[en] An attempt is made at understanding systematically some significant characteristics of an SQS discharge and their physical backgrounds. The most natural mechanism for the generation and growth of an SQS would be: (1) the space charge of positive ions produced by an electron avalanche near the central wire generates a strong local electric field in the vicinity of the cathode (wall) side end of the ion cloud, (2) some of the gas molecules in this region are photoionized by UV photons emitted from the electron avalanche, (3) the liberated photoelectrons give rise to new electron avalanches beyond the end of the existing space charge, and (4) these three processes are related successively, making an SQS develop rapidly toward the cathode wall. If the tube voltage space charge are small, electron avalanches will be reproduced always along the surface of the central wire, where the electric field is always stronger than anywhere in the tube, leading to an ordinary proportional- or GM-mode discharge. Assuming this mechanism, a rough study is made on the electric field intensities at various relevant positions in the tube as a function of the tube voltage, particularly at those points located in the average range of UV photons emitted from the original electron avalanche. (Nogami, K.)

[en] Silicon surface barrier detectors (SSBs) have two demerits in measurement of heavy ions, namely, pulse-height defect (PHD) and plasma delay. Both of these phenomena are ascribed to the formation of a plasma column in the silicon due to the incident heavy ion. One of the three major sources of PHD, i.e., energy dissipated by the recombination of electron-hole pairs in the plasma column, has not been explained quantitatively. To estimate the recombination effect quantitatively and to explain the electric field strength dependence of the plasma delay, the present report proposes new models of the formation and erosion of the plasma column. With the model of the plasma column formation, the volume, the surface area of the plasma column and the density of the electron-hole pairs can be calculated. In the model of the erosion of the plasma column, it is postulated that the plasma delay is the time interval between the formation of the plasma column and the beginning of its erosion, and that the erosion is caused by the change of the dielectric constant inside the plasma column, i.e., the change from a conductor-like plasma column to a dielectricity-like one. With this model, the dependence on the electric field strength of the plasma delay is derived. (N.K.)

[en] Electronic energy transfer processes involving excited rare gas atoms play one of the most important roles in ionized gas phenomena. Penning ionization is one of the well known electronic energy transfer processes and has been studied extensively both experimentally and theoretically. The present paper reports the deexcitation (Penning ionization) cross sections of metastable state helium He(2³S) and radiative He(2¹P) atoms in collision with atoms and molecules, which have recently been obtained by the authors' group by using a pulse radiolysis method. Investigation is made of the selected deexcitation cross sections of He(2³S) by atoms and molecules in the thermal collisional energy region. Results indicate that the cross sections are strongly dependent on the target molecule. The deexcitation probability of He(2³S) per collision increases with the excess electronic energy of He(2³S) above the ionization potential of the target atom or molecule. Another investigation, made on the deexcitation of He(2¹P), suggests that the deexcitation cross section for He(2¹P) by Ar is determined mainly by the Penning ionization cross section due to a dipole-dipole interaction. Penning ionization due to the dipole-dipole interaction is also important for deexcitation of He(2¹P) by the target molecules examined. (N.K.)

[en] The report describes experiments on the effect of allene doped in liquid argon. In the case of doped argon, a large amount of charge is obtained even at low electric fields and the measured charge increases with the field gradually. This can be explained as follows; part of deposited energy which does not form charge in pure argon contributes to charge signal in doped argon through scintillation photons which ionize allene molecules. The main factors determining the energy resolution for α-particles are considered to be (1) fluctuation in the number of produced ion-electron pairs as expressed by the Fano factor, (2) fluctuation in recombination process, (3) fluctuation in photoionization, (4) fluctuation due to the condition of radioactive source and surface of electrodes, (5) fluctuation in geometrical efficiency due to the range and emission angle of α-particles in liquid argon, and (6) electronic noise of amplifier. The factors (1) and (3) can be neglected because of a large number of associated electrons or photons. In pure liquid argon, the factor (2) may be a cause of bad resolution since the fraction of the produced ion-electron paris which do not recombine is small and the photoionization process never occurs for photons emitted through recombination. (N.K.)

