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WS09/10 Mahnke 26.1.10
4. Nuclear transformation4.1. Alpha-decay
History: Characterization of the energies of alpha-particles via theirrange in „air“, as made visable in the cloud chamber
Geiger-Nuttal-rule
WS09/10 Mahnke 26.1.10
Tunneling through a potential barrier to describe the alpha-decay
WS09/10 Mahnke 26.1.10
Systematics of alpha-decay lifetimes and energies
WS09/10 Mahnke 26.1.10
alpha-decay chain to identify new superheavy elements (e.g.Z=107)
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names of new superheavy elements
Lr 103 LawrenciumRf 104 Rutherfordium Db 105 DubniumSg 106 Seaborgium Bh 107 BohriumHs 108 Hassium Mt 109 MeitneriumDs 110 DarmstadtiumRg 111 Roentgenium
WS09/10 Mahnke 26.1.10
additional centrifugal-(angular momentum)-barrier at higher valuesof orbital angular momenta l !
Replace V(r) by V(r) + l(l+1)ħ2/(2mr2)
WS09/10 Mahnke 26.1.10
The polonium „problem“ (recent publicity), a typical alpha emitter
polonium production in a reactor by starting from Bipolonium is also produced in a decay chain (of U-238, Rn-problem)
214Pb210Pb208Pb
214Bi210Bi209Bi
218Po214Po210Po
211At
222Rn212Rn
α-Zerfall β-Zerfall stabil
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210Po
0+
206Pb
0+
2+ 0.80
0
0
>99.9%
Eα = 5.30 MeV
138 d
L=2
L=0
WS09/10 Mahnke 26.1.10
4.2. Beta-Decay
∆A=0 with ∆Z=±1 as illustrated in themass parabula
Qβ-/c2 = M(A,Z) – M(A,Z+1)
(Caution: only valid for free electron!)
Qβ+/c2 = M(A,Z) – M(A,Z-1) – 2 me
QEC/c2 = M(A,Z) – M(A,Z-1) - Xe
Example: EC 16367Ho → 16366Dy with QEC/c2 = 2.3 keV,
but for a totally stripped nucleus, inversely, beta-decay of Dy into Ho in a bound state is possible(storage ring experiment at GSI, (Jung et al.,PRL 69 (1992) 2164)) !!
WS09/10 Mahnke 26.1.10
Neutrino hypothesis: (Pauli)- continuous energy spectrum for the electron- angular momentum
Proof for the existence of the neutrino: indirectly via the recoil(Rodeback and Allen, PR86(1952)446)
EC: 37Ar + e- → 37Cl + ν +0.8MeV
Auger-e- defines the „start“, thedecay, the detection of the recoilatom the „stop“ (time-of-flight).
WS09/10 Mahnke 26.1.10
Neutrino detection:directly via a neutrino reaction(Reines and Cowan, PR113(1959)273)
ν + p → e++ n
large amount of hydrogen !
scintillator for 2γ !
Cd added for n capture !
_
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Point defect production by recoil accompanying neutrino emission
(Metzner, Sielemann et al.,PRL 53(1984)290)
In in copper
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Shape of electron spectrum N(p)dp ~ |Hif|2 p2 (E0 – T)2dp(valid only for zero neutrino mass!!)
Kurie-Plot(with Coulomb correction)
Determining the neutrino mass
(towards zero with vertical tangentat endpoint energy)
but corrections due to chemicalbinding effects!!tritium decay
small mass, but not zero!!
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Mainz Tritium-Experiment
-tritium source: thin layer of frozen tritium (low energy loss)
-energy spectrum by varying the electric field
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Selection rules:total, energy-integrated decay probabilities (as logft-values) areused to classify „multipolarities“, called degree of „forbiddenness“.
Fermi transitions (spin of e and v antiparallel): ∆I=0 Gamow-Teller-transitions (Spin of e and v parallel): ∆I=0,1
Parity violationVector- and axialvector coupling participate equally strongly. Parity violation!
Classical experiments:- Wu-experiment: nuclear orientation of 60Co(Wu et al., PR105(1957)1413)
- Goldhaber, Grodzins, Sunyar: experiment to determine theneutrino helicity using 152Sm(Goldhaber, Grodzins,Sunyar PR109(1958)1015)
WS09/10 Mahnke 26.1.10
Nuclear orientation by adiabatic demagnetizationgamma-ray anisotropy as a measure for the orientationBeta asymmetry
Electron helicity is negative! Angular distribution W(δ)= 1+A cos δ
4+
2+
0+
5+
60Ni
60Co
WS09/10 Mahnke 26.1.10
nuclear resonance fluorescence of circularly polarised gammaradiation with partial compensation of recoil from precedingneutrino emission
Neutrino is left circularly polarised ! (antineutrino right)!Leptons are left-handed, antileptons right-handed!