Multiplicity Coincidence Counting

Normal coincidence counting techniques rely on the detection of two coincident neutrons (doubles) and making an assumption based either on the multiplication or on the (a, n) neutron rate. These two analysis methods - passive calibration and known-alpha - require 

The plutonium scrap multiplicity counter (PSMC) is a high-efficiency neutron multiplicity counter with cadmium lining designed for measuring impure samples such as MOX scrap materials (Nakajima et al. 1997). The PSMC contains 80 He-filled tubes (at 4-atmosphere fill pressure) arranged in four rings embedded in polyethylene and has an efficiency of 55%. 

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Nc, Nh, Nx, Nn, Np, and C are the number of carbon atoms, hydrogen, halogen, nitrogen, phosphorous, and independent cycles, respectively. Nq-s and Nsos are the number of oxygen atoms bonded to sulfur and the number of SO3 groups, respectively. When no sulfur atoms are present, this index can be easily calculated from the chemical formula otherwise, it is coincident with the index calculated replacing b with b, the multiple bond count. 

The fissile isotopes of uranium ( U) and plutonium ( Pu, Pu) can be measured using active neutron counting techniques. This technique uses an external neutron source to induce fission in the fissile plutonium and manium content of the sample. The multiple induced fission neutrons are then measured using standard coincidence counting methods. The technique is mainly applied to determine the mass of in uranium-bearing samples (from LEU to HEU) in powder, metal, pellets, fresh fuel elements, and waste drums. It can be operated either with or without a cadmium liner (fast or thermal mode). 

More advanced applications of neutron counting were based on the expectation that spontaneous fission events of superheavy nuclei should be accompanied by the emission of about ten neutrons [41,42], distinctly more than two to four observed for any other spontaneous fission decay. Such neutron bursts can be recognized by recording neutron multiplicities - events with several neutrons in coincidence - with 3He-filled counting tubes [43,44] or large tanks filled with a liquid scintillator sensitive to neutrons [45],... 

The correction for primary coincidence is derived through Poisson probabilities of finding multiple particles in different parts of the sensing zone simultaneously. This yields the following relationship between true count N and observed count n ... 

This ID number accounts for multiple bonds in the molecule for saturated molecules each bond weight is equal to one, therefore the ID number coincides with the - total path count. 

In a conventional scintillation camera. Anger logic is used to determine the location of an interaction. The tacit assumption in this approach is that only one event is occurring at a time. At the high count rate encountered in coincidence imaging, multiple interactions are likely, and when this occurs, the events are improperly located somewhere between the two true locations. Improved algorithms have been developed that can identify multiple hits and that use a maximum likelihood calculation to correctly determine event locations. 

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