1. Decay

2. W. Udo Schröder, 2007 Nuclear Decay 2 Decay Types There are many unstable nuclei - in nature Nuclear Science began with Henri Becquerel’s discovery (1896) of uranium radioactivity and man-made: Types of decay: “weak” decays

3. W. Udo Schröder, 2007 Nuclear Decay 3 Domains of Nuclear Decay Modes N=126 Isotones Z=82 Isotopes A Neutron Dripline B n = 0 SHE Z=118 discovered (?) Proton Dripline B p = 0 E f = 0 Segré Chart stable nuclide A = 132 Isobars Stable nuclides

4. W. Udo Schröder, 2007 Nuclear Decay 4 Example: ThB ( 212 Pb) Decay Scheme 212 Pb ground state decays spontaneously by e - emission ( - decay) 212 Bi ground state has branched ( and ) decays 208 Pb ground state is stable

5. The 4 Natural Decay Series W. Udo Schröder, 2007 Nuclear Decay 5 ChainParentt 1/2 (a)Final Thorium 232 Th1.4·10 10208 Pb Neptunium 237 Np2.1·10 6209 Bi Uranium 238 U4.5·10 9206 Pb Actinium 235 U7.0·10 8207 Pb 238 U Decay Chain Np chain is not found on Earth, t 1/2  age of Earth Dominantly chain of  and  decays

6. The 4 Natural Decay Series W. Udo Schröder, 2007 Nuclear Decay 6 ChainParentt 1/2 (a)Final Thorium 232 Th1.4·10 10208 Pb Neptunium 237 Np2.1·10 6209 Bi Uranium 238 U4.5·10 9206 Pb Actinium 235 U7.0·10 8207 Pb Np chain is not found on Earth, t 1/2  age of Earth Th Series

7. W. Udo Schröder, 2007 Nuclear Decay 7 Observing a Finite Lifetime of the 198 Au g.s. E. Norman et al., http://ie.lbl.gov/radioactive decays/page2 411.8 keV Spectrum of  delayed 198 Au -rays  decay of 198 Hg exc. state is prompt:      11 measurements Each spectrum ran for 12 hours real time #11 taken 5 days after #1 # 1 # 11

8. W. Udo Schröder, 2004 Principles Meas 8 Measuring “Decay Curves”: Fast-Slow Signal Processing Radiation Source Slow Fast PreAmp Amp Produce timing signal  electron. Clock (TAC) Data Acquisition System Energy  E-Tag Produce analog signal  Binary data to computer Energy Discrim inator Time Trigger Start Stop External Time reference signal t 0 Detector Measured: Energy and time of arrival t=t-t 0 (relative to an external time-zero t 0 ) for radiation (e.g., -rays), energy discriminator to identify events (A) in a certain energy interval E by setting an identifier “tag.” Calibrate t axis channel #  time units (s, y,..) Watch that t-channel  . 0100200300400  0.01 0.1 1 i tt Activity  A(  t)/  A(t 0 )  t (Channel #)

9. Kinetics of Nuclear Decay: Logarithmic Decay Law 0100200300400 1  10 2 0.1 1 i t 0100200300400 0 0.2 0.4 0.6 0.8 1 Disintegration of Radioactive Sample i t i Sample Activity A(t)/A(0) time t

10. Sum Radioactivity W. Udo Schröder, 2007 Nuclear Decay 10 Genetically independent species: Sample with 2 components (N 1, N 2 )  same type of radiation (-rays) (N1)(N2)(N1)(N2) ( 1 ) ( 2 ) Decompose total decay curve  1, 2. Simultaneous fit or deduce constant 2 for “shallow” decay first

11. Branching Decay W. Udo Schröder, 2007 Nuclear Decay 11 Genetically dependent species: Sample depopulated by 2 decay paths ( 1, 2 ) 1 2  Partial decay constants/half lives:

12. Activation and Decay W. Udo Schröder, 2007 Nuclear Decay 12 Competition production/decay for a species with N(t) members Irradiation of sample produces unstable species N. Constant rate of production P Constant decay rate Gain- Loss Equation Irradiation inefficient for t  3  N N P Irradiation of Sample

13. Activation and Decay W. Udo Schröder, 2007 Nuclear Decay 13 Irradiate 51 V with thermal neutrons, daughter -decays to 52 Cr* A(t)/P vs. t Fit Curve 52 Cr* de-excites by  emission  intensity  activity

14. Genetically Related Decay Chain W. Udo Schröder, 2007 Nuclear Decay 14 2 1 N1N1 N2N2 N3N3 Gain and loss for i-th daughter Coupled DEq. For populations N i of nuclei in chain Check by differentiation

