J.R. Beene

Magnetic moments and half-lives of isomeric states in polonium isotopes

Abstract We have observed small violations of the additivity rule for isomeric two-proton states in 202, 208–210Po. The g-factors of the 110 ns 8+ state in 202Po and of the 24 ns 13 2 − state in 209Po were measured for the first time. The accuracy of relative g-factors which were previously measured has been considerably improved. The static quadrupole moment of 209Bi g.s. is deduced from three E2 transition probabilities in 210Po. The absolute value of Q is ≈ 15% larger than obtained by optical spectroscopy and possible reasons for the discrepancy are discussed.

Magnetic moments of N = 50 isotones and proton core polarization

Abstract Pulsed heavy-ion beams of 4He, 6Li, 32S and 35C1 have been used to populate isomeric states in N = 50 nuclei having a closed neutron shell and a rather pure ( p n 1 2 g m 9 2 ) proton configuration. The g-factors of the 3.4 μs 17 2 − state in 91Nb, the 9.3 ns 11− state in 92Mo, the 10.1 μs 17 2 in 93Tc, the 65.5 ns 6+ state and the 68 μs 8 + state in 94Ru were measured for the first time and those of 8+ states in 90Zr and in 92Mo were remeasured with improved accuracy. The g-factors increase by (4.2 ± 0.8)% as the p 1 2 proton subshell is filled and decrease by (3.5 ± 1.4)% as the number of protons in the g 9 2 shell increases from two to four. Calculations that take core polarization into account in first-order perturbation theory explain quantitatively the observed magnetic moments. One-pion exchange current contributions have also been calculated.

Knight shifts and absolute magnetic moments of (h9/2) n proton states in trans-bismuth nuclei

The Knight shiftsK(FrT1) andK(RaPb) have been measured in connection with a systematic study on magnetic moments of (h9/2)n proton states. The Knight shifts were obtained directly by a comparison of precession frequencies and, indirectly, from relaxation times involving the Korringa relation. Good agreement is found among the results from the different methods; the average values areK(FrT1)=(0.89±0.09)% andK(RaPb)=(1.05±0.15)%.

Electric quadrupole moments of the first excited states of 28Si, 32S and 34S

Abstract The reorientation effect in Coulomb excitation has been used to measure the following static electric quadrupolemoments: Q 2 + ( 28 Si ) = +17.5 ± 2.9 e · fm 2 , Q 2 ( 32 S) = −11.5 ± 4.8e · fm 2 and Q 2 + +( 34 S) = +6.3 ± 4.3 e · fm 2 . Energy spectra from the 208 Pb+ 28 Si, 32, 34 S reactions at E = 105–122 MeV were obtained with the Chalk River Q3D spectrometer. These data were fitted with accurate B ( E 2; 0 + → 2 + ) values determined from a weighted average of all previous measurements combined with those measured by the Doppler shift attenuation method by using the inverse reactions 4 He( 32, 34 S, α) where the mean 2 + 1 state lifetimes were found to be 0.236 ± 0.016 ps ( 32 S) and 0.442 ± 0.026 ps( 34 S).

Precise magnetic moments of (h92)n proton states

Abstract The induced microscopic magnetic fields (Knight shifts) for Fr and Ra recoils in metallic hosts have been determined by several independent methods. The observed accurate g-factors of ( h 9 2 ) n proton states and the magnetic moments of single-particle states are difficult to explain by a consistent theoretical approach.

Isomeric yrast states in 206Tl

Abstract We have found isometric states in 206 Tl with J π = 12 − (T 1 2 = 3.76 min ) , 7 + (10ns) and 5 + (78ns) and have identified their proton-neutron hole structure. New electromagnetic properties of proton hole orbitals have been determined.

The low solar neutrino flux: A search for a resonance in 6Be

Abstract A study of neutron time-of-flight spectra from the 4 He( 3 He, n) 6 reaction at E 3He = 38.61 MeV, sets a one standard deviation upper limit of 7 μb/sr for the cross section to a possible narrow level near the 3 He + 3 He threshold.

Search for a 0+ level near the 8.87 MeV, 2− level of 16O

Abstract The 4 He( 12 C, 4 He) 12 C reaction has been used with a differentially pumped 4 He target to search for a J π = 0 + , Γ = 100 eV resonance recently reported to occur near the J π = 2 − , 8.87 MeV level of 16 O. No evidence for such a resonance was found in the present experiment with a confidence level > 99.99 %. This supports the assumption of Hattig et al . that the β-delayed α-particles observed from this excitation energy region in 16 O are due to the parityviolating α-decay of the 2 − level.