Abstract
We have developed and evaluated a new approach to fast neutron and neutron–gamma detection based on large-area multilayer composite heterogeneous detection media consisting of dispersed granules of small-crystalline scintillators contained in a transparent organic (plastic) matrix. Layers of the composite material are alternated with layers of transparent plastic scintillator material serving as light guides. The resulting detection medium—designated as ZEBRA—serves both as an active neutron converter and a detection scintillator which is designed to detect both neutrons and gamma quanta. The composite layers of the ZEBRA detector consist of small heavy-oxide scintillators in the form of granules of crystalline ZWO, BGO, GSO(Ce), and other materials. We have produced and tested the ZEBRA detector of sizes $100 \mathrm{mm} \times 100 \mathrm{mm} \times 41 \mathrm{mm}$ , and determined that they have very high efficiency of fast neutron detection (up to 49% or greater), comparable to that which can be achieved by large sized heavy-oxide single crystals of about $\varnothing 40 \times 80 \mathrm{cm}^3$ volume. We have also studied the sensitivity variation of fast neutron detection by using different types of multilayer ZEBRA detectors of 100-cm2 surface area and 41-mm thickness (with a detector weight of about 1 kg) and found it to be comparable to the sensitivity of a 3He-detector representing a total cross section of about 2000 cm2 (with a weight of detector, including its plastic moderator, of about 120 kg). The measured count rate in response to a fast neutron source of 252Cf at 2 m for the ZEBRA-GSO(Ce) detector of size $100 \mathrm{mm} \times100 \mathrm{mm} \times41 \mathrm{mm}$ was 2.84 Hz/ng of 252Cf isotope, and this count rate can be doubled by increasing the detector height (and area) up to $200 \mathrm{mm} \times100 \mathrm{mm}$ . In summary, the ZEBRA detectors represent a new type of high efficiency and low-cost large-area solid-state neutron detector that can be used for stationary neutron/gamma portals. They may represent an interesting alternative to expensive, bulky gas counters based on 3He or 10Bneutron detection technologies.
Highlights
One of the main challenges in nuclear security is the creation of detection systems for fast neutrons and mixed neutron/gamma radiation that would be highly efficient, smallsized, inexpensive, easy-to-use, rugged and robust with respect to unfavorable conditions, and reliable in operation
We developed a new approach to neutron detector design, using single crystals of heavy-oxide scintillators (CWO, ZWO, PWO, BGO, GSO(Ce), etc.) for direct detection of fast neutrons without large scale thermalization [1-8]
We developed an original heterogeneous scintillation structure, which is comprised of a series of alternating plates of two types – plates consisting of small particles of heavy crystalline scintillator material (i.e., BGO, ZWO, PWO, GSO(Ce), etc.) embedded in a plastic scintillator matrix, and plates of a clear plastic moderator material, which simultaneously serves as a light guide for output of scintillation photons
Summary
One of the main challenges in nuclear security is the creation of detection systems for fast neutrons and mixed neutron/gamma radiation that would be highly efficient, smallsized, inexpensive, easy-to-use, rugged and robust with respect to unfavorable conditions, and reliable in operation. We developed a new approach to neutron detector design, using single crystals of heavy-oxide scintillators (CWO, ZWO, PWO, BGO, GSO(Ce), etc.) for direct detection of fast neutrons without large scale thermalization [1-8]. This allowed us to realize increased fast neutron detection efficiencies of up to 50-70%. Our further studies have shown the possibility to create a comparably efficient detector of fast neutrons on the basis of a novel composite scintillation structure, again relying on direct detection of fast neutrons through their interaction with materials of high effective atomic number. The detection of fast neutrons simultaneously over several channels of their interaction substantially increases total detection efficiency
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