Scintillation detectors neutron absorbers

In scintillation detectors, incoming radiation strikes a thin layer of crystals or a solution of organic materials that produce fight. Light output is proportional to the radiation absorbed. These devices measure alpha, beta, gamma, and slow neutron sources. 

Another possibility is to make neutron-sensitive scintillation detectors, in which neutrons are absorbed by Li (mixed with ZnS and located within a glass matrix) and the Kght quanta emitted are collected usually by photomultipliers. 

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... 

The aim with a scintillator detector is to combine the neutron absorbing element intimately with a scintillating phosphor so that the reaction products from the capture of a neutron strike the phosphor and produce a light flash, which is then detected by a photomultiplier tube (see Figure 4B). 

The KamLAND detector, shown in Figure 5, consists of a sphere of liquid scintillator, surrounded by neutron and gamma ray absorbing buffers made of liquid paraffin and water. The liquid scintillator is enclosed in a transparent nylon composite balloon that has low permeability to radon, a background-generating contaminant. The total mass of liquid scintillator is 1000 tons, filling a sphere with a radius of about 6.3 m. A 500 ton fiducial spherical volume is defined within the main volume to help reduce backgrounds from photomultiplier tubes and from external radioactive decay sources. The liquid parafrin buffer is enclosed in a spherical stainless steel vessel, which is in turn surrounded by a water Cerenkov veto counter. The entire detector is shielded by a rock overburden of 2700 meters of water equivalent (m.w.e.). 

The detector cryostat was then rebuilt to incorporate low background components. The Nal(Tl) anticoincidence system, which contained Ra, was replaced by an external plastic scintillator veto detector. A layer of cadmium and borated wax was added, to thermahze fast neutrons and absorb the thermal neutrons. This resulted in the second spectrum and count rates down to 1 X 10 to 3 X 10 counts keV min ... 

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