Energy Resolution Of Scintillators Research Articles

Simulation study on position resolution of plastic scintillator strips for cosmic muon imaging

In applications of transmission muography for large objects, plastic scintillator strips with triangular or rectangular cross-sections are frequently selected to construct imaging detectors. Triangular scintillator strips have a better position resolution over those of rectangular ones by a factor of ∼ 3.5 with the same width. The big difference has been carefully studied using Geant4. Simulations show a good agreement with those of existing muography instruments. The position resolution is influenced by the geometry (the size and base angle of triangular strips) and the energy resolution of scintillators, and angles of incoming muons. Two empirical formulas have been proposed to quantitatively estimate the position resolution with respect to the abovementioned influential factors. Perpendicularly and randomly (real angular distribution) incoming muons are considered separately in them. A more widely spread angular distribution of muons can make the position resolution worse. For commonly used triangular scintillator strips with a base angle of 45∘, the ratio of the triangle base length to the position resolution is almost fixed to ∼ 12 varying the base length or energy resolution if an uncorrected Centre of Gravity (CoG) method is used. Such a ratio has a potential to be increased by a factor of ∼ 2 if the CoG method is corrected with the muon incoming angle. The influence of the energy resolution on the position resolution can be ignored.

Utilization of YAP:Ce powder scintillator for 57Fe Mössbauer spectroscopy

Using a powder scintillator for a detection of gamma and X-rays allows to create detectors of various shapes, moreover the handling and fabrication of such scintillators is much easier than in the case of large or thin monocrystals. We report on the application of YAlO3:Ce powder to Mössbauer spectroscopy. The detection efficiency and the energy resolution of the scintillators made of powders of two different granularities (grain size ≤30μm and 50–70μm) were investigated. The powder scintillators exhibited a comparable energy resolution and detection efficiency as YAlO3:Ce monocrystal with thickness of 400μm. Burying the YAlO3:Ce grains into the epoxy resin increased the energy resolution of powder scintillators. The studied scintillators were found to be suitable for experiments in Mössbauer spectroscopy. The performance of YAP is also compared to the NaI:Tl scintillator.

Energy Resolution of Scintillators in Connection With Track Structure

The large spread of scintillator performance (light yield and energy resolution) from a theoretical limit shows that we are still far from the deep understanding of the phenomena. Usually, extrinsic aspects of resolution degradation (such as purity, defects, stoichiometry, and so on) are the subject of study. At the same time, intrinsic factors (such as track structure, excitation density, and uniformity) that depend on crystal lattice can play a dominant role in scintillator performance. Some progress in the understanding of these problems is achieved by using the concept of different efficiencies of photon emission from excited regions with different concentrations of electronic excitations. The regions with a high or low concentration of thermalized excitations result in the nonradiative losses of excitations and, therefore, produce additional event-to-event fluctuations. The technique of multidimensional analysis of the time-resolved pulse shape is proposed for the clustering of all the events according to the proximity of the waveform to some centroids of the clusters. This procedure shows that even conventional NaI:Tl and CsI:Tl scintillators allow to achieve an energy resolution of about 3% for 662-keV gamma photons.

Scintillator energy resolution and a way to improve it by kinetic waveform analysis

The energy resolution of scintillators is examined in view of the distribution of excitation density in the track region, quenching of emission in regions with high concentration of excitations, and appearance of delayed photons from the regions with low concentrations of excitations. The way to improve energy resolution based on weighting of signals from different decay intervals is discussed.

Light yield nonproportionality, intrinsic resolution and α/γ ratio of oxide single crystal scintillators

In this work, we investigate α-particle response of oxide single crystal scintillators and related to the nonproportionality of light yield (LY) and intrinsic energy resolution under excitation with γ rays. The LY and energy resolution measurements are performed at 32, 59.5 and 662 keV γ rays and 5.5 MeV α particles. The α/γ ratio for Lu3Al5O12:Pr and Y3Al5O12:Pr with different Pr3+ concentrations and for (Gd,Y)3Al2Ga3O12:Ce and (Lu,Gd)2SiO5:Ce with different host compositions are also determined. The scintillators with high α/γ ratio show good proportionality of LY down to 32 keV γ rays. The correlation between α/γ ratio and intrinsic energy resolution measured with 32, 59.5 and 662 keV γ rays is obtained. Therefore, the nonproportional response and intrinsic energy resolution of scintillators could be characterized using α/γ ratio.