15. Examples of Genetically Related Decay Chains W. Udo Schröder, 2007 Nuclear Decay 15

16. Decay

17. W. Udo Schröder, 2007 Nuclear Decay 17

18. W. Udo Schröder, 2007 Nuclear Decay 18 Radio-Activity/Units

19. W. Udo Schröder, 2007 Nuclear Decay 19 Average Radiation Exposure From Lilley, Nuclear Physics, Principles and Applications, J. Wiley & Sons, Ltd., 2001 ( 238 U, 232 Th, 40 K) ( 219 Rn, 220 Rn, 222 Rn) Tobacco absorbs Rn  210 Pb, 210 Po “hot spots” in lungs cancer risk Note unit:   Sv

20. W. Udo Schröder, 2007 Nuclear Decay 20 Biological Effects Ann. ICRP 26, 1994 Heavy charged particles: High ionization density, localized: maximum near end of range (Bragg peak) Electrons (+Bremsstrahlung): Long range, diffuse multiple scattering, low ionization density, delocalized absorption Neutrons: Indirect ionization, capture H(n, ) for E n <100 eV, keV-neutrons scatter elastically (np), 2-MeV neutrons have = 6 cm to thermalization and high ionization density. Photons: Like electrons, low ionization density, Compton scattering + photoelectric absorption, delocalized absorption Indirect chemical effects: Free radicals (neutral atom or molecule with an unpaired e - )

21. W. Udo Schröder, 2007 Nuclear Decay 21 Biologically Relevant Dose Weighting Factors TypeEnergy Range Weighting w R e ± all1 neutrons< 10 keV5 10-100 keV10 100 keV – 2 MeV 20 2 - 20 MeV10 >20 MeV5 protons< 20 MeV5 , FF, clusters 20 TissueWeight w T Gonads0.20 Red bone marrow0.12 Colon0.12 Lungs0.12 Stomach0.12 Bladder0.05 Breast0.05 Liver0.05 Oesophagus0.05 Thyroid0.05 Skin0.01 Bon surface0.01 All remaining tissue0.05 Ann. ICRP 26, 1994

22. W. Udo Schröder, 2007 Nuclear Decay 22 Effect on Complex Molecules Enzyme deoxyribonuclease (DNAse) Splits DNA Rad exposure decreases activity exponentially with dose High DNAse concentrations: expect more direct hits, direct damage of molecule Low DNAse concentration: expect fewer direct hits, less direct damage. Observation due to more free OH. and H. radicals from H 2 O dissociation. DNAse in Water Recovery: DNA molecules can repair themselves after moderate damage by X rays and minimum ionizing radiation. Approximately total recovery after small doses, no accumulation of effects More damage and less recovery after irradiation with neutrons X-rays, Assay at t 0 t 0 +5hrs Neutrons Assay at t 0 t 0 +5hrs DNA Survival Rate After Lilley, Nuclear Physics, Principles and Applications, J. Wiley & Sons, Ltd., 2001

23. W. Udo Schröder, 2007 Nuclear Decay 23 Risk Factors TissueEffectProbability/Sv BreastCancer2.0 x 10 -3 Red bone marrowLeukemia5.0 x 10 -3 LungCancer8.5 x 10 -3 ThyroidCancer8.0 x 10 -4 Bone surfaceCancer5.0 x 10 -4 Other tissueCancer3.4 x 10 -2 Whole bodyCancer effects5.0 x 10 -2 After Lilley, Nuclear Physics, Principles and Applications, J. Wiley & Sons, Ltd., 2001

24. W. Udo Schröder, 2007 Applications 24 Applications of Nuclear Instruments and Methods

25. W. Udo Schröder, 2007 Applications 25 Halflives of Radio-Isotopes for Dating years Age of Earth Nucl. Synth.   : particles measured to identify fractional abundance of radioactive isotope, K: K electron capture R : measure series of several decay products

26. W. Udo Schröder, 2007 Applications 26 Carbon Dating of Organic Objects n Conventional method:  counting Direct 14 C counting method: Accelerator Mass Spectroscopy  R  10 -16 (10 5 a) Measure 14 C/ 12 C ratio of sample at t

27. W. Udo Schröder, 2007 Applications 27 Calibration of 14 C Dating Methods (a) CE  t-dependent flux of cosmic rays (solar cycles)  t-dependent 14 C production and intake Calibration: 14 C-analyze yearly rings in trees of different ages (number and widths of rings), connect to fossils Errors in very old samples lead to underestimation of age (few hundred years). Variation in 14 C Production

28. W. Udo Schröder, 2007 Applications 28 Rb/Sr Dating of Rocks/Age of the Earth Undisturbed by erosion/transmutation All rocky objects (planets, asteroids, meteorites) of solar system crystallized ≈ simultaneously (t=0) out of interstellar dust/nebula (supernova remnants). R Different minerals in meteorite containing different amounts of N P  different x Construct isochron Age of rock (since formation)

29. W. Udo Schröder, 2007 Applications 29 Age of the Earth Terrestrial volcanic activity dated: produces younger rocks Age of Earth = 4.5·10 9 a Moon has similar age