Advanced Multilayer Composite Heavy-Oxide Scintillator Detectors for High-Efficiency Fast Neutron Detection

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 mm × 100 mm × 41 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 Ø40 × 80 cm
³
volume. We have also studied the sensitivity variation of fast neutron detection by using different types of multilayer ZEBRA detectors of 100-cm
²
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
³
He-detector representing a total cross section of about 2000 cm
²
(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
²⁵²
Cf at 2 m for the ZEBRA-GSO(Ce) detector of size 100 mm × 100 mm × 41 mm was 2.84 Hz/ng of
²⁵²
Cf isotope, and this count rate can be doubled by increasing the detector height (and area) up to 200 mm × 100 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
³
He or
¹⁰
Bneutron detection technologies.