An EDUGATE simulation toolkit based on the educational easyPET

EasyPET is a new concept of a Positron Emission Tomography (PET) scanner using an innovative acquisition method based on two rotation axes for the movement of detector pairs. Due to its simplicity, it is suitable for education purposes, to teach students about the PET technology and its basic concepts, from the radiation detecting and analogue pulse analysis to the coincidence sorting and image reconstruction. The concept allows achieving high and uniform position resolution over the whole field of view (FoV), by eliminating parallax errors due to the depth of interaction (DoI), which are typical of ring-based PET systems, so quality images are obtained even without state-of-the-art image reconstruction algorithms. The technology developed at the University of Aveiro with a patent-pending, is licensed to CAEN S.p.A, and included in the educational catalogue of the company. In this work, a simulation toolkit based in the Edugate platform was developed to simulate the EasyPET system. It can simulate all the physical aspects of the product, such us the scanning range, variable Field-of-View (FOV), scintillator energy resolution, coincidence time and energy window, among others. A simple image reconstruction algorithm based on Filtered-back-projection (FBP) is implemented. The toolkit allows a quick analysis in classroom of the simulation results. The platform was also used to study the new EasyPET 3D version, and a simulation of a NEMA NU 4-2008 IQ phantom was performed, demonstrating the capability of the platform not only for education purposes but also for research. Patent Universidade de Aveiro: PCT/IB2016/051487.

Fluctuations of ionizing particle track structure and energy resolution of scintillators

Fluctuations of ionizing particle track structure and energy resolution of scintillators

Intrinsic radioactivity of KSr2I5:Eu2+

A current need in nuclear security is an economical, yet high energy resolution (near 2%), scintillation detector suitable for gamma-ray spectroscopy. For current scintillators on the market, there is an inverse relationship between scintillator energy resolution and cost of production. A new promising scintillator, KSr2I5:Eu2+, under development at the University of Tennessee, has achieved an energy resolution of 2.4% at 662keV at room temperature, with potential growth rates exceeding several millimeters per hour. However, the internal background due to the 40K content could present a hurdle for effective source detection/identification in nuclear security applications. As a first step in addressing this question, this paper reports on a computational investigation of the intrinsic differential pulse height spectrum (DPHS) generated by 40K within the KSr2I5:Eu2+ scintillator as a function of crystal geometry. It was found that the DPHS remains relatively equal to a constant multiplicative factor of the negatron emission spectrum with a direct increase of the 1.46MeV photopeak relative height to the negatron spectrum with volume. Further, peak pileup does not readily manifest itself for practical KSr2I5:Eu2+ volumes.

Role of excitons in the energy resolution of scintillators used for medical imaging

Theoretical investigations suggest that the nonproportionality in a scintillator is caused by the high excitation density created within the track of an X-ray or γ ray photon entering in a scintillating crystal. In this paper an analytical expression for the scintillator yield is derived. For the case of BaF2 scintillator the role of excitons created within the γ-ray track in the scintillator yield is studied. By comparing the results of two theories an analytical expression is also derived for an energy parameter which could otherwise only be determined by fitting the theoretical yield to the experimental data.

Energy Resolution of Compton Electrons in LaBr$_{3}$:Ce Scintillator

A method based on the Compton coincidence technique was applied to study the energy resolution of Compton electrons in wide energy range. The experimental setup was comprised of a High Purity Germanium (HPGe) detector and a LaBr3:Ce scintillator coupled to a photomultiplier. The detectors were set in a face-to-face geometry and the source was placed between them. Thus gating on events backscattered in the scintillator and detected in HPGe allowed one to measure the energy resolution of Compton scattered electrons at an energy corresponding to the Compton edge for a given source. This study confirms the importance of the electron scattering (6-rays) as the main component of the intrinsic resolution in scintillators. The results are particularly important for discussion of the light yield non-proportionality contribution to the energy resolution of scintillators.

