S. V. Paulauskas

Evidence for Gamow-Teller Decay of

The β-delayed neutron emission of ^{83,84}Ga isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the β decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed β decay to ^{78}Ni core-excited states in ^{83,84}Ge favored by shell effects. We developed shell model calculations in the proton fpg_{9/2} and neutron extended fpg_{9/2}+d_{5/2} valence space using realistic interactions that were used to understand measured β-decay lifetimes. We conclude that enhanced, concentrated β-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense β-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models.

^{78}

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

Ni Core from Beta-Delayed Neutron Emission Studies

The low-energy level structures for the neutron-rich Co isotopes at N = 39 and N = 41 are constructed following the beta decay of the respective even-even Fe isotopes. Spin and parity assignments of the lowest energy populated state in {sup 66}Co and {sup 68}Co are consistent with a 1{sup +} spin and parity assignment and attributed to the coupling of the deformed proton configurations identified in {sup 67}Co and deformed neutron configurations inferred from neighboring Fe isotones. Comparisons along the N = 39 and N = 41 isotonic chains reveal a similarity in the structures of the Co and Mn isotopes.

Proton spectroscopy of Ni 48, Fe 46, and Cr 44

A χ2 minimization algorithm has been developed to extract sub‐sampling‐time information from digitized waveforms, to be used to instrument the future Versatile Array of Neutron Detectors at Low energies. The algorithm performance has been characterized with a fast Arbitrary Function Generator, obtaining time resolution better than 1 ns for signals of amplitudes between 50 mV and 1V, with negligible walk in the whole range. The proof‐of‐principle measurement of the beta‐delayed neutron emission from 89Br indicates a resolution of 1 ns can be achieved in realistic experimental conditions.

Low-energy structure of 2766Co 39 and 2768Co 41 populated through β decay

Neutron transfer reactions were performed in inverse kinematics using radioactive ion beams of 132Sn, 130Sn, and 134Te and deuterated polyethylene targets. Preliminary results are presented. The Q‐value spectra for 133Sn, 131Sn and 135Te reveal a number of previously unobserved peaks. The angular distributions are compatible with the expected lf7/2 nature of the ground state of 133Sn, and 2p3/2 for the 3.4 MeV state in 131Sn.

Digital Electronics For The Versatile Array Of Neutron Detectors At Low Energies

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

Studies of Nuclei Close to 132Sn Using Single-Neutron Transfer Reactions

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

Proton spectroscopy of 48Ni, 46Fe, and 44Cr

Neutron capture reactions on unstable nuclei are important for both basic and applied nuclear science. A program has been developed at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory to study single-neutron transfer (d,p) reactions with rare isotope beams to provide information on neutron-induced reactions on unstable nuclei. Results from (d,p) studies on {sup 130,132}Sn, {sup 134}Te and {sup 75}As are discussed.

Proton spectroscopy of Ni48,Fe46 , and Cr44

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

Neutron Transfer Reactions: Surrogates for Neutron Capture for Basic and Applied Nuclear Science

The recently commissioned Versatile Array of Neutron Detectors at Low Energy (VANDLE)1 was designed to measure neutron energies from nuclear excited states populated through beta decay or transfer reactions. Because the neutron energy is determined by the time-of-flight technique, a time resolution better than 1 ns is necessary. Another important design requirement was a low amplitude detection threshold needed to measure neutron energies as low as 100 keV. A fully digital data acquisition system has been developed using XIAs DGF Pixie-16 hardware. These goals have been met via essential technical developments: an algorithm for the extraction of sub-sample time information from digitized waveforms and a new triggering scheme. Both of these advancements were critical to achieve the design goals for VANDLE.