M. Kortelahti

Structure of odd-A Pm nuclei (I). 147Pm

Abstract The level structure of 147 Pm was studied by methods of in-beam γ-ray and electron spectroscopy using the 148 Nd(p, 2n) reaction. Twenty-four new levels with spins between 1 2 and ( 15 2 ) were observed. The 12 ± 2 ns h 11 2 level at 649.3 keV decays by a strongly hindered El transition (1.2 × 10 −6 s.p.u.) to the 9 2 + level at 408.2 keV and by a M2 transition (0.15 s.p.u.) to the ground state.

Beta decay and delayed proton emission of a new nuclide 59Zn

Abstract The β + decay of a new nuclide 59 Zn has been identified by β-delayed proton and γ-ray emission. Two γ-rays and 15 proton groups have been associated with the decay of 59 Zn. The total proton branching ratio was measured to be (2.3 ± 0.8) × 10 −4 . A half-life of 210 ± 20 ms was measured for 59 Zn. The superallowed β-branch to its mirror, the J π = 3 2 − ground state of 59 Cu, was shown to be (93 ± 3)%. Absolute log ft values for β-transitions associated with the observed delayed proton groups were calculated and an experimental β-transition strength function was obtained.

Beta decay of 40Sc to proton and alpha-particle unbound states in 40Ca

Delayed charged particle emission associated with the precursor nuclide 40Sc was studied by use of the He-jet technique. Altogether 40 proton groups (1.0 MeV < Ep < 3.7 MeV) and 21 α-particle groups (2.0 MeV < Eα < 4.6 MeV) were observed. Total proton and α-particle branching ratios were measured to be (4.4±0.7) × 10−3 and (0.17±0.05) × 10−3, respectively. Association of the delayed particle emitting levels with the levels observed in resonance reaction studies is discussed. The fact that the most prominent α-particle groups do not have a counterpart in resonance reaction data suggests collectivity or a cluster configuration for the emitting levels. Log ft values (upper limits) for β+ transitions to particle emitting levels were deduced from the measured absolute intensities of the proton and α-particle transitions. Beta strength function is qualitatively discussed in terms of a simple shell-model description.

Medium-spin states in the N = 80 nuclei 139Pr and 141Pm

Abstract The level structures of 139 Pr and 141 Pm have been investigated using (p, 2n), ( 3 He, 3n) and (α, 4n) reactions and methods of in-beam γ-ray and electron spectroscopy. Fourteen new levels with spins up to ( 23 2 ) + were observed in 139 Pr and seventeen new levels with spins up to 19 2 − in 141 Pm. The level structures in both nuclei can be described by coupling the odd-proton intrinsic states to the excitations of the doubly even core. The ordering of the levels in the π h 11 2 ⊗2 + multiplet is discussed on the basis of the triaxial rotor-plus-particle model calculations. The calculations suggest that a transition from a basically prolate to an oblate triaxial shape takes place between the neutron numbers N = 78 and N = 80. A γ-deformation of 34° was deduced for both 139 Pr and 141 Pm.

Medium-Spin States in the N=82 Nuclei 141Prand143Pm

The level structures of the N = 82 nuclei 141Pr and 143Pm were studied by methods of in-beam γ-ray and conversion-electron spectroscopy using the (p, 2n) and (p, 3n) reactions. The levels schemes have been built up to energy of about 3 MeV and spin of 19/2. In 141Pr we have established 14 new low- and medium-spin levels.

Beta-delayed particle emission of 36K

Abstract 36 Ar targets of 19 μg cm 2 thickness were made by a sandwich technique in which a 70 nm layer of Al was evaporated onto the implanted Al surface between five successive implantations of 36 Ar ions. The sources of 36 K were prepared by depositing the recoil atoms from the 36 Ar(p, n) 36 K reaction by means of a helium jet onto a fast transport tape. The measured delayed particle spectra revealed 11 proton groups (0.5 MeV E p E α 36 K. Total proton and α-particle branching ratios were measured to be 4.8 × 10 −4 and 3 × 10 −5 , respectively. Partial level widths and reduced proton and α-particle transition widths were determined for several individual levels with the aid of additional results from resonance reaction studies.

Medium-spin levels and A 360 ns Iπ = 192− isomer in the N = 80 nucleus 137La

Abstract The level structure of 137La has been studied using the 138Ba(p, 2n) reaction and methods of in-beam γ-ray and conversion-electron spectroscopy. The 137La level scheme has been established with 21 new levels with spins up to 19 2 −1 . A 360 ns 19 2 −1 isomer at 1870 keV has been identified and a (π g 7 2 (ν h −1 11 2 d − 3 2 ) 7 − ) 19 2 − configuration is suggested for it. The level ordering of the π h 11 2 ×2 + multiplet has been discussed on the basis of the triaxial rotor-plus-particle model which suggests a slightly oblate triaxial shape to the 137La nucleus.

In-beam study and a rotational description of low-lying levels in the N = 88 nucleus 149 Pm

Abstract Levels of 149 Pm were studied by methods of in-beamy-ray spectroscopy using the 150 Nd(p, 2nγ) reaction. About ten new medium- and high-spin states (from 7 2 to 15 2 ) were observed below 1 MeV. An axial particle-rotor model was applied to the N = 88 nucleus 149 Pm and the calculations were found to predict satisfactorily properties of most levels. Both the positive and the negative-parity band structures are strongly Coriolis-mixed. The results indicate larger deformation for the negative- parity states than for the positive-parity states.

Medium-Spin Levels in 137Ce and the Prolate-Oblate Shape Transition in Ce Nuclei

The level structure of the N = 79 137Ce nucleus has been studied with the 137Ba(3He, 3n) reaction using in beam γ-ray and conversion electron spectroscopy. The level ordering in the vh11/2-1 × 2+ multiplet has been discussed on the basis of the triaxial rotor-plus-particle model which suggests a slightly oblate triaxial shape for 137Ce and the prolate-oblate shape transition in the Ce isotopes to occur between N = 77 and 79.

In-beam study of 145Pm and the cluster-vibration model for odd Pm nuclei

Abstract The level structure of 145Pm was studied by methods of in-beam γ-ray and conversion-electron spectroscopy using the 146Nd(p, 2n)145Pm reaction. Over twenty new levels with spins up to 15 2 were observed. The cluster-vibration model was applied to 14561Pm84 under the assumption of the Z = 64 subshell closure. Positive-parity levels are explained very well when the cluster consists of three proton holes in the g 7 2 and d 5 2 shells. Our results strongly support the assumption that the Z = 64 closure persists for Z = 61 promethium nuclei.