Tenzing Joshi

Evidence against correlations between nuclear decay rates and Earth-Sun distance

We have reexamined our previously published data to search for evidence of correlations between the rates for the alpha, beta-minus, beta-plus, and electron capture decays of 22Na, 44Ti, 108Agm, 121Snm, 133Ba, and 241Am and the Earth?Sun distance. We find no evidence for such correlations and set limits on the possible amplitudes of such correlations substantially smaller than those observed in previous experiments.

First measurement of the ionization yield of nuclear recoils in liquid argon

This Letter details a measurement of the ionization yield (Q(y)) of 6.7 keV(40)Ar atoms stopping in a liquid argon detector. The Q(y) of 3.6-6.3 detected e(-)/keV, for applied electric fields in the range 240-2130 V/cm, is encouraging for the use of this detector medium to search for the signals from hypothetical dark matter particle interactions and from coherent elastic neutrino-nucleus scattering. A significant dependence of Q(y) on the applied electric field is observed and explained in the context of ion recombination.

The hunt for coherent neutrino-nucleus scattering with ionization argon detectors

Coherent scattering of neutrinos on nuclei is a well-known prediction of the Standard Model that has so far eluded all experimental attempts to detect it. The enhancement in the cross-section due to the coherence nature of the interaction makes this process interesting for the construction of high-rate, kg-size detectors for monitoring of nuclear reactors. Dual-phase noble-gas detectors are the prime technology for detection of the small recoil energy produced in the neutrino coherent scattering. We are pursuing a three-phased approach to build a compact 10kg dual-phase Argon ionization detector to attempt a first-ever measurement of coherent neutrino scattering at a power reactor. We will present here an overview and current status of the program pursued at Lawrence Livermore National Laboratory.

A Novel Source of Tagged Low-Energy Nuclear Recoils

Abstract For sufficiently wide resonances, nuclear resonance fluorescence behaves like elastic photo-nuclear scattering while retaining the large cross-section characteristic of resonant photo-nuclear absorption. We show that NRF may be used to characterize the signals produced by low-energy nuclear recoils by serving as a novel source of tagged low-energy nuclear recoils. Understanding these signals is important in determining the sensitivity of direct WIMP dark-matter and coherent neutrino-nucleus scattering searches.

A Model for the Secondary Scintillation Pulse Shape from a Gas Proportional Scintillation Counter

Proportional scintillation counters (PSCs), both single- and dual-phase, can measure the scintillation (S1) and ionization (S2) channels from particle interactions within the detector volume. The signal obtained from these detectors depends first on the physics of the medium (the initial scintillation and ionization), and second how the physics of the detector manipulates the resulting photons and liberated electrons. In this paper we develop a model of the detector physics that incorporates event topology, detector geometry, electric field configuration, purity, optical properties of components, and wavelength shifters. We present an analytic form of the model, which allows for general study of detector design and operation, and a Monte Carlo model which enables a more detailed exploration of S2 events. This model may be used to study systematic effects in currents detectors such as energy and position reconstruction, pulse shape discrimination, event topology, dead time calculations, purity, and electric field uniformity. We present a comparison of this model with experimental data collected with an argon gas proportional scintillation counter (GPSC), operated at 20 C and 1 bar, and irradiated with an internal, collimated 55Fe source. Additionally we discuss how the model may be incorporated in Monte Carlo simulations of both GPSCs and dual-phase detectors, increasing the reliability of the simulation results and allowing for tests of the experimental data analysis algorithms.

Measurement of the nuclear ionization quench factor in a dual-phase argon detector

Coherent neutrino-nuclear scattering (CNS) has long been predicted by the standard model [1], but has yet to be observed. One of the most promising approaches that could result in CNS detection is the use of a dual-phase argon detector [2], For this demanding measurement it is essential that the nuclear ionization quench factor be known, which is not the case for liquid argon at typical CN. S energies — We have built the Gamma or Neutron Argon Recoils Resulting in Liquid Ionization (G/NARRLI) detector for the purpose of measuring the nuclear ionization quench factor at CNS energies. We plan to use neutron scatter recoils to measure the nuclear ionization quench factor at ∼8 keV, while using nuclear resonance fluorescence (NRF) recoils to measure the nuclear ionization quench factor between −∼100 eV and ∼ 4.5 keV. In making these measurements, we will map the regime of reactor neutrino CNS recoil in Ar and validate Monte Carlo models for calculating the nuclear quench factor [2].