H. Ichinose

Energy resolution for alpha particles in liquid argon doped with allene

Abstract The charge response of liquid argon doped with small quantities of allene (C 3 H 4 ) to α-particles has been studied. The addition of allene increased the amount of collected charge through photoionization and greatly improved the energy resolution of the incident α-particles. The noise subtracted resolution was 1.4% FWHM at the best with 4 ppm allene doped liquid argon.

Energy resolution for gamma-rays and electrons from 207Bi in liquid Xe doped with TEA

Abstract The energy resolution for γ-rays and conversion electrons from 207 Bi has been studied by using a liquid xenon ionization chamber doped with photoionizing dopant TEA. Although a significant improvement in the resolution is found at a low electric field by doping with TEA, improvement at a high electric field was not observed in marked contrast to a “δ-ray recombination model”.

Search for supermassive relics

Abstract We have conducted an underground search for supermassive relic particles by an 80 m 2 array consisting of three layers of track detector CR-39. The non-observation of penetrating tracks places the velocity-dependent flux upper limits down to 2 × 10 −14 cm −2 s −1 sr −1 for various electrically or magnetically charged particles under assumptions on their energy losses in the low- velocity region. Assuming that the nuclear recoils are effective to the track formation of CR-39, this experiment sets the best flux limits for such relic particles in the velocity region 4 × 10 −5 β −4 .

A new limit on the flux of strange matter

Abstract A search has been made for strange matter with a CR-39 track-etch detector with an array of 160 m2, exposed for 8 months at mountain altitude. The non-observation of penetrating tracks places a new stringent upper limit on the flux of strange matter, 2.2x10−14cm−2s−1sr−1 (90% confidence level) in the velocity range β(≡ v c )>4x10 −5 .

CR-39 plastic for massive magnetic monopole search

Abstract A new CR-39 plastic containing a small amount of antioxidants (Naugard-445) has been developed for use in a search for massive magnetic monopoles. Its characteristics have been investigated from the standpoint of the “heavy etching method”, which was proposed several years ago. The results are compared with those of pure CR-39 plastics measured under the same conditions.

Measurement of liquid xenon scintillation from heavy ions using a silicon photodiode

Abstract Scintillation light in liquid xenon excited by 100 MeV/n Al ions was detected with a home-made silicon photodiode. The diameter of the photodiode was 2 inch. The effective quantum efficiency was observed to be 22% for the wavelength of liquid xenon scintillation light (170 nm), while the effective quantum efficiency for 5.486 MeV alpha-particle excitation was 44%. An energy resolution of 0.5% rms was achieved for the energy deposition of 2.5 GeV in liquid xenon using a fast preamplifier ( ∼ 20 ns).

Energy resolution for 1 MeV electrons in liquid argon doped with allene

Abstract The energy spectrum of conversion electrons (976 keV) from 207 Bi has been measured by an ionization chamber filled with pure or allene-doped liquid argon. The collected charge in allene-doped liquid argon was increased compared to that in pure liquid argon. The resolution was not improved by doping liquid argon with allene in high electric fields, but it was improved in low fields. This indicates that the recombination process is not a main cause of the observed resolutions. The best resolution was about 30 keV which is the same as the best value obtained so far. This is several times worse than the theoretical ultimate value based on the Fano factor.

CR-39 detector and experimental techniques of cosmic supermassive particles search

Abstract The characteristics of CR-39 plastic for cosmic supermassive particles search are described. The long-term effects of temperature, oxygen, and water vapor on the sensitivity of CR-39 and the pre-soaking effect were investigated. For processing the large number of CR-39 plates, a way of mass etching was also investigated and a large etching system was developed. In addition, the procedure of the experiment searching for cosmic supermassive particles is presented.

Search for GUTs monopoles with track-etch detectors

Abstract We outline a large-scale (4000 m 2 ) search for supermassive magnetic monopoles with improved CR-39 track detector array. By applying a heavy etching method, this experiment intends to reach a flux limit below the “Parker bound” and down to ≈ 10 −16 cm −2 sr −1 s −1 within a few years. Properties of newly developed CR-39 together with the etching and the scanning method are also summarized briefly.

Characteristics of CR-39 doped with chlorinated compounds

Abstract Characteristics of CR-39 plastic containing chlorinated compounds such as HCB and DCD have been studied using relativistic heavy ions from the LBL Bevalac. These results are compared with those of pure CR-39, focusing in particular on etching properties and on whether a penetrating etch hole is produced along each particle path by a long duration etch. The relation between the reduced track etch rate and the etchant concentration for CR-39 containing HCB is quite different from that of pure CR-39. Dilute etchants gives much higher track sensitivities than do more concentrated solutions in a wide range of REL. Since type HCB/DCD CR-39 loss its sensitivity in the interior of the bulk material for low REL produced by 2.1 GeV/ n Ne ions, penetrating etch holes are not produced along the particle paths after a heavy etching.