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

构造了一个多线比例腔的布拉格曲线计数器，并测量了该计数器的背景电平。原始计数率约为每分钟一次。由于所有计数都记录为输出信号的波形数据，因此通过分析波形数据可以确定每个信号是否由α粒子引起，以及该粒子以什么角度进入计数器。因此，在测试样本所在的地方周围释放的α粒子被发现为每小时4次。这仍然是一个最终的背景，不能被拒绝，即使应用波从切割。由于这个背景看起来来自于计数器材料中包含的α发射器，因此该材料被α发射较少的材料所取代。然后，最后的背景减少到每小时0.4次。使用环境样品进行测量——使用布拉格曲线计数器对用作涂漆管的铅板进行α粒子计数。从原始数据中选择了看起来像是从铅样品附近的地方发射的α粒子的事件。结果发现，放置铅样品时的事件数约为未放置样品时的10倍，即S/ n比约为10。这一结果适用于连续α光谱样品。对于离散谱样本，在源强度相同的情况下，期望信噪比远高于此值。因此，如果结合α发射材料的提取技术，现在构建的α计数系统可以适用于各种环境材料的低水平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.