Concentration detection device and concentration detection method

A concentration detection device comprising:

• a neutron source that emits neutrons to a surface of an inspection target so that specific gamma rays having different energies and derived from a target component in the inspection target are generated in the inspection target as a result of interactions between the target component and the neutrons;
• a gamma ray detection device that includes a gamma ray detector detecting a specific gamma ray included in the specific gamma rays, and determines, for each of the different energies, a number of times the gamma ray detector detects the specific gamma ray;
• and
• a concentration calculation device that includes a storage unit storing a plurality of relational expressions;
• wherein a plurality of arrangement relations are each defined as one or both of a position relation and an orientation relation among the neutron source, the gamma ray detector, and the inspection target;
• each of the plurality of relational expressions is set for corresponding one of the different energies or for corresponding one of a plurality of combinations, and each of the plurality of combinations is a combination of one of the different energies and one of the plurality of arrangement relations;
• the inspection target is assumed to be virtually divided into a plurality of layers, and a plurality of concentrations are each defined as a concentration of the target component in corresponding one of the plurality of layers;
• each of the plurality of relational expressions expresses, by unknown values of the plurality of concentrations and a plurality of predetermined coefficients, a variable of a number of times the gamma ray detector detects the specific gamma ray for the corresponding one of the different energies or the corresponding one of the plurality of combination;
• and
• the concentration calculation device:
• assigns, for each of the different energies or each of the plurality of combinations, the determined number of times to the variable in corresponding one of the plurality of relational expressions, and
• calculates, as the concentration of the target component in one or each of the plurality of layers, one or each of the unknown values, from the plurality of relational expressions in each of which the determined number of times has been assigned to the variable.