P. T. Prokofjev

Nuclear levels in152Eu

The transitional nucleus152Eu has been studied using the (n, e), (n, γ), (nres,γ), (n, γγ), (d, p), (d, t) and (p, d) reactions. The experiments have been performed at nine different laboratories. A model independent level scheme was established including 95 levels below 510 keV and nearly 900 transitions by combination of low energy transitions and reaction data. More than 20 additional levels result from gamma rays and/or charged particle reactions. The level scheme is interpreted in terms of the Nilsson model indicating that152Eu is a deformed nucleus. Seven rotational bands and Nilsson configurations are established. An additional 27 rotational bands are tentatively or speculatively assugned. Gallagher-Moszkowski splittings are discussed. The neutron binding energy was determined as 6305.2±0.5 keV. The energy of the 9.3 h 0− isomer is 45.599 keV. The lifetimes of four levels were measured.Nuclear Reactions151Eu(n,γ),En=thermal and resonance; measuredEγ,Iγ,Ec.e.,Ic.e.,γγ Coinc.,γγΔt coinc.;151Eu(d, p),E=12MeV and 14MeV;153Eu(d, t),E=12MeV;153Eu(p, d),E =18MeV; deduced level scheme of152Eu,J, π, T1/2,cc, Nilsson configurations. Magnetic electron spectrometer, curved crystal spectrometer, Ge(Li) and Si(Li) detectors, magnetic spectrographs. Enriched targets.

Levels in 154Eu populated by (n, γ) and (d, p) reactions

Abstract The structure of the doubly-odd nucleus 154 Eu was investigated using neutron capture and (d, p) reactions on 153 Eu. The low-energy γ-ray and conversion electron spectra from thermal neutron capture, as well as the γ-ray spectrum for primary energies up to 6.5 MeV, were measured with precision instruments at the Institut Laue-Langevin, Grenoble. The multipolarities were determined for most of the detected low-energy transitions. The (n res , γ high ) spectrum measurements with 2 keV, 2 eV and 3 eV neutrons were performed at Brookhaven National Laboratory for primary transitions leading to the 0–600 keV excitation energies. The 153 Eu(d, p) 154 Eu reaction was measured with the Q3D spectrograph at TU Munich. A level scheme below 600 keV excitation energy comprising 99 levels was deduced and the parities and most probable spin values were determined from the experimental data. The low-lying levels were interpreted as due to the two-particle Nilsson configurations, taking into account the proton orbits 5 2 + [413], 5 2 − [532], 3 2 + [411] , and the neutron orbits 11 2 − [505], 3 2 + [651], 3 2 − [521], 3 2 − [532], 5 2 + [642], 3 2 + [402], 5 2 − [523], 1 2 + [400], 1 2 − [530] . The 145.3 (± 0.3) keV level observed in the (d, p) reaction can be identified with the isomeric level with T 1 2 = 46 min . The neutron separation energy for 154 Eu was determined to be 6442.0 ± 0.3 keV.

Levels of 137Ba studied with neutron-induced reactions

Abstract The nucleus 137 Ba has been studied via primary and secondary γ-rays as well as γγ-coincidences following thermal-neutron capture and inelastic neutron scattering. A level scheme was established up to 4.7 MeV consisting of 37 levels including 91 transitions. The neutron binding energy was determined to be 6905.59(8) keV. The thermal-neutron-capture cross section and isomer production of the 11 2 − state at 661.6 keV were determined to be 0.65 −0.04 +0.08 and 0.0098(4) b respectively. The experimental data on excitation energies and electromagnetic properties are compared with predictions of the SU(5) limit of the interacting boson-fermion model. A satisfactorily good agreement between experiment and theory can be stated.

Levels of 155Eu from thermal neutron capture

Abstract The γ-ray and conversion electron spectra of 155 Eu from the (n, γ) reaction were studied at the Institut Laue-Langevin using the curved crystal spectrometers GAMS 1, GAMS 2/3, the β-spectrometer BILL and the pair spectrometer. The γ-transition multipolarities were determined in the energy region 40–1200 keV. The level scheme of 155 Eu was developed with 51 levels up to the excitation energy of 1.7 MeV; these levels were depopulated via 140 transitions out of 360 transitions observed in the γ-ray spectrum. The levels were grouped into 13 rotational bands, and of these 3 2 − [541], 1 2 − [550], 5 2 + [413]+Q 20 , 3 2 + [411]+Q 20 were entirely new for 155 Eu was found B n = 8151.3(3) keV. It has been determined that the E1 transitions of ΔK = 0 type were enhanced in comparison with these of the ΔK = 1 type. The Nilsson + RPC, cranked shell model and odd RV model calculations have indicated the presence of strong collectivization, even for the 155 Eu lowest states.

