1、8/4/20221Zhang Yongxue核医学物理基础8/4/20222K L MAtomneutrons protonsnucleon+electrons -Configuration of AtomAtomNucleusProtonQuark10-8 cm 10-12 cm 10-13 cm 20,ratio of n:p neccesary more than will be stable.8/4/20225Stable&radionuclideStable&radionuclideP83的核素，核力不能与质子间的斥力保持平衡，故全是不稳定的放射性核素。P82的核素，天然的放射性核素
2、很少，多由人工生产。8/4/20226Proton rich nucleiNeutron rich nucleiZ=N05010015050100PROTON NUMBERNEUTRON NUMBERNeutron-proton ratio with line nuclear stability8/4/20227Nuclear decayAlpha()decayAlpha()decay Alpha particles is a helium nuclei consisting of 2 protons and 2 neutrons.4HeQHeYXAZAZ4242937.44222286226
3、88HeRnRa8/4/20228Characteristic of alpha particle粒子实质上是He原子核，衰变发生在原子序数大于82的重元素核素。粒子的速度约为光速的1/10，即万km/s，2s绕地球周。在空气中的射程约为3-8cm，在水中或机体内为0.06-0.16mm。因其射程短，一张纸即可阻挡但粒子的电离能力很强。8/4/20229Beta decayBeta decayEmit particles and capture orbital electrons.To be a companion to increase or decrease of atomic numbe
4、r,but the mass number of the new nuclei is the same.Including,and electron capture.Velocity of particle is 200 thousand km/s in vacuum.Penetrability is more than alpha particle.8/4/202210-decayEmit particlesNeutron rich nucleiNeutron protonThe mass number of new nuclei is the same as the parent nucl
5、ei,atomic number increase 1n p+QMeVSP71.1321632158/4/202211 decayEmission of particleNeutron poor nucleiA proton to neutron transformationArtificial radionuclidep n+e+189F188O+0.66MeV8/4/202212Electron capture,ECAn orbital electron is captured to form a neutron.Neutron poor nucleiA proton to neutron
6、 P+e-nCharacteristic X-rayAuger electronMneFe552555268/4/202213Gamma decay and internal conversionGamma decay may be a part of another decay process,such as,EC or-Metastable to stable state transition and emission of electromagnetic(transition)New nuclei mass and proton is the same,but energy change
7、d Internal conversion and Internal conversion electronInternal conversionelectronray)140(994369943669942keVTcTcMohmh8/4/202214 Characteristic of rayGamma ray is photonNo electric chargePenetrability is more than charged particleLow ionization ability8/4/202215Comparison of three decayalpha decaybeta
8、 decaygamma decayMass changedyesnonoProton changedyesyesnoEnergy changedyesyesyes8/4/202216The law of nuclear decay 放射性核素是不稳定的，它要自发地发生衰变而变成新元素的核。放射性原子核并不是同时衰变的，对于某一个原子核而言，何时衰变是各自独立没有规律的，但对于某一种原子核的群体而言，它的衰变是有规律的，即原子核数目随时间增长按指数规律减少。8/4/202217Decay constant(Decay constant()衰变常数：某种放射性核素的核在单位时间内自发衰变的几率；它
9、反映该核素衰变的速度和特性；值值大衰变快，小则衰变慢，不受任何影响。大衰变快，小则衰变慢，不受任何影响。8/4/202218The formula of decayDecay formula：Nt=Noe-tCharacteristic：不同的放射性核素有不同的Commonness：任何放射性核素的衰变，原子核数目随时间增长按指数规律减少 tNlogNt8/4/202219Half life 半衰期半衰期Physical half life，(T1/2)在单一的放射性核素衰变过程中，放射性活度降至原来一半所需的时间；长者可达1010a，短者仅有10-10s。半衰期1.02 MeVPositron,electron,annihilatin photons8/4/202234思考题核素、同位素、同质异能素的定义核衰变及其类型半衰期与放射性活度的定义射线与物质的相互作用
