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The average numbers of scintillation photons and liberated electrons produced by 5.49-MeV α - particles were measured in high-density gaseous xenon. The density range is 0.12–1.32 g/cm3 for scintillation measurements at zero electric field, and 0.12–1.03 g/cm3 for the scintillation and ionization measurements under various electric fields. The density dependence of scintillation yield at zero electric field was observed. The W s - value , which is defined as the average energy expended per photon, increases with density and becomes almost constant in the density range above 1.0 g/cm3. Anti-correlations between average numbers of scintillation photons and liberated electrons were found to vary with density. It was also found that the total number of scintillation photons and liberated electrons decreases with increasing density. Several possible reasons for the variation in scintillation and ionization yields with density are discussed.

The time profile of recombination luminescence of dense xenon gas irradiated by an α -particle was absolutely measured in the density range of 0.027 – 0.112 g / cm 3 with the aim to investigate the intensities of recombination luminescence at zero electric field. It was found that the number of scintillation photons due to the recombination luminescence increases with xenon density up to around 0.05 g / cm 3 , and then becomes nearly constant ( = 2.32 × 10 5 photons for an α -particle with 5.49 MeV). The probability of recombination between electrons and ions at zero electric field is about 88% in the density range of 0.05 – 0.112 g / cm 3 . It was also found that the percentage of slow component ( ∼ sub-milliseconds) in the recombination luminescence decreases with density from 73% to 33% in the density range from 0.027 to 0.112 g / cm 3 .

Fluctuation in ionization, scintillation and gas proportional scintillation (GPS) yields have been measured in gaseous xenon as a function of the reduced electric field strength E / N in Td (townsend), where E is the electric field strength in volts/cm and N the atomic number density of xenon. 1 Td is defined as 1×10 −17 V cm 2 . The measurements are made under the pressures of 0.1 and 0.2 MPa by a plane parallel ionization chamber (PPIC) equipped with a photo-multiplier tube (PMT) sensitive to VUV photons. It is found that the fluctuation in ionization is largely improved in PPIC if alpha-particles were almost vertically emitted to the plane of the electrode and their track lengths were nearly equal to the distance between the electrodes. The fluctuation in the scintillation is 33.5% (full-width at half-maximum (FWHM)) at the pressure of 0.1 MPa and 35.6% (FWHM) at the 0.2 MPa, respectively, including the fluctuation of 10% (FWHM) in the alpha-particle energy. The season may be attributed to the fluctuations in several parameters on PMT. In GPS, it is turned out that the proportional gain of about 17 photons/electron at 3.8 Td–45 photons/electron at 4.6 Td is easily achieved and its fluctuation is about a few percent. It is equal to twice of that value at the same reduced field in the case of 0.2 MPa. The fluctuation in the photon yields in GPS shows just equal to one of the ionization yields.

The high precision gamma-ray spectrometer (GRS) is scheduled to be launched on the lunar polar orbiter of the SELENE mission in 2007. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals as an anticoincidence detector. A Stirling cryocooler was adopted in cooling the Ge detector. The flight model of SELENE GRS has been completed and an energy resolution of 3.0 keV (FWHM) at 1.332 MeV has been achieved. The spectrometer aims to observe nuclear line gamma rays emitted from the lunar surface in a wide energy range from 100 keV to 12 MeV for one year and more to obtain chemical composition on the entire lunar surface. The gamma-ray data enable us to study lunar geoscience problems including crust and mantle composition, and volatile reservoirs at polar regions.

Acoustic signals were observed with a lead–zirconate–titanate (PZT) element that was directly irradiated with a 368 MeV/n xenon beam. Using an array comprising PZT elements, the energy loss in the PZT was studied. These elements are sensitive to an energy deposit of 100 nJ. A series of values of output voltage vs. integrated thickness of PZT was represented along a line similar to the ionization loss calculated by the Bethe–Bloch formula. The induced voltage was attributed to several processes—ionization, thermal, elastic, and piezoelectric processes. This study describes the possible applications of the PZT element as an active medium for calorimeters and a monitor for hypervelocity impact of space dust.

The photon-to-photoelectron conversion efficiency and the reflectance of a photomultiplier have been measured as a function of the photon incident angle. Appreciably large conversion efficiency and reflectance were obtained for a incident angle near 45°. A calculation was made for an optical model of a photomultiplier. The results were consistent with the experimental results.

The scintillation response to an α source (241Am) and the ionization yield in pure gaseous xenon and its mixtures with 0.2–2% of methane were measured at a pressure of 26 atm and different values of reduced electric field E/N. Both light and ionization yields in xenon were shown to decrease with increasing percentage of methane.

The acoustic signals generated by bombarding 400 MeV/n xenon ions in water were studied using an array of piezoelectric lead–zirconate–titanate elements. The observed signal was reduced to a bipolar form through Fourier analysis. The output voltage corresponded to the amount of energy deposit in water, and it tailed off beyond the range of 400 MeV/n xenon in water. This magnitude was explained qualitatively as cumulative processes. Its behavior was consistent with the calculations based on the Bethe–Bloch formula. Possible applications of this detector to radiology and heavily doped radiation detectors are described.

The luminescence yield of gaseous xenon by alpha particles is measured as a function of electric field strength under the pressures of 1.0 and 2.0 atm. The luminescence yield rapidly decreases as increase of the electric field and reaches a constant yield at higher electric field strength. The constant luminescence yield suggests an average energy expended per photon (W/sub s/) is determined from its value. In this study, the W/sub s/ is obtained to be 59.4/spl plusmn/2.4 eV and the ratio of average luminescence yield to average ionization one is calculated to be 0.37/spl plusmn/0.02, which agrees well with Platzman's prediction.

Scintillation and ionization yields in xenon gas for 5.49 MeV alpha-particles were measured in the range of pressure from 0.35 to 3.7 MPa and the electric field strength (E) over the number density of xenon atoms (N), E/N from 0 to 5×10−18 V cm2. When our data are normalized at the data point measured by Saito et al., the number of scintillation photons is 2.3×105 while the number of ionization electrons is 2.0×105 at 2.6 MPa and at 3.7×10−18 V cm2. The scintillation and ionization yields of xenon doped with 0.2% hydrogen, High-Pressure Xenon gas[H2-0.2%], at 2.6 MPa was also measured. Scintillation yield of the Xe–H2 mixture gas is 80% as high as that of pure xenon. It is found that the scintillation yield is luminous enough to generate a trigger pulse of the high-pressure xenon time projection chamber, which is expected as a promising MeV Compton gamma-ray camera.

To apply scintillation material to radiation detectors, a quantity such as the W-value, defined as an average energy expended per ion-pair in gaseous detectors, must be determined experimentally. The authors define the effective W/sub S/-value as E/sub 0//N/sub p/ an average energy dissipated to emit a scintillation photon, if the energy of radiation E/sub o/ is completely absorbed in material and the number of scintillation photons N/sub p/ are emitted. They have attempted to determine N/sub p/ in liquid xenon due to alpha-particles with an energy of 5.303 MeV from /sup 210/Po to estimate W/sub S/ for scintillation in liquid xenon. The absolute scintillation yield was obtained as 3.26*10/sup 5/ for alpha-particles for 5.303 MeV in liquid xenon. This result followed from fitting the absolute photo-electron yields measured with a VUV sensitive photomultiplier, which was used as a photodiode, to the results of Monte Carlo simulation. >