No abstract available

No abstract available

[en] The shape of allowed Β spectra have a small contribution from the interference of the vector, weak-magnetism and axial GT matrix elements. According to CVC plus charge-symmetry of nuclear interactions, in a 0⁺→ 1⁺ transition like the Β and γ decays of the A=14 system, the weak-magnetism and electro-magnetic-Ml matrix elements should be equal. A measurement of the shape of the ¹⁴O spectrum, however, disagrees, by a factor of two with naive calculation described above. It has been speculated that because of the high supression of GT matrix element in the A=14 system, one could understand this discrepancy based on small charge-symmetry-effects. We have used shell-model wave functions adjusted to fit ¹⁴N(e,e^') inelastic scattering, the width of the M1-γ transition, and the Β log f t's, and show that reasonable assumptions lead to estimates that are very close to the naive CVC estimation. We propose that the ¹⁴O discrepancy is important and that new experiments should be done to measure the shape of the spectrum

[en] Isospin-mixing corrections for superallowed Fermi transitions in fp-shell nuclei are computed within the framework of the shelf model. The study includes a re-evaluation of three nuclei that are part of the set of nine accurately measured transitions and five new cases that are expected to be measured in the future at radioactive-beam facilities. For the heavier fp-shell nuclei, both the configuration mixing term, δ_IM, and the radial-overlap mis-match correction, δ_RO, are much larger than in the case of the previous nine transitions. For the nine accurately measured transitions, excellent agreement with the CVC hypothesis is found. but the CKM matrix is found to violate the unitarity condition at the level of 3 σ

[en] Shell-model calculations of charge radius differences in the Pb isotopes are discussed. Core quadrupole oscillations are found to be significant factors in the calculations. Existing data on the ²¹⁰Pb isotope shift and the B(E2) strengths in ²¹⁰Pb are shown to be inconsistent. Ground-state correlation effects in light nuclei (i.e., 0 and Ca isotopes) introduce odd-even staggering effects and other qualitative features in agreement with existing data

[en] The effect of isospin symmetry breaking on level statistics has been examined with the nuclear shell model. The eigenvalues and electromagnetic transitions were calculated with the program OXBASH for the nuclide ²⁶Al for conserved isospin and for broken isospin. The long-range correlations of the eigenvalues, as measured by Δ₃, show good agreement between the experimental results and the calculations. However, there are discrepancies between data and calculations for the short-range correlations of the eigenvalues

[en] The motivation for considering the ⁷¹Ga(p,n)⁷¹Ge reaction is to help determine the properties of ⁷¹Ga as a detector of solar neutrinos. The proposed solar neutrino experiment, ⁷¹Ga(nu,e^-)⁷¹Ge, has a threshold of only .236 MeV, and is thus sensitive to neutrinos produced in the basic burning process in the sun p + p → ²H + e⁺ + nu, which has a .420 MeV endpoint. The excitation of the (5/2)^- state at .175 MeV in ⁷¹Ge could be important, however. Were the Gamow-Teller (G-T) transition to the 175 keV state equal in strength to the ground state transition there would be approx. 25% added to the detector signal, the greater part of this coming from the ⁷Be neutrinos; the desired sensitivity to the p-p neutrinos would then be less

[en] Theoretical calculations for magnetic moments of T = O collective states in N = Z nuclei are compared with recent experimental results. The Jsup(π) = 2⁺ and 3^- states considered all have 0.49 < gsub(theor) < 0.51 if the wavefunctions have pure T = O isospin. Isospin mixing increases the calculated ¹⁶O 3^-g factor by 9%, consistent with experiment, but has a much smaller effect on the 2⁺ states. A reported negative experimental g factor for the 4⁺ state in ²⁰Ne is in complete disagreement with theory. (author)

[en] We have measured excitation functions of the #betta#-rays resulting from the bombardment of ₁₅N by polarized and unpolarized protons in the energy range E/sub p/ = 2.5 to 9.5 MeV with emphasis on identifying dipole decays to the first (0⁺) and second (3^-) excited states in ₁₆O. Resonances in #betta#¹² are observed at E/sub x/ = 16.21, 16.45, 16.82, 17.12, 18.03, 18.98, 19.90 and 20.41 MeV. The 16.21 and 17.12 MeV resonances in #betta#¹² are identified as M1-decays of the 1⁺ T = 1 states to the 6.05 MeV 0⁺ state in ₁₆O. The measured ratio of reduced strengths B(m1,#betta#¹)/(B(M1,#betta#⁰) is 0.48 +- 0.03 for decays from the 16.21 MeV state and 0.55 +- 0.04 for decays from the 17.12 MeV state. The 18.03 MeV resonance is due to a 3^- T = 1 state in ₁₆O with a strength Gamma/sup p/Gamma/sub gamma 2//Gamma = (1.96 +- 0.27) eV and the 18.98 MeV resonance is due to the 4^- T = 1 stretched particle-hole state with a strength of (0.85 +- 0.10) eV. We determine absolute particle and #betta# widths for these states. The M1 #betta#²-width of the 18.98 MeV state, (7.1 +- 3.1) eV, is in agreement with a shell-model calculation. Resonances in #betta#³ are observed at 16.82 and 17.27 MeV and in #betta#⁴ at 17.88 MeV. The excitation energies and widths of these levels as well as the strengths of the #betta# transitions suggest T = 1 character for all of the resonances for which capture #betta#-rays are observed. Correspondences of our resonances to levels in ₁₆N are given. We compare #betta# widths, including ground-state M1 decays, and allowed #betta# transition rate in A = 16 nuclei with shell model calculations and obtain rough agreement. Additional shell model calculations for M1 and GT (Gamow-Teller) decays in the A-14, 15, 17 and 18 nuclei are presented, which indicate that GT matrix elements are quenched by approx. 20% relative to shell model predictions and also relative to the spin part of the M1 matrix elements

[en] The intensities of γ-rays emitted following the β⁺ decays of ³⁹Ca and ³⁵Ar were measured by using a Ge(Li) detector to detect the delayed radiation from a KCl target bombarded by 13-MeV protons. From these results the experimental log(ft) values and related B(GT) values for the ³⁵Ar and ³⁹Ca decays are deduced. These are compared with shell-model calculations together with a recent computation by Towner and Khanna of the higher-order corrections due to configuration-mixing outside the sd shell, isobar currents and other meson-exchange currents. We concentrate on the significance of the l-forbidden 1d/sub 3/2/ - 2s/sub 1/2/ Gamow-Teller transition in mass 39 and comment on its relation to the corresponding M1 transitions in ³⁹Ca and ³⁹K. 38 references