F.P. Santos

FULL-ENERGY ABSORPTION OF X-RAY ENERGIES NEAR THE XE L- AND K-PHOTOIONIZATION THRESHOLDS IN XENON GAS DETECTORS : SIMULATION AND EXPERIMENTAL RESULTS

Distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range, which includes the xenon L- and K-absorption edges, were simulated in xenon gas detectors with the Monte Carlo technique. These simulated full-energy absorption distributions are calculated as frequency plots of the number of primary electrons produced per incident x-ray photon. The simulation includes the absorption of x-rays and the de-excitation of the residual xenon ions, followed by the development of the primary electron cloud. The discontinuities observed in the Fano factor, w-value, energy linearity and energy resolution reflect the discontinuities of the Xe photoionization cross-section at the photoabsorption edges. The simulation results are compared with experimental values measured with a gas proportional scintillation counter, and with recent data from other authors. The discontinuities in energy linearity produce an ambiguity in determining the x-ray energy in certai...

Three-dimensional Monte Carlo calculation of the VUV electroluminescence and other electron transport parameters in xenon

The paper presents a set of electroluminescence and other transport parameters calculated using a detailed three-dimensional Monte Carlo method, which simulates the drift of electrons in gaseous xenon (p=760 Torr, T=293 K) under reduced electric fields E/N in the 3 to 16 Td range (E/P approximately 1 to 5 V cm-1 Torr-1), which is the region for secondary scintillation production in xenon filled gas proportional scintillation counters. Results are compared with available experimental or theoretical data as well as an earlier one-dimensional Monte Carlo simulation. The calculated parameters are the excitation and scintillation efficiencies and the reduced light yield, together with mean time intervals, mean drift distances and mean number of elastic collisions between xenon excitation collisions. The authors also present electron drift velocities, mobilities and characteristic energies, as well as mean electron energy and electron energy distribution functions.

OPERATION OF GAS PROPORTIONAL SCINTILLATION COUNTERS IN A LOW CHARGE MULTIPLICATION REGIME

The operation of a xenon filled gas proportional scintillation counter under low charge multiplication gains is discussed. It is shown that the best energy resolution for X-rays is obtained for a reduced electric field, E/p, of about 8Vc m~1 Torr~1, leading to a charge gain (for inter-grid distance of 5 mm) of about 1.05, as calculated by a Monte Carlo simulation method. A discussion is presented concerning the dependence of the E/p values for better detector performance, on the inter-grid distance. ( 1999 Elsevier Science B.V. All rights reserved.

First proof of topological signature in high pressure xenon gas with electroluminescence amplification

A bstractThe NEXT experiment aims to observe the neutrinoless double beta decay of 136Xe in a high-pressure xenon gas TPC using electroluminescence (EL) to amplify the signal from ionization. One of the main advantages of this technology is the possibility to reconstruct the topology of events with energies close to Qββ. This paper presents the first demonstration that the topology provides extra handles to reject background events using data obtained with the NEXT-DEMO prototype.Single electrons resulting from the interactions of 22Na 1275 keV gammas and electronpositron pairs produced by conversions of gammas from the 228Th decay chain were used to represent the background and the signal in a double beta decay. These data were used to develop algorithms for the reconstruction of tracks and the identification of the energy deposited at the end-points, providing an extra background rejection factor of 24.3 ± 1.4 (stat.)%, while maintaining an efficiency of 66.7 ± 1.% for signal events.

The Fano factor in gaseous xenon: a Monte Carlo calculation for X-rays in the 0.1 to 25 keV energy range

Abstract A calculation of the Fano factor for gaseous xenon is carried out using a detailed Monte Carlo simulation of the absorption of X-rays in the 0.1 to 25 keV energy range. This factor is found to be energy dependent with values ranging from 0.17 to 0.32 and has sharp increases near the xenon absorption edges. An interpretation of the calculated results is made in terms of the relative importance of photoelectron and Auger/Coster-Kronig cascading electron processes.

