C. Broude

Dependence of the Doppler shift lifetime method on slowing environment

Abstract To check for systematic analysis errors in the Doppler shift attenuation method for nuclear lifetimes, a mean life in 22 Ne has been measured in 39 different solid elemental slowing materials. A range of lifetimes of 1.9, strongly correlated with atomic number is observed.

A new measurement of the 7Be(p,γ)8B cross-section with an implanted 7Be target

Abstract The 7 Be(p, γ ) 8 B capture reaction is of major importance to the physics of the sun and the issues of the “solar neutrino puzzle”. We report here on a new determination of the absolute cross section of this reaction, using a novel method which overcomes some of the major experimental uncertainties of previous measurements. We utilize a 7 Be target implanted into a Cu substrate and a uniformly scanned particle beam larger than the target spot, eliminating issues of target homogeneity and backscattering loss of 8 B reaction products. The target was produced using a beam of 1.8·10 10 /s 7 Be nuclei extracted at ISOLDE (CERN) from a graphite target bombarded by 1 GeV protons in a two-step resonant laser ionization source. The 7 Be nuclei were directly implanted into a copper substrate to obtain a target of 2 mm diameter with a total of 3.10 15 atoms. The measurement of the 8 B production cross section was carried out at the Van de Graaff laboratory of the Weizmann Institute of Science. We obtain for the S factor of the reaction: S 17 ( E cm = 1.09 MeV) = 22.7(1.2) eV. barn and S 17 ( E cm = 1.29 MeV) = 23.8(1.5) eV. barn, somewhat higher than other recent measurements. The present results can serve as a benchmark for further measurements of this cross section.

The g-factor of the 8+ yrast level in 84Sr via a tilted multi-foil experiment☆

Abstract The g-factor of the 8+ yrast level of 84Sr has been measured using the polarized hyperfine fields of a tilted multi-foil target. The sign of the g-factor has been determined to be negative to better than six standard deviations. Calibration using similar measurements on levels in 77Se and 80Se ions yields the value of g=−0.15 (7), indicating a ν g 9 2 −4 configuration for this level.

Magnetic moments at backbending and spectroscopy of 134Ce

Abstract Employing the static hyperfine fields at cerium nuclei in magnetized Fe and Gd hosts, the g -factor of the 134 Ce(10 + ) state at backbending ( E x = 3719.3 keV ) has been determined as g = − 0.30 (25). The coexistence of this neutron-dominated state with the ( v h 11 2 ) n 10 + isomer ( E x = 3208.5 keV, g = −0.19(1)) is unexpected. A comprehensive spectroscopic study following the 122 Sn( 16 O, 4n) reaction, including γ-angular distributions, prompt and delayed γ coincidence and recoil-distance measurements has yielded new information on quasi-collective bands of both parities. The properties of the low-lying positive-parity states are well described by the interacting boson model.

Nuclear polarization of high-spin levels and the sign of the quadrupole moment of 54Fe(10+)

Abstract The determination of the sign of the quadrupole deformation at high spins requires an observation of the electric quadrupole interaction of polarized isomers in single crystals of non-cubic metallic hosts. The 54Fe(10+) isomer was polarized, subsequent to its population by the (12C, p2n) reaction, by passage through an array of tilted carbon foils. The isomers were then recoil implanted into single crystals of zinc and cadmium and the tune differential modulations of the angular distribution of decay γ-rays were observed. Nuclear polarization values of PI = 0.08(3)−0.18(5) were found for 13–17 polarizing foils, respectively, and a positive sign of the quadrupole moment was deduced. An improved value was established for the quadrupole moment: Q[ 54 Fe (10 + )] = + 29.7(4) e · fm 2 , in agreement with current shell-model predictions.

Electric quadrupole interaction of192Tl(8−) nuclei in hexagonal Tl and in tetragonal in metals

The TDPAD technique has been used to measure the electric quadrupole coupling constants for the192Tl(8−) isomer in hexagonal Tl at different temperatures and in tetragonal In at room temperature. The values measured weree2qQ/h=24.0(15) MHz extrapolated toT=0K, and 33.1(16) MHz at 293K for the Tl and In hosts,respectively, The electric field gradient for Tl impurities in In was determined from systematics of isoelectric systems, yielding |Q[192T1(8−)]|=0.44(7)b.The almost perfect symmetry of the T1 crystalline structure makes this metal a sensitive probe to current models for electric field gradients in metals. The magnitude and temperature dependence of the field gradient in thallium metal are discussed within the framework of such models.

Nuclear polarization and signs of quadrupole moments of high-spin Gd isomers

Abstract Time-differential perturbed-angular-distribution (TDPAD) experiments have been performed on polarized intermediate- and high-spin isomers 144 Gd (10 + ) and 147 Gd ( 13 2 + , 27 2 − , 49 2 + ) . Excited Gd nuclei populated by ( 28 Si , x n ) reactions were polarized by the tilted-multifoil technique and implanted in a Gd single-crystal host. Observation of the subsequent electric quadrupole interaction with the known electric field gradient yielded negative values of the sign of the deformation for all isomers studied. The magnitude of the induced nuclear polarization PI was also determined from the TDPAD data and compared to model calculations in order to deduce the average atomic angular momentum and polarization of Gd ions at v/c ∼ 0.018.

Two neutron-dominated 10+ states in 134Ce

A 10 + isomer has been established at E X = 3208.5keV with τ = 485(20)ns and g = −0.19(1). The coexistence of this state with the other neutron-dominated 10 + state at backbending [ E X = 3719.3keV, τ = 8(1)ps, g = −0.20(20)] is unexpected.

Single particle signatures in high-spin, quasicontinuum states in 193,194Hg from g-factor measurements

The average g factors of high spin, high-excitation energy, quasicontinuum structures in {sup 194,193}Hg were measured by observing the precessions of the angular distributions of {gamma}-ray transitions in several normal-deformation bands that coalesce in the decay of the entry distribution of states. The average g factors of the states leading to the three main bands in the {sup 193,194}Hg isotopes were: {l_angle}g({sup 193}Hg){r_angle}=+0.19(1) and {l_angle}g({sup 194}Hg){r_angle}=+0.26(1), respectively. These average g factors are smaller than the average of the g factors of the high energy states in the three superdeformed bands of {sup 194}Hg, {l_angle}g(SD; {sup 194}Hg){r_angle}=+0.41(8). While the nucleus in the superdeformed well behaves like a rigid rotor, the present results demonstrate the important role played by multiple, quasiparticle neutron configurations in the structure of normal-deformation, highly-excited nuclear states.

g-factors of short-lived isomers in 147,148Gd and the role of the 3− core excitation☆

Abstract The magnetic moments of short lived Gd isomers have been determined in a time differential measurement using the internal hyperfine field in ferromagnetic Gd host. The results g[ 147 Gd ( 13 2 + )]=+ 0.075(3) and g[ 148 Gd (9 − )]=− 0.018(2) are discussed in terms of the contribution of the 3 − core excitation. The 3 − ⊗ vf 7 2 n components in the respective wave functions are found to be dominant.