A Van de Graaff generator for a 300 KV electron microscope has already been reported. However, it was difficult to obtain a stable high voltage of any desirable value. This inconvenience is eliminated by the use of a new spray device. The effective spray width of the device is made adjustable with a pair of insulated covers which are driven by a servomotor. If the spray voltage is sufficiently high so that the spray current is in a saturated state, the corona discharge from the spray needle and the spray current are not affected by the fluctuation of spray voltage. The spray current is increased proportionally to the effective spray width and the output high voltage is determined by the effective width. Thus, the output voltage from 50 KV to 400 KV can be covered continuously. A relative fluctuation of the order of 10-4 has been obtained at 390 KV during 30 seconds by using a smoothing condenser of 0.02 pF in capacity. It is found that the gradual change;in running speed of the belt-driving motor is now the main cause of the voltage fluctuation. The construction of the spray device and some experimental results are described.
A Simple, low cost automatic sample changer is described. The instrument is composed of three parts. The sample changing system consists of a turn-table on which six samples are located as shown in Fig. 1, a phono-motor which drives the table and a sample changing vacuum-tube circuit. The time recording system consists of a synchronous motor which generates time signals and six registers each of which records the time required for 64 counts. The scaler is a usual type of scale of 64. When No. 1 sample is counted by a G-M counter, No. 1 register circuit is closed and it records the time signals. At the moment of the 64th count, a signal from the scaler is sent to trigger the sample changing circuit and A. C. line of the motor is closed and the table begins to turn. No. 1 register circuit is then opened and the time recording is finished. When No. 2 sample is brought to the counting position, No. 2 register circuit is closed and the time signals bigin to be recorded on that register. A formula is deduced representing the statistical error of the measurement. It is slightly different from that obtained by the usual method, especially when the counting rate is large. It is found that this instrument is quite adequate for the measurement of samples of low level activity, because it can count the sample and the background alternatively and can record the sum of the counting times of each cycle for each sample.
This is a supplement to the previous paper on a high speed locator of radioactive sources in fields and mines. In the present paper, characteristic of the scanning collimator which is attached to the contrivance and features of the patterns which are frequently obtained with U-Scope are treated analytically. Examples of typical patterns and their classification are given: for examples, simple patterns, compound patterns, complex patterns, background patterns, diffused or granite patterns and over-scale patterns. All of them are illustrated with some explanations. From these examples it can easily be concluded that the C. R. T. display of U-Scope is the most effective method of data indication, as it gives the complete information concerning the presence of radio-active sources around the observer, in fact, the feature of this method is the simultaneous exhibition of directional distribution of the intensity of radiation, plotting new data from moment to moment, and visualizing the records that last long enough for observation then fade gradually. U-Scope is taken for a universal detector of radioactivity with the advantages of being a locator, a counter, a ratemeter and a recorder. It helps the geologist in discovering radioactive resources directly without being misled by pseud sources such as granite stones on the road, a granite quarry and the like. No doubt, topographical and geological knowledge will still more facilitate the reconnaissance of radioactive minerals. Use of U-Scope is also invaluable in detecting stray radioactive rays in the surroundings of hospitals, institutes, factories and so on.