In the measurement of neutrons from the medical electron accelerator by a rem counter, two problems disturb accurate measurements. One is the pile-up of signals produced by X-rays during each X-ray burst and the other is the increased counting loss caused by bunched nature of yielded neutrons. The time spectrum of neutrons measured by the rem counter 2202D (manufactured by Studsvik) rises up to a maximum value by about 20 μs and then falls down exponentially with a time constant of about 90μs. On the other hand, that of X-rays is roughly rectangular with several μs width. A time discriminating system was prepared to be combined with the rem counter, which was triggered by leading edge of electron beam pulses, rejected pile-up signals due to X-ray bursts, and counted pulses of neutrons in a specified time window. The system discriminated the pile-up enough to measure neutrons at a X-ray dose rate of at least 30 mGy/h. Nonparalyzable counting loss correction was practicable upto about 10 mSv/h for the beam pulse rate of 85 Hz, in which the dead time of the rem counter was estimated as 4μs.
The concentrations of deuterium oxide (D2O) in the root tissue water of winter rye seedlings equilibrated with the external D2O concentration within 30 min and in the shoot tissue water after 5-6 h. The equilibrated value in the root water was 87% and in the shoot water, 55% of the external concentration. The K+absorption rate of the seedlings decreased from a value of 39 to 18μmol g-1 h-1 when the D2O concentration was changed through a range from 0% to 97%. D2O suppressed the absorption of water and K+by the seedlings. The higher the D2O concentration the greater the suppression, but it was less than with similarly treated rice plants. However, the process of D2O absorption by the seedlings was similar to that of rice seedlings (Envir, exp. Bot., 24, 369) .