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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

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Tunneling through a potential barrier to describe the alpha-decay

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Systematics of alpha-decay lifetimes and energies

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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

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additional centrifugal-(angular momentum)-barrier at higher valuesof orbital angular momenta l !

Replace V(r) by V(r) + l(l+1)ħ2/(2mr2)

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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

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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)) !!

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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).

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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)

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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

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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!