Victor M. Gehman

Neutron inelastic scattering processes as a background for double-{beta} decay experiments

We investigate several Pb(n,n{sup }{gamma}) and Ge(n,n{sup }{gamma}) reactions. We measure {gamma}-ray production from Pb(n,n{sup }{gamma}) reactions that can be a significant background for double-{beta} decay experiments which use lead as a massive inner shield. Particularly worrisome for Ge-based double-{beta} decay experiments are the 2041-keV and 3062-keV {gamma} rays produced via Pb(n,n{sup }{gamma}). The former is very close to the {sup 76}Ge double-{beta} decay endpoint energy and the latter has a double escape peak energy near the endpoint. We discuss the implications of these {gamma} rays on past and future double-{beta} decay experiments and estimate the cross section to excite the level that produces the 3062-keV {gamma} ray. Excitation {gamma}-ray lines from Ge(n,n{sup }{gamma}) reactions are also observed. We consider the contribution of such backgrounds and their impact on the sensitivity of next-generation searches for neutrinoless double-{beta} decay using enriched germanium detectors.

Multilayer Scintillator Responses for Mo Observatory of Neutrino Experiment Studied Using a Prototype Detector MOON-1

An ensemble of multi-layer scintillators is discussed as an option of the high-sensitiv ity detector Mo Observatory Of Neutrinos (MOON) fo r spectroscopic measurements of neutrino-less double beta decays. A prototype detector MOON-1, which c onsists of 6 layer plastic-scintillator plates, was built to study the sensitivity of the MOON-type detector. The scintillation photon collection and the ener gy resolution, which are key elements for the high-sensitivity experim ents, are found to be 1835±30 photo-electrons for 976 keV electrons and V = 2.9±0.1 % ( E/E = 6.8±0.3 % i n FWHM) at the QEE ~ 3 MeV region, respectively. The multilayer plastic-scintillator structure with good energy resolution as well as good background suppression of E J rays is crucial for the MOON-type detector to ach ieve the inverted hierar chy neutrino mass sensitivity. PACS: 14.60.Pq; 23.40.-s; 29.40.McAn ensemble of multilayer scintillators is discussed as an option of the high-sensitivity detector MOON (Mo Observatory of Neutrinos) for spectroscopic measurements of neutrinoless double beta decays. A prototype detector MOON-1, which consists of 6-layer plastic scintillator plates, was built to study the photon responses of the MOON-type detector. The photon responses, i.e., the number of scintillation photons collected and the energy resolution, which are key elements for high-sensitivity experiments, are found to be 1835 � 30 photoelectrons for 976 keV electrons and � ¼ 2:9 � 0:1% (� E=E ¼ 6:8 � 0:3% in FWHM) at the Q�� � 3 MeV region, respectively. The multilayer plastic scintillator structure with high energy resolution as well as a good signal for the background suppression of � –� rays is crucial for the MOON-type detector to achieve inverted-hierarchy neutrino-mass sensitivity. It will also be useful for medical and other rare-decay experiments as well.

Neutrino studies in 100Mo and MOON - Mo Observatory of neutrinos

Abstract The MOON (Molybdenum Observatory Of Neutrinos) project is a hybrid ββ and solar ν experiment with 100 Mo. It aims at high sensitive studies of ββ decays with a sensitivity of m ν > ∼ 0.03 eV and real-time studies of pp and 7 Be solar νs. The double β rays from 100 Mo are measured in prompt coincidence for the 0νββ studies, and the inverse β rays from solar-ν captures of 100 Mo are measured in delayed coincidence with the subsequent β decay of 100 Tc. Measurements with good position resolution enable one to select true signals by spatial and time correlations.

Solubility, light output and energy resolution studies of molybdenum-loaded liquid scintillators

The search for neutrinoless double-beta decay is an important part of the global neutrino physics program. One double-beta decay isotope currently under investigation is 100 Mo. In this article, we discuss the results of a feasibility study investigating the use of molybdenum-loaded liquid scintillator. A large, molybdenum-loaded liquid scintillator detector is one potential one design for a low-background, internal source 0 search with 100 Mo. The program outlined in this article included the selection of a solute containing molybdenum, a scintillating solvent and the evaluation of the mixture’s performance as a radiation detector.

Systematic effects in pulse shape analysis of HPGe detector signals for 0νββ

Abstract Pulse shape analysis is an important background reduction and signal identification technique for next generation of 76Ge 0 ν β β experiments. We present a study of the systematic uncertainties in one such parametric pulse-shape analysis technique for separating multi-site background from single-site signal events. We examined systematic uncertainties for events in full-energy gamma peaks (predominantly multi-site), double-escape peaks (predominantly single-site) and the Compton continuum near Q β β (which will be the dominant background for most 0 ν β β searches). In short, we find total (statistical plus systematic) fractional uncertainties in the pulse shape cut survival probabilities of: 6.6%, 1.5% and 3.8% for double-escape, continuum and γ ‐ ray events, respectively.

MOON for a next-generation neutrino-less double-beta decay experiment; present status and perspective

The performance of the MOON detector for a next-generation neutrino-less double-beta decay experiment was evaluated by means of the Monte Carlo method. The MOON detector was found to be a feasible solution for the future experiment to search for the Majorana neutrino mass in the range of 100-30 meV.

The Majorana Project: A Next‐Generation Double‐Beta Decay Experiment

The Majorana Project will endeavor to provide direct limits on the effective Majorana mass of the electron neutrino through the measurement of 0νββ decay in 76Ge. Our goal is an experiment with a scalable sensitivity starting at 100 meV (corresponding to the quasi‐degenerate mass scale) and ultimately extending well below that level. The current Majorana design consists of several modules, each a close‐packed array of 57 Ge detectors, enriched to 86% in 76Ge, in a single cryostat. The ultimate background goal for Majorana is of order one count per tonne of Ge per year in the four keV region of interest around Qββ. This background will allow us to reach an effective Majorana‐neutrino mass sensitivity approximately five times better than current results and should cover the quasi‐degenerate mass scale.