A.E. Blaugrund

E2M1 mixing ratios and K conversion coefficients in odd-mass rotational nuclei

Abstract The E 2 M 1 mixing ratios and K conversion coefficients of the first two rotational transitions in 155Gd, 159Tb, 167Er, 173Yb, 175Lu, 179Hf, 181Ta, 185Re and 187Re have been measured. The mixing ratios are determined from angular distributions of gamma rays following Coulomb excitation of the second rotational level. Events belonging only to the decay by cascade of the second rotational level were selected by a coincidence circuit. The same experimental arrangement was used for determination of K conversion coefficients from X-ray and gamma intensity ratios. The agreement between the experimental values of the mixing ratios and the predictions of the rotational model is fair except in the case of 179Hf. The agreement between the experimental and theoretical values of the K conversion coefficients is good. In addition E2/M1 mixing ratios of the 99 and the 141 keV transitions in 195Pt have been determined.

E2/M1 mixing ratios and K conversion coefficients of some rotational transitions

Abstract The E2/M1 mixing ratios and K conversion coefficients of the first two rotational transitions in Eu153 and Ho165 have been measured by observing the decay of the second rotational level in these nuclei. This level was Coulomb excited and its decay by two cascade transitions was detected in a coincidence arrangement. The mixing ratios were determined from the angular distributions of the two gamma rays. The same coincidence arrangement was used to measure the K conversion coefficients of these transitions. The E2/M1 mixing ratio of the 110 keV transition in Tm169 was also determined. The following results were obtained: Eu153−δ(109 keV = 0.585±0.050, αK(83.4 keV) = 2.34±0.13, αK(109 keV) = 1.15±0.09; Ho165−δ(95 keV) = 0.173±0.036, δ(114 keV) = 0.171±0.032, αK(95 keV)= 2.64±0.10, αK(114 KeV) = 1.49±0.07; Tm169-δ(110 keV) = −0.146±0.016. In the case of Ho165 and Tm169 the experimental mixing ratios agree with predictions of the rotational model. This is not true for Eu153. The measured K conversion coefficients are in good agreement with theoretically calculated values.

The lifetimes of the first excited states of Re185 and Re187

Abstract Lifetimes of the first excited states of Re185 and Re187 were measured with the microwave method. From the slopes of the delayed curves a mean life of (1.45−0.20+0.14×10−11 sec was found for the 134 keV level of Re187 and an upper limit of 1.2×10−11 sec could be determined for the 125 keV level in Re185.

The mean life of the 210 keV 32− state in Pt195

Abstract The lifetime of the 3 2 − 210 keV level in Pt195 was measured with the microwave method. An average mean life of 97±7 psec was derived from the slope of the exponential decay and also from an analysis involving Fourier series expansion of the experimental data. The resulting B(M1) value of (0.032±0.003) ( e h /2Mc) 2 is 0.23 times the single particle value for a p 3 2 → p 1 2 transition. A sampling system has been constructed which analyses directly the pulsed beam. The time duration of the beam pulses in the sampling experiment could be made shorter than 30 psec. From this an upper limit of 20 psec could be established for the intrinsic time spread of the beam pulse.

The mean lifetimes of the 4+ levels in 158Dy and 164Er

Abstract Mean lifetimes of the 4 + levels in the ground-state rotational bands of 158 Dy and 164 Er were measured. Both levels were excited through (p, 2n) reactions. The lifetime of the level in 158 Dy was measured using a recently developed multi-channel version of the microwave method. The measurement in 164 Er was carried out with the earlier version of the microwave technique. The results of these measurements are τ( 158 Dy) = 108±12 ps, τ( 164 Er) = 124±12 ps. The B (E2; 4 + → 2 + ) are compared with the corresponding B (E2; 2 + → 0 + ) values and found to be in agreement with the rotational model.

The mean lifetime of the 203 keV level in 109Cd

Abstract The mean lifetime of the 7 2 + , 203 keV level in 109 Cd was measured using a recently developed multi-channel version of the microwave method. The level was excited by means of the 109 Ag(p,n) 109 Cd reaction. A mean life τ( 109 Cd, 203 keV) = 52 +9 −6 ps was measured. The multipolarity of the 260 keV transition was determined to be M2.

Lifetimes of three levels in 22Na measured by the doppler shift attenuation in gases

Abstract Lifetimes of levels at 0.891, 2.210 and 2.572 MeV in 22 Na have been measured by the Doppler shift attenuation method using C 2 F 6 gas as the stopping medium. The lifetimes of the three states are 10.8±1.8, 12±2 and 4.5±1.0 ps, respectively. The states were produced by the (α, n) reaction on 19 F near threshold. Gamma rays were detected with a Ge(Li) detector. The applicability of a gaseous stopping medium for attenuated Doppler shift measurements is discussed.

K Conversion Coefficients of Mixed E2-M1 Rotational Transitions

Publisher Summary This chapter discusses the K conversion coefficients of mixed E2-M1 rotational transitions. κ conversion coefficients of the two lowest rotational transitions have been measured in several odd-mass deformed nuclei in the region 153 ≤ A ≤ 187. Electromagnetic radiation emitted by the target nuclei is detected by two NaI(Tl) scintillation crystals. By requiring coincident outputs from the two counters, only those events are picked out that corresponded to an excitation and decay of the second rotational level by two cascade transitions. Therefore, the spectrum recorded by the 55° counter in coincidence with γ3 consists of two lines, viz., γ1 and the corresponding κ conversion X-rays. The κ conversion coefficient of γ1 can be obtained from the intensity ratio of these two lines. In the same way, the spectrum recorded in coincidence with γ1 yields the κ conversion coefficient of the transition γ3. The two coefficients are measured simultaneously by connecting two single channel pulse-height analyzers to the 2п counter—one of them tuned to γ1 and the other to γ3.