Pulse Shape Discrimination Electronics Research Articles

A Hand-Held, Intra-Operative Positron Imaging Probe for Surgical Applications

We have developed a prototype intra-operative $\beta^{+} $ imaging probe to help tumor removal and malignant tissue resection. The probe can be used during surgery to provide clear delineation of malignant tissues. Our probe consists of a hybrid scintillator coupled to a silicon photomultiplier (SiPM) array with associated front-end electronics encapsulated in an ergonomic aluminum housing. Pulse shape discrimination electronics has been implemented and integrated into the downstream data acquisition system. The field of view of the probe is $10 \times 10~\hbox{mm}^{2}$ realized by a 0.4 mm thick CsI:Tl scintillator coupled to a 1 mm thick LYSO. While CsI:Tl layer acts as $\beta^{+} $ sensitive detector, LYSO detects gamma radiation where the gamma response can be subtracted from the total signal to improve SNR and contrast. The thickness of the LYSO scintillator is optimized such that it acts as light diffuser to spread the scintillation light generated in CsI:Tl over multiple SiPM pixels for accurate estimation of the $\beta^{+} $ interaction location. The probe shows $ FWHM spatial resolution in the presence of large background radiation. The probe was used to study rabbits with tongue tumors. The experimental results show that the probe can successfully locate the tongue tumors in its active imaging area.

Simultaneous recording of high-energy photon spectrum using phoswich detector

Phoswich detector with its pulse shape discrimination (PSD) electronics is being used for estimating actinides in lung as part of in vivo monitoring. In this application, only the signals from thin NaI (low energy measurement) are effectively utilized. The high-energy gamma interactions in thick CsI portion of phoswich are merely used for background reduction in the low-energy regions. The present PSD electronics was suitably modified; both lower and higher energy photon spectra from a single phoswich detector are recorded simultaneously. This feature helps in identifying any fission product gamma emitters and also detects the increase in background during lung counting measurements. This paper outlines the modifications incorporated in the PSD electronics and the suitability of phoswich detector as a gamma ray spectrometer. The typical spectrometric characteristics of the detector such as energy linearity, full width at half-maximum, point source efficiency, and so on, estimated through experiments, and some of the salient results are highlighted.

Calibration of phoswich-based lung counting system using realistic chest phantom

A phoswich detector, housed inside a low background steel room, coupled with a state-of-art pulse shape discrimination (PSD) electronics is recently established at Radiological Safety Division of IGCAR for in vivo monitoring of actinides. The various parameters of PSD electronics were optimised to achieve efficient background reduction in low-energy regions. The PSD with optimised parameters has reduced steel room background from 9.5 to 0.28 cps in the 17 keV region and 5.8 to 0.3 cps in the 60 keV region. The Figure of Merit for the timing spectrum of the system is 3.0. The true signal loss due to PSD was found to be less than 2 %. The phoswich system was calibrated with Lawrence Livermore National Laboratory realistic chest phantom loaded with (241)Am activity tagged lung set. Calibration factors for varying chest wall composition and chest wall thickness in terms of muscle equivalent chest wall thickness were established. (241)Am activity in the JAERI phantom which was received as a part of IAEA inter-comparison exercise was estimated. This paper presents the optimisation of PSD electronics and the salient results of the calibration.

Balloon flight test of pulse shape discrimination (PSD) electronics and background model performance on the HIREGS payload

We flew a prototype of the INTEGRAL/SPI PSD electronics with a narrow-bore coaxial Ge γ-ray detector on the January 1998 Antarctic balloon flight of the HIREGS payload. The first goal for this test flight was to demonstrate the performance of the PSD electronics in a radiation background and space environment similar to that in which SPI will operate, which was successfully demonstrated. The second goal was to measure the fraction of the background due to localized β −-decays, and to validate the model used to predict SPI's background and the sensitivity improvement due to the PSD background rejection. Our background measurements show good agreement with the models developed for SPI, and strongly support the expected improvement in sensitivity due to PSD on SPI.

Room temperature semiconductor detectors for safeguards measurements

A summary is given of the principal areas of application where CdTe detectors are presently used by the IAEA in nuclear material safeguards. Hemispheric detectors with a sensitive volume of about 20 mm 3 have their principal application in the verification of irradiated nuclear material. Larger volume hemispheric detectors are used for the verification of unirradiated material. Their availability, however, is still limited. Problems with the commercial supply of detectors and with ruggedizing the design of the miniature detection probes need to be solved. New results which are relevant for future applications are described. It has been shown that hemispheric detectors made of CdZnTe provide a resolution of 3–4% and a peak/Compton ratio larger than two for 137Cs. Large volume planar CdZnTe have been used in conjunction with pulse shape discrimination electronics. The detector efficiency, however, still remains below the values expected from their geometric dimensions. A new technique to achieve single charge collection in large volume CdZnTe detectors has been developed. Planar detectors with PIN structure and Peltier cooling have further improved. However, the problem of long term stability has not been solved yet. Silicon detectors are increasingly used in unattended radiation monitoring systems. They have a proven long term stability and can cover a signal range of 5–6 decades if used with fast pulse counting electronics.