Lloyd G. Mann

Coulomb matrix elements from β-γ(CP) correlation measurements in 57Ni and 65Ni

Abstract Measurements of the β−γ(CP) correlation have been made for the 3 2 − (β + , 0.84 MeV ) 3 2 − (γ, 1.38 MeV ) 7 2 − (ground-state) cascade in the decay of 57Ni and for the 5 2 − (β − , 1.02 MeV ) 5 2 − (γ, 1.12 MeV ) 3 2 − (ground-state) cascade in the decay of 65Ni. The values obtained for the 57Ni and 65Ni asymmetry parameters are A = +0.071±0.011 and A = +0.23±0.04, respectively. The 57Ni results verify the shell-model prediction of 3 2 for the spin of the 57Ni ground state. Thus, both cases are mixed β-transitions, and our measurements determine values for the Coulomb matrix elements connected with the Fermi part of the decays. The Coulomb matrix elements are 54±10 keV for 53Ni and 3.6±5.7 keV for 65Ni. A theoretical calculation in the case of 57Ni indicates that the anti-analogue state is mixed to a small extent into the ground state of 57Ni, which could account for the relatively large matrix element. The zero or near-zero matrix element in the case of 65Ni is consistent with a vibrational-quantum number change of one in the β-decay to 65Cu which corresponds to a difference in this same quantum number between the mixing states.

Isospin conservation in the β-decay of Sc44, Zr95 and Nb95

The angular correlation between β rays and circularly polarized γ rays has been measured by the method of rapid alternation in the cases of Sc44, Zr95 and Nb95. The present result for Sc44 indicates that the Fermi matrix element is very small or zero, within experimental error. This agrees with results obtained previously at this laboratory for Sc46 and A41 (also by the method of rapid alternation), but disagrees with the measurement of Boehm and Wapstra. In the case of Zr95 excellent agreement is obtained with the results of Appel and Schopper, but a different interpretation of the results is offered here which eliminates the need for their conclusion that interference exists between the Gamow-Teller and Fermi transitions. Our interpretation requires (as theirs does) that at least one of the pertinent excited states in Nb95 has spin 72 (preferably the 726-keV state). The agreement between theory and the measurement is then very close and requires almost no mixingin any of the radiations. Nb95, measured for the first time here, decays a pure Gamow-Teller (ΔJ = 1) transition followed by an almost pure M1 radiative transition. In this case no other alternative has any reasonable probability. The spin of the level at 762 keV in Mo95 is 72, and the spins of Sc44 and the level at 1.16 MeV in Ca44 are definitely 2.

High-resolution Ge(Li) study of the decay of 129gTe and 128mTe

Abstract The decay of 129m Te and 129g Te to levels in 129 I has been studied using Ge(Li) detectors for high-resolution γ-ray spectroscopy with some supporting data from NaI(Tl) detectors in coincidence. A total of 46 gamma rays is accounted for by 16 excited states (one tentative) in 129 I up to 1401.6 keV. These include ten new gamma rays not previously reported, a new level in 129 I at 1282.1 keV ( 5 2 + ) and a probable new level at 1204.2 keV ( 3 2 + , 5 2 + ) (values of J π in parentheses). The decay scheme was arrived at primarily on the basis of precise γ-ray energy determinations (to ±50 eV in many cases and never worse than ±200 eV). Beta-decay log ƒt values were determined from our γ-ray intensity balances coupled with published β-branchings. Most-probable spins and parities were deduced based on the γ-ray branching, the log ƒt value and published angular correlations of other workers. The J π = 1 2 + state predicted by Kisslinger and Sorensen in the region of 200 eV and observed in 125 I and 127 I is not seen; we find log ƒt ≧10.6 for the allowed β-decay from 129g Te to such a level. We likewise find no evidence for the 11 2 − state at ≈ 930 keV as predicted by Kisslinger and Sorensen; the allowed β-decay to this state would have log ƒt ≧ 11.0 .

64Ga spin from β-γ(CP) correlation data and decay to 64Zn levels☆

Abstract The decay of 2.6 min 64Ga produced by the reaction 64Zn(p, n)64Ga has been studied by Ge(Li) γ-ray spectroscopy, NaI(TI) crystals both singly and in coincidence, and β-γ(CP) correlation measurements. A transmission type of polarimeter was used in the correlation measurements to give good discrimination against lower energy γ-rays. The decay was found to populate excited states in 64Zn at 991.3, 1799.2, 1909.8, 2608.5, 3186.2, 3261.7, 3365.9 3425.0, 3795.0, 4453.5 keV, and possibly 3623 keV. The decay properties of these states were generally found to agree well with the (p, p′γ) work of Van Patter and co-workers. Beta-gamma (CP) correlation measurements were made on β rays in coincidence with strong ground state γ-ray transitions from the states at 3365.9 and 3425.0 keV. The combined asymmetry parameter of −1.00±0.05 strongly favours a spin of 0 for the 64Ga ground state; a spin of 1 would be possible only if the mixing into the 64Ga ground state involves a very large Coulomb matrix element of ⪸ 344 keV . Possible explanations of the unusualy large Coulomb matrix element (35 keV) between the analogue of the 64Zn ground state and the 64Ga ground state are discussed.

