Dual-phase argon ionization detector for measurement of coherent elastic neutrino scattering and medium-energy nuclear recoils

We propose to build and deploy a 10-kg dual-phase argon ionization detector for the detection of coherent neutrino-nucleus scattering, which is described by the reaction; (V) + (Z,N) {yields} (v) + (Z,N). Our group would be the first to make this measurement. Its detection would validate (or refute) central tenets of the Standard Model. The existence of this process is also relevant to astrophysics, where coherent neutrino scattering is assumed to impede energy transport within neutron stars. We have built a gas-phase argon ionization detector to determine the feasibility of measuring small recoil energies ({approx}1keV) predicted from coherent neutrino scattering, and to characterize the recoil spectrum of the argon nuclei induced by scattering from medium-energy neutrons. We present calibrations made with 55-Fe, a low energy x-ray source, and describe a planned measurement of the recoil spectra from the 60keV Lithium-target neutron generator at LLNL. A high signal-to-noise measurement of the recoil spectrum will not only serve an important milestone in achieving the sensitivity necessary for measuring coherent neutrino-nucleus scattering, but will break new scientific ground by providing a first ever measurement of low-energy quenching factors in argon. Coherent scattering occurs when the momentum transfer from a neutrino to the nucleus is much smaller than the inverse size of the recoil nucleus. A detection of coherent neutrino-nucleus scattering would verify an unconfirmed Standard Model prediction [1], explore non-standard neutrino-quark interactions, confirm stellar collapse and supernova energy transport and neutrino opacity models, and could be applied to the measurement of the flavor-blind neutrino spectrum from next nearby supernova, or could be used to promote non-intrusive reactor power monitoring [2]. We propose detecting the ionization induced by recoiling argon nuclei using a 10 kg dual-phase argon detector. The principle of dual-phase detection has been described elsewhere [3]. We propose using a 3 GW commercial nuclear reactor as a source of antineutrinos. We have designed and built a gas-phase prototype of the detector with which we have measured the 200-electron equivalent ionization signals from a 6keV Fe-55 source with a signal-to-noise threshold of 50 electrons. This prototype also enables study of scintillation properties of Argon and investigation of electron and nuclear recoils in Argon. We will measure medium energy neutron-nuclear recoils in our prototype detector using the recently-commissioned LLNL compact pulsed neutron source

Materials analysis using positron beam lifetime spectroscopy

We are using a defect analysis capabilities based on two positron beam lifetime spectrometers: the first is based on a 3 MeV electrostatic accelerator and the second on our high current linac beam. The high energy beam lifetime spectrometer is routinely used to perform positron lifetime analysis with a 3 MeV positron beam on thick sample specimens. It is being used for bulk sample analysis and analysis of samples encapsulated in controlled environments for in situ measurements. A second, low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopy is under development at the LLNL high current positron source. This beam will enable defect-specific, 3-dimensional maps of defect concentration with sub-micron location resolution. When coupled with first principles calculations of defect specific positron lifetimes it will enable new levels of defect concentration mapping and defect identification

High current pulsed positron microprobe

We are developing a low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopy to provide a new defect analysis capability at the 10{sup 10} e{sup +}s{sup -l} beam at the Lawrence Livermore National Laboratory electron linac. When completed, the pulsed positron microprobe will enable defect specific, 3-dimensional maps of defect concentrations with sub-micron resolution of defect location. By coupling these data with first principles calculations of defect specific positron lifetimes and positron implantation profiles we will both map the identity and concentration of defect distributions

A 2nd generation cosmic axion experiment

An experiment is described to detect dark matter axions trapped in the halo of our galaxy. Galactic axions are converted into microwave photons via the Primakoff effect in a static background field provided by a superconducting magnet. The photons are collected in a high Q microwave cavity and detected by a low noise receiver. The axion mass range accessible by this experiment is 1.3-13 micro-eV. The expected sensitivity will be roughly 50 times greater than achieved by previous experiments in this mass range. The assembly of the detector is well under way at LLNL and data taking will start in mid-1995.Comment: Postscript, 6 pages, 4 figures; submitted to proceedings of: XXXth Recontres de Moriond, 'Dark Matter in Cosmology", Villars-sur-Ollon, Switzerland, Jan 21-28, 199

