A. Nakamoto

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.

Inclusive production of π0'S in the fragmentation region at the SppS collider

Abstract The inclusive production of π0s has been measured in the nucleon fragmentation region at the S p pS Collider at 630 GeV center of mass energy. Average transverse momentum and rapidity distributions compared with lower energy ISR data show no sizable violation of Feynman scaling in the fragmentation region.

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.

New two-dimensional position sensitive silicon detector with good position linearity and resolution

Abstract A two-dimensional position sensitive silicon detector (PSSD) with a good linear response, consisting of a square ion-implanted resistive anode with a boundary of an additional resistive-strip electrode, was newly developed. Linearity and resolution for the PSSD were investigated using 40 MeV helium and 95 MeV nitrogen ion beams. The PSSD has an effective area of 45 mm×45 mm, a thickness of 400 μm, a junction capacitance of 500 pF, a surface resistance of the ion-implanted resistive anode of 18 kω□ and a resistance of the strip line of 1.4 kω. The nonlinearities and resolutions (FWHM) of the position were 0.75% and 1.97 mm for 40 MeV helium ions obtained by 6 μs pulse shaping, and 0.47% and 0.71 mm for 95 MeV nitrogen ions obtained by 12 μs pulse shaping, respectively.

A liquid xenon proportional scintillation counter

Abstract The characteristics of a liquid xenon proportional scintillation counter have been studied by using conversion electrons from 207 Bi. Pulse shapes of the induced charge and the scintillation in the ionization chamber mode were observed and the variations of relative photon yield of the proportional scintillation against the applied voltage were measured. The energy spectra of the proportional scintillation for 207 Bi were compared with those of the charge. The best resolution of the proportional scintillation was about 18% fwhm for 1 MeV electrons, which was almost the same as that of the charge. The linear relation between the normalized photon yield at constant electric field strength on wire surface and wire radius as expected from analogy with gas was not obtained but the tendency of increase in the normalized photon yield for wire radius was confirmed.

Test of a dual-type gridded ionization chamber using liquid xenon

Abstract A liquid xenon dual-type gridded ionization chamber designed as a gamma-ray spectrometer was constructed and some tests for gamma-rays were made by using highly purified xenon gas. The energy resolution of 8.6% at fwhm was obtained for collimated gamma-rays of 662 keV. The resolutions at fwhm for non-collimated gamma-rays were (9.6 ± 0.4)% at 662 keV, (6.5 ± 0.3)% at 1332 keV and (4.5 ± 0.3)% at 2614 keV. These results show that, for gamma-ray energies above 1600 keV, the energy resolution for the liquid xenon ionization chamber is better than that for a conventionally available 1 3 4 ″ diameter × 2″ NaI(Tl) crystal. This characteristic of the chamber was kept nearly constant for more than 24 h. The resolution obtained experimentally were compared with the theoretical values and the causes of the differences between them are discussed.

Electron (0.19–3.2 MeV) and proton (0.58–35 MeV) precipitations observed by OHZORA satellite at low latitude zones L = 1.6–1.8

Abstract Characteristics of observed electron (0.19–3.2 MeV) and proton (0.58–35 MeV) precipitation at low latitude zones (L = 1.6–1.8) are described. The precipitation zones were observed by instrumentation on the OHZORA satellite between March 1984 and September 1986. The results are presented as intensity time profiles of particle precipitation, energy spectra, pitch angle distributions and the geographical distribution of the particle precipitation zone. It is shown that the zone is centered near L = 1.71, the width of the zone is ΔL = ± 0.16, the maximum energy of the precipitating particle is less than 1 MeV, and the maximum of the pitch angle distribution is around 90°. No particle precipitation at the low latitude zone is observed over the North Atlantic Ocean and Europe.

Intensity maps of MeV electrons and protons below the radiation belt

Abstract Global distributions of energetic electrons (0.19—3.2 MeV) and protons (0.64—35 MeV) are presented in the form of contour maps. The data were obtained by two identical energetic particle telescopes using ΔE × E solid state detectors on board the satellite OHZORA . The observed altitude range is 350–850 km, which is divided into three ranges for contour representation. Ten-degree meshes in longitude and latitude were used to obtain the intensity contours. A pitch angle distribution of J ( α ) = J (90) · sin n α with n = 5 is assumed in order to get the intensity whose pitch angle is perpendicular to the geomagnetic line of force. In the map of the highest altitude region, a “ridge” extending from the South Atlantic Anomaly to the Northern Hemisphere exists above Mexico. A contour map in the B - L diagram is also presented. Here we can see some discrepancies at L = 1.1—1.5 from the radiation environment model of NSSDC. The data analyzed here were obtained during three years from February 1984 to January 1987. No geomagnetic activity was concerned.

Improvement of mass resolution of cosmic ray nuclei using a ΔE × E Si detector telescope

Using 5-in.-diameter Si(Li) detectors with a detector thickness of 1, 2 and 3 mm combined with 62 mm × 62 mm position-sensitive Si detectors, an excellent isotope telescope has been constructed for the Geotail mission. The performance of the telescope and the individual detectors has been investigated using 56Fe beams with energies between 430 and 696 MeV/n. The nonuniformity of the detector thickness as measured by exposing the detectors to a monochromatic Fe beam is 0.44% for 1 mm thick detectors, 0.54% for 2 mm thick detectors and 0.15% for 3 mm thick detectors. The secondary isotopes of Al through Fe produced by 430 MeV/n 56Fe in a polyethylene target were clearly resolved by the telescope. The measured mass resolution for Si, Ca and Mn were 0.36 amu, 0.42 amu and 0.44 amu in FWHM, respectively. The telescope has the following two key features: an excellent resolution (better than 0.5 amu) and an exceptionally high sensitivity (SΩ = 43 cm2sr) for a broad range of species from He through Ni with energies between 2.4 and 210 MeV/n.

A 4-inch silicon/tungsten calorimeter for p-p collider experiments

Abstract A 4-inch diameter silicon/tungsten sandwich calorimeter with 64 cm 2 in active area and 18 radiation lengths in depth has been constructed. The performance has been investigated for incoming electrons of 500 MeV to 4.5 GeV. The calorimeter shows a good linearity over the electron energy region and the energy resolution is well expressed by σ (rms)/ E = 17√ t / E %, where t represents the unit sampling thickness in radiation lengths and E the incident electron energy in GeV. The agreement between these results and a Monte Carlo simulation is quite satisfactory. The center of shower has been determined with the accuracy of better than 2 mm at energies exceeding 1 GeV.