Pulse shape analysis of individual gamma events—Correlation to energy resolution and the possibility of its improvement

Abstract

The measurement in 2014 of the nonproportionality of each decay component in CsI:Tl found opposite slopes of the fast and tail nonproportionality curves above about 10 keV. Somewhat earlier experiments on nonproportionality and resolution versus shaping time in NaI:Tl and CsI:Tl showed that proportionality and intrinsic resolution could be improved by including the slower “tail” component of the scintillation pulse. The observed opposing nonproportionality trends of fast and tail components constitute a basis for improvement of scintillator nonproportionality if they are added in a suitable linear combination. We examine whether combining the rise and decay components pulse by pulse with an algorithm of optimized proportions may also improve energy resolution. The premise is that a scintillation pulse carries more information about the particle stopping event than is conveyed in a simple measurement of the pulse height. In this work, we measured pulse shapes of individual gamma events in CsI:Tl and other scintillators using an eMorpho multichannel analyzer as a digital oscilloscope. Decomposition of every scintillation pulse into a rise and three exponential decay components allowed us to represent the pulse height spectrum as a linear combination of them. We found that energy resolution of CsI:Tl can be altered and improved through changing the weight of decay components in the linear combination.

Energy Resolution of Scintillators in Connection With Track Structure

“…Different curves for centroids at each peak correlate with the trends of the decay curves described in Section II and with the role of fast and slow components of decay shown in [30]. In particular, a cluster with lower amplitude (blue curves) is characterized by a low value of intermediate-to-fast ratio, which corresponds to the result shown in Fig.…”

“…For more information, see https://creativecommons.org/licenses/by/4.0/ All attempts to alter the materials or modify technology to improve energy resolution, while keeping the cost low, did not bring us closer to the fundamental limit. Another possible way to achieve this goal is to try to use pulse shape information to improve energy resolution value [30]- [33]. This idea is based on the dependence of decay kinetics on the energy of created electrons and on the topology of the tracks generated in different events (see [30,Fig.…”

“…Another possible way to achieve this goal is to try to use pulse shape information to improve energy resolution value [30]- [33]. This idea is based on the dependence of decay kinetics on the energy of created electrons and on the topology of the tracks generated in different events (see [30,Fig. 7] and [33,Figs.…”

“…The simplest way to take advantage of the pulse shape analysis to improve the energy resolution is the weighting of signals obtained in some time domains (e.g., fast, intermediate, and slow, as proposed in [30] and [36]). Nevertheless, the problem of choosing weight coefficients and length of time domains has no simple solution since theoretical models can give only the illustrative estimations.…”

“…Nevertheless, the problem of choosing weight coefficients and length of time domains has no simple solution since theoretical models can give only the illustrative estimations. Even detailed multiparameter models (e.g., [30]) should be tuned for each specific scintillator. At present, each scintillation pulse can be digitized with high precision (e.g., [37], [38]), and it is promising to take advantage of such possibility.…”