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Register a new userDouble Beta Decays into Excited States in $^{110}$Pd and $^{102}$Pd
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A search for double beta decays of $^{110}$Pd and $^{102}$Pd into excited states of the daughter nuclides has been performed using three ultra-low background gamma-spectrometry measurements in the Felsenkeller laboratory, Germany, the HADES laboratory, Belgium and at the LNGS, Italy. The combined Bayesian analysis of the three measurements sets improved half-life limits for the $2 ubetabeta$ and $0 ubetabeta$ decay modes of the $2^+_1$, $0^+_1$ and $2^+_2$ transitions in $^{110}$Pd to $2.9cdot10^{20}$ yr, $4.0cdot10^{20}$ yr and $3.0cdot10^{20}$ yr respectively and in $^{102}$Pd to $7.6cdot10^{18}$ yr, $8.8cdot10^{18}$ yr and $1.4cdot10^{19}$ yr respectively with 90% credibility.
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The neutron-rich nuclei $^{109}$Pd and $^{111}$Pd were produced as fission fragments following the $^{30}$Si + $^{168}$Er reaction at 142 MeV. Using the identification based on the coincidences with the complementary fission fragments, the only positive-parity bands observed so far in $^{109}$Pd and $^{111}$Pd emerged from this work. A band, built on top of the 5/2$^+$ ground state exhibiting $Delta I$ = 1 energy-level staggering, was observed in each of these nuclei. Both nuclei of interest, $^{109}$Pd and $^{111}$Pd, are suggested to lie in the transitional region of Pd isotopes of maximum $gamma$-softness. The ground states of both nuclei are predicted by TRS calculations to be extremely $gamma$-soft with shallow triaxial minima. The first crossing in the new bands is proposed to be due to an alignment of $h^2_{11/2}$ neutrons.
Double-beta decay is a rare nuclear process in which two neutrons in the nucleus are converted to two protons with the emission of two electrons and two electron anti-neutrinos. We measured the half life of the two-neutrino double-beta decay of $^{150}$Nd to excited final states of $^{150}$Sm by detecting the de-excitation gamma rays of the daughter nucleus. This study yields the first detection of the coincidence gamma rays from the 0$^+_1$ excited state of $^{150}$Sm. These gamma rays have energies of 333.97 keV and 406.52 keV, and are emitted in coincidence through a 0$^+_1rightarrow$2$^+_1rightarrow$0$^+_{gs}$ transition. The enriched Nd$_2$O$_3$ sample consisted of 40.13 g $^{150}$Nd and was observed for 642.8 days at the Kimballton Underground Research Facility, producing 21.6 net events in the region of interest. This count rate gives a half life of $T_{1/2}=(1.07^{+0.45}_{-0.25}(stat)pm0.07(syst.))times 10^{20}$ years. The effective nuclear matrix element was found to be 0.0465$^{+0.0098}_{-0.0054}$. Finally, lower limits were obtained for decays to higher excited final states. Our half-life measurement agrees within uncertainties with another recent measurement in which no coincidence was employed. Our nuclear matrix element calculation may have an impact on a recent neutrinoless double-beta decay nuclear matrix element calculation which implies the decay to the first excited state in $^{150}$Sm is favored over that to the ground state.
We report on the experimental search for the bound state of an $eta$ meson and $^{3}hspace{-0.03cm}mbox{He}$ nucleus performed using the WASA-at-COSY detector setup. In order to search for the $eta$-mesic nucleus decay, the $pdrightarrow$ $^{3}hspace{-0.03cm}mbox{He} 2gamma$ and $pdrightarrow$ $^{3}hspace{-0.03cm}mbox{He} 6gamma$ channels have been analysed. These reactions manifest the direct decay of $eta$ meson bound in $^{3}hspace{-0.03cm}mbox{He}$ nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to an $^3$He-$eta$ nucleus width $Gamma$ above 20 MeV and binding energy $B_s$ between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the $eta$-mesic $^{3}hspace{-0.03cm}mbox{He}$ nucleus formation followed by the $eta$ meson decay which varies between $2$ nb and $15$ nb depending on possible bound state parameters.
New rotational bands built on the $ u$$(h_{11/2})$ configuration have been identified in $^{105}$Pd. Two bands built on this configuration show the characteristics of transverse wobbling: the $Delta$$I$=1 transitions between them have a predominant E2 component and the wobbling energy decreases with increasing spin. The properties of the observed wobbling bands are in good agreement with theoretical results obtained using constrained triaxial covariant density functional theory and quantum particle rotor model calculations. This provides the first experimental evidence for transverse wobbling bands based on a one-neutron configuration, and also represents the first observation of wobbling motion in the $A$$sim$100 mass region.
The contributions of three different types of driving terms are included in the estimation of the pd -> pd eta reaction at low energies. Near threshold, it is predicted that a two-step model involving an intermediate pion should be the most important but, as the energy approaches the threshold for eta production in the free nucleon--nucleon reaction, a pick-up mechanism with a spectator proton should become dominant. The total cross sections are underestimated by about a factor of two compared to experimental data but the discrepancies in the angular distributions are more serious, with no sign in the data for the peaks corresponding to the pick--up diagram.
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