Measurement of Cosmic-ray Muon-induced Spallation Neutrons in the Aberdeen Tunnel Underground Laboratory

AbstractMuon-induced neutrons are one of the major backgrounds to various underground experiments, such as dark matter searches, low-energy neutrino oscillation experiments and neutrino-less double beta-decay experiments. Previous experiments on the underground production rate of muon-induced neutrons were mostly carried out either at shallow sites or at very deep sites. The Aberdeen Tunnel experiment aims to measure the neutron production rate at a moderate depth of 611 meters water equivalent. Our apparatus comprises of six layers of plastic-scintillator hodoscopes for tracking the incident cosmic-ray muons, and 760 L of gadolinium-doped liquid-scintillator for both neutron production and detection targets. In this paper, we describe the design and the performance of the apparatus. The preliminary result on the measurement of neutron production rate is also presented

Quantitative explanation of the enhancement of surface mobility of the metallic glass Pd40Cu30Ni10P20 by the Coupling Model

Surface diffusion coefficient Ds(T) measured for the canonical metallic glass, Pd40Cu30Ni10P20, by the method of surface-grating decay was found to be more than eight orders of magnitude larger than the bulk diffusion coefficient. So far no theory has attempted to account quantitatively for this spectacular enhancement of diffusion at the surface. The objective of the research reported in this paper is the application of the Coupling Model (CM) to predict the size of the surface diffusion found in Pd40Cu30Ni10P20. The prediction compares well with the size of the enhancement obtained by experiment. There is yet another prediction of the CM, which is Ds(T) having the same Arrhenius activation energy as the bulk diffusion coefficient DvCo of the tracer 57Co atoms in the same metallic glass. This prediction is also verified by the experimental data, and it provides additional support of the theoretical explanation of the enhancement of diffusion at the surface. A successful application of the CM to account for the decoupling of diffusion coefficient of P from that of Pd in the bulk of a similar metallic glass, Pd43Cu27Ni10P20, is recalled because the physics involved therein is similar to the present problem

Thermal effects in singly resonant continuous-wave optical parametric oscillators

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