Scintillation neutron detectors based on solid-state photomultipliers and lightguides
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RACTION AND SCATTERING OF NEUTRONS
Scintillation Neutron Detectors Based on Solid-State Photomultipliers and Lightguides V. S. Litvin, V. N. Marin, S. K. Karaevsky, D. N. Trunov, S. N. Axenov, A. A. Stolyarov, and R. A. Sadykov Institute for Nuclear Research, Russian Academy of Sciences, pr. Shestidesyatiletiya Oktyabrya 7a, Moscow, 117312 Russia e-mail: [email protected] Received March 6, 2015
Abstract—Neutron detectors based on scintillation screens ZnS(Ag)/LiF and solid-state photomultipliers have been developed. Lightguides are used to collect light. The application of a coincidence scheme provides a low dark count and a neutron detection efficiency as high as 70%. A scheme of x‒y neutron detector based on wavelength shifting fibers is also proposed. Tests of the proposed versions of detectors in a neutron beam have shown their efficiency. DOI: 10.1134/S1063774516010090
INTRODUCTION The most widespread neutron detectors are proportional counters filled with 3He. Recently, in view of the deficit of helium isotope and its high cost, alternative versions (basically scintillation) have been actively sought [1]. A ZnS/LiF scintillator is of special interest due to its high specific light yield (about 1.6 × 105 photons/neutron), low sensitivity to γ rays, and relatively low cost. However, energy is partially lost in LiF; in addition, the fine-grained structure of this material facilitates light scattering. Therefore, the real average specific light yield of these scintillators does not exceed 10 4 photons [2]. Photoelectron multipliers (PMs) or microchannel amplifiers are used to record light pulses. Light from the scintillator output is recorded either directly through the PM optical contact or using different lightguides or wavelength shifting fibers glued to the scintillator [3, 4]. The latter scheme also makes it possible to design one- and twocoordinate detectors. Since the efficiency of capturing light and its subsequent reemission by a wavelength shifting fiber is about 5%, the obtained signal amplitudes are at a level of few photoelectrons. Therefore, one must use low-noise PMs to record signals. The complicated fabrication technology, high cost, and large sizes of these devices stimulate the search for detectors of other types with compact and inexpensive photodetectors. Recently, commercial photodetectors of a new type―multipixel avalanche photodiodes (APDs) or silicon photomultipliers (SiPMs)―have been developed in Russia [5, 6]. Compactness, high (∼106) gain, high (20–50%) quantum efficiency, and relatively low production cost make these devices an attractive alter-
native to expensive and cumbersome PMs. At the same time, the small sensitive area of photodiodes calls for developing special methods of light collection from large scintillators. Today, several different approaches to the use of SiPMs in scintillation detectors of thermal neutrons have been developed. Neutron detectors based on LiI(Eu) and ZnS(Ag)/LiF scintillators were investigated in [7]; in these devices, SiPMs record light either directly
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