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Low lying states of $^{198}$Hg have been investigated via $^{197}$Au($^{7}$Li, $ alpha $2n$ gamma $)$ ^{198} $Hg reaction at E$ _{text{beam}} $ = 33 MeV and 38 MeV and the members of $ gamma $-vibrational band have been identified. Results are compared with the systematic of this mass region and found in agreement. Observed band structures have been interpreted using the theoretical framework of microscopic triaxial projected shell model (TPSM) approach and it is shown that TPSM results are in fair agreement with the observed energies.
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High-spin states in the doubly-odd $^{198}$Bi nucleus have been studied by using the $^{185,187}$Re($^{16}$O, xn) reactions at the beam energy of 112.5 MeV. $gamma-gamma$ coincidence were measured by using the INGA array with 15 Compton suppressed clover HPGe detectors. The observed levels have been assigned definite spin-parity. The high spin structure is grouped into three bands (B1, B2 and B3), of which two (B1 and B2) exhibit the properties of magnetic rotation (MR). Tilted axis cranking calculations were carried out to explain the MR bands having large multi-quasiparticle configurations. The calculated results explain the bands B1 and B2 very nicely, confirming the shears mechanism and suggest a crossing of two MR bands in both the cases. The crossing is from 6-qp to 8-qp in band B1 and from 4-qp to 6-qp in band B2, a very rare finding. A semiclassical model has also been used to obtain the particle-hole interaction strengths for the bands B1 and B2, below the band crossing.
The Gamow-Teller strength distribution of the decay of $^{186}$Hg into $^{186}$Au has been determined for the first time using the total absorption gamma spectroscopy technique and has been compared with theoretical QRPA calculations using the SLy4 Skyrme force. The measured Gamow-Teller strength distribution and the half-life are described by mixing oblate and prolate configurations independently in the parent and daughter nuclei. The best description of the experimental beta strength is obtained with dominantly prolate components for both parent $^{186}$Hg and daughter $^{186}$Au. The approach also allowed us to determine an upper limit of the oblate component in the parent state. The complexity of the analysis required the development of a new approach in the analysis of the X-ray gated total absorption spectrum.
Shape coexistence in the $Z approx 82$ region has been established in mercury, lead and polonium isotopes. Even-even mercury isotopes with $100 leq N leq 106$ present multiple fingerprints of this phenomenon, which seems to be no longer present for $N geq 110$. According to a number of theoretical calculations, shape coexistence is predicted in the $^{188}$Hg isotope. The $^{188}$Hg nucleus was populated using two different fusion-evaporation reactions with two targets, $^{158}$Gd and $^{160}$Gd, and a beam of $^{34}$S, provided by the Tandem-ALPI accelerators complex at the Laboratori Nazionali di Legnaro. The channels of interest were selected using the information from the Neutron Wall array, while the $gamma$ rays were detected using the GALILEO $gamma$-ray array. The lifetimes of the excited states were determined using the Recoil Distance Doppler-Shift method, employing the dedicated GALILEO plunger device. Using the two-bands mixing and rotational models, the deformation of the pure configurations was obtained from the experimental results. The extracted transition strengths were compared with those calculated with the state-of-the-art symmetry-conserving configuration-mixing (SCCM) and five-dimentional collective Hamiltonian (5DCH) approaches in order to shed light on the nature of the observed structures in the $^{188}$Hg nucleus. An oblate, a normal- and a super-deformed prolate bands were predicted and their underlying shell structure was also discussed.
New high precision total and differential cross sections are reported for the $dpto {}^3textrm{He},eta$ reaction close to threshold. The measurements were performed using the magnetic spectrometer ANKE, which is an internal fixed target facility at the COSY cooler synchrotron. The data were taken for deuteron beam momenta between $3.14641~textrm{GeV}/c$ and $3.20416~textrm{GeV}/c$, which corresponds to the range in excess energy $Q$ for this reaction between $1.14~textrm{MeV}$ and $15.01~textrm{MeV}$. The normalization was established through the measurement in parallel of deuteron-proton elastic scattering and this was checked through the study of the $dpto {}^3textrm{He},pi^0$ reaction. The previously indicated possible change of sign of the slope of the differential cross sections near the production threshold, which could be explained by a rapid variation of the $s$- and $p$-wave interference term, is not confirmed by the new data. The energy dependence of the total cross section and the $90^{circ}$ slope parameter are well explained by describing the final state interaction in terms of a complex Jost function and the results are significant in the discussion of $eta$-mesic nuclei. In combination with recently published WASA-at-COSY data [P. Adlarson $et, al.$, Phys. Lett. B 782, 297 (2018)], a smooth variation of the slope parameter is achieved up to an excess energy of $80.9~textrm{MeV}$.
The $^{174}$Yb($^{29}$Si,5n) reaction at 148 MeV with thin targets was used to populate high-angular momentum states in $^{198}$Po. Resulting $gamma$ rays were observed with Gammasphere. A weakly-populated superdeformed band of 10 $gamma$-ray transitions was found and has been assigned to $^{198}$Po. This is the first observation of a SD band in the $A approx 190$ region in a nucleus with $Z > 83$. The ${cal J}^{(2)}$ of the new band is very similar to those of the yrast SD bands in $^{194}$Hg and $^{196}$Pb. The intensity profile suggests that this band is populated through states close to where the SD band crosses the yrast line and the angular momentum at which the fission process dominates.
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