Search for a decay of Te-104 with a novel recoil-decay scintillation detector

A search for superallowed α decay of N=Z nuclei Te104 and Xe108 was carried out using a novel recoil-decay scintillator detector at the tandem accelerator facility at the Japan Atomic Energy Agency (JAEA). Inorganic crystal scintillation material YAP:Ce (yttrium aluminum perovskite) coupled to a position-sensitive photomultiplier tube (PSPMT) was implemented for the first time in a radioactive decay experiment. Residues from the fusion-evaporation reaction Ni58+Fe54→Xe∗112 were separated by the JAEA Recoil Mass Separator (RMS) and implanted into the YAP:Ce crystal. α decays of neutron-deficient tellurium isotopes were identified and proton emission of I109 was observed. The α-decay chain Xe109→Te105→Sn101 was recorded with a time interval of 960 ns between two α pulses. Position localization in the crystal for decays and ions in the energy range from hundreds of keV to 60 MeV was achieved with an accuracy of 0.67 mm, proving that this detector is capable of making temporal and spatial correlations for fast decay events. No conclusive evidence was found for the decay chain Xe108→Te104→Sn100 within 3 days of experiment. However, two events were observed with properties consistent with the reported observation at the Fragment Mass Analyzer (FMA), but with a separation between signals of less than 4 ns. The cross section limit of 130 pb was obtained for production of two events of Xe108, about an order of magnitude below the expectation based on earlier cross section measurements and the hivap fusion-evaporation code

First beta-decay spectroscopy of In-135 and new beta-decay branches of In-134

The beta decay of the neutron-rich In-134 and In-135 was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z = 50 above the N = 82 shell. The beta-delayed gamma-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three beta-decay branches of In-134 were established, two of which were observed for the first time. Population of neutron-unbound states decaying via. rays was identified in the two daughter nuclei of In-134, Sn-134 and Sn-133, at excitation energies exceeding the neutron separation energy by 1 MeV. The beta-delayed one- and two-neutron emission branching ratios of In-134 were determined and compared with theoretical calculations. The beta-delayed one-neutron decay was observed to be dominant beta-decay branch of In-134 even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of Sn-134. Transitions following the beta decay of In-135 are reported for the first time, including. rays tentatively attributed to Sn-135. In total, six new levels were identified in Sn-134 on the basis of the beta.. coincidences observed in the In-134 and In-135 beta decays. A transition that might be a candidate for deexciting the missing neutron single-particle 13/2(+) state in Sn-133 was observed in both beta decays and its assignment is discussed. Experimental level schemes of Sn-134 and Sn-135 are compared with shell-model predictions. Using the fast timing technique, half-lives of the 2(+), 4(+), and 6(+) levels in Sn-134 were determined. From the lifetime of the 4(+) state measured for the first time, an unexpectedly large B(E2; 4(+)-> 2(+)) transition strength was deduced, which is not reproduced by the shell-model calculations.Peer reviewe

Low-energy level schemes of 66,68Fe and inferred proton and neutron excitations across Z = 28 and N = 40

Background: The nuclei in the region around 68Ni display an apparent rapid development of collectivity as protons are removed from the f7/2 single-particle state along the N = 40 isotonic chain. Proton and neutron excitations across the Z = 28 and N = 40 gaps are observed in odd-A 27Co and 26Fe isotopes. Little spectroscopic information beyond the excited 2+ and 4+ is available in the even-even (66,68)26Fe nuclei to compare with shell model calculations. Purpose: Our goal is to determine the low-energy level schemes of 66,68Fe and compare the observed excitations with shell model calculations to identify states wherein a contribution from excitations across Z = 28 and N = 40 are present. Method: The low-energy states of 66,68Fe were populated through the beta decay of 66,68Mn produced at the National Superconducting Cyclotron Laboratory. Beta-delayed gamma-ray transitions were detected and correlated to the respective parent isotope to construct a low-energy level scheme. Results: The low-energy level schemes of 66,68Fe were constructed from observed gamma-ray coincidences and absolute gamma-ray intensities. Tentative spin and parity assignments were assigned based on comparisons with shell model calculations and systematics. The two lowest 0+ and 2+ states were characterized in terms of the number of protons and neutrons excited across the respective shell gaps. Conclusion: The removal of two protons from 68Ni to 66Fe results in an inversion of the normal configuration and the one characterized by significant excitation across the Z = 28 and N = 40 gaps. Approximately, one proton and two neutrons are excited across their respective single-particle gaps in the ground state of 66Festatus: publishe

Experimental study of the β decay of the very neutron-rich nucleus 85Ge

The β-decay properties of the very neutron-rich nucleus 85Ge, produced in the proton-induced fission of 238U, were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The level scheme of 8533As52 populated in 85Geβγ decay was reconstructed and compared to shell-model calculations. The investigation of the systematics of low-energy levels in N=52 isotones together with shell-model analysis allowed us to provide an estimate of the low-energy structure of the more exotic N=52 isotone 81Cu.status: publishe

beta and beta-n decay of the neutron-rich Ge-84 nucleus

The β-decay properties of the very neutron-rich 84Ge nucleus were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Several new γ-transitions and levels were added to its decay scheme and the order of the two lowest-lying levels in the daughter 84As was corrected. For the first time γ radiation following β-delayed neutron emission was observed. The shell-model calculations and apparent β transition intensities were used to guide the spin assignment to the 84As levels, in particular for the low-energy part of the level scheme. The new spin-parity (2−) proposed for the ground state of 84As is supported also by the systematics of N=51 isotones.status: publishe

Shape coexistence along N = 40

The low-energy level structures of 64Mn39 and 66Mn41 were investigated through both the decay of Mn metastable states and the population of levels following the β decay of 64Cr and 66Cr. The deduced level schemes and tentatively assigned spins and parities suggest the coexistence of spherical and deformed configurations above and below N = 40 for the odd-odd Mn isotopes. The low-energy deformed configurations are attributed to the coupling between a proton in a K = 1/2− level with neutrons in either the K = 1/2− or the K = 3/2+ levels originating from the πp3/2, νp1/2, and νg9/2 single-particle states, respectively.status: publishe

Analogous intruder behavior near Ni, Sn, and Pb isotopes

© 2015 American Physical Society. ©2015 American Physical Society. Near shell closures, the presence of unexpected states at low energies provides a critical test of our understanding of the atomic nucleus. New measurements for the N=42 isotones Co2769 and Cu2971, along with recent data and calculations in the Ni isotopes, establish a full set of complementary, deformed, intruder states astride the closed-shell Ni28 isotopes. Nuclei with a one-proton hole or one-proton particle adjacent to Z=28 were populated in β-decay experiments and in multinucleon transfer reactions. A β-decaying isomer, with a 750(250)-ms half-life, has been identified in Co422769. It likely has low spin and accompanies the previously established 7/2- state. Complementary data for the levels of isotonic Cu422971 support the presence of a deformed, ΔJ=1 band built on the proton intruder 7/2- level at 981 keV. These data, together with recent studies of lower-mass Co and Cu isotopes and extensive work near Ni68, support the view that intruder states based on particle-hole excitations accompany all closed proton shells with Z≥28.status: publishe