Browsing by Subject "Neutrinos"

An experimental study of the two-neutrino double-beta (2νββ) decay of 150Nd to various excited final states of 150Sm was performed at Triangle Universities Nuclear Laboratory (TUNL). Such data provide important checks for theoretical models used to predict 0νββ decay half lives.

The measurement was performed at the recently established Kimballton Underground Research Facility (KURF) in Ripplemeade, Virginia using the TUNL-ITEP double-beta decay setup. In this setup, two high-purity germanium detectors were operated in coincidence to detect the deexcitation gamma rays of the daughter nucleus. This coincidence technique, along with the location underground, provides a considerable reduction in background in the regions of interest.

This study yields the first results from KURF and the first detection of the

coincidence gamma rays from the 0+₁ excited state of 150Sm. These gamma rays

have energies of 334.0 keV and 406.5 keV, and are emitted in coincidence through a 0+₁→2+₁→0+_gs transition. The enriched Nd₂O₃ sample obtained from Oak Ridge

National Laboratory consists of 40.13 g 150Nd. This sample was observed for 391 days, producing 29 raw events in the region of interest. This count rate gives a half life of T_1/2 = (0.72+0.36_−0.18 ± 0.04(syst.)) × 1020 years, which agrees within error with

another recent measurement, in which only the single deexcitation gamma rays were detected (i.e., no coincidence was employed). Lower limits were also obtained for decays to higher excited final states.

There are few existing measurements of low energy neutrino-nucleus interactions. The COHERENT collaboration is seeking to measure several of these processes using the intense pulsed neutrinos produced at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL).

The primary process of interest to COHERENT is coherent elastic neutrino-nucleus scattering (CEvNS), a process predicted in 1974 but only first measured by COHERENT in 2017. In a CEvNS interaction, a neutrino elastically scatters off a nucleus, causing its nucleons to recoil in phase, leading to a large increase in the scattering cross section. The large cross section provides several potential applications of CEvNS, however the signature of interaction, a keV-scale nuclear recoil, can be difficult to detect.

This thesis highlights experimental work to develop and measure neutrino-nucleus interactions on a variety of targets, including both CEvNS interactions and inelastic neutrino-nucleus interactions. This includes the development a ton-scale sodium-iodide scintillator array, a 185-kg prototype NaI detector, and analysis of neutrino-induced neutron detectors seeking to study unobserved neutrino-nucleus interactions on lead and iron. In addition, supporting measurements carried out at the Triangle Universities Nuclear Laboratory (TUNL) to measure quenching factors in NaI[Tl] are discussed.

Neutrinos have long been considered a powerful tool for exploring physics beyond the standard model, and have been recognized as having applications in nuclear reactor monitoring and non-proliferation efforts. In particular, there is interest on the part of both the physics and nuclear security communities in a discrete neutrino detector; however, the experimental difficulties associated with detecting neutrinos in a high background environment have hampered past efforts, forcing experiments underground. I discuss my work on a variety of novel neutrino technologies meant to overcome such difficulties. These include the design of a compact optical time projection chamber (TPC) capable of reconstructing inverse beta decays, work on the CHANDLER detector technology systems, the first measurement of nuclear quenching effects in Cerium Bromide scintillator, measurements of nuclear quenching in a gaseous dark matter detector, and a world leading measurement of nuclear quenching in liquid Xenon. Many of these technologies, either singly or in combination, may meet the needs of the nuclear security and dark matter communities and provide a mechanism to reduce backgrounds in fundamental neutrino physics searches.

An inclusive measurement of the cross section of the electron neutrino charged-current interaction on $^{127}$I can probe the quenching of g$_{A}$, the axial-vector coupling constant, which affects the rate of neutrinoless double beta decays, and contribute to the design of next-generation solar neutrino detectors. At the Los Alamos Meson Production Facility (LAMPF), an exclusive measurement of the flux-averaged cross section was measured to be [2.84 $\pm$ 0.91 (stat) $\pm$ 0.25 (syst)] $\times\; 10^{\boldsymbol{-}40}$ cm$^2$ [1]. This measurement has a large statistical error and only counts the number of {$^{127}$Xe} in the bound state. To make a first measurement of the inclusive cross section with lower statistical uncertainties, a 185-kg NaI[Tl] prototype detector, NaI$\upnu$E-185, was deployed by the COHERENT collaboration at the Spallation Neutron Source. To study electron neutrino charged-current interaction detection efficiencies, simulations were performed. To explore new approaches of steady state background rejection, a convolutional neural network (CNN) classifier and a XGBoost based classifier were developed. The best 4-class model, tested with simulations, achieved a 50.2\% classification accuracy. To address the non-linearity of NaI[Tl] crystals at high energies, calibrations using Michel positrons from stopped muon decays were performed. The cross section measurement was done through probability density function (PDF) fitting. The flux-averaged total inclusive cross section, excluding forbidden transitions, was measured to be [9.2 + 2.1 $-$ 1.8 (stat+syst)] $\times\; 10^{\boldsymbol{-}40}$ cm$^2$, rejecting the null hypothesis by 5.8 $\sigma$.

[1] J. R. Distel, B. T. Cleveland, K. Lande, C. K. Lee, P. S. Wildenhain, G. E. Allen, and R. L. Burman. Measurement of the cross section for the reaction $^{127}\mathrm{I}({\ensuremath{\nu}}_{e},{e}^{\ensuremath{-}})^{127}{\mathrm{Xe}}_{\textrm{bound states}}$ with neutrinos from the decay of stopped muons, Phys. Rev. C, 68:054613, Nov 2003.