Nondestructive inspection method and apparatus comprising a neutron source and a gamma-ray detection device for determining a depth of a target component in an inspection target

A nondestructive inspection method for determining a depth of chlorine that may exist in a concrete structure including reinforcing steel bars whose corrosion maybe caused by chlorine, the nondestructive inspection method comprising:

• an emission step of emitting a neutron beam including at least fast neutrons to a surface of a concrete structure including reinforcing steel bars and corrosive chlorine Cl;
• a gamma ray detection step of detecting intensities of a plurality of types of specific gamma rays, based on respective different specific energies of the plurality of types of specific gamma rays that are generated from the chlorine Cl in the concrete structure due to the neutron beam;
• and
• a ratio calculation step of calculating, as an index value indicative of a depth of the chlorine Cl in the concrete structure, a ratio between the detected intensities of the plurality of types of specific gamma rays.

A nondestructive inspection apparatus for inspecting concrete structures including reinforcing steel bar, the nondestructive inspection apparatus comprising:

• a neutron source that emits a pulsed neutron beam including at least fast neutrons to a surface of a concrete structure including reinforcing steel bars and corrosive chlorine Cl, and thereby makes the at least fast neutrons incident on the surface of the concrete structure;
• a gamma ray detection device that detects gamma rays including a specific gamma ray generated from the chlorine Cl in the concrete structure due to the pulsed neutron beam, detects an energy spectrum of the detected gamma rays at each time point, and generates time-difference-to-spectrum data, in which each time point is associated with the detected energy spectrum of the gamma rays detected at each time point;
• a time-point specifying unit that specifies, in a relation to a reference time point, a time point, at which the specific gamma ray is detected, based on the time-difference-to-spectrum data generated by the gamma ray detection device;
• and
• a depth detection unit that determines a depth of the chlorine Cl within the concrete structure, based on the time point specified by the time-point specifying unit.

A nondestructive inspection method for a concrete structure including reinforcing steel bars, the nondestructive inspection method comprising:

• an emission step of emitting a pulsed neutron beam including at least fast neutrons to a surface of a concrete structure including reinforcing steel bars and corrosive chlorine Cl, and thereby making the at least fast neutrons incident on the surface of the concrete structure;
• a gamma ray detection step of detecting a specific gamma ray generated from the chlorine Cl in the concrete structure due to the pulsed neutron beam;
• a time-point specifying step of specifying, in a relation to a reference time point, a time point, at which the specific gamma ray is detected;
• and
• a depth detection step of determining a depth of the chlorine Cl, based on the time point specified at the time-point specifying step.

A nondestructive inspection apparatus for emitting, to an inspection target, a neutron beam including at least fast neutrons, detecting and identifying a specific gamma ray generated due to the neutron beam, and determining a depth, at which a target component exists, based on a result of detecting and identifying the specific gamma ray generated due to the neutron beam, the nondestructive inspection apparatus comprising:

• a neutron source that emits a neutron beam to a surface of an inspection target;
• and
• a gamma ray detection device that detects a specific gamma ray generated due to the neutron beam incident on the inspection target,
• wherein the gamma ray detection device includes a gamma ray detector for detecting the specific gamma ray, and a gamma ray shielding portion comprising a gamma ray passage hole, the gamma ray passage hole includes an opening, through which gamma rays are allowed to enter, the gamma ray detector is arranged in the gamma ray passage hole so as to be at a position shifted to a deep side from the opening, and the opening and the gamma ray detector are positioned on a reference straight line,
• the gamma ray shielding portion includes a gap and two shielding blocks separated by the gap from each other, and the gap is the gamma ray passage hole,
• the gap extends along the reference straight line, and
• a size of the gap in a first direction perpendicular to the reference straight line is smaller than a size of the gap in a second direction perpendicular to both the reference straight line and the first direction.