Thermal-neutron-capture studies on 135Ba

Abstract The nucleus 135 Ba has been studied via primary, secondary γ-rays, γγ coincidences following thermal-neutron capture. A level scheme was established up to 3.7 MeV consisting of 41 levels including 114 γ-transitions. The neutron binding energy was determined to be 6971.78(17) keV. The total thermal cross section and isomer production of the 11 2 − state were determined to be σ(tot) = 1.4(4) and σ( 135 Ba) = 0.11(2) barn. The level energies, E2 and M1 transitions and electromagnetic moments were compared with model predictions of the interacting boson-fermion model (IBFM).

Investigation of the low-lying levels of 179Hf with the (n, γ) and (n, e) reactions

The excited levels of 179Hf are investigated using the thermal neutron capture γ-ray and conversion electron spectra measured with the bent crystal diffraction spectrometer in Riso and the β-spectrograph in Riga. The level scheme contains the odd parity rotational bands 72−[514], 12−[510], 52−[512], 12−[521], 32−[512] and 72−[503]. The energies of these levels and the intensity ratios of the transitions between them are calculated taking into account the rotation-particle coupling (RPC). The following even parity levels are proposed: 859.0 and 942.2 keV (72+ and 92+ of the 72+ [633] band); 1004.1 and 1079.2 keV (52+ and 72+ of the 92+[624] + Q(22) band); 1186.0, 1199.2 and 1296.4 keV (12+, 52+ and 32+ of the 12+[651] band). The levels at 1249.8, 1269.7, 1432.9, 1482.2 and 1755.5 keV, supported by the analysis of the γγ coincidence spectrum and Ge(Li) singles data, are discussed.

Study of the187W states excited in the (n, γ) reaction

A singlesγ-ray spectrum and a spectrum of summed amplitudes of coinciding pulses (SACP) were measured in the186W(n, γ)187W reaction experiment on the thermal neutron beam. It was for the first time that the data on187Wγ-transitions were obtained in the excitation energy region from 1500–2500 keV. The neutron binding energy was determined to beBn=5467.25 (4) keV (statistical error only). In result the level scheme of187W was developed in the excitation energy interval 1<Ef< 3.4 MeV, which contained 105 levels with about 70 of them being identified for the first time. The experimental values for summed intensities of two-step cascades were established to exceed those predicted by the modern statistical theory (by 36±6%). This is explained by a considerable contribution of few-quasiparticle components to wave functions of compound and intermediate states.

Level structure of the odd-odd nucleus 156Eu

Abstract The reaction chain 153 Eu(n, γ) 154 Eu(n, γ) 155 Eu(n, γ) 156 Eu was studied using 153 Eu targets. The γ-ray and internal conversion electron spectra were measured with high resolution spectrometers. Using several subsequent measurement series, as well as the radiation spectra from the reaction-decay chain 154 Sm(n, γ) 155 Sm 155 Eu(n, γ) 156 Eu, we assigned 95 transitions to 156 Eu, and 70 multipolarities were determined for them. 31 levels with spin values from 0 to 5 were found up to 515 keV. These levels are assigned to 13 rotational bands interpreted using proton orbits p 5 2 + [413]↓, p 5 2 − [532]↑, p 3 2 + [411]↑ and neutron orbits n 5 2 + [642]↑, n 3 2 − [521]↑, n 5 2 − [523]↓, n 11 2 − [505]↑ . Comparison with the decay of 156 Sm to 156 Eu indicates a 0.7% β-branch to the 1 − level at 266.95 keV, and log ƒt = 7.1 . The 434.230(2) keV energy is proposed for the level 448 ± 15 keV , 3 − , p 5 2 + [413]↓− n 11 2 − [505]↑ , earlier known from the 154 Eu(t, p) measurements. Model calculations are in agreement with the Gallagher-Moszkowski rule for four doublets Ω p ±Ω n . The calculated mixing amplitudes explain origin of some two-particle transitions. Comparatively intense E1 transitions between levels of bands with ΔK = 0 and opposite parities allow to propose existence of octupole deformation in 156 Eu which results in observation of parity doublets. It can be estimated that the 156 Eu level scheme is complete up to about 240 keV excitation energy for all spin values.

Particle-hole states in 138Ba

Abstract The thermal-neutron-capture gamma rays and γγ-coincidences were measured by means of Ge detectors. Using primary and secondary (n, γ) data, the level scheme of 138 Ba was established with 63 levels up to an excitation energy of 5 MeV. The level energies and (d, p) transfer data were compared with model predictions of the interacting boson-fermion-fermion model. As shown, this model provides a basic understanding of the neutron particle-hole states of 138 Ba in the energy range of 3.5 – 5.0 MeV.

Excited levels of Ho166

Abstract The internal conversion electron spectrum in the reaction Ho165(n, γ)Ho166 has been measured with a β-spectrograph. Within the energy interval 40–300 keV, energies and intensities of conversion electron lines have been determined. The scheme of low-energy levels in Ho166 is discussed. The characteristics 3−, 4− are proposed for the levels at 170.6 keV and 240.1 keV instead of assignments existing in the literature.