1、12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)1Zhang Yongxue核醫學物理基礎12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)2K 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.12/21/2021核醫學物理基礎(BasicPhysicsof

2、Nuclear)5Stable & radionuclideStable & radionuclideP83的核素，核力不能與質子間的斥力保持平衡，故全是不穩定的放射性核素。 P82的核素，天然的放射性核素很少，多由人工生產。 12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)6Proton rich nucleiNeutron rich nucleiZ=N05010015050100PROTON NUMBERNEUTRON NUMBERNeutron-proton ratio with line nuclear stability12/21/20

3、21核醫學物理基礎(BasicPhysicsofNuclear)7Nuclear decayAlpha()decayAlpha()decay Alpha particles is a helium nuclei consisting of 2 protons and 2 neutrons. 4HeQHeYXAZAZ4242937. 4422228622688HeRnRa12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)8Characteristic of alpha particle粒子實質上是He原子核，衰變發生在原子序數大于82的重元素核素。粒子的速度約為光速

4、的1/10，即萬km/s，2s繞地球周。在空氣中的射程約為3-8cm，在水中或機體內為0.06-0.16mm。因其射程短，一張紙即可阻擋但粒子的電離能力很強。12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)9Beta decayBeta decayEmit particles and capture orbital electrons.To be a companion to increase or decrease of atomic number,but the mass number of the new nuclei is the same. Inclu

5、ding , and electron capture. Velocity of particle is 200 thousand km/s in vacuum.Penetrability is more than alpha particle.12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)10- decayEmit particlesNeutron rich nucleiNeutron protonThe mass number of new nuclei is the same as the parent nuclei,atomic number incr

6、ease 1n p+ +QMeVSP71.21/2021核醫學物理基礎(BasicPhysicsofNuclear)11 decayEmission of particleNeutron poor nucleiA proton to neutron transformationArtificial radionuclidep n+e+189F188O + + + 0.66MeV12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)12Electron capture,ECAn orbital electron is captured to f

7、orm a neutron.Neutron poor nucleiA proton to neutron P+e- nCharacteristic X-rayAuger electronMneFe5525552612/21/2021核醫學物理基礎(BasicPhysicsofNuclear)13Gamma decay and internal conversionGamma decay may be a part of another decay process,such as ,EC or -Metastable to stable state transition and emission

8、 of electromagnetic(transition)New nuclei mass and proton is the same,but energy changed Internal conversion and Internal conversion electronInternal conversionelectronray)140(994369943669942keVTcTcMohmh12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)14 Characteristic of rayGamma ray is photonNo electric ch

9、argePenetrability is more than charged particleLow ionization ability12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)15Comparison of three decayalpha decaybeta decaygamma decayMass changedyesnonoProton changedyesyesnoEnergy changedyesyesyes12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)16The law of nuclear decay 放

10、射性核素是不穩定的，它要自發地發生衰變而變成新元素的核。放射性原子核并不是同時衰變的，對于某一個原子核而言，何時衰變是各自獨立沒有規律的，但對于某一種原子核的群體而言，它的衰變是有規律的，即原子核數目隨時間增長按指數規律減少。12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)17Decay constant()Decay constant()衰變常數：某種放射性核素的核在單位時間內自發衰變的幾率；它反映該核素衰變的速度和特性；值值大衰變快，小則衰變慢，不受任何影響。大衰變快，小則衰變慢，不受任何影響。12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)18The 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變，原子核數目隨時間增長按指數規律減少 tNlogNt12/21/2021核醫學物理基礎(BasicPhysicsofNuclear)19Half life 半衰期半衰期Physical half life，(T1/2) 在單一的放射性核素衰變過程中，放射性活度