LUX-ZEPLIN

Abstract:

The luminescence spectra of CaW O4, CaMo O4, and ZnW O4 scintillating crystals were investigated in the temperature range 8-400 K. The excitation photon energy was varied from the ultraviolet (4.5 eV) to the hard x-ray region (35 keV). It is found that as the excitation energy decreases the relative intensity of the low-energy luminescence band, attributed to the extrinsic emission of defect centers in CaW O4 and CaMo O4 crystals, increases. This observation is interpreted in terms of the total absorption of incident radiation, i.e., the variation of the mean penetration depth of the photons with their energy. It indicates that the centers responsible for the extrinsic emission in the crystals with scheelite structure are mainly localized in a thin (∼100 nm) surface layer. On the other hand no noticeable changes with the excitation energy were found in the emission spectra of ZnW O4 crystals with wolframite structure. The possible implication of this finding is discussed. The light yield of the crystals is compared at low temperature using monochromatic x-ray excitation and it is shown that ZnW O4 has ∼10% higher light yield than CaW O4, while this parameter has a factor of 4 lower in CaMo O4. © 2005 American Institute of Physics.

Abstract:

The Antarctic Impulsive Transient Antenna (ANITA) experiment is being developed to search for ultra-high-energy (UHE) neutrino interactions ($>3\times10^{18}$ eV) in the Antarctic ice cap. A neutrino interaction in the ice will produce a radio pulse by the means of the Askaryan effect. The large radio transparency of ice allows for such a pulse to be recorded by a cluster of balloon-borne antennas. The details of the ANITA instrument, now in a construction phase, and the science we hope to achieve is discussed. In order to prepare for the main mission, we have flown ANITA-lite during the 2003/04 austral season. ANITA-lite consisted of two quad-ridge horn antennas and a prototype RF (radio frequency) triggering and recording system. Here we present the results of an impulsive RF background survey of Antarctica, as well as proof-of-principle gain, tracking, and timing calibrations conducted by observing solar radio emissions and calibration radio-pulses. A preliminary UHE neutrino flux limit based on ANITA-lite data is also presented.

Abstract:

In this study, we examined the luminescence response of Ti-doped Al2 O3 crystals to high-energy vacuum ultraviolet (UV) excitation. In addition to the thoroughly studied emission band of Ti3+ in the near-infrared region and blue emission at 420 nm, we detected a UV emission band at 290 nm. The excitation spectra of all emission bands were measured over the 4-20 eV spectral range. Our results indicate that intrinsic anion defects are involved in the process of the excitation of the 420 nm emission assigned to the charge transfer transitions 2p O2- →3d Ti4+. Analysis of the spectral and decay characteristics of the UV emission enables us to suggest that this band is associated with radiative decay of excitons localized at Ti ions. © 2005 American Institute of Physics.