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The article of record as published may be found at http://dx.doi.org/10.1016/j.apradiso.2015.05.011 Neutron howitzers are routinely used in universities to activate samples for instructional laboratory experiments on radioactivity. They are also a convenient source of neutrons and gammas for research purposes, but they must be used with caution. This paper describes the modeling, design, construction, and testing of a portable, economical shield for a 1.0 Curie neutron howitzer. The Monte Carlo N Particle Transport Code (MCNP5) has been used to model the 239PuBe source and the howitzer and to design the external neutron and gamma shield.

The Cryogenic Dark Matter Search (CDMS) employs massive ionization- and phonon-mediated detectors to search for WIMPs via their elastic scattering interactions with nuclei while discriminating against interactions by other background particles. Limits on the WIMP-nucleon scattering cross-section, based on 3.1 kg d of exposure, exclude new parameter space in the 10–30 GeV WIMP mass region and also a portion of the region allowed by the DAMA annual modulation search (Bernabei, Phys. Lett. 450 (1999) 448).

Normal conductor-insulator-superconductor (NIS) junctions promise to be interesting for x-ray and phonon sensing applications, in particular due to the expected self-cooling of the N electrode by the tunneling current. Such cooling would enable the operation of the active element of the sensor below the cryostat temperature and at a correspondingly higher sensitivity. It would also allow the use of NIS junctions as microcoolers. At present, this cooling has not been realized in large area junctions (suitable for a number of detector applications). In this article, we discuss a detailed modeling of the heat flow in such junctions; we show how the heat flow into the normal electrode by quasiparticle back-tunneling and phonon absorption from quasiparticle pair recombination can overcompensate the cooling power. This provides a microscopic explanation of the self-heating effects we observe in our large area NIS junctions. The model suggests a number of possible solutions.

In September 1999, the Cryogenic Dark Matter Search (CDMS) completed a nine month run with the first generation detectors (0.5 kg of germanium BLIPs sensing thermal phonons and ionization). The data acquired in this run significantly decrease the upper limits on WIMP interaction in germanium by a factor 2.5 to 10 depending on the mass region and begin to probe supersymmetry. The results are however strongly inconsistent with the claims of the DAMA experiment.

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV c-2 WIMP mass and. at > 75% CL. the entire 3σ allowed region for the WIMP signal reported by the DAMA experiment.

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons in all ways tested. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}. These limits border, but do not exclude, parameter space allowed by supersymmetry models and accelerator constraints. Results are compatible with some regions reported as allowed at 3-sigma by the annual-modulation measurement of the DAMA collaboration. However, under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the DAMA most likely value at >99.9% CL, and are incompatible with the model-independent annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit., 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D; v.2:clarified conclusions, added content and references based on referee's and readers' comments; v.3: clarified introductory sections, added figure based on referee's comments

We have developed a “full wafer” process for producting Al/Al2O3/Cu superconductor-insulator-normal (SIN) tunnel junctions for use as X-ray and phonon sensors. We describe microfabrication details and present I–V data.

Electrons which tunnel from the normal electrode to the superconducting electrode of an SIN tunnel junction ultimately combine to form Cooper pairs. If this occurs close to the tunneling region, the phonons emitted during the combination process may enter the normal electrode and heat it. We compared 6 keV X-ray pulse data from Al/Al2O3/Cu SIN series paris having narrow leads with pulse data from identical SIN pairs having very wide leads. We found that quasiparticle diffusion in the wide leads was not sufficient to remore the quasiparticles from the junction region.

The thermal and electrical conductivities of two pure single crystals of tin have been measured. The samples were oriented at 72\ifmmode^\circ\else\textdegree\fi{} and 6\ifmmode^\circ\else\textdegree\fi{} with respect to the tetragonal axis of tin. The thermal conductivity values for the two samples were fit to the relation ${(\ensuremath{\alpha}{T}^{n}+\frac{\ensuremath{\beta}}{T})}^{\ensuremath{-}1}$ from 4 to 12 \ifmmode^\circ\else\textdegree\fi{}K with $n$ approximately 3.2 for both samples. This large value is attributed to dispersion in the phonon spectrum which causes an approximate 4.2-power dependence with temperature of the specific heat over the same temperature range. The electrical-resistivity value of the two pure samples was found to obey the Bloch-Gr\"uneisen expression over a wide range with a Debye temperature of 125 \ifmmode^\circ\else\textdegree\fi{}K and with a small additional residual resistivity. The anisotropy of the thermal conductivity exhibits a slight maximum at 10 \ifmmode^\circ\else\textdegree\fi{}K, attributable to the relative effect of impurity scattering and an anisotropic band structure. The anisotropy of the electrical conductivities exhibits a more pronounced maximum around 20 \ifmmode^\circ\else\textdegree\fi{}K because of an additional effect of area differences of Brillouin-zone segments on the Fermi surface when small-angle scattering dominates. The ratio of electrical anisotropy to thermal anisotropy at the maximum was found to be approximately 1.27, which compares well with the theoretically predicted value of 1.26 from the area differences at the zone segments in the 90\ifmmode^\circ\else\textdegree\fi{} and 0\ifmmode^\circ\else\textdegree\fi{} orientations.

Phonon dispersion relations along $[10\overline{1}0]$ in the hcp phase of ${\mathrm{He}}^{4}$ have been determined by triple-axis neutron spectrometry. Optical as well as acoustic branches were observed at 27 atm and 0.99\ifmmode^\circ\else\textdegree\fi{}K in a single crystal grown from the superfluid phase.

Phenomena which occur at solid surfaces during ion implantation and the short term property changes which result during this exposure may be studied by sending surface acoustic waves across the implant region. Quartz and lithium niobate have been exposed to 100 keV Argon(+) ions; later these implanted regions have been studied while being exposed to intense light from an argon laser. The strength of the received surface acoustic waves is attenuated (by over 20 dB in lithium niobate) during an extended exposure to the ion beam. Upon ceasing ion bombardment there is a fast but incomplete recovery of the received acoustic signal with a time constant of the order of ten seconds. Laser light of comparable or greater intensity produces a rapid rise in attenuation of only a few dB, with a rise time of about three seconds. Upon ceasing illumination, recovery is similarly rapid but complete. From the different results produced by ion and light beams of comparable intensity, we conclude that the changes in material properties which are being observed are produced by mechanisms not entirely thermal in origin. (Author)

Preliminary measurements of the thermal conductivity of 1 MeV electron-irradiated Al2O3 with about 0.01% impurities have shown that below 50 K the thermal conductivity decreased about 20 – 25% upon irradiation and recovered almost completely upon annealing.

We have fabricated interdigital electrode structures on polished glass plaques. By placing the plaques next to the surface of a piezoelectric material and exciting the electrode of the transmitting plaque with pulsed rf energy of the appropriate frequency, good acoustic surface waves are received at a similar plaque at the opposite end of the sample. The plaque electrodes are fragile but reusable if handled with care.

Detection of the beats between the internal modes of a commercially available laser is used to determine the speed of light. A fast response photodiode attached to the uhf terminals of a television set permits the beats to be detected and displayed.