Monte Carlo simulation study of the Fano factor, w value, and energy resolution for the absorption of soft x rays in xenon–neon gas mixtures

Xenon gas proportional-scintillation counters (GPSC) have many applications in the detection of soft x rays where their energy resolution, R, is comparable to solid-state detectors when large window areas are required. However, R is known to deteriorate for energies Exr below 2–3 keV due to electron loss to the entrance window. Since the addition of a lighter noble gas increases the absorption depth, we have investigated the use of Xe–Ne gas mixtures at atmospheric pressure as detector fillings. The results of a Monte Carlo simulation study of the Fano factor, F, the w value, and the intrinsic energy resolution, R=2.36(Fw/Exr)1/2, are presented for Xe–Ne mixtures and pure Xe and Ne. The results show that the addition of Ne to Xe reduces the intrinsic energy resolution R but this never compensates for the reduction in scintillation yield in GPSC applications, implying that the instrumental energy resolution R will only improve with the addition of Ne when electron loss to the window in pure Xe is significa...

Present Status and Future Perspectives of the NEXT Experiment

NEXT is an experiment dedicated to neutrinoless double beta decay searches in xenon. The detector is a TPC, holding 100 kg of high-pressure xenon enriched in the 136Xe isotope. It is under construction in the Laboratorio Subterraneo de Canfranc in Spain, and it will begin operations in 2015. The NEXT detector concept provides an energy resolutionbetter than 1% FWHM and a topological signal that can be used to reduce the background. Furthermore, the NEXT technology can be extrapolated to a 1 ton-scale experiment.

Variation of energy linearity and w value in gaseous xenon radiation detectors for X-rays in the 0.1 to 25 KeV energy range: a Monter Carlo simulation study

Abstract For X-ray photon energies in the range E = 0.1 to 25 keV, a calculation of the mean energy to produce an electron-ion pair, w, in gaseous xenon, and the average number of primary electrons produced, N , is carried out, using a detailed Monte Carlo simulation. We found that the curve N (E) is a nonlinear function, with sharp steps close to the xenon absorption edges. Moreover, w was found to be energy dependent, with values ranging from 21.7 to 24.6 eV. An interpretation of the calculated result is made in terms of the contribution of the different subshells for photoelectron and Auger/Coster-Kronig electron production.

The transmission of photoelectrons emitted from CsI photocathodes into Xe, Ar, Ne and their mixtures: a Monte Carlo study of the dependence on E/N and incident VUV photon energy

Although ultraviolet photosensor devices offer many advantages when used in radiation detectors, there is often a significant reduction in pulse amplitude when the photosensor operates in a detector filled with a noble gas. This is due to the backscattering of electrons by the noble gas atoms. In this study, we investigate the problem of the backscattering of the photoelectrons emitted from a CsI photocathode into Xe, Ar, and Ne and the binary mixtures Xe–Ar, Ar–Ne and Xe–Ne using a detailed Monte Carlo simulation. Results for the photoelectron transmission efficiencies are presented and discussed for the case of a CsI photocathode irradiated with photons with energies in the range Eph = 6.8–9.8 eV (183–127 nm) and for applied reduced electric fields in the range E/N = 1–40 Td. The dependence on incident photon energy, nature of the gas and applied electric field are examined, and the results are explained in terms of electron scattering in the different noble gases.

Initial results of NEXT-DEMO, a large-scale prototype of the NEXT-100 experiment

This work was supported by the following agencies and institutions: the Ministerio de Economia y Competitividad of Spain under grants CONSOLIDER-Ingenio 2010 CSD2008-0037 (CUP) and FPA2009-13697-C04-04; the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231; and the Portuguese FCT and FEDER through the program COMPETE, project PTDC/FIS/103860/2008. J. Renner (LBNL) acknowledges the support of a US DOE NNSA Stewardship Science Graduate Fellowship under contract no. DE-FC52-08NA28752.