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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.

In order to identify a daughter ion of Ba+ with laser-induced fluorescence just after a candidate event of double beta decay of 136Xe is found in a liquid xenon ionization drift chamber, the size of the laser beam directed to the vertex position is determined to be 1.6 mm in diameter by simulating the signal amplitudes of scintillation and ionization due to two beta rays with the EGS4 simulation code. The detection efficiencies of the apparatus and the trigger threshold of scintillation signals, which are obtained with the simulation, are also discussed in detail.

Temporal and spatial distribution of 222 Rn and 220 Rn and their progeny concentrations in the open atmosphere, 222 Rn and 220 Rn exhalation rates, radioactivities in soil and underground water, including some meteorological factors, were measured at a spot of high 222 Rn and 220 Rn concentrations to investigate the source and occurrence mechanism. Hourly mean concentrations of 222 Rn and 220 Rn during August 1993 were about 230 Bq m −3 and 130 Bq m −3 at 1 m above ground surface. Diurnal variations were high at daytime and low at nighttime, which gives an inverse variation compared with the typical variation in the normal environment. 222 Rn concentrations varied quickly in a few minutes and reached a maximum of about 14 kBq m −3 . The maximum daily mean 222 Rn concentration at 5 cm above ground surface was 11 kBq m −3 . Concentrations of 218 Po, 214 Pb, 214 Bi, and 220 Rn progeny were 8∼61 Bqm −3 , 1∼7 Bqm −3 , 0.5∼5 Bq m −3 , and 0.02∼0.14 Bq m −3 , respectively. The equilibrium factor for 222 Rn was estimated to be 0.01∼0.2. The main source of the mysterious spot of high 222 Rn and 220 Rn concentrations was a small but deep channel between the basement of the building and the surrounding soil, and the extremely localized weather condition.

A relation of radon (Rn) daughters concentration in the air to meteorological parameters is investigated. The atmospheric radon daughter concentration and the related meteorological parameters are treated as a simple time series data. The power sprctrum of radon daughter concentration and temperature after fourier transfer are fit to 1/f closely. This fact confirms that the common dynamics exist between the variations of the parameters.

An automatic measuring instrument for the radon daughters concentration of precipitation has been constructed and used successfully. The precipitation collected by a poly-ethylene funnel during 15 min is led to a glass cell set in a well-type NaI(Tl) scintillator, and after 5 min counting the water sample is pumped out. A sequence of operations of sampling, measurement, recording, draining out and correction for the volume of the water sample is performed automatically, and is repeated at every 15 min. The instrument has sensitivity and durability enough for practical use at outdoors. This instrument enables the measurement of radon daughters concentration as low as 0.5 Bq/ml at precipitation rate as small as 0.5 mm/h. For the improvement of accuracy of the monitoring system of environmental 7-radiation, the effect of radon daughters accumulated on the ground surface by precipitation can be eliminated on real time by means of providing it with the output of this instrument. This instrument can be used for...

The contribution of gamma-rays originating from the atmospheric radon daughters to the environmental radiation is observed to be from ∼ 10 to 25%. In the measurement of diurnal variation of the environmental gamma-ray intensity and the atmospheric radon daughters concentration, we have found a looping correlation between them. By using a model calculation, the cause of this phenomenon is confirmed to be the diurnal variation of the altitudinal radon daughters concentration.

With the thin thermalox BeO disk, we have measured TSEE (thermally stimulated exoelectron emission) of α and β rays, and have found that it depends only on the stopping power of the thin surface layer of the material. It has been made clear that absorbed dose of high energy β-rays in a rather deep layer from the surface does not contribute to the exoelectron emission. This is a serious problem to measure the surface absorbed dose by the solid state detector.

Time variation of radon daughters concentration in snowfall was measured continuously. The relations of radon daughters concentration in snowfall to the precipitation and to atmospheric radon daughters concentration were investigated. It has become clear that when precipitation is small, radon daughters concentration in snowfall is distributed in a wide range, and that the quantity of radon daughters brought to ground surface by snowfall is proportional to precipitation. Washout effect of the snowfall on atmospheric radon daughters was also investigated.

It was found that thin films evaporated onto a substrate in vacuum exhibit both thermoluminescence (TL) and thermally stimulated exoelectron emission (TSEE) when they are heated without any stimulative pre-treatment. These phenomena were observed only once after evaporation, and succeeding repeated heating showed neither TL nor TSEE. The heating rates used were 0.5°C/s for TL and 1°C/s for TSEE. In this study, the temperature at the main glow peak of TL or TSEE from the unirradiated films was found to be higher than that from these irradiated with gamma-rays.

The efficiency of thermally stimulated exoelectron emission (TSEE) was studied for the surfaces of exoelectron materials excited by α, β and γ-rays. The measured efficiencies correspond reasonably well with the mean dE/dx of a surface thin layer. There remain problems regarding the counting efficiency of the 2π flow counter system and the number of the missing exoelectrons that escaped before a measurement. Regarding the β-ray excited group, it can be concluded that the origin of the observed exoelectrons was in a thin surface layer with a thickness of several hundred angstroms and that the contribution of the bulk origin was negligible.

The TSEE glow peaks from a LiF crystal after being exposed to ionizing radiation were observed at 125, 180 and 230°C with a Q-gas flow counter. For irradiation with X-rays (20 R), the TSEE glow peak at 125°C was more dominant than the other peaks. We found that the 125°C peaks for the (110) and (111) surfaces were more intense than for the (100) cleaved surface. When methane was used as a counting gas, the glow peak of the (100) surface at 125°C was weaker than for the case of Q-gas, and the ratio of these intensities was less than one tenth. The TSEE glow peaks from a CaF2 crystal were observed at 85, 180 and 270°C after X-ray excitation. The TSEE intensity at 85°C for CaF2 cleaved surfaces showed almost the same tendency as for LiF with regard to the effects of crystal orientation.