Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Patent
1981-09-30
1984-07-31
Howell, Janice A.
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
250308, 2503581, G01T 120, G01N 2300
Patent
active
044632630
ABSTRACT:
A radiographic method and apparatus for nondestructively monitoring a specimen for density variations are disclosed.
A positron-annihilation-radiation-emitting point source is situated approximately midway along the axis separating two detectors sensitive to positron-annihilation (0.511-MeV photon) radiation. The outputs of the two detectors are fed to an electronic circuit that reckons only time-coincident events that are sensed simultaneously in the two detectors. The specimen to be measured is positioned between the source and one of the detectors such that the cone of detected, i.e., coincident, photons intercepts the region of interest. The number of coincidences that are counted in a preset time interval are recorded, or, alternatively, the coincidence count rate is monitored directly with a ratemeter.
A linear scan of the region of interest is performed by the sequential displacing of the source/detectors axis with respect to the measured specimen, or the specimen with respect to the source/detectors axis. The number of coincidence counts accumulated within a preset time interval are recorded for each displacement. The spatial variation of density within the specimen is inferred from corresponding variations in the coincidence count rate.
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Grumman Aerospace Corporation
Howell Janice A.
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