Tests of a solution-grown stilbene scintillator in mono-energetic neutron beams of 565 keV and 5 MeV
Introduction
The development of detectors capable of measuring the continuous-energy neutron spectrum in the intermediate-to-fast range (5 keV to 15 MeV) is of interest in numerous applications. Accurate neutron spectrum measurements in the intermediate range (5 keV to 600 keV) in mixed neutron–gamma-rays are notoriously difficult. The present work is motivated by the development of a fast neutron spectrometer for the MASURCA critical facility [1], [2], but it is also relevant to applications such as steady-state and pulsed neutron beam characterization, prompt and delayed fission neutrons in nuclear physics, fission and fusion reactors, in-core and out-of-core (neutron leakage) spectra in low-flux critical experiments, transmission and shielding benchmarks, neutron-induced material irradiations, detector calibration, neutron radiography, nuclear safeguards, etc. Among the aforementioned, measurements of the prompt fission neutron spectrum away from the 1 MeV peak have received considerable attention in recent years, since such data have major repercussion on fission models and applications [3], [4], [5], [6], [7].
The specific needs are for detectors having a reasonably good energy resolution (<10%) so as to distinguish broad peaks and valleys in the spectra, a small size for good spatial resolution (less than 50 mm), sufficient sensitivity and high efficiency so as to operate in low flux levels, able to discriminate neutrons from gamma-rays, reliable without requiring frequent calibrations or complicated correction factors, easy to handle and operate. Such neutron detectors would nicely complement classical low-resolution techniques, which rely on small foil activation and ionization chamber measurements, in combination with calculations, to infer detailed neutron energy distributions.
Organic scintillators are good candidates for such a purpose, being easy to set up and use, and representing a good compromise between detection efficiency, energy resolution and discrimination capability. Liquid scintillators, such as BC501A, are generally considered reference detectors for neutron spectrometry in mixed radiations fields [8], but alternatives exist, in particular solid scintillators based on a plastic matrix or on stilbene crystals [9], [10], [11]. Among the latter, melt-grown-type stilbene single crystals have been used for measuring the outgoing neutron and gamma fields in transmission experiments [12], and for in-core and out-of-core neutron spectrum characterization in low-flux research reactors [13], [14]. The possibility of employing a single type of detector to form a spectrometric system covering a wide energy domain is an attractive feature of stilbene. In [15], it is stated that a set of stilbene crystals (with sizes varying from 20 mm 10 mm to 40 mm 40 mm) could be used for covering the neutron energy range between 0.4 and 20 MeV, and in [12] a similar set is used together with a lead cover for the 0.1–16 MeV energy domain.
Fairly recently, a promising new type of stilbene crystals has been produced by a different technique: solution-grown stilbene [16], [17]. Thanks to a more homogeneous structure, these crystals are expected to deliver an even greater light output and higher PSD FoM (Pulse Shape Discrimination Figure of Merit: 30%–40%) than liquid and classical melt-grown stilbene. However, possible limitations could arise from the anisotropy of their response [18], [19], [20], [21].
In this paper, the results of tests performed with a 25 mm solution-grown stilbene detector at reference mono-energetic neutron fields are reported. The aim of these tests was to assess the properties of this novel crystal scintillator compared to those of a well-known BC501A liquid scintillator.
Section snippets
Description of the experiment
The test measurements were performed at the AIFIRA facility situated at CENBG near Bordeaux [22]. The AIFIRA accelerator is a 3.5 MV Singletron from the HVEE Company. Different ion beams can be produced: 1H, 2H and 4He. The “physics beamline” placed at the −45° exit of the switching magnet was used for the experiments. To produce the 565 keV and 5 MeV neutron fields, a 2295 keV proton beam and a 1791 keV deuteron beam of about 1 A, were sent onto a 45 g/cm2 thick LIF target and a 200 g/cm2
Energy calibration
Small gamma-rays sources (Cs, Na and Bi) as well as a Cf neutron source were used for calibrating and setting-up the time thresholds for Pulse Shape Discrimination of the two scintillators at every irradiation. The dependence between the channel number (X) and the electron equivalent energy (Y in MeV) was taken to be linear: For the stilbene detector, the linearity was verified for the different gains used at 5 MeV and 565 keV, and is shown in Fig. 2. The focus was on
Results of the measurements at 5 MeV
The Stilbene and BC501A organic scintillators were both used at the 5 MeV neutron field. The Pulse Shape Discrimination capability, the Pulse Height Spectrum (PHS) and the anisotropy of the response were studied.
Results of the measurements at 565 keV
Organic scintillators, like BC501A, are routinely used for characterizing neutron spectra in mixed radiation fields above about 1 MeV [8]. At lower energies, other detectors are used, e.g. recoil proton proportional counters filled with gas containing hydrogen [28], [29] or lithium glass detectors [4]. Therefore, for comparison and validation purposes, the measurement at 565 keV was also performed with the SP2 proportional counter (Fig. 8 (b)).
The experimental results are summarized in Fig. 7,
Conclusion
The response of a 25 mm solution-grown stilbene crystal has been investigated in two mono-energetic neutron fields (565 keV and 5 MeV) and compared with that of a BC501A liquid scintillator.
The results show an overall better discrimination capability of the crystal scintillator, with a FoM 35% higher at 5 MeV. PSD was also possible at 565 keV, implying that solution-grown stilbene detectors should be of interest to many applications.
The measurements show that the stilbene crystal response is
Acknowledgments
The authors would like to thank the AIFIRA staff, particularly Dr. S. Sorieul for her efficient assistance during all the measurements; the CENBG ACEN group; the Laboratoire d’études de Physique (CEA/DEN/CAD/DER/SPRC/LEPh) and the Laboratoire de Mesures Nucléaires (CEA/DEN/CAD/DTN/SMTA/LMN).
This work has been carried out thanks to the support of the A*MIDEX grant (no ANR-11-IDEX-0001-02) funded by the French Government “Investissements d’Avenir” program and to the support of the SPECTRAL
References (29)
- L. Dioni, R. Jacqmin, B. Stout, M. Sumini, PHYSOR 2016: Unifying Theory and Experiments in the 21st...
- L. Dioni, R. Jacqmin, B. Stout, M. Sumini, International Conference on Nuclear Data for Science and Technology,...
- J. Taieb, T. Granier, T. Ethvignot, M. Devlin, R.C. Haight, R.O. Nelson, J.M. O’Donnell, D. Rochman, International...
- et al.
Nucl. Instrum. Methods Phys. Res. A
(2013) - et al.
Nucl. Data Sheets
(2014) - Robert Haight, Matthew Devlin, Luca Zanini, John O’Donnell, Ani Aprahamian, Juerg Saladin, Online report....
- A. Chatillon, G. Belier, Th. Granier, B. Laurent, J. Taıeb, M. Devlin, R.C. Haight, S. Noda, R.O. Nelson, J.M....
Radiat. Prot. Dosim.
(2003)- et al.
Rev. Sci. Instrum.
(1960) - et al.
Nucl. Instrum. Methods Phys. Res. A
(2015)
Nucl. Instrum. Methods Phys. Res. A
Nucl. Instrum. Methods Phys. Res. A
Appl. Radiat. Isot.
Ann. Nucl. Energy
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