An experimental model of automatic recording scintillation gamma spectrometer for gamma-ray energy measurements has been constructed with a NaI(T1) crystal, an EMI 6262 photomultiplier tube, a linear amplifier, a single channel pulse height analyzer, a counting rate meter, a recorder, a stabilized power supply, and a stabilized H. T. power supply. The NaI(T1) crystal was made by Harshaw Chemical Co., cylindrical in shape, 1" in diameter and 1" in height. The linear amplifier consists of a pre-amplifier and a main amplifier. Its total gain is about 70 db. and the rise time is less than 0.1 μscc. The single channel pulse height analyzer has the same circuit as ATOMIC Model 510 pulse height analyzer. The rotation of the base line potentiometer of this analyzer is coupled with the feed of the chart paper by means of Selsyns. Results of the experiments: The resolution of this spectrometer is 12.4 percent at the photo-peak of the gamma-ray of 137Cs, and the relation between gamma-ray energy and the pulse height of its photo-peak is accurately linear.
The method of measuring the roughness of metal-surface by using jelly containing radio isotope (2411Na) was given in the 1st report. Instead of jelly, use of powder is also effective for non-metal surfaces, vis. paper, wood, etc. By this method, 3-dimensional mean spaceroughness Hs2), the mean height of minute protuberances that make the surface rough, is measured on paper, emery-paper and wood and found that, for the emery-paper the relation Hs=Ar holds, in which A is a constant and r is the grain-size (diameter: r) of emery, and for the wood Hs∝(Hmax)2 holds, Hmax being the maximum height.
U-SCOPE is a new contrivance built on radar principle for rapid detection of radioactive sources in field survey. A scanning collimator, the axis of which is kept either vertically or horizontally, revolves arround a set cylindrical scintillation crystal with a constant angular velocity of 60°/s. Pulses from the scintillator caused by gamma rays coming from the direction to which the collimator window is faced are picked up and the intensity of radiation as well as the direction of the sources located arround the observer are simultaneously indicated on a screen without any other auxilliary instrument such as scalar, pulse recorder etc. There are two modes of observation, Type A and Type B, with the U-Scope. Type A has the advantage in measuring weak fields in that every pulse is transformed into a video signal and put into the cathode of the radar tube so that a brilliant dot appears on the survey vector sweeping along the radius at that instant. The intensity of radiation is directly obtained from the density of brilliant dots within the segments bordered by rings and radial vectors forming a polar coordinate system. The area of each segment is swept out in 0.1 second. Hence, the number of dots found within the segment multiplied by 10 gives the counting rate per second. With Type B, which is suited to measuring strong fields, the UScope serves as an automatic tracer of curves denoting the azimuthal intensity distribution of radioactivity.
As ZnS(Ag) -paraffin scintillator is known to be suitable for the measurement of fast neutron under high background of γ-rays, investigations are, Made on the following details of -the scintillator: (a) rise time and decay time of scintillation, (b) influence of scintillator -thickness, (c) influence of ZnS-paraffin mixing ratio upon the pulse height distribution. The scintillator thickness between 1.3 and 4mm give no difference on the pulse height .distribution. The optimum mixing ratio of ZnS: paraffin is found to lie between 1 and 2. In observed samples, ZnS(Ag) for the radar tube proved to have best characteristics. Contraryto the photoluminescence, the decay of ZnS(Cu) is so rapid that it is nearly comparable to -that of ZnS-(Ag), being about 1μ sec for neutrons and 0.2μ sec for γ-rays.
With scintillation counters, there are various methods of pulse-height analysis which can be divided into two groups. One is to measure the voltage pulse amplitude directly, and the other is to convert the input voltage pulses of various amplitudes into other measurable physical quantities such as time, deflection of electron beam etc. Taking microwave frequency as the corresponding physical quantity, an Amplitude-to-Frequency convertor is devised by using reflection type klystron 2K25 in 9600 MC/S region as the convertor. In these klystrons, the repeller voltage change of 10 volts induces linear frequency modulation of about 20 MC/S, so that the maximum input voltage of 10 volts from pulse amplifier is sufficient for this converter system. The induced frequency changes due to input voltage pulses are measured by taking beat frequency with another local oscillator klystron. In this single channel Pulse-Height Analyzer, time resolution is as short as 10 μs in all voltage regions of input pulse and this is about 10 times shorter than the Pulse-Height Analyzer of time conversion principle. At present, energy resolution of 4 to 5% is obtained by this Analyzer, but this figure will probably be reduced below 1%. This converter may be suitable for multichannel Pulse-Height Analyzer having over 100 channels.