R.A. Braga

Very slow M4 transitions and shell-model intruder states in 199, 201Bi

Abstract The isomeric decays of the 1 2 + shell-model intruder states in 199,201Bi have been investigated. In the case of 201Bi we show that the s 1 2 → h 9 2 isomeric transition is pure M4 within experimental error and is 2200 times slower than any other M4 transition observed in odd-mass nuclei. Its l-forbiddenness and the possibility of an E5 admixture and penetration effects are discussed.

The UNISOR ISOL data acquisition system

Abstract The data collection system of the on-line separator at Oak Ridge (UNISOR) is described including an overview of the operation and a discussion of some new techniques. Tape transport and computer based data acquisition systems have been developed which allow several experiments to be performed simultaneously on a given mass chain and also enable experiments to be changed quickly. To make efficient use of the cyclotron beam time, methods have been developed for quickly extracting short-lived side masses from the separator. Also described are an on-line scanning Gerholm lens spectrometer, a multiple time analysis system and an angular correlation station for the tape transport.

The decay of 133Pm and the structure of 133Nd

Abstract The decay of 133 Pm to 133 Nd has been studied with mass-separated sources from the UNISOR facility. Multiscaled spectra of γ-rays, X-rays, and conversion electrons, as well as γγt-, Xγt-, eγt-, and eXt-coincidences were obtained. The half life of 133 Pm was measured to be 15±3 s. A decay scheme has been constructed consisting of 51 excited states and 106 transitions in 133 Nd. Isomers decaying by M3 and E1 transitions are established in 133 Nd. The low-lying levels are discussed in terms of the particle-plus-triaxial-rotor model and the onset of deformation in the region bounded by Z ⩾ 58, N ⩽ 76.

Decay of mass-separated 3.0 min 195gBi to levels in 195Pb and shape coexistence in the neutron-deficient odd-mass Pb isotopes

Abstract The radioactive decay of mass-separated 3.0 m 195g Bi to 195 Pb has been studied with the UNISOR and LISOL facilities. Time-sequenced spectra of γ-rays, X-rays, and conversion electrons have been obtained, together with γγt, γXt, eγt, and eXt coincidence data. From this information, a decay scheme has been constructed consisting of 23 excited states and 34 transitions in 195 Pb. Transitions with E0 multipole admixtures, indicative of shape coexistence, have been found to de-excite positive-parity levels at 1093, 1329, and 1380 keV. The beta-decay energy of the 195 Bi ground state is deduced to be Q EC = 4800 −550 +600 keV based on the measurement of γ-ray-gated K / β + ratios. The excitation energy of the i 13 2 isomer in 195 Pb has been determined to be 203±4 keV from the α-decays of 199m,g Po.

Half-life of the h92 shell-model intruder-state isomer 187mAu

The half-life of the 92− shell-model intruder-state isomer in 187Au has been measured by employing a technique in which each incoming event is tagged with a digital representation of time by means of a real-time clock. With this method we obtain a 2.3 ± 0.1 sec half-life for the h92 → d32 E3 isomeric transition resulting in a retardation of 50 relative to the Weisskopf single-particle estimate.

The decays of mass-separated 133m,gNd to 133Pr

Abstract The decay of 133m Nd (J π = 1 2 + ) and 133g Nd (J π = 7 2 + ) to 133Pr have been studied with mass-separated sources from the UNISOR facility. Multiscaled spectra of γ-rays, X-rays, and conversion electrons, as well as γγt, γXt, eγt, and eXt coincidences were obtained. A decay scheme for 133gNd has been constructed consisting of 49 excited states and 153 transitions in 133Pr. The β decay of the isomer, 133m Nd (J π = 1 2 + ) , is reported for the first time. A decay scheme has been constructed with 13 excited states and 26 transitions in 133Pr. This isomer decays predominantly by an allowed β decay to an excited state at 402.8 keV in 133Pr. The low-energy structure of 133Pr is discussed in terms of the particle-plus-triaxial-rotor model and the onset of deformation in the region bounded by Z ⩾ 58, N ⩽ 76. The π[411] 3 2 configuration is suggested as the ground state of 133Pr, and a low-lying π[413] 5 2 bandhead is also proposed.

Decay of mass-separated 201mPo and 201gPo

Abstract The decays of 201Po (9.0 min) and 201gPo (15.3 min) have been studied with mass-separated sources from the UNISOR facility. Time-sequenced spectra of γ-rays, X-rays, and conversion electrons, as well as γγt and Xγt (coincidences were obtained. A decay scheme has been constructed incorporating 93% of the decay intensity assigned to 201Bi. Levels resulting from h 9 2 , f 7 2 and i 13 2 particle states have been observed.

207Bi L-subshell orbital electron capture probabilities and decay energy

Abstract The L 1 subshell orbital electron capture probability P L1 in the decay of 33.4 y 207 Bi to the 2339.89 keV level in 207 Pb is measured to be 0.518 ± 0.081 (95% confidence) by a new method in which L 1 subshell characteristic X-rays in the L γ X-ray peak are observed in an X γt coincidence mode with 1770.23 keV γ-rays. The value of P L2 is 0.047 ± 0.015 (95% confidence). From these results a value of Q EC = 39 -8 +21 keV is obtained for capture transitions to the 2339.89 keV level. The absence of K-capture to this level also is established by absence of K X-rays in coincidence with 1770.23 keV γ-rays.

Decay of mass-separated 7.4 min 203At

Abstract The radioactive decay of 7.4 min 203 At to 203 Po has been studied with mass separated sources from the UNISOR facility. Time-sequenced spectra of γ-rays. X-rays, and conversion electrons were obtained, together with γγt, γXt, e − γt, and e − Xt coincidence data. A decay scheme has been constructed that incorporates approximately 90% of the decay intensity assigned to 203 At. All excited states below 1 MeV have been assigned unique spin-parity values, and the observed level scheme can be qualitatively understood in terms of a particle-core weak coupling description. The ground-state decay energy has been deduced to be Q EC = 5.06 ± 0.20 MeV from γ-ray-gated EC/β + ratios.

Determination of corrections for tailing in low energy coincidence intensity measurements

Abstract A new method for the evaluation of the net intensity of each component of a partially resolved multiplet in a low energy photon ( α 1 and K α 2 X-rays in coincidence with L X-rays from the decays of 10.4 h 165 Er and 4.68 y 155 Eu.