数字快成形算法用于慢衰减闪烁体的高计数率能谱读出

摘要

The pulse signals of the output of preamplifier from the scintillator detector (NaI(Tl),CsI(Tl) etc.) have a long rising time,which causes the serious ballistic deficit existing in the process of the charge collection.In order to reduce the influence of the ballistic deficit on the energy resolution in the later pulse shaping,generally,a wide flat-toped shape can be used to increase the time of the charge collection.But under the circumstance of high radiation fluence rate,due to the serious pulse pile-up of the scintillator detector with the slow decay time,the measured pulse count rate and energy resolution using traditional pulse shaping approach are significantly reduced.In order to overcome this problem,a digital fast shaping algorithm was presented based on the digital deconvolution in this paper.This algorithm can remove the current tails of the scintillator detectors with the slow decay time to obtain an ideal impulse current.Then a narrow pulse can be obtained through pulse shaping,which can thoroughly eliminate the influence of the ballistic deficit.Through the measurement of the 137Cs gamma source,when the shaping time is 1.5 μs,the energy spectrum measurement system using the traditional pulse shaping algorithm yields a 6.99％ energy resolution of the photoelectric peak and count rate of 68 000 s-1.While the digital fast shaping system yields a 6.37％ energy resolution and count rate of 102 000 s-1 at the same condition.Thus,the digital fast shaping algorithm can effectively restore deformation and tail of the narrow pulse shaping under the circumstance of high radiation fluence rate,which can improve the pile-up discrimination ability.%慢衰减型闪烁体(NaI(Tl)、CsI(Tl)等)探测器经过前放输出的脉冲信号具有较长的上升时间,造成电荷在收集的过程中出现严重的弹道亏损.在后续脉冲成形中为了降低弹道亏损对能量分辨率的影响,一般采用较宽的成形平顶来增加电荷的收集时间.但在高辐射粒子注量率的场合下,由于慢衰减型闪烁体输出的脉冲堆积严重,采用传统的滤波成形方式获得的脉冲计数率和能量分辨率明显降低.为解决此问题,本文提出了一种以数字反褶积为核心的数字快成形算法.该算法可去掉慢衰减型闪烁体探测系统的衰减电流拖尾,获得一理想的冲激脉冲电流,然后再通过滤波成形为一窄脉冲,并彻底消除弹道亏损的影响.通过对137Cs γ源测量,使用传统成形算法的能谱测量系统在成形时间为1.5 μs时,其光电峰能量分辨率为6.99％,计数率为68 000 s-1;而使用数字快成形系统,在相同情况下获得6.37％的能量分辨率,计数率可达102 000 s-1.因此数字快成形算法可有效地修复在高辐射粒子注量率下,窄脉冲成形引起的信号变形和拖尾,从而提高了脉冲堆积甄别能力.