Photocathode non-uniformity contribution to the energy resolution of scintillators

This paper introduces the basics of the light transport simulation in scintillators and the wavelength-dependencies in the process. The non-uniformity measurement of the photocathode surface is undertaken, showing that for the photocathode used in this study the quantum efficiency falls to about 4 % of its maximum value, especially in areas far from the centre. The wavelength- and position-dependent quantum efficiency is implemented in the Monte Carlo light transport code, showing that, the contribution of the photocathode non-uniformity to the energy resolution is estimated to be around 18 %, when all position- and wavelength-dependencies are included.

Scintillator Non-Proportionality: Present Understanding and Future Challenges

Scintillator non-proportionality (the fact that the conversion factor between the energy deposited in a scintillator and the number of visible photons produced is not constant) has been studied both experimentally and theoretically for ~50 years. Early research centered on the dependence of the conversion factor on the species of the ionizing radiation (gamma, alpha, beta, proton, etc.), and researchers during the 1960s discovered a strong correlation between the scintillation efficiency and the ionization density. In more recent years, non-proportionality has been proposed as the reason why the energy resolution of most scintillators is worse than that predicted by counting statistics. While much progress has been made, there are still major gaps in our understanding of both the fundamental causes of non-proportionality and their quantitative link to scintillator energy resolution. This paper summarizes the present state of knowledge on the nature of the light-yield non-proportionality and its effect on energy resolution.

Intrinsic energy resolution and light output of the Lu0.7Y0.3AP:Ce scintillator

Abstract Light output and energy resolution for a 2×2×10 mm 3 LuYAP:Ce crystal coupled to a XP2020Q photomultiplier were studied. The measured light output of 8530 photons/MeV includes the correction for the quantum efficiency of the XP2020Q photomultiplier. An energy resolution of 7.33% was obtained for 662 keV γ -rays with a long face coupled to the PMT. The measured number of 2130 phe / MeV implies a photoelectron statistical contribution of 6.59% and hence a LuYAP intrinsic energy resolution of 3.21%. The relative light output of the LuYAP scintillator measured for photon energies varying from 31 keV to 1.333 MeV was constant within 7%. These observations are consistent with results for the YAP:Ce scintillator, and with the assumption that there is a direct correlation between the energy resolution of scintillators and non-proportionality of their light output versus energy in the low-energy domain. The results are compared to the relative light output of the LSO:Ce scintillator measured for varying energies.

Statistical studies on the light output and energy resolution of small LSO single crystals with different surface treatments combined with various reflector materials

The optimization of light output and energy resolution of scintillators is of special interest for the development of high resolution and high sensitivity PET. The aim of this work is to obtain statistically reliable results concerning optimal surface treatment of scintillation crystals and the selection of reflector material. For this purpose, raw, mechanically polished and etched LSO crystals (size 2×2×10 mm 3) were combined with various reflector materials (Teflon tape, Teflon matrix, BaSO 4) and exposed to a 22Na source. In order to ensure the statistical reliability of the results, groups of 10 LSO crystals each were measured for all combinations of surface treatment and reflector material. Using no reflector material the light output increased up to 551±35% by mechanical polishing the surface compared to 100±5% for raw crystals. Etching the surface increased the light output to 441±29%. The untreated crystals had an energy resolution of 24.6±4.0%. By mechanical polishing the surface it was possible to achieve an energy resolution of 13.2±0.8%, by etching of 14.8±0.7%. In combination with BaSO 4 as reflector material the maximum increase of light output has been established to 932±57% for mechanically polished and 895±61% for etched crystals. The combination with BaSO 4 also caused the best improvement of the energy resolution up to 11.6±0.2% for mechanically polished and 12.2±0.3% for etched crystals. Relating to the light output there was no significant statistical difference between the two surface treatments in combination with BaSO 4. In contrast to this, the statistical results of the energy resolution have shown the combination of mechanical polishing and BaSO 4 as the optimum.

