3876 Rabsorbed doseDGy (J/kg)rad1 Gy = 100 rad =6.24 eV/gbiological doseHSv (QF*Gy)rem1 Sv = 100 rem C/kg charge produced by exposure to radiation Effective Dose EquivalentIn a human, different organs have different radiological sensitivities,To account for different orga

27、n sensitivities and the differentdoses received by the various organs a special dose unit, the effective dose equivalent HE, is used to describe better the hazard a human body experiences when placed in a radiation field.Tissue weighting factors adopted by the ICRP 1977 for use in determining the ef

28、fective dose equivalent.Naturally occurring radionuclides in the human body deliveran annual dose to the various tissues and organs of the body as follows: lung 36 mrem, bone surfaces 110 mrem, red marrow 50 mrem, and all other soft tissues 36 mrem. What is the annual effective dose equivalent that

29、a human receives?Kerma kinetic energy of radiation absorbed per unit mass 比释动能 indirectly ionizing (uncharged) radiationIf Etr is the sum of the initial kinetic energies of all the charged ionizing particles released by interaction ofindirectly ionizing particles in matter of mass m, then(a) Energy

30、deposition for photon energy involved in the interactions in an incremental volume of material, (b) Formulas for the energy per unit mass of the material in the incremental volume, corresponding to the various energy increments in (a), (c) Linear coefficients defined by their proportionality to the

31、mass energy relationships in diagrams (a) and (b).total moss interaction coefficient tri which account for fewer secondary photons escaping from the interactionsite, are sometimes encountered.the linear energy absorption coefficientPhoton Kerma and Absorbed DoseIf, at some point of interest in a med

32、ium, the fluenceof radiation with energy E is , the kerma at that point isf(E) is the fraction of the fraction of the incident radiation articles energy E that is transferred to secondary charged particles(E)/ is the mass interaction coefficient for the detector material. tr(E)/ for charged secondar

33、y particles and excludes the energy carried away from the interaction site by secondary photons一定物质对特定能量的间接致电离粒子的质量能量转移系数。Example What are the iron kerma and absorbed dose rates from uncollided photons 1 meter from a point isotropic source emitting 1014 5 MeV gamma rays per second into an water medi

34、um? the total mass interaction coefficient for 5-MeV photons isfound to . The uncollided flux density 1 meter from the source is, Example : What is the dose equivalent 15 meters from a point source that emitted 1 MeV photons isotropically into an infinite air medium for 10 minutes at a rate of 109 p

35、hotons per second?neglect air attenuation over a distance of 15 mQF = I0.15 SvDosimeters for Dosage MonitoringDosimeters are devices to measure exposed doses.Film-badges, electroscopes, ionization chambers, biological and chemical dosimeters have been used for radiation monitors.Plants, cells, bacte

36、ria, and viruses reacting to radiation are biological dosimeter candidates.Ferrous sulfate, FeSO4, solution is a chemical dosimeter due to the reaction:4 Fe2+ + energy + O24 Fe3+(brown) + 2 O2-Some glasses and crystals serve as solid state dosimeters.Shelf life, linearity, stability, usage simplicit

37、y, easy-to-read, dose-rate and equal responses to various radiation are some considerations.Chemical 3-dimensional DosimeterFerrous ions, Fe2+, are oxidized by ionizing radiation, and convert to ferric ions, Fe3+, which complexes with xylenol（二甲苯酚） orange dye to give an orange compound.When the samp

38、le is prepared in a gel form, it serves as a 3-dimensional dosimeter, because the complexes are localized in the gel. These dosimeters are useful for planning radiation medical treatments such as radiation cancer treatment.Historical RootsDosimetric QuantitiesNatural Exposures for HumansRadiation Ef

39、fects2.3 Radiation Doses and hazard Assessment3) Natural Exposures for HumansThe uranium decay series.222Rn is responsible for higher levels of background radiation in many parts of the world. because it is a gas and can easily seep out of the earth into unfinished basements and then into the houseR

40、adioactivity in NatureRadonSummary of the annual effective dose equivalents from various sources of natural background radiation in the United States. Source: NCRP 1987.Some Natural Occurring Radioactive NuclidesNuclides (t 106-15 y)Radiation235, 238U, 232Th and offsprings, , 144Nd, 147, 148, 149Sm,

41、 152Gd, 186Os, 190, 192Pt ()40K, 87Rb, 115In, 123Te, 138La, 176Lu, 187Re, 210Bi etc.+, , EC ()Nuclides produced by cosmic rays14C (5730 y), 3T (15 y), 7Be (53 d), 10Be (2.7106 y)Historical RootsDosimetric QuantitiesNatural Exposures for HumansRadiation Effects2.3 Radiation Doses and hazard Assessmen

42、tRadiation EffectsSomatic effects damages to cells passed on to succeeding cell generations, acute or chronicGenetic effectsdamages to genes that affect future generations.Genes are units of hereditary information that occupy fixed positions (locus) on a chromosome. Genes achieve their effects by di

43、recting the synthesis of proteins.Somatic EffectsDamages to cell membranes, mitochondria(线粒体） and cell nuclei result in abnormal cell functions, affecting their division, growth and general heath. Organs such as skin, lining of gastrointestinal tract（胃肠道）, embryos, and bone marrow, whose cells proli

44、ferate rapidly are easily damaged.Bone marrow makes blood, and its damage leads to reduction of blood cell counts and anemia.Damage to germinal ( 幼体 tissues reduces cell division, and induces sterility.Cellular EffectsCell deathCell repairCell changeIs this change good or bad?Dividing Cells are the

45、Most RadiosensitiveRapidly dividing cells are more susceptible to radiation damage.Examples of radiosensitive cells are;Blood forming CellsThe intestinal liningHair follicles（毛囊）A fetusThis is why the fetus has a exposure limit (over gestation period) of 500 mrem (or 1/10th of the annual adult limit

46、)Median effective absorbed doses D50 and threshold doses Dth for exposure of different organs and tissues in the human adult to gamma photons at dose rates 200 mSv (UNSCEAR)Human LD50Typical mission dose on Int. Space StationTypical annual dose for commercial airline flight crewsBone (Tc-99m)Thyroid (I-123)Chest X-rayDental X-rayICRP Negligible DoseNRC Dose Limit for PublicNatural backgroundSite Decommis