Importance of high-angular-momentum channels in pseudopotentials for quantum Monte Carlo

Quantum Monte Carlo methods provide in principle a highly accurate treatment of the many-body problem of calculating the ground and excited states of condensed systems. In practice, however, uncontrolled errors, such as those arising from the fixed-node and pseudopotential approximations can be problematic. We show that the accuracy of some quantum Monte Carlo calculations is limited by the properties of currently available pseudopotentials. The use of pseudopotentials involves several approximations, and we will focus on one that is relatively simple to correct during the pseudopotential design phase. It is necessary to include angular-momentum channels in the pseudopotential for excited angular-momentum states and to choose the local channel appropriately to obtain accurate results. Variational and diffusion Monte Carlo calculations for Zn, O, and Si atoms and ions demonstrate these issues. Adding higher-angular-momentum channels into the pseudopotential description reduces such errors without a significant increase in computational cost

Novel Technique for Ultra-sensitive Determination of Trace Elements in Organic Scintillators

A technique based on neutron activation has been developed for an extremely high sensitivity analysis of trace elements in organic materials. Organic materials are sealed in plastic or high purity quartz and irradiated at the HFIR and MITR. The most volatile materials such as liquid scintillator (LS) are first preconcentrated by clean vacuum evaporation. Activities of interest are separated from side activities by acid digestion and ion exchange. The technique has been applied to study the liquid scintillator used in the KamLAND neutrino experiment. Detection limits of <2.4X10**-15 g 40K/g LS, <5.5X10**-15 g Th/g LS, and <8X10**-15 g U/g LS have been achieved.Comment: 16 pages, 3 figures, accepted for publication in Nuclear Instruments and Methods

Progress Relating to Civilian Applications During August 1961

Progress is reported on development studies on reactor materials and components, fuels, fuel elements, gaspressure bonding of ceramic fuel elements, uranium carbides, growth of UO/sub 2/ single crystals, radioisotope and radiation applications, materials evaluations, coated-particle fuel materials, corrosion in fiuoride-volatility processes, cold-bonding processes, radiation effects on MGCR fuel materials, radiation effects on SM-2 fuels, gas-cooled reactor program, and gas-pressure bonding of beryllium-clad fuel elements. (B.O.G.

In situ radiological surveying at the Double Tracks site, Nellis Air Force Range, Tonopah, Nevada

A team from the Remote Sensing Laboratory conducted a series of in situ radiological measurements at the Double Tracks site on the Nellis Air Force Range just east of Goldfield, Nevada, during the periods of April 10-13 and June 5-9, 1995. The survey team measured the terrestrial gamma radiation at the site to determine the levels of natural and man-made radiation. This site includes the areas covered by previous surveys conducted from 1962 through 1993. The main purpose of the first expedition was to assess several new techniques for characterizing sites with dispersed plutonium. The two purposes of the second expedition were to characterize the distribution of transuranic contamination (primarily plutonium) at the site by measuring the gamma rays from americium-241 and to assess the performance of the two new detector platforms. Both of the new platforms performed well, and the characterization of the americium-241 activity at the site was completed. Several plots compare these ground-based system measurements and the 1993 aerial data. The agreement is good considering the systems are characterized and calibrated through independent means. During the April expedition, several methods for measuring the depth distribution of americium-241 in the field were conducted as a way of quickly and reliably obtaining depth profiles without the need to wait for laboratory analysis. Two of the methods were not very effective, but the results of the third method appear very promising

Charge asymmetry in hadroproduction of heavy quarks

A sizeable difference in the differential production cross section of top and antitop quarks, respectively, is predicted for hadronically produced heavy quarks. It is of order $\alpha_s$ and arises from the interference between charge odd and even amplitudes respectively. For the TEVATRON it amounts to approximately 5-10% in the region where the cross section is large and could therefore be measured in the next round of experiments. At the LHC the asymmetry can be studied by selecting appropriately chosen kinematical regions.Comment: LaTeX, 5pp, 5 figures, uses revtex. The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/ Final version as published in Phys.Rev.Let

Measurement of the neutron β-asymmetry parameter A_0 with ultracold neutrons

We present a detailed report of a measurement of the neutron β-asymmetry parameter A_0, the parity-violating angular correlation between the neutron spin and the decay electron momentum, performed with polarized ultracold neutrons (UCN). UCN were extracted from a pulsed spallation solid deuterium source and polarized via transport through a 7-T magnetic field. The polarized UCN were then transported through an adiabatic-fast-passage spin-flipper field region, prior to storage in a cylindrical decay volume situated within a 1-T 2×2π solenoidal spectrometer. The asymmetry was extracted from measurements of the decay electrons in multiwire proportional chamber and plastic scintillator detector packages located on both ends of the spectrometer. From an analysis of data acquired during runs in 2008 and 2009, we report A_0=−0.11966±0.00089_(−0.00140)^(+0.00123), from which we extract a value for the ratio of the weak axial-vector and vector coupling constants of the nucleon, λ=g_A/g_V=−1.27590±0.00239_(−0.00377)^(+0.00331). Complete details of the analysis are presented