Chris Hagmann

Two-phase emission detector for measuring coherent neutrino-nucleus scattering

Coherent scattering is a flavor-blind, high-rate, as yet undetected neutrino interaction predicted by the Standard Model. We propose to use a compact (kg-scale), two-phase (liquid-gas) argon ionization detector to measure coherent neutrino scattering off nuclei. In our approach, neutrino-induced nuclear recoils in the liquid produce a weak ionization signal, which is transported into a gas under the influence of an electric field, amplified via electroluminescence, and detected by phototubes or avalanche diodes. This paper describes the features of the detector, and estimates signal and background rates for a reactor neutrino source. Relatively compact detectors of this type, capable of detecting coherent scattering, offer a new approach to flavor-blind detection of man-made and astronomical neutrinos, and may allow development of compact neutrino detectors capable of nonintrusive real-time monitoring of fissile material in reactors.

Cosmic-ray shower generator (CRY) for Monte Carlo transport codes

The CRY software library generates correlated cosmic-ray particle shower distributions at one of three elevations (sea level, 2100 m, and 11300 m) for use as input to transport and detector simulation codes. Our simulation is based on precomputed input tables derived from full MCNPX simulations of primary cosmic rays on the atmosphere and benchmarked against published cosmic-ray measurements. Our simulation provides all particle production (muons, neutrons, protons, electrons, photons, and pions) with the proper flux within a user-specified area and altitude. The code generates individual showers of secondary particles sampling the energy, time of arrival, zenith angle, and multiplicity with basic correlations, and has user controls for latitude (geomagnetic cutoff) and solar cycle effects. We provide a function library, callable from C, C++, and Fortran, and interfaces to popular Monte Carlo transport codes (MCNP, MCNPX, COG, Geant4). The software library and examples can be downloaded from http://nuclear.llnl.gov/simulation.

Monte Carlo Simulation of Proton-induced Cosimc Ray Cascades in the Atmosphere

We have developed a Monte Carlo model of the Earths atmosphere and implemented it in three different codes (GEANT4, MCNPX, and FLUKA). Primary protons in the energy range of 1 GeV-100 TeV are injected at the top of the atmosphere. The codes follow the tracks of all relevant secondary particles (neutrons, muons, gammas, electrons, and pions) and tally their fluxes at selectable altitudes. Comparisons with cosmic ray data at sea level show good agreement.

Low-energy (<10keV) electron ionization and recombination model for a liquid argon detector

Abstract Detailed understanding of the ionization process in noble liquid detectors is important for their use in applications such as the search for dark matter and coherent elastic neutrino-nucleus scattering. The response of noble liquid detectors to low-energy ionization events is poorly understood at this time. We describe a new simulation tool which predicts the ionization yield from electronic energy deposits ( E 10 keV ) in liquid Ar, including the dependence of the yield on the applied electric drift field. The ionization signal produced in a liquid argon detector from 37Ar beta decay and 55Fe X-rays has been calculated using the new model.

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.

Testing of CMOS Devices in NIF's Harsh Neutron Environment

Vendor supplied CMOS sensors were exposed to 14 MeV neutrons on yield shots in NIF and examined for damage. The sensors were exposed to multiple shots with a maximum fluence on one of the sensors of 4.3E11 n/cm2. The results of post-shot testing will be presented. LLNL is investigating the suitability of CMOS imaging sensors for use in the camera of the ARIANE diagnostic which will mitigate the effects of the NIF neutron environment by dumping photoelectrons during the neutron pulse and then recording an image stored on a long persistence phosphor.

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].

Axions from cosmic string and wall decay

If inflation occurred with a reheat temperature > T{sub PQ}, axions from the decay of global axion strings and domain walls would make an important contribution to the cosmological energy density, comparable to that from vacuum misalignment. Several groups have numerically studied the evolution of axion strings and walls in the past, however substantial uncertainties remain in their contribution to the present density {Omega}{sub a,string+wall} {approx} 1-100 (f{sub a}/10{sup 12} GeV){sup 7/6}, where f{sub a} is the axion decay constant. I will describe the numerical methods used in our simulations and show results for several string and wall configurations.