A high-energy resolution observed from a YAP : Ce scintillator

An energy resolution of 4.38±0.11% was obtained for 662 keV γ-rays with a 3×3×20 mm 3 YAP : Ce crystal with its long face coupled to an XP2020Q photomultiplier. The measured number of photoelectrons of 5290±80 phe/MeV implies a photoelectron statistical contribution of 4.18±0.04% and hence a YAP intrinsic energy resolution of 1.3±0.5%, the lowest value ever observed for scintillators. The relative light output of the YAP crystal measured for energies between 14.4 keV and 1.275 MeV was constant within ±2%. These observations are consistent with the assumption that there is a direct correlation between the energy resolution of scintillators and nonproportionality of their light output versus energy.

The light yield nonproportionality component of scintillator energy resolution

The scintillator energy resolution component which is due to light yield nonproportionality has been characterized for NaI(Tl) and LSO. Results are based on a discrete convolution of measured electron response data and the electron energy distribution resulting from full-energy absorption events. The behavior of this energy resolution component as a function of energy is observed to be strongly dependent on the shape of the electron response. Furthermore, in some energy regions, the light yield nonproportionality component is observed to be larger than the resolution predicted by assuming Poisson photoelectron statistics. Characterization of this energy resolution component will facilitate deconvolution of other components from the total energy resolution.

Lithium loaded glass detectors for tritium breeding measurements

Abstract A technique based on the response differences of enriched 6 Li and 7 Li glass scintillators has been developed for the real time measurement of the tritium production rate from the 6 Li isotope in an experimental breeder blanket of a D—T fusion reactor. The effectiveness of the method is dependent on the degree to which the scintillation responses of two glasses can be matched for all interactions arising from the neutron and gamma fields within the assembly. However, the energy resolution of the scintillation pulses contains a component that is dependent on the composition of the glass which cannot be compensated for either electronically or analytically. The glasses used must therefore be carefully selected to ensure that the difference between their intrinsic scintillation resolutions is minimal. This paper describes measurements of the scintillation energy resolution for a range of commercially available glasses as a function of energy for electrons, protons, deuterons, and alpha particles. The results showed that systematic errors in the measurement of tritium breeding from 6 Li, using the proposed technique, are minimized if the glasses of different lithium enrichment have the same chemical composition. Analysis of the results indicated that for optimum accuracy the total lithium content of the glasses should be small (about 2%).

Optimizing the energy resolution of scintillation counters at high energies

The influence of the position dependent light collection within scintillator assemblies on the pulse height resolution is demonstrated by means of Monte-Carlo simulation of the light transport for different sizes of the scintillator. The dependence on the reflectivity of diffuse reflecting boundary surfaces as the most important optical parameter is discussed. For cylindrical scintillators, partially-coated light guides are recommended to minimize the locus-dependent variation of the light collection. The high energy limit of experimentally determined resolution functions proved the theoretical results.

Improvement of scanner performance by subtraction of Compton scattering using multiple energy windows.

In many radiological imaging situations photon scattering leads to degradation of image quality. Energy discrimination can substantially reduce the effects of scatter in radiosotope imaging. However, with low energy isotopes such as 99TCm the limited energy resolution of scintillators allows only imperfect discrimination against scattered photons. With only a single energy channel available in a rectilinear scanner or gamma camera, a choice must be made between (a) the use of a high base-line energy, resulting in reduced sensitivity because of rejection of unscattered photons, or (b) a low base-line settng to maximize the countrate at the expense of image contrast and resolution. Sanders et al. (1969), and Beck and Harper (1966), have examined the effects of energy selection to establish the optimum window setting for 99Tcm brain scanning. Rollo and Schulz (1971), and Sanders et al. (1972), extended this work to include an assessment of the detectability of lesions by observe-performance measurements. The...