T. Hayashi

A multicounter goniometer for gamma-gamma angular correlation measurements

Abstract A multicounter goniometer for gamma-gamma angular correlation measurements was newly designed and constructed. It consists of 12 photomultipliers with NaI(Tl) crystals placed radially at intervals of 30° and a 12 × 12 coincidence matrix circuit which follows 12 linear amplifiers and 2 × 12 single channel pulse height analyzers. Coincidence counts at 11 angles between 30° and 330° are taken simultaneously for each of the 12 counters, so that with this method angular correlation measurements can be made within a time reduced by a factor 12 × 11, as compared with the ordinary method.

Low-spin states in 110Cd and 112Cd

Abstract Gamma-transitions in the decays of 24.7 sec 110g Ag and 13.3 min 112g In have been studied with Ge(Li) detectors and a multi-counter goniometer to elucidate low-spin excited states in 110 Cd and 112 Cd. Five new levels at 1732, 2079, 2287, 2332 and 2662 keV in 110 Cd and three new levels at 2124, 2155 and 2300 keV in 112 Cd have been established from the decays of 1 + states of parent nuclei. The 0 + assignments to the levels at 1473, 2079 and 2662 keV in 110 Cd and at 1224 and 1870 keV in 112 Cd have been confirmed by angular-correlation measurements. Mixing ratios of the 2 3 + −2 1 + transitions have been determined. Log ft values of allowed β-decays from the 1 + states are presented. Discussions on the low-spin states of the Cd isotopes are given in the light of the collective model.

IMPROVEMENT OF A MULTICOUNTER GONIOMETER FOR GAMMA--GAMMA ANGULAR CORRELATION MEASUREMENTS.

Abstract A multicounter goniometer previously reported has been improved to increase the efficiency of the system and was successfully applied for gamma-gamma angular correlation measurements of short-life nuclei such as 43 sec 104Rh.

The structure of the low-lying energy levels in 187Re

Abstract Gamma radiations and conversion electrons in the decay of 23.9 h 187 W to 187 Re have been investigated using Ge(Li) detectors and a Si(Li)-Ge(Li) conversion electron spectrometer. Forty-one γ-ray lines are observed, including seven new lines. Gamma-gamma angular correlations of the 551.57−134.25, 479.56−72.02, 479.56−(72.02)−134.25, 72.02−134.25 and 246.33−618.35 keV cascades have been measured. From the measurements of the conversion coefficients and the γ-γ angular correlations, the E2/M1 mixing ratios were determined as δ (134.25) = 0.184 ± 0.003, δ (238.82) δ (246.33) δ (589.12) = |0.58 +∞ −0.58 |, −1.5 〈 δ (618.35)−0.4 and δ (772.85) = |0.41 +0.28 −0.41 |. Theoretical calculations based on the Nilsson model in which Coriolis coupling and quasiparticle-phonon and rotation-vibration interactions are taken into consideration have been performed. The low-lying levels could be assigned to the Nilsson states mixed with the quadrupole vibrations: β vibration (K = Ω) and γ ± vibration ( K = Ω ± 2 ). Good agreement between experimental and calculated energy levels was obtained and the calculated mixing ratios were consistent with experimental results.

Excited states in 108Pd from the decay of 2.42 min 108Ag

Abstract Excited states and γ-transitions in 108 Pd have been studied through the decay of 2.42 min 108 Ag. Eleven γ-ray lines were observed altogether, including six previously unreported lines. The electron capture and positon transitions have been newly confirmed to lead to levels in 108 Pd at 433.9 ± 0.3, 930.9 ± 0.7, 1052.8 ± 0.4, 1314.1 ± 0.4, 1441.1 ± 0.3 and 1540.0 ± 0.4 keV in addition to the transition to the ground state. Gamma-gamma angular correlation measurements have established the spins of levels at 1052.8 and 1441.1 keV as 0 and 2, respectively. The 1007.2 keV transition from the 1441.1 keV level to the 433.9 keV first excited state has been found to be M1 + (5.3 ± 1.4) % E2 with δ = −0.24 ± 0.04. The experimental results are compared with the predictions for vibrating spherical nuclei.