Particle-octupole coupling in N=83 nuclei from neutron transfer studies with polarized deuterons☆

Abstract Neutron pick-up measurements have identified the s 1 2 and d 3 2 holes states in 147 Gd, 145 Sm, and 143 Nd. The results also locate the 1 2 + and 3 2 + members of the v f 7 2 ×3 − septuplet via their admixtures from these hole states. Additional energy perturbations of the septuplet result largely from a negative quadrupole moment of the octupole phonon, with a Z -dependence consistent with the microscopic structure of the 3 − excitation in the N =82 nuclei.

Observation of a full set of coexisting intruder excitations in 98Zr: Evidence for correlated excitations?

Abstract Results from multiparameter in-beam spectroscopy studies of 98Zr58 reveal the existence of two distinct sets of levels with strong intra-set transitions. The nine levels identified in the excited set are found to correlate well with the first nine levels of 102Ru. Similar sets in Zr isotopes and isotones of 98Zr58 are shown for this mass region.1446

Gamma‐Ray Circular Polarization Analyzer Using a Rapidly Alternating Magnetic Field

Gamma rays from substances with half‐lives approaching 0.1 sec may be analyzed using a magnet whose saturated field reverses in 0.4 msec. Laminated magnetic material and transistor circuitry are used to achieve the fast field reversal. The magnet consists of 4‐mil Supermendur tape wound on a toroidal core. The high permeability and low loss of this material permits it to be driven by a single turn at reasonable currents. The circuit uses a low voltage, high current power supply, and charging inductors to provide the necessary voltage pluses. These pulses are developed across switches consisting of ten 2N1358 power transistors operated in parallel. The system has operated 2000 h without a failure.

The 154Eu(t, p) reaction: Some new systematics in the N = 90 spherical-deformed transition region

A radioactive target of 154Eu(8.3y) has been used to study the 154Eu(t, p)156Eu reaction at an incident energy of 17 MeV. The bandhead and one rotational state of the {;π52[413]; ν112[505]}K = 3− configuration have been identified in 156Eu. The excitation energy of the 3− bandhead is determined to be 448 ± 15 keV. The angular distribution of the first excited rotational state is anamolous and may indicate evidence for a strong two-step component in the reaction mechanism. The energy systematics of the Eu-Sm transition region are also investigated. We find that the systematics of h22I suggest that at N = 87 the 150Eu {π52[413]; ν112[505]}K = 3− excited configurations has a significantly more stable deformed structure than the corresponding 112[505] one-quasiparticle structure in 149Sm.

Electron spectroscopy in coincidence with protons from the (t,p) reaction☆

Abstract An electron spectrometer has been operated in coincidence with a thin annular Si(Au) proton detector to obtain conversion-electron spectra associated with the (t,p) reaction. Electrons are transported from the target to a Si(Li) detector through a solenoidal magnetic field in a two-loop baffle arrangement. Proton detection efficiencies of up to 14% were obtained with a 98 Mo target by optimizing the forward-angle position of the Si(Au) detector.

Circular polarization measurements and first-forbidden matrix elements in 72Ga and 124Sb

Abstract Circular polarization measurements are reported for the γ-rays following the outer beta transitions in the decay of 72Ga and 124Sb. We find for 72Ga the degree of polarization Pc = 0.69±0.13 at θβγ = 146° and Pc = 0.7±0.08 at θβγ = 157° while for 124 Sb P c = 0.51±0.05 at θβγ=146°. These results were combined with published data on the β spectrum shape and the β−γ directional correlation by using a computer programme based on the equations of Newsome and Fischbeck which calculated nuclear matrix elements for these two cases. In both cases our results indicate that the 〈Bij〉 matrix element makes the dominant contribution while the three rank-1 matrix elements are suppressed by a factor of about 100 compared with single-particle predictions. The conserved vector current ratio (Λ = 〈iα〉/〈r〉) of Fujita was also used in both cases to determine a set of nuclear matrix elements. It appears, however, that the uncertainties in predicting this ratio are so large that Λ is essentially without significance in the determination of nuclear matrix elements.