1. Sizes

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. W. Udo Schröder, 2004 Principles Meas 5 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 #)

6. W. Udo Schröder, 2007 Nuclear Decay 6 Example: Determination of the 198 Au g.s. Lifetime 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

7. 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

8. W. Udo Schröder, 2007 Nuclear Decay 8 Radio-Activity/Units

9. W. Udo Schröder, 2007 Nuclear Decay 9 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

10. W. Udo Schröder, 2007 Nuclear Decay 10 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 - )

11. W. Udo Schröder, 2007 Nuclear Decay 11 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

12. W. Udo Schröder, 2007 Nuclear Decay 12 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

13. W. Udo Schröder, 2007 Nuclear Decay 13 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

14. W. Udo Schröder, 2007 Nuclear Decay 14 0100200300400 1  10 2 0.1 1 i t Activity A(t)/A(t 0 )

15. W. Udo Schröder, 2007 Nuclear Decay 15

16. W. Udo Schröder, 2007 Nuclear Decay 16 Intrinsic Nuclear Spin Nuclei can be deformed  can rotate quantum mech.  collective spin and magnetic effects (moving charges) Intrinsic spin? Nucleons have spin-1/2 Demonstrate via interaction with external odd-A : I= half-integer multiple of ħ even-A: I= integer multiple of ħ even-Z & even-N: I = 0 Quantum mechanical spin: “good” quantum numbers: I, m I Interactions via magnetic moment mIħmIħ  z x y quantization axis Nuclear Magneton expt fact