# Nuclear Security Detection Workshop

15-16 April 2019
University of Surrey
Europe/London timezone

## Enhanced Resolution in Large Volume $SrI_2:Eu$ Detectors

16 Apr 2019, 12:30
15m
University of Surrey

#### University of Surrey

Guildford, UK
Oral Presentation Detectors & Systems

### Speaker

Jamie Brown (University of York)

### Description

Strontium Iodide ($SrI_2\colon Eu$) shows great promise as a high-resolution scintillator material for gamma ray detection, principally due to it’s exceptional brightness – ~120,000 photons/MeV[1], cf. 63,000 photons/MeV for $LaBr_3\colon Ce$ [2]. Resolutions <2.7% FWHM (@ 662 keV) have been reported for small (<1cm3) $SrI_2\colon Eu$ crystals [3] – comparable to $LaBr_3\colon Ce$ – and the material exhibits a number of other advantageous properties such as: high $Z_{eff}$, low internal radioactivity, suitability to grow large crystals, excellent proportionality, and an emission spectrum (435 nm peak emission) well matched to many leading silicon photomultipliers (420-450 nm, cf. 380 nm for $LaBr_3\colon Ce$). This makes $SrI_2\colon Eu$ of interest for nuclear security applications for its ability to clearly identify gamma rays over a broad range of energies, thus making it suitable for the detection and discrimination of special and naturally occurring nuclear material. However, this potential has not been realised in large volume crystals (~10 cm3). This is due to self-absorption/re-emission processes creating significant non-uniformity in light collection for interactions at different points within the crystal. Peak shifts in excess of 1% have been observed for different interaction positions [4] leading to significant degradation of the energy resolution (>2.9%). These effects can be mitigated to some extent through manipulation of the dopant concentration [5], however this leads to a compromise between brightness and light collection uniformity.

We propose an alternative method to enhance the energy resolution of large $SrI_2\colon Eu$ crystals by applying a position dependant energy correction. A full treatment of this would require 3D position determination, and should yield energy resolutions comparable to that achieved for small crystals, without compromising the light yield. In this work, we will demonstrate the principle in one dimension through experimental and simulation work, and identify the challenges in extending and generalising to two and three dimensions.

[1] E. V. van Loef, et al. (2009). Crystal Growth and Scintillation Properties of Strontium Iodide Scintillators. IEEE Transactions on Nuclear Science, 56(3), 869–872
[2] https://www.crystals.saint-gobain.com/products/brillance-labr3-lanthanum-bromide
[3] B. W. Sturm, et al. (2011). Effects of packaging $SrI_2(Eu)$ scintillator crystals. Nuclear Inst. and Methods in Physics Research, A, 652(1), 242–246
[4] B. W. Sturm, et al. (2010). Evaluation of large volume $SrI_2(Eu)$ scintillator detectors. 2010 IEEE Nuclear Science Symposium and Medical Imaging Conference (2010 NSS/MIC), 1607–1611
[5] C. M. Wilson, et al. (2008). Strontium iodide scintillators for high energy resolution gamma ray spectroscopy. Proc. SPIE, 7079, 707917.

### Primary author

Jamie Brown (University of York)

### Co-authors

Dr Stefanos Paschalis (University of York) Dr Pankaj Joshi (University of York) Prof. David Jenkins (University of York)

### Presentation Materials

 4 BROWN NuSec SrI.pdf 4 BROWN NuSec SrI.pptx