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41.
Superallowed nuclear beta decay between 0+ analog states is a sensitive probe of the weak interaction, with the established strength – or Ft value – of each such transition being a direct measure of the vector coupling constant, GV. Each transition’s Ft value depends on the half-life of the parent nucleus as well as on the Q-value and branching ratio for the transition of interest. It also depends on small (1%) transition-dependent theoretical corrections, of which the most sensitive accounts for isospin symmetry breaking. We have recently published a new survey of world superallowed-decay data, which establishes the Ft values of 14 separate superallowed transitions to a precision of order 0.1% or better. The results from this very robust data set yield the value of Vud, the up-down quark mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, and lead to the most demanding test available of CKM unitarity. The survey results and their outcome are described, as is the current direction of experiments that focus on testing the validity of the isospin-symmetry-breaking corrections. 相似文献
42.
Stone N.J. White G.N. Rikovska J. Ohya S. Giles T.J. Towner I.S. Brown B.A. Fogelberg B. Jacobsson L. Hjorth-Jensen M. 《Hyperfine Interactions》1999,120(1-8):645-649
Recent on-line nuclear orientation measurements of nuclear magnetic dipole moments by the method of NMR on oriented nuclei
(NMR/ON) have yielded significant new odd-A moments. These include those closest to double magic 132Sn, namely, 133Sb [132Sn plus one g7/2+ proton] and 133Tem [132Sn with a pair of g7/2+ protons and one hole in the h11/2- neutron sub-shell]. These close-to-double-magic results allow stringent tests of nuclear moment theory including, as main
contributions to deviations from the simple free nucleon (Schmidt limit) values, configuration mixing in the nuclear wavefunction
and mesonic exchange current modification to the dipole moment operator. Comparison with theoretical prediction, using established
approaches to both these corrections, is discussed showing success in medium mass nuclei comparable to results previously
established in light [to 40Ca] and heavy [near 208Pb] nuclei.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
43.
White G.N. Stone N.J. Rikovska J. Ohya S. Giles T.J. Towner I.S. Brown B.A. Fogelberg B. Jacobsson L. Hjorth-Jensen M. 《Hyperfine Interactions》1999,120(1-8):651-655
Recent on-line nuclear orientation measurements of odd-A nuclear magnetic dipole moments of odd-A Sb, Te and I isotopes by
the method of NMR on oriented nuclei mean that we now have complete series of odd-A moments up to, and including, those closest
to the double shell closure at 132Sn. In this paper we consider the systematic changes in the measured moments as a function of proton number for the isotonic
sequence 133Sb [g7/2+]1–139La [g7/2+]7 and as a function of neutron number for the isotopic sequences 125-133Sb and 127-135I and their interpretation using collective and shell model approaches.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
44.
O. Häusser T.K. Alexander T. Faestermann D. Horn D. Ward H.R. Andrews I.S. Towner 《Physics letters. [Part B]》1978,73(2):127-130
The time-differential perturbed angular distribution method was used to determine the g-factors of the states in 43Ti and 43Sc. The results for the mass 43 mirror pair are: , . Considering in addition the magnetic moments in A = 41 and 42, it is suggested that the deformed states considered by Johnstone and Castel and by Erikson are responsible for the observed large deviations from the Schmidt values. 相似文献
45.
46.
47.
D. Horn I.S. Towner O. Häusser D. Ward H.R. Andrews M.A. Lone J.F. Sharpey-Schafer N. Rud P. Taras 《Nuclear Physics A》1985,441(2):344-380
High-spin states in 150–152Dy have been investigated. Gamma-gamma coincidences in all three isotopes have been studied with Compton-suppressed Ge(Li) detectors. For 151Dy, lifetimes of the high-spin states have been measured by the recoil-distance technique. The spin and parity assignments, transition rates, and level systematics support the interpretation of the observed states as proton particle-hole excitations coupled to aligned valence neutron configurations. Shell-model calculations, based on effective interactions and a 146Gd core, quantitatively reproduce the observed level patterns, and the predicted transition rates qualitatively agree with the observed values. 相似文献
48.
I. S. Towner 《Czechoslovak Journal of Physics》1986,36(3):360-367
Experimental evidence for pion enhancement in axial charge transitions as predicted by softpion theorems is reviewed. Corrections from non-soft-pion terms seem to be limited. For transitions involving the space part of the axial-vector current, soft-pion theorems are powerless. Meson-exchange currents then involve a complicated interplay among competing process. Explicit calculations in the hard-pion model for closed-shell-plus (or minus)-one nuclei, A=15 and A= =17, are in reasonable agreement with experiment. Quenching in the off-diagonal spin-flip matrix element is larger than in the diagonal matrix element.Invited talk to the symposium Mesons and Light Nuclei, Bechyn. Czechoslovakia. May 27–June 1, 1985. 相似文献
49.
Precise measurements of the ft-values for superallowed nuclear β-decay yield results that support conservation of the weak vector current but violate the
unitarity of the Cabibbo-Kobayashi-Maskawa matrix by more than two standard deviations. This apparent violation of the Standard
Model has led to considerable theoretical and experimental activity largely focussed on reducing uncertainties in the small
correction terms that account for charge-dependent nuclear effects. This activity is outlined and the prospects for future
sharpening of the unitarity test are assessed.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: hardy@comp.tamu.edu 相似文献
50.
I.S. Towner 《Nuclear Physics A》1973,216(3):589-602
The difference in ft values for mirror Gamow-Teller β-decays has been estimated for the p-shell mass multiplets A = 8, 9, 12 and 13. Most important are the binding energy effects which are calculated with various Saxon-Woods single-particle models. The results are very parameterdependent; nevertheless all models predict a larger asymmetry δ in even-A than in odd-A multiplets. This is contrary to experimental data. The effects of charge-dependent Coulomb mixing are considered by repeating the Cohen-Kurath shell model calculations in a proton-neutron formalism. In most cases the effects were small, but in some odd-A decays a significant contribution to δ was obtained, which partially resolves the discrepancy just noted. The influence on δ of second-forbidden matrix elements and radiative corrections is small. 相似文献