Shinzou Kubota

Mechanism of proportional scintillation in argon, krypton and xenon

Abstract The mechanism of photon emission in the rare-gas proportional scintillation counter is ascribed to the radiative de-excitation of excited molecules, R 2 ∗ →R+R+hv , by determining emission spectra experimentally.

A new scintillation material: Pure CsI with 10 ns decay time

Abstract The properties of pure CsI have been studied with respect to its application as a scintillation material.

Drift velocities of electrons, saturation characteristics of ionization and W-values for conversion electrons in liquid argon, liquid argon-gas mixtures and liquid xenon

Abstract The drift velocities of electrons, the saturation characteristics of ionization and the W -values for internal conversion electrons emitted from 207 Bi in liquid argon, liquid argon-gas (xenon, nitrogen, methane and ethylene) mixtures and liquid xenon have been measured by using gridded ionization chambers. The drift velocity of electrons in xenon or nitrogen-dopes liquid argon shows little increase compared with that in liquid argon, while that in liquid argon-methane or -ethylene mixtures shows a remarkable increase. From each saturation curve, the so-called “recombination coefficient” k is obtained, assuming that the electric field ( E ) dependence of the collected charge ( Q ) is represented by Q∝( 1+ k E ) −1 , and the values for liquid rare gases as shown above are tabulated. The W -values in liquid argon-xenon mixture and liquid xenon have been determined by comparing with that in liquid argon. It is shown that admixing liquid argon with a small amount of xenon results in the reduction of the W -value and that the W -value in liquid xenon is much smaller than that in the gas phase. On the basis of these experimental results, the applicability of the liquid rare gases to detector medium is discussed.

A new type of luminescence mechanism in large band-gap insulators: Proposal for fast scintillation materials

Abstract Luminescence components of BaF 2 (180–230 nm), CsF (220–500 nm), CsCl (200–300 nm), CsBr (220–280 nm), and RbF (200–450 nm) have been investigated at room temperature by using synchrotron radiation as a light source. These luminescence components have excitation thresholds at the energy differences from the outermost Ba 2+ 5p, or M + m p ( m = 4 and 5 for M = Rb and Cs, respectively) core state to the conduction band, and are attributeted to the radiative decay of electrons in the X − n p halogen valence bands ( n = 2, 3, and 4 for X = F, Cl and Br, respectively) to the outermost-core hole states. Single bunch operation of synchrotron radiation has been used to determine the lifetime of the above luminescence. The measured lifetimes in ns are: BaF 2 : 0.88±0.02; CsF: 2.9±0.1; CsCl: 0.88±0.07; CsBr: 0.07±0.03; and RbF: 1.3±0.1 From the above results, it is proposed that insulators having large band-gap energy compared to the energy difference between the valence band and the outermost-core state are candidates for fast scintillation materials, for example, CsCl, CsBr, RbF, KF, BaCl 2 , BaBr 2 , and BaI 2 .

Estimation of Fano factors in liquid argon, krypton, xenon and xenon-doped liquid argon

Abstract Fano factors in liquid argon, krypton, xenon and xenon-doped liquid argon are estimated from the Fano formula by using the parameters in the energy balance equation for the absorbed energy of ionizing radiation. As a result, it is shown that the values for liquid argon, krypton and xenon are smaller than those in the gas phase and the value for xenon-doped liquid argon is smaller than that for liquid argon as in argon-molecular gas mixture. In particular, the value for liquid xenon is extremely small, i.e. about 0.05, which is comparable to that for Ge(Li) detectors. Using the so obtained Fano factor and an electronic noise level which can easily be achieved, the fwhm in the liquid xenon ionization chamber is estimated to be about 3 keV for 1 MeV electrons.

Liquid and solid argon, krypton and xenon scintillators

Abstract The time dependence of uv emission in liquid and solid argon, krypton and xenon excited by 207Bi internal conversion electrons and alpha particles has been investigated. Decay curves in the solid are similar to those for the liquid. For the case of solid or liquid xenon excited by electrons, a drastic decrease in a slow component was observed with an applied electric field of about 1 kV/cm. Variation of scintillation decay in liquid argon or xenon excited by electrons and by alpha particles has been observed. The relative intensities of the fast component increase with increasing ionization density, which is contrary to the effect in organic scintillators. The ratios (Lα/Eα)/(Le/Ee) of the intensity per unit energy excited by alpha particles to that by electrons are 1.08, 1.02 and 1.15 for liquid argon, krypton and xenon, respectively. The decay curves for xenon, nitrogen or carbon dioxide doped liquid argon scintillators have been investigated.

Variation of luminescence decay in BaF2 crystal excited by electrons, alpha particles and fission fragments

Abstract The time dependence of the luminescence from BaF 2 crystal excited by electrons, alpha particles and fission fragments has been studied for wavelengths of 180–400 nm by a single-photon counting technique. A (220 ± 10) nm component with a lifetime of 0.88 ns is observed for electron and fission fragment excitation. No 220 nm component is observed for alpha particle excitation. The (300+50(−40)) nm component has lifetimes of 600 and 100 ns for electron excitation, 550 and 50 ns for alpha particle excitation, and 580 and 9 ns for fission fragment excitation. The variation in time dependence is attributed to the difference in track structure produced by ionizing charged particles for different LET.

Evidence for a triplet state of the self-trapped exciton states in liquid argon, krypton and xenon

The lifetimes of luminescence from liquid argon, krypton and xenon excited by energetic electrons have been studied with such a high electric field that all of the observed decay characteristics have to be attributed to the self-trapped exciton luminescence. In all cases the decay shows two exponential components. The lifetimes of the fast components are in the range from 2 to 5 ns, and major second components have lifetimes of 860+or-30 ns for argon, 80+or-3 ns for krypton and 27+or-1 ns for xenon. These lifetimes are interpreted in terms of two self-trapped exciton states, one predominantly singlet in character, the other triplet; this is the first strong evidence for the triplet assignment. The variation in triplet-state lifetimes is attributed to the different spin-orbit couplings.

Non-Metastable Penning Effect in the Alpha-Particle Ionization of Inert Gas Mixtures

An experimental investigation has been performed of the ionization yield by α particles in binary gas mixtures over the whole range of mixing ratio. The ionization yield for A-N 2 mixture, in which their ionization potentials are almost equal, agrees numerically well with the estimate from the theory proposed by Huber et al. on the assumption that the ionization yield in the individual component gas is proportional to the energy dissipated primarily by the α-particle in the gas. The additional ionization yield over the estimate from the theory is observed for He-Ne, A-Kr, A-Xe and Kr-Xe mixtures when the second gas is contained more than several percent in the mixture. This can be interpreted by the non-metastable Penning (NMP) ionization. For He-A mixture, the relative contribution of the NMP and metastable Penning (MP) process to the total ionization yield is estimated.

Proportional counter filled with highly purified liquid xenon

Abstract The electron avalanche in highly purified liquid xenon is observed with reproducible gain. The electronegative ion pumping is effective for suppressing spurious discharges rather than for purifying liquid xenon.