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The ability to understand and predict the response of matter at extreme conditions requires knowledge of a materials equation-of-state (EOS) including the location of phase boundaries, transition kinetics, and accurate measurements of temperature at pressure. Recent developments in optical pyrometry have provided methods for measuring temperature in the shocked state, and these have been used to study the phase diagram for some metals including cerium. Cerium has received significant attention because it exhibits a rich phase diagram that includes an anomalous melt boundary and a low-pressure shock-melt transition. In this work, we continue our study of shock-melting using optical pyrometry to measure the temperature and stress states for two-phase cerium (γ-Ce and β-Ce) shocked into the high-pressure liquid phase. Details of the experimental methods, analysis, and results are presented. [ABSTRACT FROM AUTHOR]

The database at http://www.radiopurity.org is the world's largest public database of material radio-purity measurements. These measurements are used by members of the low-background physics community to build experiments that search for neutrinos, neutrinoless double-beta decay, WIMP dark matter, and other exciting physics. This paper summarizes the current status and the future plan of this database. [ABSTRACT FROM AUTHOR]

Inertial confinement fusion research at Los Alamos National Laboratory is focused on high-leverage areas of thermonuclear ignition to which LANL can apply its historic strengths and that are complementary to high-energy-density-physics topics. Using the Trident and Omega laser facilities, experiments are pursued in laser-plasma instabilities, symmetry, Be technologies, neutron and fusion-product diagnostics, and defect hydrodynamics. [ABSTRACT FROM AUTHOR]

The decay of common radioactive gases, such as radon, produces stable isotopes by a sequence of daughter particles with varied half-lives. These daughter particles are a significant source of gamma, neutron, and alpha (_) particle backgrounds that can mimic desired signals in dark matter and neutrinoless double beta decay experiments. In the LUMINA Laboratory at Southern Methodist University (SMU), studies of radon plate-out onto copper samples are conducted using one of XIA's first five UltraLo 1800 alpha counters. We present results from investigations into various mitigation approaches. A custom-built copper holder (in either plastic or metal) has been designed and produced to maximize the copper's exposure to 220Rn. The 220Rn source is a collection of camping lantern mantles. We present the current status of control and experimental methods for addressing radon exposure levels. [ABSTRACT FROM AUTHOR]

Rejection and protection from background is a key issue for the next generation SuperCDMS SNOLAB experiment that will have a cross-section sensitivity of better than 8 × 10-46 cm2 for spin-independent WIMP-nucleon interactions. This paper presents the details of the methods used to reject electromagnetic backgrounds using the new iZIP detectors that are currently operated in the Soudan Underground Laboratory, MN and the methods the collaboration is investigating to protect against neutron background in the next generation SuperCDMS experiment. [ABSTRACT FROM AUTHOR]

Southern Methodist University houses one of five existing commercially available UltraLo 1800 production model alpha counters made by XIA LLC. The instrument has an electron drift chamber with a 707 cm2 or 1800 cm2 counting region which is determined by selecting the inner electrode size. The SMU team operating this device is part of the SuperCDMS screening working group, and uses the alpha counter to study the background rates from the decay of radon in materials used to construct the SuperCDMS experiment. We have studied four acrylic samples obtained from the MiniCLEAN direct dark matter search with the XIA instrument demonstrating its utility in low background experiments by investigating the plate-out of 210Pb and comparing the effectiveness of cleaning procedures in removing 222Rn progenies from the samples. [ABSTRACT FROM AUTHOR]

The low-background physics community has been performing assays of material radiopurity for decades and many thousands of such measurements exist. Some are available in publications and others in databases, but most are still communicated informally. No standard data format exists for encoding material assays and there is no central location to store them. The aim of the work reported here is to address this long-standing problem, through the creation of a concise and flexible material assay data format and powerful database software to use it. A public installation of this software may serve as a long-term repository for the community's material assay data. It is available at http://www.radiopurity.org. [ABSTRACT FROM AUTHOR]

