The CLYC-6 and CLYC-7 response to γ-rays, fast and thermal neutrons
Introduction
In the last 15 years, the search for high performing scintillators produced several new materials [1]. In particular, Lanthanum Halide [2], [3], [4], [5], [6], [7], [8], Elpasolite [9], [10], [11], [12], [13], [14], [15], [16], [17], SrI2:Eu [1], [18], CeBr3 [1], [19], [20] and Ceramic scintillators [1], [21] show better performances than those of the very well-known NaI:Tl, CsI:Tl, BGO or BaF2 scintillators.
A promising class of scintillators are the Elpasolite, discovered about 10 years ago. The Cs2LiYCl6:Ce (CLYC), Cs2LiLaCl6:Ce (CLLC) and Cs2LiLaCl6:Ce (CLLB) scintillators belong to this class. They are characterized by a good energy and time resolution, high linearity, especially at low energy. In particular, the CLYC scintillators are characterized by a light yield of ~20 ph/keV, a density of 3.3 g/cm3 and an energy resolution of less than 5% at 662 keV. They can identify and measure γ rays and neutrons at the same time via pulse shape discrimination (PSD) [9], [10], [11], [12], [13], [14], [15], [16], [17], [22], [23], [24], [25], [26], [27].
The sensitivity to thermal neutrons is given by the well known reaction 6Li+n=3H+α which has a cross-section of 940 barns [9], [10], [11], [12]. The emitted tritium (3H) and the α particles deposit approximately 3.2 MeVee (MeV electron equivalent). The sensitivity of CLYC to fast neutrons, instead, was found to be given by the reactions on 35Cl (35Cl+n=35S+p and 35Cl+n=32P+α), which have cross-sections of the order of 100–300 mb [13], [14], [15], [16], [22], [23], [24]. In addition, the energy of the outgoing proton and α particle scales linearly with the kinetic energy of the incident fast neutron [13], [15], [24]. Therefore, the energy of the incident neutron can be directly deduced from the pulse generated by the detector. This unique capability makes CLYC a very promising scintillator for both γ and neutron spectrocopy in base research and application.
Since the capability of CLYC to detect thermal neutrons is provided by 6Li, the selection of 6Li or 7Li enrichment allows to control the sensitivity of a CLYC scintillator to thermal neutrons. In particular, an enrichment in 6Li (CLYC-6) increases the sensitivity to thermal neutrons while an enrichment in 7Li (CLYC-7) suppresses the sensitivity to thermal neutrons allowing a better detection of fast neutrons.
It has been shown that the CLYC emission light spectrum is characterized by fast and slow components [16]. The fast component is predominantly induced by γ-rays and it is in the UV part of the spectrum (approximately 220–320 nm). It is generally associated to the CVL (Core to Valence Luminescence) scintillation light which could be partially or totally reabsorbed and re-emitted by Ce dopant. It has been shown [16] that the intensity of CVL is suppressed as temperature increases. However the PSD effectiveness in n–γ identification is not reduced. The medium and slow components of the scintillation light are located in the blue region of the light spectrum (approximately 350–500 nm) and it was shown that they are present in both γ-rays and neutrons induced signals [13], [14], [15], [16], [17].
There are in literature several studies on the properties of 6Li enriched detectors (see for example Refs. [9], [10], [11], [12], [13], [14], [15], [16], [17]). However there are few works on i) 7Li enriched crystals (almost insensitive to thermal neutrons but good for neutron spectroscopy) [15], ii) the measurement of CLYC internal radiation [9] and iii) the effects in CLYC performances with timing PMT or a quartz window PMT. In the first part of this work (Section 2) we present the general properties of the used CLYC-6 (enriched at 95% of 6Li, as reported in RMD datasheets) and CLYC-7 (with an enrichment of 7Li larger than 99%, as reported in RMD datasheets) scintillators [25]. Both detectors show the typical energy resolution already measured in Refs. [9], [10], [11], [12], [13], [14] but slightly better than the one reported in [15]. Section 2.2 discusses the measurement of internal radiation in a CLYC-6 crystal showing that it is at least 50 times smaller than that measured in Ref. [5] for a LaBr3:Ce of equal size. In the successive Section 2.3 the neutron-γ discrimination is discussed. We have focused our attention also on the consequences in the CLYC performances if the UV component of the scintillation light is fully collected (using a quartz window PMT) or if the extremely fast risetime of the scintillation light (in case of γ-rays) is preserved in the measurement by using a timing-fast PMT. In fact, the majority of the published works use a borosilicate window – spectroscopic PMT (usually Hamamatsu 6231-100/6233-100 as for example in Ref. [14], [15]). The thermal/fast neutron identification of CLYC-6 and CLYC-7 is described in Section 3. Section 3.1 focuses on thermal neutrons detection pointing out the differences between CLYC-6 and CLYC-7, while Section 3.2 describes the fast neutron detections at 14.1 and 2.5 MeV. The conclusions of the work are described in Section 4.
Section snippets
CLYC properties
Two crystals were used in this work: a CLYC enriched at 95% of 6Li (CLYC-6) and a CLYC with an enrichment of 7Li larger than 99% (CLYC-7). Both crystals were produced by RMD and have a cylindrical shape, a diameter of 1″ and a thickness of 1″. For these measurements the CLYC-6 and CLYC-7 scintillators were coupled to HAMAMATSU R6231-100mod PMTs and to standard voltage dividers (HAMAMATSU E1198-26 and HAMAMATSU E1198-27 for CLYC-6 and CLYC-7, respectively).
Neutron identification
For the following measurements, the CLYC-6 and CLYC-7 scintillators were used. They were coupled to HAMAMATSU R6231-100mod PMTs and to standard voltage dividers (HAMAMATSU E1198-26 and HAMAMATSU E1198-27 for CLYC-6 and CLYC-7, respectively). Data were taken with a 12 bit LeCroy Wave Runner oscilloscope (HDO ZI66).
Conclusions
In this work, we presented the results from the investigation of the performances of two 1″×1″ samples of CLYC scintillator: one enriched with 95% of 6Li (CLYC-6) and the other with an enrichment of 7Li larger than 99% (CLYC-7). The CLYC scintillators exhibit good energy resolution under γ-ray excitation. We measured 4.8% and 4.5% at 662 keV for CLYC-6 and CLYC-7, respectively. An important property of these scintillators is the capability to identify and measure γ rays and neutrons via pulse
Acknowledgments
This work was supported by NuPNET - ERA-NET within the NuPNET GANAS Project, under grant agreement No. 202914 and from the European Union, within the “7th Framework Program” FP7/2007-2013, under grant agreement No. 262010 – ENSAR-INDESYS. This work was also supported by “Programmi di Ricerca Scientifica di Rilevante Interesse Nazionale” (PRIN) No. 2001024324_01302.
References (29)
J. Lumin.
(1999)Nucl. Instrum. Method A
(2007)Nucl. Instrum. Method A
(2013)Nucl. Instrum. Method A
(2015)Nucl. Instrum. Method
(2009)J. Cryst. Growth
(2013)Nucl. Instrum. Method
(2015)- et al.
Nucl. Instrum. Method
(2015) Radiat. Meas.
(2014)Nucl. Instrum. Method A
(2013)
Nucl. Instrum. Method A
Nucl. Instrum. Method
Nucl. Instrum. Method
J. Nucl. Mater.
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