Localizability of Tachyonic Particles and Neutrinoless Double Beta Decay

The quantum field theory of superluminal (tachyonic) particles is plagued with a number of problems, which include the Lorentz non-invariance of the vacuum state, the ambiguous separation of the field operator into creation and annihilation operators under Lorentz transformations, and the necessity of a complex reinterpretation principle for quantum processes. Another unsolved question concerns the treatment of subluminal components of a tachyonic wave packets in the field-theoretical formalism, and the calculation of the time-ordered propagator. After a brief discussion on related problems, we conclude that rather painful choices have to be made in order to incorporate tachyonic spin-1/2 particles into field theory. We argue that the field theory needs to be formulated such as to allow for localizable tachyonic particles, even if that means that a slight unitarity violation is introduced into the S matrix, and we write down field operators with unrestricted momenta. We find that once these choices have been made, the propagator for the neutrino field can be given in a compact form, and the left-handedness of the neutrino as well as the right-handedness of the antineutrino follow naturally. Consequences for neutrinoless double beta decay and superluminal propagation of neutrinos are briefly discussed.Comment: 12 pages, 5 figure

Nondestructive Neutron And Gamma-Ray Technologies Applied To GNEP And Safeguards

In recent years, LLNL has developed methods for diagnosing significant quantities of special nuclear material (SNM). Homeland security problems have recently focused our attention on detection of shielded highly enriched uranium (HEU), which is a weak signal problem. Current and advanced safeguards applications will require working in the opposite extreme of strong but buried signals. We will review some of the technologies that have been developed at LLNL for homeland security applications and discuss how they might be used in support of international safeguards

Active Detection of Small Quantities of Shielded Highly-Enriched Uranium Using Low-Dose 60-keV Neutron Interrogation

Active interrogation with low-energy neutrons provides a search technique for shielded highly-enriched uranium. We describe the technique and show initial results using a low-dose 60 keV neutron beam. This technique produces a clear induced fission signal in the presence of small quantities of {sup 235}U. The technique has been validated with low-Z and high-Z shielding materials. The technique uses a forward-directed beam of 60 keV neutrons to induce fission in {sup 235}U. The induced fission produces fast neutrons which are then detected as the signature for {sup 235}U. The beam of neutrons is generated with a 1.93 MeV proton beam impinging on a natural lithium target. The proton beam is produced by a radio-frequency quadrupole (RFQ) LINAC. The 60 keV neutron beam is forward directed because the {sup 7}Li(p,n) reaction is just at threshold for the proton energy of 1.93 MeV

Status of the large-scale dark-matter axion search

If axions constitute the dark matter of our galactic halo they can be detected by their conversion into monochromatic microwave photons in a high-Q microwave cavity permeated by a strong magnetic field. A large-scale experiment is under construction at LLNL to search for halo axions in the mass range 1.3 - 13 {mu}eV, where axions may constitute closure density of the universe. The search builds upon two pilot efforts at BNL and the University of Florida in the late 1980`s, and represents a large improvement in power sensitivity ({approximately}50) both due to the increase in magnetic volume (B{sup 2}V = 14 T{sup 2}m{sup 3}), and anticipated total noise temperature (T{sub n} {approximately}3K). This search will also mark the first use of multiple power-combined cavities to extend the mass range accessible by this technique. Data will be analyzed in two parallel streams. In the first, the resolution of the power spectrum will be sufficient to resolve the expected width of the overall axion line, {approximately}{bigcirc} (1kHz). In the second, the resolution will be {bigcirc}(O.01-1 Hz) to look for extremely narrow substructure reflecting the primordial phase-space of the axions during infall. This experiment will be the first to have the required sensitivity to detect axions, for plausible axion models

Neutron time-of-flight measurements of charged-particle energy loss in inertial confinement fusion plasmas

Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4  keV and particle densities of n≈(12-2)×10^{24}  cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data