119843682
The selection and performance of diamond radiators used in coherent bremsstrahlung experiments
The bremsstrahlung emitted as a result of scattering electrons in thin diamond crystals provides a useful source of high energy photons for use in photonuclear experiments, since the coherent bremsstrahlung produced is linearly polarized. Techniques for selecting the most favorable diamonds have been investigated. These are optical polaroid analysis, X-ray topography and rocking curve measurements. The diamonds are characterized with a view to determining their performance as radiators, and bremsstrahlung spectra from a diamond radiator used at the Mainz MAMI-B facility are presented. The changes caused by high energy electrons to the crystal properties of the diamond and to the resulting coherent bremsstrahlung spectra are discussed.
111274459
Microgap multiwire chambers
The multiwire proportional counter (MWPC) is well established device for capturing x-ray images at synchrotron sources such as at the synchrotron radiation source (SRS) at Daresbury. The latest generation of synchrotrons can deliver much more intense x-ray fluxes than the SRS which itself produces xray fluxes well beyond the capabilities of current photon counting detectors. There is an imminent demand for 2-D photon counting detectors which can cope with rates >10 5 photons/mm 2 /sec locally and readout systems with an unbuffered throughput of >10 7 events per second. This must be achieved with a high dynamic range and a good efficiency. The detector development group at the SRS have developed the wire microgap detector to address these problems. A new readout system has been designed using a highly parallel approach. Each detector channel in the detector is separately instrumented, and the data is accumulated using fast, state-of-the-art electronics systems. A prototype of the system has been constructed and tested with the 2 dimensional wire microgap detector. We report the results of the use of a wire microgap linear detector on the SRS and the first results from the 2D wire microgap detector system.
8275774
Equation of state measurements in liquid deuterium to 70 GPa.
Using intense magnetic pressure, a method was developed to launch flyer plates to velocities in excess of 20 km/s. This technique was used to perform plate-impact, shock wave experiments on cryogenic liquid deuterium ( L-D(2)) to examine its high-pressure equation of state. Using an impedance matching method, Hugoniot measurements were obtained in the pressure range of 30-70 GPa. The results of these experiments disagree with previously reported Hugoniot measurements of L-D(2) in the pressure range above approximately 40 GPa, but are in good agreement with first principles, ab initio models for hydrogen and its isotopes.
40099983
First observation of excited states in Li-12
The neutron-unbound ground state and two excited states of {sup 12}Li were formed by the two-proton removal reaction from a 53.4-MeV/u {sup 14}B beam. The decay energy spectrum of {sup 12}Li was measured with the Modular Neutron Array (MoNA) and the Sweeper dipole superconducting magnet at the National Superconducting Cyclotron Laboratory. Two excited states at resonance energies of 250 +- 20 keV and 555 +- 20 keV were observed for the first time and the data are consistent with the previously reported s-wave ground state with a scattering length of a{sub s}=-13.7 fm.
119247141
Are falling planets spinning up their host stars
We investigate the effects of tidal interactions on the planetary orbits and stellar spin rates of the WASP-18 and WASP-19 planetary systems using a forward integration scheme. By fitting the resulting evolutionary tracks to the observed eccentricity, semimajor axis and stellar rotation rate, and to the stellar age derived from isochronal fitting, we are able to place constraints on the stellar and planetary reduced tidal quality factors, Q ' s and Q ' p . We find that for WASP-18, log(Q ' s ) = 8.21 +0.90 ―0.52 and log(Q ' p ) = 7.77 +1.54 ―1.25 , implying a system age of 0.579 +0.305 ―0.250 Gyr. For WASP-19 we obtain values of log(Q ' s ) = 6.47 +2.19 ―0.95 and log(Q ' p ) = 6.75 +1.86 ―1.77 , suggesting a system age of 1.60 +2.84 ―0.79 Gyr and a remaining lifetime of 0.0067 +1.1073 ―0.0061 Gyr. We investigate a range of evolutionary histories consistent with these results and the observed parameters for both systems, and find that the majority imply that the stars have been spun up through tidal interactions as the planets spiral towards their Roche limits. We examine a variety of evidence for WASP-19 A's age, both for the value above and for a younger age consistent with gyrochronology, and conclude that the older estimate is more likely to be correct. This suggests that WASP-19 b might be in the final stages of the spiral-in process, although we are unable to rule out the possibility that it has a substantial remaining lifetime.
117134508
Experimental Study of Background Induced in High Energy Gamma Ray Telescopes that use a Coded Aperture Mask
10985334
Searching for Double Beta Decay with the Enriched Xenon Observatory
The Enriched Xenon Observatory (EXO) Collaboration is building a series of experiments to search for the neutrinoless double beta decay of 136Xe. The first experiment, known as EXO‐200, will utilize 200 kg of xenon enriched to 80% in the isotope of interest, making it the largest double beta decay experiment to date by one order of magnitude. This experiment is rapidly being constructed, and will begin data taking in 2007. The EXO collaboration is also developing a technique to identify on an event‐by‐event basis the daughter barium ion of the double beta decay. If successful, this method would eliminate all conventional radioactive backgrounds to the decay, resulting in an ideal experiment. We summarize here the current status of EXO‐200 construction and the barium tag R&D program.
123009611
A search for weakly interacting dark matter with the LUX experiment
Cosmological and astrophysical measurements indicate that our galaxy is filled with a new type of matter previously unknown to physics. This "dark matter" apparently has no electromagnetic or strong interactions, but an interaction of the strength of the weak nuclear force is strongly suggested by the data. The LUX collaboration is attempting to detect the faint signature of weakly interacting dark matter as it passes through the earth. The experiment searches for recoiling atomic nuclei in a target consisting of 350 kg of liquefied xenon. LUX is the largest experiment of its type ever attempted, and it is expected to improve upon current experimental sensitivities by two orders of magnitude. The experiment is being assembled at the Sanford Underground Science and Engineering Laboratory (SUSEL) in Lead, South Dakota, USA, and first data is expected in 2011. We report on the status of LUX and the prospects for future large-scale dark matter searches with liquid xenon.
118405481
Detection of krypton in xenon for dark matter applications
Abstract We extend our technique for observing very small concentrations of impurities in xenon gas to the problem of krypton detection. We use a conventional mass spectrometer to identify the krypton content of the xenon, but we improve the sensitivity of the device by more than five orders of magnitude with a liquid nitrogen cold trap. We find that the absolute krypton concentration in the xenon can be inferred from the mass spectrometry measurements, and we identify krypton signals at concentrations as low as 0.5×10 −12  mol/mol (Kr/Xe). This technique simplifies the monitoring of krypton backgrounds for WIMP dark matter searches in liquid xenon.