[en] GaSe has been studied as a radiation detector which operates at room temperature. In this study the effect of Ge doping was investigated. The energy resolution for ²⁴¹Am 5.5 MeV alpha particles did not improve by the addition of Ge, inspite of the substantial decrease in the leakage current. Nevertheless, it is noteworthy that all detectors with Ge concentration from about 0.01 to 1 at% showed fairly good energy resolutions not so inferier to the best one of pure GaSe detectors, although many pure GaSe detectors did not operate because of their too large leakage currents. (author)

[en] The liquid argon time projection chamber (LATPC) is currently developed for detecting solar neutrons or proton decays. A dual type gripped ionization chamber with different drift distances of liberated electrons is constructed to measure the purity of liquid argon. A purification system of gaseous argon for LATPC with a drift space of about 150 cm is also constructed. The performances of both the dual type gripped ionization chamber and the purifier are tested seeking to develop a large scale LATPC. It is demonstrated that the attenuation length of electrons and also the impurity level in liquid argon can be well determined in the dual type gripped ionization chamber. In the case of the purifier, there still remains unknown low-level impurities in purified liquid argon. The results are compared with UCI data which were obtained with liquid argon mixed with water vapor. the same tendency is found in the attenuation length of their data as in the present results. This seems to suggest the dominant impurity remaining in the purifier is still water. The present apparatus was previously tested with liquid argon purified by other purification system of Ti-Ba getters. The attenuation length obtained by those tests was almost 100 cm. (N.K.)

[en] The author has recently developed a novel method of measuring the intensity of light pulses, employing a photon counting technique, which permits accurate and successive measurements of variations in light pulse intensity, free from the changes in PMT gain. In the present work, an attempt is made to apply the method to measurement of the temperature dependence of scintillations in NaI(Tl) crystals. It is a unique feature of the present experiment that temperature coefficients of both 'scintillation' and 'scintillation + phosphorescence' can be simultaneously measured by the new method with reasonable accuracy. The scintillations are produced in an 1.5'' x 1.75'' NaI(Tl) crystal excited by Cs-137 gamma-rays (0.662 MeV). The crystal is optically coupled to a PMT through a lucite light guide so that the scintillations are introduced to the PMT with a reasonable high efficiency. Fiber optics is employed to transmit a small portion of scintillations from the NaI(Tl) crystal to a particular type of PMT kept at a constant temperature in another thermostatic chamber, and used to measure the variations in scintillation yield. The temperature coefficients of 'scintillations' and those of 'scintillation + phosphorescence' determined are presented. (N.K.)

[en] A ultra sensitive neutron imaging system has been deviced with a 2-dimensional photon counting camara (ARGUS 100). The imaging system is composed by a 2-dimensional single photon counting tube and a low background vidicon followed with an image processing unit and frame memories. By using the imaging system, electronic neutron radiography (NTV) has been possible under the neutron flux less than 3 x 10⁴ n/cm²·s. (author)

[en] Although specialists in the field of electric discharges have known about the streamer phenomenon for many years, the discovery of the SQS phenomenon was made by detector physicists, many of whom were not so familiar with the underlying theory of electrical discharges. Consequently, many specialists in the field of electric discharges are still not fully aware of the existence and the potential importance of the SQS mode. This may be one of the principal reasons why the mechanism responsible for the SQS mode is still not fully understood. If the potential importance of the SQS phenomenon were to be emphasized to specialists in the field of electrical discharges, they would surely have a deep interest in it, and from this interest many useful insights would certainly follow. What is needed is an understanding of the underlying physical mechanism responsible for the SQS phenomenon ahd its dependence on the independent variables such as voltage, the identity of gases, their concentrations, etc. Accelerator physicists have shown a great interest in detectors based on the SQS phenomenon. Such detectors can have extensive applications outside the fields of high energy and nuclear physics. By selecting the gases and their pressures advantageously it should be possible to develop SQS detectors that are equal to or better than GM counters. (N.K.)

[en] A high-pressure proportional counter system is constructed. The high pressure 4πβ counter system constructed is made of aluminum and is divided into two 2π counters. The gas pressure is controlled with a pressure regulator and very fine leak valves to keep the balance of a stable pressure and constant flow rate. Investigation of characteristics of th counter shows that there is an almost linear relation between voltage and pressure. The linearlity of gas gain of this counter to the electron energies is measured with different gas pressures. Quite good linear gas multiplication is obtained at 0.9 MPa. Another investigation is made of application of to activity measurement of ¹⁰⁹Cd. When the gas pressure is over 0.5 MPa, the proportion of collected conversion electrons to absolute activity comes to a constant value of 96 %. This is quite good agreement with the decay data of 96.4 % conversion electron emission rate. The study indicated many excellent features for activity measurement. Especially the efficiency variation technique is good for automatic data acquisition with a programmable high voltage supplier. Moreover, since it is possible to obtain absolute activity with only one sample, it will be quite useful for limited samples experiments. (N.K.)