DETECTION OF LOW LEVEL ALPHA EMITTING MATERIAL USING A BRAGG CURVE COUNTER

背景计数采用多线正比室构成布拉格曲线计数器，并测量了该计数器的本底电平。由于所有计数都被记录为输出信号的波形数据，因此通过分析波形数据来确定每个信号是否源于α粒子以及粒子进入计数器的角度。结果，发现在测试样品将被定位的地方周围发射的阿尔法粒子是每小时4次计数。这仍然是即使通过施加来自CUT的波也不能被拒绝的最终背景。由于该背景看起来起源于包含在计数器材料中的阿尔法发射器，使用环境样品Alpha粒子计数表进行测量，用Bragg曲线计数器制作用作画管的铅片。从原始数据中选择看起来是从铅样品附近发射的阿尔法粒子的事件。发现当放置铅样品时，事件数量大约是没有样品时的10倍，即，S/N-比值约为10。这一结果是针对连续α光谱样品得出的。对于离散光谱样品，在源强相同的情况下，S/N有望远远高于这个值。因此，如果结合α发射物质的提取技术，所构建的α计数系统可以适用于各种环境物质的低水平α计数。

Background CountingA Bragg curve counter using a multi-wire proportional chamber was constructed and the background level of this counter was measured.A raw counting rate was about one per minute.Since all the counts were recorded as waveform data of output signals, it was determined whether each signal was due to an alpha particle or not and what angle did the particle entered into the counter by analyzing waveform data.As a result of this, alpha particles emitted around the place where a test sample will be located was found to be 4 counts per hour.This remains as a final background which cannot be rejected even by applying wavefrom cut.Since this background looked to originate from alpha emitters contained in the counter material, the material was replaced by a less alpha emitting one.Then the final background was reduced to 0.4 count per hour.Measurement using an environmental sampleAlpha particle counting form a lead sheet used as a painting tube was made by the Bragg curve counter.The events which looked to be alpha particles emitted from the place near the lead sample were selected from the raw data.It was found that the number of events when the lead sample was placed were about 10 times larger than that without the sample, that is, S/N-ratio was about 10.This result was obtained for the sample of continuous alpha spectrum.For the sample of discrete spectrum S/N is expected to be much higher than this value if the source strength is same.Thus the alpha counting system now constructed can be applicable to low level alpha counting of various environmental materials if combined with the extracting technique of alpha emitting material.