S. Beshai

Rotational bands in 195, 197Tl

Abstract High-spin states in 195, 197 Tl have been populated with ( α , x n) reactions and studied by means of in-beam γ-ray and e − spectroscopic methods. Complementary studies of the decay of 195, 197 Pb to 195, 197 Tl have been carried out. Several new features have been observed in these nuclei. The 9 2 − bands of 195, 197 T1. extended to 27 2 (−) and 29 2 (−) , respectively, show a quenching of energy spacings between the 23 2 − , 25 2 − , 27 2 (− and 29 2 (− states. This has been interpreted as resulting from the coupling of a h 9 2 proton to the ( π h −2 11 2 ) 8+, 10+ configurations in the core nuclei 194, 196 Hg. Furthermore, positive-parity bands based on 15 2 + states were established up to the 35 2 (+) and 29 2 (+) states in 195, 197 Tl respectively. Probably these bands originate from the coupling of a h 9 2 proton to a broken neutron pair. This pair consists of a rotation-aligned i 13 2 neutron and a low- j neutron in the P 1 2 , P 3 2 or f 5 2 shell. It is known to constitute the 5 − bands in 194, 196 Hg.

Band crossing in184Pt

The levels in the ground band of184Pt are identified up to the member with spin 20 in an in-beam spectroscopy experiment on theγ-rays following the177Hf(12C, 5n)184Pt reaction. In contrast to the situation in the heavier Pt isotopes, where the 10+ to 12+ level spacing is very small, the transition energies in184Pt show a monotonie increase with spin. However, between spin 10+ and 14+ the moment of inertia grows quite rapidly and this appears to be reminiscent of the much more pronounced irregularity encountered in the isotopes of larger mass. This property of the moment of inertia is discussed within a model where twoi13/2 neutron quasiparticles or twoh9/2 orh11/2 proton quasiparticles may be excited and coupled to the rotation of the core.

A unified model calculation of states in odd-mass technetium isotopes

States in93, 95, 97, 99, 101Tc are studied in a unified model calculation without any adjustable parameters except the excitation energy of the first 1/2−state. The positive parity states are described as a mixture of (p1/2)2(g9/2)J3and (p1/2)0(g9/2)J5 proton configurations coupled to a core undergoing quadrupole oscillations. For the negative parity states a proton quasi-particle in thep1/2,p3/2 andf5/2 orbits is coupled to the vibrations. Calculated energies and electromagnetic moments agree quite well with available data.

Gamma-gamma directional correlation measurements in192Os

E2/M1 mixing ratios of transitions in192Os have been determined by the gammagamma directional correlation technique. The results are: δ(484.5 keV)= −10±1, δ(283.3 keV)= −3.8± 0.7 and δ(201.3 keV)= −4.6±1.

Gamma-gamma angular correlation studies in97Tc

By use of a multichannel goniometer gamma-gamma angular correlations have been measured in97Tc. The obtained angular correlation coefficients are (energies in keV): 108.8–215.7A2=0.38(3)A4=−0.06(5) 754.0–215.7A2=0.01(2)A4=−0.01(2) 569.3–215.7A2=0.25(1)A4=0.00(2) 460.6–324.6A2=0.08(2)A4=−0.02(2) 645.2–324.6A2=0.09(4)A4=0.03(3).These data are used to deduce theE2/M1 mixing-ratios of several transitions. The spin of the 785.0 keV level is found to be 5/2. The reduced transition strengths as well as relative transition strengths are calculated for some transitions and are compared with the predictions of a recent theoretical calculation.

Levels and transitions in126Te

The decay of126Sb to126Te is studied by use of Ge(Li) detectors in singles and coincidence arrangements. The gamma-gamma directional correlations of six cascades are measured. A level scheme is constructed where all transitions observed are located. The characteristics of several of the levels are assigned, on basis of the logft values deduced and the directional correlation results. Mixing ratios are deduced for three transitions. From the comparison of the relative intensities ofE1 andE2 transitions depopulating the same levels, threeE1 transitions are concluded to be strongly retarded.

Gamma-ray multipolarities in 206Pb studied by gamma-gamma directional correlations

Abstract Gamma-gamma directional correlations have been measured in the decay of 206Bi. Using a multichannel goniometer with 2 Ge and 6 NaI detectors the directional correlations have been measured for 17 cascades in 206Pb. From the results, electromagnetic multipole mixing ratios are deduced and limits to transition strengths are estimated.

Angular correlation measurements in 131Xe

Abstract An experiment is described determining the angular correlations of five γ-γ cascades in 131 Xe appearing in the decay of 131 I. Using a 12-channel goniometer the following results were obtained: 325.8–177.2 keV, A 2 = 0.018(11), A 4 = −0.003(10); 318.1–404.8 keV, A 2 = −0.18(4), A 4 = −0.05(3); 272.5–364.5 keV, A 2 = 0.15(4), A 4 = −0.03(3); 284.3–80.2 keV, A 2 = −0.005(7), A 4 = 0.005(15); 318.1–324.6 keV, A 2 = 0.24(5), A 4 = −0.01(5). The result for the 318.1–324.6 keV cascade has not been corrected for a small influence from the 318.1–404.8 keV cascade. Four E2/M1 mixing ratios are deduced from the angular correlation coefficients (energies in keV): −0.28 ≦ δ(325.8) ≦ t 0.20 , −0.19 ≦ δ (318.1) ≦ −0.035, −1.5 ≦ δ (324.6) ≦ −0.05, δ (272.5) = −0.38(17). Transition strengths and limits to transition strengths are calculated for several transitions. The properties of negative parity states in 131 Xe are investigated theoretically in a model where three neutron holes in the h 11 2 orbit are coupled to the quadrupole vibrations of the even core. The experimental energies of the lowest negative parity states and the strengths of the transitions between these states are very well accounted for by the calculation.

The g-factor of the 1 291.5 keV State in 59Co

The g-factor of the 1 291.5 keV state in 59Co has been determined by the IPAC method. A multichannel goniometer was used in the study of the perturbed angular correlation of the 142.5-1 291.5 keV cascade. Four sources were used, 59Fe:Fe, 59Fe:Co, 59Fe:Ni and 59Fe:Cu. The g-factor was found to be 1.69 (8) based on an analysis of the iron, nickel and copper data. The corresponding magnetic moment, μ = 2.54 (12)μN, is compared with the prediction of a unified vibrational model. Neglecting the static electric quadrupole interaction between the 59Co nucleus and its environment in cobalt metal, the magnetic hyperfine field experienced by 59Co in cobalt was found to be -217 (22) kG at room temperature.

Gamma-gamma directional correlations in the decay of206Po

Directional correlations of gamma-gamma cascades in the decay of206Po have been measured for the first time. Using a multichannel goniometer with 2 Ge(Li) and 6 NaI(Tl) detectors theA2 andA4 coefficients have been measured for five cascades in206Bi. From the results,E2/M1 mixing ratios of nine transitions are determined. Upper limits of the transition strengths are presented. Three of the measured mixing ratios are compared with theoretical estimates based on magnetic dipole and electric quadrupole moments of neighbouring nuclei.