LUX-ZEPLIN

Abstract:

The future application of ZnWO 4 scintillator in a cryogenic search for rare events is the motivation for optimization of this material. We present results on the effect of Ca doping on the structure and scintillation properties of ZnWO 4. X-ray diffraction analysis revealed that there is no mixing in the CaWO 4-ZnWO 4 pseudobinary system due to a significant mismatch of the crystal structures of CaWO 4 and ZnWO 4. The lattice parameters of Ca-doped ZnWO 4 samples obtained from X-ray powder diffraction data confirmed this finding. It is also shown that ZnWO 4 retains the monoclinic wolframite structure when cooling, at 12 K exhibiting the following lattice parameters: a = 4.6826(2) Å, b = 5.7088(2) Å, c = 4.9230(2) Å and β = 90.541(2)°. The scintillation light yield of the Zn 1-x,Ca xWO 4 was measured using the multi-photon counting technique and it is found that small concentrations of Ca (x = 0.001 - 0.02) cause no deterioration of this parameter. Ca doping of ZnWO 4 is expected to facilitate production of a single-crystalline scintillator. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Abstract:

The Monte-Carlo refractive index matching (MCRIM) technique was developed to determine the physical properties of heavy inorganic scintillators (HIS) which are difficult to measure experimentally. It was designed as a method for obtaining input parameters for Monte-Carlo (MC) simulations of experimental arrangements incorporating HIS in their setups. The MCRIM technique is used to estimate the intrinsic light yield, the scattering coefficient and the absorption coefficient, herein referred to as indirect measurement properties. The MCRIM technique uses an experiment/MC combination to determine these indirect measurement properties. The MCRIM experimental setup comprises a crystal placed on a photomultiplier tube window with the possibility of introducing materials of different refractive indices in a small gap between the crystal and photomultiplier tube (PMT) window. The dependence of the measured light yield on the refractive index of the material in the gap can only be reproduced by simulations if the correct values of scattering, absorption and intrinsic light yield are used. The experimental setup is designed to minimise the presence of optical components such as unpolished surfaces and non-ideal reflectors, which are difficult to simulate. The MCRIM technique is tested on a 1.03×1.00×0.82 cm³ crystal of CaWO4 which is found to have a scattering coefficient of 0.061±0.005 cm^-1, an absorption coefficient of 0.065±0.005 cm^-1, and an intrinsic light yield of 22700±1700 photons/MeV. © 2006 Elsevier B.V. All rights reserved.

Abstract:

The ANtarctic Impulsive Transient Antenna (ANITA) searches for ultra high energy neutrinos interacting in the Antarctic ice cap. It is a long duration balloon experiment composed of an array of broadband dual-polarized horn antennas that had its first science flight over Antarctica in December 2006 through January 2007. ANITA relies upon the Askaryan effect, in which a particle shower in a dense medium emits coherent Cherenkov radiation at radio wavelengths, for the detection of a neutrino induced shower. ANITA is designed to detect-or constrain flux models of-ultra high energy neutrinos created by the interaction of ultra high energy cosmic rays with the cosmic microwave background. In this paper we discuss the detector performance during the first ANITA flight.

Abstract:

The balloon-borne ANITA neutrino telescope successfully launched from McMurdo Station, Antarctica during the 2006-2007 austral summer. In this paper we present ongoing studies of the energy resolution and system response of the ANITA detector, which provide an excellent test bed for validating the ANITA Monte Carlo and will be of great interest if ANITA discovers signal events. While in view of the launch site ANITA received calibration pulses from two antennas, located on the surface and in a borehole in the Ross Ice Shelf, which facilitate these studies.