Neutron detection with scintillators

The activation [672] of Lil with Eu2+ and the use of an activated Lil phosphor as a scintillation detector for slow neutron detection [673] has been investigated. Blue, fluorescent Lil (0.03 mole % Eu) phosphor was found to be the most useful [673] phosphor because of its ease to growth, relatively high light output, chemical stability and good match with spectral characteristics of the 6260 type photomultiplier. Lil (Eu), however, does have an interfering y radiation sensitivity. Fast neutron scintillation spectra of Li6(w, a)H3 in Eu doped Lil crystals has also been investigated [674]. 

Many types of plastic scintillators are commercially available and find applications in fast timing, charged particle or neutron detection, as well as in cases where the rugged nature of the plastic (compared to Nal), or very large detector sizes, are appropriate. Sub-nanosecond rise times are achieved with plastic detectors coupled to fast photomultiplier tubes, and these assemblies are ideal for fast timing work. 

During the past two decades, there have been extensive investigations on the use of inorganic nanocrystals in scintillation detectors. Brown and coworkers present a survey of representative organic nanoparticles and inorganic nanocrystals embedded in various matrices, along with their performances in beta, alpha, or neutron detection. This study leads towards the ability to identify the most suitable nanoparticle-based scintillation materials for specific radiation detection purposes, and to a better understanding of how certain nanoparticle-based scintillators behave under radiation interactions. 

PPO and POPOP are among the most commonly used organic primary and secondary fluors, respectively. Despite their high efficiencies in both liquid and plastic scintillators, one limitation is their incompatibility with hydrophilic reagents. In liquid scintillation techniques, an efficient extraction of radioactive nuclides into the organic phase where PPO and POPOP dissolve is often mandatory. In neutron detection by plastic scintillators, the use of an efficient, yet hydrophilic, neutron absorber, Li, is strictly limited if not prohibited. 

Fio. 9.2 Decay curve of thermal neutrons diffusing out of HjO cylinder as detected with Li I(Eu) scintillation counter. 

Scintillators which have hydrogen as a constituent, such as organic liquids for example, may be used for fast neutron detection, since the protons produced by fast neutron collisions create the ionization required to operate the detector. In order to adapt a sodium iodide scintillator for the detection of slow neutrons, a small concentration of boron may be distributed in the crystal, giving a particles on neutron capture as discussed above. Alternatively, it is possible to add a neutron absorber which emits 7 rays following the (n, y) capture reaction. Another possibility is the use of lithium iodide (Lil) which, in addition to its own suitability as a scintillator, interacts with neutrons through the reaction... 

Radiometric ore sorting has been used successfully for some uranium ores because uranium minerals emit gamma rays which may be detected by a scintillation counter (2). In this appHcation, the distribution of uranium is such that a large fraction of the ore containing less than some specified cut-off grade can be discarded with tittle loss of uranium values. Radioactivity can also be induced in certain minerals, eg, boron and beryllium ores, by bombarding with neutrons or gamma rays. 

Neon is also used in scintillation counters, neutron fission counters, proportional counters, and ionization chambers for detection of charged particles. Its mixtures with bromine vapors or chlorine are used in Geiger tubes for counting nuclear particles. Helium-neon mixture is used in gas lasers. Some other applications of neon are in antifog devices, electrical current detectors, and lightning arrestors. The gas is also used in welding and preparative reactions. In preparative reactions it provides an inert atmosphere to shield the reaction from air contact. 

One of the most developed of these methods is the technique usually referred to as pulsed fast neutron analysis (PENA) [3,11-13], The operation is illustrated in Fig. 7 [11], Neutrons in the range of 8 MeV are generated by an accelerator (not shown) by the reaction D(d,n)He. The accelerator is pulsed with a 1 ns pulse width to produce 1 ns pulses of neutrons with a repetition rate of 1 MHz. Gamma rays are detected in a series of scintillation detectors. The time difference between the accelerator pulse and the... 

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