Patent ID: 7408148

Claim:
A method for detecting a relevant ionizing radiation source in an environment that includes a potential background ionizing radiation shielding material positioned to obstruct the detection, the method comprising: (a) selecting at least a first and a second ionizing radiation energy region of interest wherein: the first and the second ionizing radiation energy regions of interest each have a spectral width, and the first ionizing radiation region of interest is selected to include detectable emissions from the relevant ionizing radiation source, and the second ionizing radiation region of interest is selected to have an energy range that does not have substantial emissions from the relevant ionizing radiation source; (b) acquiring a first background ionizing radiation measurement in the first ionizing radiation energy region of interest and a second background ionizing radiation measurement in the second ionizing radiation energy region of interest, each of the first background ionizing radiation and the second background ionizing radiation measurements being taken substantially in the absence of the relevant ionizing radiation source; (c) normalizing the second background ionizing radiation measurement to the first background ionizing radiation measurement to determine a calibration constant; (d) acquiring a first total ionizing radiation measurement in the first ionizing radiation energy region of interest and a second total ionizing radiation measurement in the second ionizing radiation energy region of interest, each of the first total ionizing radiation and the second total ionizing radiation measurements being taken in the presence of a potential relevant radiological source and in the presence of a potential background ionizing radiation shielding material positioned to obstruct the detection of the potential relevant ionizing radiation source; (e) applying the calibration constant to normalize the second total ionizing radiation measurement to determine a normalized second total ionizing radiation measurement; and (f) subtracting the normalized second total ionizing radiation measurement from the first total ionizing radiation measurement to determine a net difference there between to indicate the presence of the relevant ionizing radiation source.