Masami Fujii

Improvements in the sensitivity and the etching properties of CR-39

Abstract The sensitivity and the etching properties of CR-39 plastic track detectors have been improved by adding small quantities of chlorinated compounds to pure CR-39. The type TPD2, containing 2% diallyl chlorendate, shows an indication of increased sensitivity compared to pure CR-39. The type TPH0.5 containing 0.5% hexachlorobutadiene, does not show a sensitivity increase, but it is remarkably transparent even after etching for one week in 6.7N NaOH at 70°C.

Thermosetting resins for nuclear track detection

Abstract Several new thermosetting resins with a three dimensional network structure like CR-39 were polymerized to study their characteristics for use as nuclear track detectors. During the course of this study, thermosetting resins with good etching properties and various sensitivities have been obtained. The comparison of the molecular structures of these resins gives us an important clue for the development of highly sensitive polymeric track detectors. They will also be useful for observations of ultra-heavy cosmic rays and heavily ionizing particles at low energies.

γ-Ray burst observed at balloon altitude

SINCE the γ-ray burst was discovered in 1973, approximately 50 events have been observed using artificial satellites1,2. In addition, several bursts of smaller size have been found using balloon-borne detectors3–6 with large sensitive areas. No burst has yet been located on the celestial sphere, with an adequate precision to associate it with an astronomical object. To determine the precise position of a γ-ray burst which had not been predicted to occur, the detector must have a wide field of view and the capability of precise location of the source. A rotating cross-modulation-collimator (RCMC) proposed7 as a device to fulfill these apparently conflicting requirements was used in the series of balloon observations reported here. A small γ-ray burst was found during ∼ 150 h of observations and its celestial position was determined with a precision of ∼ 0.3°.

X-ray emission associated with gamma-ray bursts

The energy spectra of gamma-ray bursts differ from those of black-body radiation and are similar to the thermal bremsstrahlung spectra of optically thin plasma. This could be realized if the source is located in the outer atmosphere of a neutron star. In this case, almost one half of the emitted photons hit the surface of the star. The surface of the star is heated to a temperature of the order 107 K, and a dominant flux of X-rays with a black-body spectrum would be expected. The X-rays produced by this mechanism are detectable in the energy range from a few keV to 10 keV. This model is discussed in relation to the recent observations in the X-ray region at the time of gamma-ray bursts, and modifications of this model are also presented. The observation in this energy range will bring us valuable information on the nature of gamma-ray burst sources.

Study on Detection of Epileptic Discharges Based on a Duffing Oscillator Model

In order to establish a quantitative detection method for appearance in epileptic discharges (EDs), we propose using the model parameters in a Duffing oscillator, which is a nonlinear mathematical model. Extracting four frequency bands of delta, theta, alpha and beta waves from the time history of the electrocorticogram (ECoG) obtained from rats with induced EDs, we applied a sweep window to the time history for each band. So as to fit the equation for the Duffing oscillator to the time history of the ECoG, we used the least square method to determine the model parameters expressing characteristics of ECoG. The Duffing oscillator has three kinds of vibrational parameters and four kinds of parameters about the amplitude for the driving force with two predominant frequencies contained in ECoG. In order to examine the appearance time of the EDs and the change of ECoG characteristics, we determined the model parameters for each sweep window. When epilepsy occurs, we found that the amount of the parameters related to “conservation”, “dissipation” and “input quantities” increases. On the other hand, the parameter value corresponding to nonlinearity tends to decrease. It is found that the proposed method by the model parameters of the Duffing oscillator can be used in quantitative detection for EDs.Copyright

A development of a balloon made of fiber reinforced film

In present ballooning missions, as payloads increasingly become heavier and more sophisticated, much higher reliability is required in the balloon itself and in the launch operational technique. Hence, ISAS (the Institute of Space and Astronautical Science) has developed a balloon made of relatively thick films reinforced with high-strength fiber fabric (ref. 1 to 3). In order to verify structural properties and manufacturing quality, partial strength tests together with a trial production of small scale balloons have been car ied 5 . out. In 1990, a sub-scale B5 (5,000 m In volume) size balloon was produced, and a full inflation test on the ground prior to a flight experiment was implemented on account of demonstrating the basic capability of the fiber reinforced balloon. This paper describes research and development of the proposed balloon associated with selection and verification study of the high-strength fiber reinforced film.