Beta decay of the proton-f5/2 ground state of 77Cu studied with 255 MeV and 0.2 MeV purified radioactive beams

Isobarically purified beams of 77Cu with energies of 225 and 0.2 MeV were used at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory to study beta decay into states in 77Zn. Data taken at 225 MeV allowed the determination of absolute branching ratios relative to the decay of 77Cu for this beta decay as well as its daughters. From these we obtained a refined beta-delayed neutron emission probability of 30.3(22)% and a probability that the decay proceeds through 77Zn(g) of 49.1(26)%. A total of 64 gamma rays were placed in a level scheme for 77Zn containing 35 excited states including one state above the neutron separation energy, whereas two gamma rays were observed for the βn branch to states in 76Zn. The growth and decay curves of some prominent gamma rays indicate a single beta-decaying state with a half-life of 480(9) ms. The decay pattern for 77Cu, with observed feeding of 8(3)% to 7/2+ 77Zn(g) and 6(3)% to 1/2− 77Zn(m), in contrast to the large feeding observed for decay of proton-p3/2 73Cu(g) to 1/2− 73Zn(g), strongly suggests a proton-f5/2 ground state for the studied 77Cu activity.status: publishe

β-decay studies of the transitional nucleus 75Cu and the structure of 75Zn

The β decay of 75Cu [t1/2 = 1.222(8) s] to levels in 75Zn was studied at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory. The γγ and βγ data were collected at the Low-energy Radioactive Ion Beam Spectroscopy Station using the high-resolution isobar separator to obtain a purified 75Cu beam with a rate of over 2000 ions per second. The excited states in 75Zn have been identified for the first time. A total of 120 γ-ray transitions were placed in a level scheme containing 59 levels including two states above the neutron separation energy and a previously unknown 1/2− isomeric state at 127 keV. Spins and parities of several states were deduced and interpreted based on the observed β feeding and γ-decay pattern.status: publishe

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

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