Narrow Results

Our contribution aims to celebrate the immeasurable contribution that Tom Kuo has provided to the understanding of the structure of atomic nuclei, and also of the infinite nuclear matter, in terms of the fundamental principles governing the realistic nuclear potential. The authors want to testify Tom Kuo’s heritage and impact on their approach to the study of nuclear systems by reviewing some recent findings on the role of the two-body component of shell-model effective $\beta$-decay operators. The focus is spotted on the so-called Pauli-blocking effect that plays a nonnegligible role in nuclei characterized by a large number of valence nucleons.

Quantitative bounds on Lorentz symmetry violation in the neutrino sector have been obtained by analyzing existing laboratory data on neutron β decay and pion leptonic decays. In particular some parameters appearing in the energy–momentum dispersion relations for ν_e and ν_μ have been constrained in two typical cases arising in many models accounting for Lorentz violation.

The β-decay spectroscopy on ²⁴Si was carried out in order to investigate characteristic properties of proton-rich nuclei from a perspective of mirror asymmetry. We observed two β transitions to low-lying bound states in ²⁴Al for the first time. The B(GT) of ²⁴Si were deduced to be 0.13(2) and 0.14(2), which were smaller than those of the mirror transition by 22(11)% and 10(8)%, respectively. Through the comparison with theoretical calculations taking into account the Coulomb force and the Thomas-Ehrman shift, the mirror asymmetry of B(GT) is attributed to the lowering of the proton 1s_1/2 orbital.

We present a new study of the low-lying states in ¹²⁴Te nucleus by γ-ray spectroscopy following ¹²⁴Iβ⁺/ε decay. The β radioactive sources were produced in the ¹²⁴Te(p, n)¹²⁴I reaction induced by 11 MeV protons, delivered by the Bucharest FN Tandem Accelerator. The γ-rays were measured in a low background area with three large volume HPGe detectors. A total number of 276 milion double coincidence events were recorded in a six-day run. Most of the gamma line intensities previously measured were confirmed with improved accuracy and several gamma lines were obtained for the first time. Our results, combined with those from a recent (n, γ) study are compared with the predictions of the E(5) critical point symmetry model and numerical IBA-1 model calculations at the critical point of the U(5)–O(6) phase transition.

β-delayed neutron emission is often the dominant decay mode for neutron-rich nuclei near the drip-line. The large decay energy (Q value) allows to populate the highly excited states of the daughter nucleus, which are of special importance to study the nuclear structure of the unstable nuclei. So far many experiments of this kind have been carried out in several laboratories.

We present here briefly the experimental method and basic detection setups for the experiment of this kind. The major detector systems in the world are outlined and their performances are compared to each other. The latest experimental results are presented, including the study of the β-delayed neutron and gamma emission of the isotopes ^18,21N and the excited states of the daughter nuclei ^18,21O, respectively.

We perform a joint analysis of current data from cosmology and laboratory experiments to constrain the neutrino mass parameters in the framework of bayesian statistics, also accounting for uncertainties in nuclear modeling, relevant for neutrinoless double β decay (0v2β) searches. We find that a combination of current oscillation, cosmological and 0v2β data provides results that are dominated by the cosmological and oscillation data, so they are not affected by uncertainties related to the interpretation of 0v2β data, like nuclear modeling, or the exact particle physics mechanism underlying the process. We then perform forecasts for forthcoming and next-generation experiments, and find that in the case of normal hierarchy, and given a total mass of 0.1 eV, it will be possible to measure the total mass itself, the effective Majorana mass and the effective electron mass with an accuracy at 95% C.L.. This assumes that neutrinos are Majorana particles. We argue that more precise nuclear modeling will be crucial to improve these sensitivities.

The 8π spectrometer at TRIUMF-ISAC-I and a powerful suite of ancillary detectors support a wide program of research in the fields of nuclear structure, nuclear astrophysics and fundamental symmetries with low-energy radioactive beams.Work is underway to upgrade the Ge detectors and DAQ aspects of the facility to a new state-of-the-art γ-ray spectrometer, GRIFFIN, which will become operational in 2014. GRIFFIN will constitute an increase in the γ-γ efficiency of close to a factor of 300 over the current setup and extend the capabilities for investigations of exotic nuclei produced at ISAC.

Studying the weak nuclear response, especially the Gamow-Teller (GT) transitions, starting from stable as well as unstable pf-shell nuclei, is one of the key issues in nuclear and nuclear-astro physics. We study the GT transitions starting from T_z = ±2 mirror nuclei, respectively, by means of β decays and complementary hadronic (³He, t) charge-exchange reactions. Under the assumption that isospin is a good quantum number, symmetry is expected for the structure of mirror nuclei and the GT transitions starting from them. The β-decay halflife and branching ratios and the strength distribution of GT transitions from the (³He, t) reaction are compared and also combined for the understanding of the nuclear structure of pf-shell far-from-stability nuclei.

The β decay properties of ⁷⁵Cu [t_1/2 = 1.222(8) s] and ⁷⁷Cu [t_1/2 = 480(9)ms] were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Presented is a short overview of obtained results.

In trap-based lifetime experiments, the key to extrapolating the neutron β-decay rate is the understanding of non-β-decay losses of the ultracold neutron (UCN) population in the trap. Use of a magnetic trap eliminates the potential for UCN to be lost at surface boundaries. However, these traps also introduce additional systematic errors, such as spin-flip loss when neutrons cross regions of zero field. In addition, the NIST lifetime experiment reported the unexpected presence of quasi-bound, high-energy neutrons that significantly reduced the measured storage lifetime. We discuss the precision required in measuring these sources of non-β-decay losses and strategies to mitigate some of these effects. The discussion will focus on the magneto-gravitational trap used in the UCN_τ experiment.