T.M. Muminov

Electromagnetic transitions in some doubly odd deformed nuclei

Abstract Nanosecond lifetimes of excited states in doubly odd deformed nuclei have been determined by in-beam measurements applying the method of delayed γ-γ coincidences as well as by experiments in the radioactive decay with the method of delayed γ-ce coincidences, respectively. Analysing the time distributions and delayed γ-ray spectra, the following half-lives of isomeric states could be obtained for the first time: T 1 2 (63.7 keV in 160 Tb ) = 60 ± 5 ns , T 1 2 (138.7 keV in 160 Tb ) = 5.7 ± 0.5 ns , T 1 2 (82.0 keV in 156 Ho ) = 1.25 ± 0.20 ns , T 1 2 (87.2 keV in 156 Ho ) = 58.5 ± 3.5 ns , T 1 2 (139.2 keV in 158 Ho ) = 1.85 ± 0.10 ns , T 1 2 (38.3 keV in 162 Ho ) = 1.2 ± 0.2 ns , T 1 2 (179.9 keV in 162 Ho ) = 8.7 ± 0.2 ns , T 1 2 (342.8 keV in 164 Ho ) = 2.6 ± 0.2 ns , T 1 2 (295.1 keV in 166 Ho ) = 1.10±0.15 ns , T 1 2 (44.6 keV in 162 Tm ) = 1.40±0.15 ns , T 1 2 ,(163.4 keV in 162 Tm ) = 1.1 ± 0.1 ns , T 1 2 (220.1 keV in 178 Ta ) = 8.5 ± 1.0 ns , T 1 2 (289.5 keV in 178 Ta ) = 2.0 ± 0.5 ns , T 1 2 (392.8 keV in 178 Ta) ≈ 1 ns, T 1 2 (316.5 keV in 186 Re ) = 0.20 ± 0.10 ns , T 1 2 (300.2 keV in 188 Re ) = 1.5 ± 0.2 ns and T 1 2 (482.2 keV in 188 Re ) = 0.26 ± 0.10 ns . Furthermore, upper limits for the half-lives of fifteen excited states in 160Tb, 164, 166Ho and 186, 188Re have been estimated. For eight isomeric levels in 186, 188Re, the lifetimes earlier determined have been remeasured. Unlike previous studies, the existence of isomeric states at 87.2 keV in 156Ho and at 179.9 keV in 162Ho is suggested. Absolute γ-ray transition probabilities are deduced and compared with single-particle estimates according to Weisskopf and Nilsson, the latter also including pairing correlations. The K-, Ω- and f-forbidden transitions can qualitatively be explained in terms of configuration mixings. Experimental El, ΔK= 1 transition matrix elements in odd-odd deformed nuclei are supposed to be appreciably influenced by higher-order vibrational admixtures coupled via RPC and p-n interaction mixings.

Core polarization for l-forbidden M1 transitions in light nuclei

Abstract The experimental systematics of 2 s 1 2 ↔ ld 3 2 1- forbidden M1 transition rates in light nuclei with N, Z ≲ 20 are studied. Some surprising deviations from the expected behavior are qualitatively discussed in terms of an interplay between first- and second-order core polarization contributions. The B(M1) values in mirror pairs turn out to be close to each other within the experimental errors, the proton transition strengths being slightly larger. Isovector dominance is shown to account for this phenomenon.

The behavior of l-forbidden M1 transitions near Z = 50, N = 82

Abstract The behavior of l -forbidden M1 transitions around Z = 50 and N = 82 is investigated. In the decay of 131 Ce, lifetimes of excited states in 131 La have been measured for the first time as T 1 2 (26.2 keV ) = 0.85 ± 0.10 ns , T 1 2 (145.5 keV ) ≦ 0.3 ns , and T 1 2 (195.5 keV = 0.08 ns . In the decay of 133 La, the lifetime of the 12.3 keV state in 133 Ba has been measured as T 1 2 (12.3 keV ) = 7.0 ± 0.3 ns in contradiction to a recently published result. From the value B( M 1, 5 2 → 3 2 ) exp , possible conclusions on the structure of the ground state in 131 La are drawn. All the available data on l -forbidden M1 transitions n (2 d 3 2 ↔ 3 s 1 2 ) and p (1 g 7 2 ↔ 2 d 5 2 ) in nuclei with 100 A jj closed shell N = 82 is discussed in terms of quadrupole deformations. This approach is supported by the systematics of rotational B (M1) values in deformed nuclei (150 A

Excited states of the doubly odd deformed nucleus 160Tm

Abstract The decay of 4.8 min 160 Yb has been investigated by means of Ge(Li) detectors, toroidal and magnetic-lens β-spectrometers and scintillation counters. The singles spectra of γ-rays and conversion electrons as well as prompt and delayed γ-γ and γ-ce coincidences have been measured. The 160 Tm level scheme is proposed including 94.5% of the total γ-ray intensity observed in the 160 Yb decay. The lifetimes of the 42.02, 174.40 and 215.78 keV states have been determined to be 1.6±0.3, 17±1 and 0.65±0.15 ns, respectively. From the analysis of the experimental data, the quantum characteristics of 160 Tm levels are proposed. Experimental γ-ray transition probabilities are compared with Weisskopf and Nilsson estimates, the latter also taking into account pairing correlations.

Levels in 161Tm excited in the decay of 4.2 min 161Yb

Abstract The decay of 161 Yb ( T 1 2 = 4.2 min ) has been investigated with Ge(Li) and Si(Li) detectors and a toroidal β-spectrometer. Isobarically separated samples produced by the YASNAPP facility at Dubna Institute were used. The singles γ-ray spectrum, the conversion electron spectrum, γ-γ-τ and e-γ coincidences have been measured. In all, 67 γ-ray transitions have been observed. A decay scheme for 161 Yb is proposed involving 12 excited states in 161 Tm. The 7 2 + [404], 7 2 − [523] and 5 2 + [402] levels have been identified. The interpretation of the high-lying levels is discussed. The Q -value of 161 Yb decay has been determined to be 3850 ± 250 keV. The A -dependence of the energies of the one-quasiparticle states in odd- A Tm isotopes is demonstrated.