W.C. Olsen

Polarization and angular correlation measurements following the 40Ar(p, nγ)40K reaction

Abstract Gamma-ray angular distributions and polarization correlations have been measured using the reaction 40Ar(p, nγ)40K. All the experiments were carried out with bombarding energies close to threshold for the states under investigation. Comparison with compound nuclear predictions has yielded the following spin assignments to states in 40K; 1.959(2+), 2.047(2−), 2.070(3−), 2.103(1−), 2.261(3+), 2.290(1+), 2.291(4, (3)), 2.419(2,3), 2.575(2,4) and 2.625(0−). Multiple mixing ratios together with the gamma-ray branching ratios have been determined for all these levels. A short theoretical treatment of the polarization of gamma rays from aligned nuclei using the phase-consistent formalism of Brink and Rose is included.

A study of 30P levels below 5 MeV

Abstract Spins of 16 excited states of 30 P have been investigated in conjunction with multipole mixing and branching ratios of a number of gamma transitions via the reaction 28 Si( 3 He, p γ ) 30 P. Spin assignments are consistent with those of other investigators in all cases except for the 4.921 MeV level whose branching ratios are also in disagreement with those previously reported. Assuming, as suggested by the present results, a transition from the 4.921 MeV level to the 0.680 MeV level rather than to the 0.709 MeV level, a unique assignment of J = 1 is made to the 4.921 MeV level. A new probable assignment of J = 1 has been made to the 3.736 MeV level. The previously unstudied 2.839, 3.836, 3.928 and 4.734 MeV levels have been assigned possible spin values together with branching ratios and multipole mixing ratios for their decay transitions. Branching ratios for transitions from the 3.736, 3.836, 3.928 and 4.501 MeV levels are in serious disagreement with those of previous studies. Using shell-model wave functions, calculations of lifetimes, multipole mixing ratios and branching ratios corresponding to five low-lying states showed agreement with experimental values for only the first two excited states.

Investigation of high spin states in 55Fe from the 55Mn(p, nγ) reaction

Abstract Electromagnetic decay properties of the low-lying states in 55 Fe were studied using the 55 Mn(p, nγ) 55 Fe reaction. The measurement of γ-ray angular distributions together with predictions based on the compound nuclear statistical model has permitted unique spin assignments to be made to the following excited states in 55 Fe: 1.316 MeV ( 7 2 ), 1.408 MeV ( 7 2 ), 2.144 MeV ( 5 2 ), 2.211 MeV ( 9 2 ), 2.301 MeV ( 9 2 ) and 2.470 MeV ( 3 2 ). Some multipole mixing ratios were also determined. Comparison is made with the shell-model calculations of Ohnuma and Vervier.

A study of the excited states of 53Cr via the 52Cr(d, pγ)53Cr reaction

The decay modes of many of the excited states of 53Cr below 4.25 MeV excitation energy have been determined by means of the 52Cr(d, pγ)53Cr reaction. Previous tentative spin assignments of 52−, 32− and 92+ to the 1.006 MeV, 2.324 MeV and 3.715 MeV levels respectively have been confirmed. New spin assignments are the following: 52 or 92 to the 2.227 MeV level, 32− to the 3.190 MeV level, 52 to the 3.271 MeV level and 12 or 32 to the 3.971 MeV level. Multipole mixing ratios are given for many of the observed transitions. Comparison is made with available theoretical calculations based on both the unified and shell models.

Levels in 21Ne using the 18O(α, nγ)21Ne reaction

Abstract The 18O(α, nγ)21Ne reaction and the method of triple angular correlations were used to determine the spins of the 0.35, 1.75 and 2.87 MeV levels of 21Ne and the multipole mixing ratios of the gamma rays emitted from these states. The angular correlations of the gamma rays from the 0.35 and 1.75 MeV levels were measured at a bombarding energy of 4.43 MeV with the neutron counter located at zero degrees with respect to the beam direction. The results, when analysed in terms of previously measured lifetimes, yielded spin assignments of J = 5 2 and J = 7 2 for the 0.35 and 1.75 MeV levels, respectively, and multipole mixing ratios δ 0.35 = +0.08±0.03, δ 1.40 = +0.18±0.03 and δ 1.75 = +0.03±0.04 . The 1.75 MeV level was found to decay 4.6%±2.0% to the ground state. At a bombarding energy of 5.50 MeV the neutron-gamma-ray correlations yielded a spin of 9 2 as most probable for the 2.87 MeV level with δ1.12 = +0.12±0.06 and δ2.52 = +0.03±0.04. This level was found to decay 63%±4% to the 1.75 MeV level.

