E. Šimečková

Low temperature nuclear orientation of239Np in gadolinium host

The angular distribution of γ-radiation from the decay of239Np oriented at low temperatures in gadolinium host was investigated. The orientation parameters B2 and B4 were determined. The attenuation factors for two long-living states in239Pu at 391.5 keV and 285.4 keV were calculated. From the anisotropies measured the multipole mixing ratios for 11 gamma-transitions in239Pu were deduced. The results obtained support the assignment of spins of the levels at 492.2 keV and 391.6 keV as 3/2− and 7/2−, respectively.

Decay of oriented149Nd and levels in theN=88149Pm nucleus

Levels in the149Pm nucleus populated via149Nd decay were studied using the low temperature nuclear orientation technique. The parent149Nd nuclei were oriented in a gadolinium host. The normalized gamma-ray intensities were determined for twenty five transitions in the daughter149Pm nucleus. The spins of the149Pm levels at 288.2 and 425.3 keV were determined as 9/2 and 7/2, respectively, and for several other149Pm levels the previous spin-assignments could be unambiguously confirmed. Substantial new information on multipole mixing ratios of gamma-transitions in149Pm is presented. Low-energy level spacing in the149Pm nucleus is found to be in reasonable agreement with recent particle-rotor model calculations including the variable moment of inertia.

Low temperature nuclear orientation of206Bi in gadolinium and iron hosts

Gamma-ray anisotropies were measured for the206Bi radioisotope oriented at low temperature in iron and gadolinium hosts. Multipole mixing ratios for 20 gamma transitions in206Pb nucleus have been deduced, 12 of them for the first time. Several of these data could be compared with predictions of the shell model including the residual interaction of P2-type. Such comparison indicated that interpretation of the present experimental results needed a more developed theoretical description of the206Pb nucleus. A first evidence of orientation of the206Bi nuclei in gadolinium was obtained. Considerable attenuation of several gamma-ray anisotropies due to the 2200 keV isomeric state in206Pb has been found and corresponding attenuation factors G2= =0·71(6) and 0·63(6) have been deduced for iron and gadolinium hosts, respectively.

Low temperature nuclear orientation of238NpGd

The decay of238Np oriented at low temperatures in gadolinium host was investigated. Multipole mixing ratios for beta-transition to the level 1028.6 keV and nine gamma-transitions in238Pu were calculated from the anisotropies of gamma radiation. The attenuation factor for the isomeric state of238Pu at 1082.6 KeV and orientation parameters for238NpGd were deduced from the experimental results.

Nuclear orientation study of the decay of\({}^{205}Bi\underline {Gd} \)

Angular distribution of gamma radiation from the decay of205Bi oriented at low temperatures in gadolinium host was investigated. The orientation parameters B2 and B4 were determined. The spin 9/2 could be uniquely assigned to the positive-parity level at 2252.3 keV. No attenuation was observed for the isomeric level at 1013.8 keV. Seven new values of multipole mixing ratios of E2/M1 gammatransitions in205Pb were determined, two earlier measured values were confirmed.

Nuclear orientation study of the decay of204BiFe

The decay of204Bi nuclei (Iπ=6+, T1/2=11·22 h) oriented in an iron host was investigated on the JINR low-temperature nuclear orientation facility SPIN. The orientation parameterB2=1·17 (6) was obtained from the analysis of six prominent E1 gamma-transitions. From the measured normalized intensities of the gamma-rays observed some 70 values of multipole mixing ratios δ for the gamma-transitions in204Pb nucleus were determined for the first time. The spins 6, 6, 5 and 4 could be uniquely assigned to the204Pb negative parity levels at 3891·5 keV, 3768·4 keV, 3301·5 keV and 2338·2 keV, respectively. The spin-parity assignments of the levels at 4183·8 keV, 4094·2 keV, 3782·0 keV, 2506·9 keV and 2065·1 keV were confirmed as 6−, 6−, 5−, 5− and 5+, respectively. For the level at 3105·1 keV spin-parity 5− was suggested and spinparity 7− of the level at 2696·4 keV was called in question. The possible placements of the gammatransitions 3 1351·7 keV and 1353·4 keV in the decay scheme is discussed. The reorientation parameters for the long-living levels at 2264·2 keV (T1/2=0·45 μs) and 1273·9 keV (T1/2= =265 ns) were determined asG2=0·41 (14) andG2=0·60 (17), respectively. For the isomeric level at 2185·7 keV (T1/2=67·2 min) the value ofG2=0·88 (49) was proposed.