0000000000170040
AUTHOR
R. Lucas
Gamma-ray spectroscopy of191,193Bi
Very neutron-deficient Bi-191,Bi-193 nuclei have been studied at the Department of Physics, University of Jyvaskyla, Finland (JYFL) employing the Jurosphere II Ge-detector array coupled to the gas-filled recoil separator RITU and different tagging techniques. For the first time in heavy odd-mass nuclei, a collective band (oblate) is identified above the 2p-1h (1/2(+)) proton intruder state in Bi-191. In both Bi-191,Bi-193, a band based on isomeric 13/2(+) state has been observed and oblate deformation for this state has been deduced. ispartof: Acta Physica Polonica B vol:32 issue:3 pages:1019-1023 ispartof: location:POLAND, ZAKOPANE status: published
Investigation of E0 Transition in 74Kr
The N = Z+2 nucleus 74Kr has been investigated by in-beam conversion electron (CE) and γ ray spectroscopy. The electric-monopole (E0) decay was examined in order to confirm the evidence for a low-lying isomeric 0+2 state and to give insight into the mixing between the predicted coexisting prolate and oblate shapes.
In-beam spectroscopy of $^{253,254}$No
In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei 253,254No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator RITU at the University of Jyvaskyla. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations. The implications for the ground-state configuration of 253No are discussed.
First observation of excited states in 184Pb: spectroscopy beyond the neutron mid-shell
Excited states have been identified for the first time in 184Pb, the first even-even Pb isotope beyond the 82 < N < 126 mid-shell, using the recoil-decay tagging (RDT) technique. A collective band built on the first-excited 2+ state has been observed. This resembles those seen in 186,188Pb and the Hg isotones, and can thus be associated with a prolate-deformed shape. Variable moment of inertia (VMI) fits of the prolate 0+ level energies in 184,186,188Pb indicate that the minimum appears at N= 103, the same neutron number at which the corresponding minimum in Hg isotopes is observed.
Structure of rotational bands in 253No
In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the $\ensuremath 9/2^-[734]_{\nu}$ ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work.
New shape isomer in the self-conjugate nucleus $^{72}$Kr
A new isomeric ${0}^{+}$ state was identified as the first excited state in the self-conjugate ($N=Z$) nucleus $^{\mathrm{72}}\mathrm{K}\mathrm{r}$. By combining for the first time conversion-electron and gamma-ray spectroscopy with the production of metastable states in high-energy fragmentation, the electric-monopole decay of the new isomer to the ground state was established. The new ${0}^{+}$ state is understood as the band head of the known prolate rotational structure, which strongly supports the interpretation that $^{\mathrm{72}}\mathrm{K}\mathrm{r}$ is one of the rare nuclei having an oblate-deformed ground state. This observation gives in fact the first evidence for a shape isomer…
Angular distributions in quasi-fission reactions
Abstract Angular distributions for fission-like fragments were measured in the systems 50Ti, 56Fe + 208Pb by applying an off-line K X-ray activation technique. The distributions d2σ/dθdZ exhibit forward-backward asymmetries that are strongly Z-dependent. They result from a process (quasi-fission) which yields nearly symmetric masses in times comparable to the rotational period of the composite system. A method for obtaining the variance of the tilting angular momentum, K02, from these skewed, differential angular distributions is described. The results indicate that the tilting mode is not fully excited in quasi-fission reactions. The results are compared to the sum of the variances of all …
Spectroscopy of transfermium nuclei: No-252(102)
An in-beam study of excited states in the transfermium nucleus 252 No has been performed using the recoil separator RITU together with the JUROSPHERE II array at the University of Jyväskylä. This is the second transfermium nucleus studied in an in-beam experiment. Levels up to spin 20 were populated and compared to levels in 254 No . An upbend is seen at a frequency of 200 keV/ħ corresponding to spin 16. We also use an improved systematics to connect the energy of the lowest 2 + state with its half-life and find that the deformation of both 2 5 2 , 2 5 4 No is slightly larger than previously assumed. peerReviewed
Fission fragment angular distributions in the capture reactions 50Ti, 56Fe + 208Pb
The analysis of %-ray mult ip l ic i t ies measured I in coincidence with capture fission events in reactions of 26Mg through 54Cr, 58Fe, and 64Ni with 208pb in terms of Ko and~eff revealed1 that the resulting values of ~ /~e f f were rather independent of for a given system and, in a compound nucleus picture, were more in agreement with the 'shape of the non-rotating saddle than with the actually expected rotating saddle I f non-compound systenmhave to be considered these values of ~/J~ff__ shapes. suggested at least that the captured systems near the turning point from the inward radial motion to symmetric fragmentation had reached a remarkable compactness.
Angular distributions in quasi-fission reactions: Evidence for incomplete relaxation of the tilting mode
Angular distributions of fission-like fragments have been measured for50Ti+208Pb and56Fe+208Pb collisions. Z-dependent asymmetries around Θincm= 90° preclude their interpretation in terms of compound nucleus fission with the transition state theory. Fits of the data with a simple ansatz for statistical angular momentum fluctuations (tilting) give evidence for an incomplete relaxation of the tilting mode in quasi fission reactions.
In-beam study of 254No
Excited states of the Z = 102 nuclide 254No have been studied in the reaction 208Pb(48Ca,2n) by means of in-beam γ -ray spectroscopy in combination with recoil gating and recoil decay tagging. A Ge detector array, consisting of four clover detectors, and a gas-filled separator were used. Six γ-ray lines were observed and associated with E2 transitions in the ground state band of 254No, the highest-lying of these being the 16+→ 14+ transition. Based on global systematics and the extrapolated 2+ 1 excitation energy, the value β2= 0.27 ± 0.03 was extracted for the quadrupole deformation. An improved value for the half-life of 254No, T1/2= (48 ± 3) s, was determined.