SuperCDMS employs 1-inch thick germanium crystals operated below 50mK in a dilution cryostat. Each detector produces ionization and phonon signals. Ionization signals are amplified by JFETs operating at 150K within an assembly mounted on the 4K cryostat stage. These high impedance signals are carried to the FETs by superconducting “vacuum coaxes” which minimize thermal conductivity, stray capacitance, and microphonics. Transition edge sensors produce low-impedance phonon signals, amplified by SQUID arrays mounted on a 600mK stage. Detectors are mounted in a six-sided wiring configuration called a “tower”, which carries signals from 40mK to 4K. A flex circuit 3 meters in length carries amplified signals for each detector from 4K to a vacuum bulkhead. We describe the methods used to support the detectors, wiring and amplifier elements at various thermal stages, minimizing electrical noise and thermal loads. [ABSTRACT FROM AUTHOR]

The Cryogenic Dark Matter Search experiment (CDMS) is using Phonon+Ionization detectors to search for Dark Matter in the form of Weakly Interactive Massive Particles (WIMPs). We report on new results from the operation of CDMS five “towers” at Soudan underground laboratory. With new and more massive detectors, SuperCDMS project has been started since March 2009. We report on the current status of SuperCDMS and its perspective. [ABSTRACT FROM AUTHOR]

The Cryogenic Dark Matter Search (CDMS) searches for Weakly Interacting Massive Particles (WIMPs) with cryogenic germanium particle detectors. These detectors discriminate between nuclear-recoil candidate and electron-recoil background events by collecting both phonon and ionization energy from interactions in the crystal. Incomplete ionization collection results in the largest background in the CDMS detectors as this causes electron-recoil background interactions to appear as false candidate events. Two primary causes of incomplete ionization collection are suface and bulk charge trapping. Recent work has been focused on reducing surface trapping through the modification of fabrication methods for future detectors. Analyzing data taken with test devices shows that hydrogen passivation of the amorphous silicon blocking layer does not reduce the effects of surface trapping. Other data shows that the iron-ion implantation used to lower the critical temperature of the tungsten transition-edge sensors increases surface trapping, causing a degradation of the ionization collection. Using selective implantation on future detectors may improve ionization collection for events near the phonon side detector surface. Bulk trapping is minimized by neutralizing ionized lattice impurities. Detector investigations at testing facilities and at the experimental site in Soudan, MN have provided methods to optimize the neutralization process and monitor running conditions to maintain maximal ionization collection. [ABSTRACT FROM AUTHOR]

For its dark matter search the SuperCDMS collaboration has developed new Ge detectors using the same athermal phonon sensors and ionization measurement technology of CDMS II but with larger mass, superior sensor performance and increased fabrication efficiency. The improvements in fabrication are described, a comparison of CDMS II and SuperCDMS detector production yield is reported, and future scalability addressed. [ABSTRACT FROM AUTHOR]

We have conducted a series of free surface shock experiments on cerium metal at peak shock pressures from 0.9–7.6 GPa. These experiments were done to examine the elastic-plastic behavior, the solid-solid phase transition occurring at 0.7–0.8 GPa, and the spall strength of the material as a function of peak stress. The elastic and low-pressure plastic waves exhibit long rise times while the post-transition plastic wave is sharp. Spallation wave profiles obtained using optical techniques are presented and discussed. [ABSTRACT FROM AUTHOR]

The standard regime for the laser wakefield accelerator (LWFA) usually requires external injection of MeV electrons. Ideally, the injected electron bunch should be injected into the proper phase of the accelerating wake, have a bunch length that is small compared with the plasma wavelength, and a low emittance and energy spread. This paper reports Hamiltonian analysis and simulation studies of two ‘nonideal’ injection schemes that demonstrate strong phase bunching and good accelerated beam quality in a channel-guided laser wakefield accelerator. For the case of monoenergetic, unphased (long bunch) injection, there is an optimum range of injection energies for which the LWFA can trap a significant fraction of the injected pulse while producing an ultrashort, high-quality accelerated pulse. Phased and unphased injection in a channel-guided LWFA with a broad injected energy spread has also been simulated. Although the trapping fraction is generally much smaller than in the monoenergetic case, some simulations exhibit final accelerated bunches with remarkably small energy spread. These results suggest that relatively poor quality injection pulses may still be useful in LWFA demonstration experiments. Implications for planned LWFA experiments at NRL are discussed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]