Excited states and transitions in 199Au

Abstract Gamma radiations and conversion electrons in the decay of 31 min 199Pt to 199Au have been investigated by using Ge(Li) detectors and a Si-Ge(Li) conversion coefficient spectrometer. Thirty-nine gamma-ray lines were observed, including ten unreported lines. New levels have been confirmed at 822.3 ± 0.5, 1069.6 ± 0.5, 1103.2 ± 0.3, 1158.7 ± 0.5, 1249.0 ± 0.4and 1395.6 ± 0.5 keV on the basis of NaI(Tl)-Ge(Li) coincidence measurements. The spin and parity of the 791.4 keV level were determined as 3 2 + from the M1 character of the 714.1 keV transition. Angular correlations of four gamma-ray cascades of 191.7–542.7, 468.0–246.5, 474.5–317.0 and 714.1–77.1 keV have been measured. The results are consistent with the spin assignments of 1 2 and 3 2 to the 77.1 and 323.6 keV levels respectively, the 1 2 assignment to the latter level being excluded. From the measured conversion coefficients and angular correlation coefficients, the following M1-E2 mixing ratios have been determined: 317.0 keV, M1 + (25 ± 10) % E2; 468.0 keV, M1 +

A 1 Ge(Li) - 3 NaI(Tl) detector system for γ-γ angular correlation measurements

Abstract A multi detector system consisting of one Ge(Li) and three NaI(Tl) detectors has been constructed for measuring γ-γ angular correlations. In the present apparatus the angular positions of the three NaI(Tl) detectors are intercharged in cyclic repetition, so that different characteristics of the NaI(Tl) detectors and associated circuitries can be averaged. Whole operations including goniometer driving and data taking are performed automatically under the instruction of a programmed controller. The performance of the system has been tested by measuring the g -factor of the 100 keV level in 182 W.

The magnetic moments of three excited states in 149Pm

Abstract The magnetic moments of three excited states in 149 Pm were determined through the measurements of g-factors of the corresponding states by the perturbed γγ angular correlation method using a Ge(Li) detector and an Nal(TI) scintillation counter. The results obtained are μ = 2.0±0.2, 2.2±0.6 and 3.6±0.2 n.m. for the 114, 189 and 270 keV states, respectively. The experimental values are discussed in comparison with contemporary models of the nucleus.

Gamma transition studies of 125Sb from the decay of 9.7 min l25mSn

Abstract Gamma transitions of 125 Sb from the decay of 9.7 min 125m Sn have been studied with Ge(Li) detectors and angular correlation measurements for five cascades have been performed by using a multicounter goniometer. The lifetime of the first excited state has been determined by the βγ delayed coincidence method as T 1 2 = 163 ± 10 ps. The internal conversion coefficient of the first to ground state transition has been found to be α k = 0.018 ± 0.005 by using a Si-Ge(Li) conversion coefficient spectrometer. The value of B (E2) obtained for the 332 keV transition is 0.02 e 2 ·. b 2 , which is 1.1 times as large as the single-particle unit. The present experimental results are compared with the intermediate coupling model for 125 Sb.

Gamma--gamma angular correlation apparatus with on-line irradiation system for the study of short-lived isotopes

Abstract For the angular correlation measurements on short-lived isotopes produced by (n, γ) reactions, a NaI(Tl)ue5f8Ge(Li) angular correlation apparatus connected with on-line irradiation system has been developed. A counting-rate discriminator is used to get sources of the same initial strength and the amount of errors associated with this method is estimated. A multicounter goniometer has also been used in a similar on-line arrangement. Using these systems angular correlation measurements have been made on several short-lived isotopes. Details of the apparatus and some of the results obtained are presented.