Neutron detection
Further, the hardware setup also defines key experimental parameters, such as source-detector distance, solid angle and detector shielding.
[13][14] Scintillating fiber was demonstrated by Atkinson M. et al. in 1987[15] and major advances were made in the late 1980s and early 1990s at Pacific Northwest National Laboratory where it was developed as a classified technology.
The fibers ends are optically coupled to a pair of photomultiplier tubes (PMTs) to detect photon bursts.
The scintillating fiber detectors have excellent sensitivity, they are rugged, and have fast timing (~60 ns) so that a large dynamic range in counting rates is possible.
Europium doped LiCaAlF6 has the advantage over other materials that the number of optical photons produced per neutron capture is around 30.000 which is 5 times higher than for example in neutron-sensitive scintillating glass fibers.
The maximum intrinsic efficiency for single-coated devices is approximately 5% for thermal neutrons (0.0259 eV), and the design and operation are thoroughly described in the literature.
Reaction products originating at distances further from the film/semiconductor interface can not reach the semiconductor surface, and consequently will not contribute to neutron detection.
Devices coated with natural Gd have also been explored, mainly because of its large thermal neutron microscopic cross section of 49,000 barns.
[37][38] However, the Gd(n,γ) reaction products of interest are mainly low energy conversion electrons, mostly grouped around 70 keV.
[39] Overall, devices coated with either 10B or 6LiF are preferred mainly because the energetic charged-particle reaction products are much easier to discriminate from background radiations.
The low efficiency of coated planar diodes led to the development of microstructured semiconductor neutron detectors (MSND).
These detectors have microscopic structures etched into a semiconductor substrate, subsequently formed into a pin style diode.
BP and Bas can decompose into undesirable crystal structures (cubic to icosahedral form) unless synthesized under high pressure.
BN can be formed as either simple hexagonal, cubic (zincblende) or wurtzite crystals, depending on the growth temperature, and it is usually grown by thin film methods.
Thin film chemical vapor deposition methods are usually employed to produce BP, BAs, BN, or B4C.
The Nowotny–Juza compound LiZnAs has been demonstrated as a neutron detector;[58] however, the material is difficult and expensive to synthesize, and only small semiconductor crystals have been reported.
Finally, traditional semiconductor materials with neutron reactive dopants have been investigated, namely, Si(Li) detectors.
However, the dopant concentration is relatively low in Li drifted Si detectors (or other doped semiconductors), typically less than 1019 cm−3.
With adequate energy resolution, pulse height discrimination can be used to separate the prompt gamma-ray emissions from neutron interactions.
In other words, the majority of events add to the Compton continuum rather than to the full energy peak, thus, making discrimination between neutrons and background gamma rays difficult.
A directional fast-neutron detector has been developed using multiple proton recoils in separated planes of plastic scintillator material.
The same experiment is performed today with more sophisticated equipment to obtain more definite results related to the original EMC effect.
The main components of background noise in neutron detection are high-energy photons, which aren't easily eliminated by physical barriers.
The other sources of noise, such as alpha and beta particles, can be eliminated by various shielding materials, such as lead, plastic, thermo-coal, etc.
In this setup, the incoming particles, comprising neutrons and photons, strike the neutron detector; this is typically a scintillation detector consisting of scintillating material, a waveguide, and a photomultiplier tube (PMT), and will be connected to a data acquisition (DAQ) system to register detection details.
If the tail size extracted is a fixed proportion of the total pulse, then there will be two lines on the plot, having different slopes.
The effectiveness of any detection analysis can be seen by its ability to accurately count and separate the number of neutrons and photons striking the detector.
If clear plots can be obtained in the above steps, allowing for easy neutron-photon separation, the detection can be termed effective and the rates manageable.
If the rates are so high that one event cannot be distinguished from another, physical experimental parameters (shielding, detector-target distance, solid-angle, etc.)
Scintillation detectors were invented in 1903 by Crookes but were not very efficient until the PMT (photomultiplier tube) was developed by Curran and Baker in 1944.