The alpha-particle breakup of the 12.71 and 11.83 MeV levels in C12

Abstract The alpha-particle decay of states in C 12 , with special emphasis on those at 11.83 and 12.71 MeV excitation, has been studied using the B 11 (d, n)C 12 reaction. Neutron time-of-flight spectra and semiconductor detector charged-particle spectra were analysed by a two-parameter pulse-height analyser. Angular and energy distributions of the alpha particles from the 12.71 and 11.83 MeV states indicate that these states decay sequentially through Be 8 . The 1 + spin-parity assignment for the 12.71 MeV state is supported by the fact that no transitions to the ground state of Be 8 were observed. Approximately 90% of the transitions from the 11.83 MeV state proceed via Be 8 (2.9 MeV) while the remaining 10% feed the ground state. There is some evidence to indicate that the 10.84 MeV state of C 12 decays exclusively to Be 8 (0). The 3 − assignment for the 9.64 MeV state in C 12 is favoured over 1 − on the basis of the angular distribution of the alpha particles from this state to the Be 8 ground state. This work, together with other reported in the literature, justifies the representation of C 12 as a Be 8 +α two-body cluster from the alpha-particle threshold to 16 MeV excitation. Such a representation is in accordance with the two-body cluster model of Phillips and Tombrello.

A study of levels of 27Mg by the 27Mg(d, pγ)27Mg reaction

Abstract Spins of levels in 27 Mg below 5 MeV and the branching ratios and multipole mixing parameters of their gamma decays have been investigated using the 26 Mg(d, pγ) 27 Mg reaction and method II of Litherland and Ferguson. The present results combined with previous work lead to an assignment of J π = 3 2 + for the 3.782 MeV level and J = 7 2 for the 3.757 MeV level. The spins of the 3.109 and 4.394 MeV levels have been limited to J = 3 2 or 7 2 and J = 3 2 , 5 2 or 9 2 , respectively. Several previously known spins have been confirmed. The decay modes of most of the levels up to E x ≈ 5 MeV have been determined. The experimental data are compared with the predictions of the Nilsson model and shell model.

Gamma-ray angular correlation studies of low-lying levels in 23Na

Gamma-gamma correlations following the bombardment of 23Na with 4.71 and 5.12 MeV protons have been measured using method I of Litherland and Ferguson. Experiments have been carried out on gamma rays cascading from the 2.08, 2.39, 2.71 and 2.98 MeV levels in 23Na. The deduced spins of the 2.08 and 2.71 MeV levels are 72 and 92, respectively. The mixing ratios of the 0.44 → 0, 2.08 → 0.44 and 2.71 → 2.08 MeV gamma rays are −0.06 ± 0.04, −0.24 ± 0.07 and −0.02 ±0.09, respectively. Evidence consistent with a spin assignment of 12 to the 2.39 MeV level is presented.

A study of γ-rays of 37Ar

Abstract The mean lifetime of levels in 37Ar below 3.30 MeV excitation were measured via the 37Cl(p, nγ)37Ar reaction with the Doppler-shift attenuation method. Gamma-ray angular distributions were obtained at various incident energies and compared with the predictions of the statistical compound nuclear model. The angular distribution and lifetime results yield an assignment of J π = 5 2 (+) for the 3.171 MeV level and J π = 9 2 − for the 3.185 MeV level. The experimental results are discussed and compared with shell-model calculations.

Electromagnetic properties of 55Fe

Abstract Measurements of level positions, lifetimes, decay modes and the deduction of spins in 55 Fe have been carried out using the 55 Mn(p, nγ) 55 Fe reaction. Lifetimes of 12 levels between 1.3 and 3.1 MeV excitation are reported. Spin and mixing ratio assignments are made for levels above 2.2 MeV excitation using a statistical compound nuclear calculation. The measured lifetimes are compared with recent shell-model and intermediate-coupling predictions.