Prompt gamma neutron activation analysis system
First Claim
1. A method for analyzing an interrogation volume containing a prescribed target element, comprising the steps of:
- (a) irradiating an interrogation volume with a neutron burst characterized by an intensity and pulse width, and thereby effecting an emission of gamma radiation from said interrogation volume;
(b) acquiring groups of gamma radiation data during a plurality of time intervals, each group being indicative of the number or intensity of gamma rays and energy levels of said gamma rays during a corresponding time interval, and a first group corresponding to a first interval during which said neutron burst is on, and at least one other group corresponding to a time interval during which said neutron burst is off; and
(c) analyzing said gamma data to detect the presence and determine the amount of said prescribed target element in said interrogation volume and to determine whether said prescribed target element is present within a prescribed depth range in said interrogation volume; and
(d) determining calibration data by carrying out the following sub-steps;
(1) placing a slug of mass M of said target element at a plurality of depths, including;
0 inches;
X1, where X1 is the deepest depth from which gamma rays of energy E1 can escape the interrogation volume in sufficient numbers to be detected; and
X2, where X2 is the deepest depth from which gamma rays of energy E2 can escape the interrogation volume in sufficient numbers to be detected; and
measuring yields YE1 (0), YE1 (X1) of gamma rays of energy E1 at depths of 0 inches and X1, respectively, and YE2 (0), YE2 (X1), YE2 (X2) of gamma rays of energy E2 at depths of 0 inches, X1 and X2, respectively;
(2) defining the following ratios;
##EQU9## performing a field measurement of yields y(E1), y(E2) of gamma rays of energies E1, E2, respectively;
performing a depth inference calculation by determining whether y(E2)/y(E1) is greater than R21 (X1) and whether y(E1) is greater than 0, and then determining a range of depths at which said target element is located by the following formulas;
Case 1if y(E2)/y(E1) is greater than R21 (X1) and y(E1) is greater than 0, then the target element is present between 0 and X1 and between X1 and X2 ;
Case 2if y(E2)/y(E1) is less than R21 (X1) and y(E1) is greater than 0, then the target element is between 0 and X1 ;
Case 3if y(E2) is greater than 0 and y(E1) is 0, then the target element is between X1, and X2 ; and
then, performing an equivalent mass calculation by the following formulas;
##EQU10## wherein ESmax and ESmin represent the maximum and minimum equivalent mass within the specified ranges;
wherein steps a, b, and c are performed with a neutron source, detector and analysis system, respectively, wherein said neutron source, detector and analysis system are maintained outside said interrogation volume and in a non-contacting relation with said target element.
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Accused Products
Abstract
A system for determining depth profiles of concentrations of hazardous elements in soils comprises a neutron source for generating neutrons of a first energy level and irradiating a volume of soil with the neutrons. Nuclear reactions are effected within the soil and gamma radiation is emitted from the soil. The system also includes an array of gamma detectors for detecting gamma radiation emitted from the soil; source electronics for controlling the width of regularly repeated pulses of neutrons generated by the neutron source; detector electronics associated with the gamma detectors for amplifying and digitalizing signals generated by the gamma detectors and storing data representing the digitalized signals; spectral analysis software for analyzing the data and determining the concentrations of selected target elements in the soil; and an acquisition interface module (AIM). The AIM controls the timing of the source and detector electronics such that the neutron source generates neutrons in regularly repeated bursts of a prescribed pulse width and the detectors and detector electronics detect gamma rays during a plurality of time intervals associated with the burst and acquire groups of data. Each group is indicative of a number of gamma rays emitted and their energy levels during a corresponding time interval. The system also includes a mobile platform carrying the neutron source, array of gamma ray detectors and software for determining a depth profile of a target element. Trace elements can also be detected with the disclosed system.
71 Citations
12 Claims
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1. A method for analyzing an interrogation volume containing a prescribed target element, comprising the steps of:
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(a) irradiating an interrogation volume with a neutron burst characterized by an intensity and pulse width, and thereby effecting an emission of gamma radiation from said interrogation volume; (b) acquiring groups of gamma radiation data during a plurality of time intervals, each group being indicative of the number or intensity of gamma rays and energy levels of said gamma rays during a corresponding time interval, and a first group corresponding to a first interval during which said neutron burst is on, and at least one other group corresponding to a time interval during which said neutron burst is off; and (c) analyzing said gamma data to detect the presence and determine the amount of said prescribed target element in said interrogation volume and to determine whether said prescribed target element is present within a prescribed depth range in said interrogation volume; and (d) determining calibration data by carrying out the following sub-steps; (1) placing a slug of mass M of said target element at a plurality of depths, including;
0 inches;
X1, where X1 is the deepest depth from which gamma rays of energy E1 can escape the interrogation volume in sufficient numbers to be detected; and
X2, where X2 is the deepest depth from which gamma rays of energy E2 can escape the interrogation volume in sufficient numbers to be detected; and
measuring yields YE1 (0), YE1 (X1) of gamma rays of energy E1 at depths of 0 inches and X1, respectively, and YE2 (0), YE2 (X1), YE2 (X2) of gamma rays of energy E2 at depths of 0 inches, X1 and X2, respectively;(2) defining the following ratios;
##EQU9## performing a field measurement of yields y(E1), y(E2) of gamma rays of energies E1, E2, respectively;performing a depth inference calculation by determining whether y(E2)/y(E1) is greater than R21 (X1) and whether y(E1) is greater than 0, and then determining a range of depths at which said target element is located by the following formulas; Case 1 if y(E2)/y(E1) is greater than R21 (X1) and y(E1) is greater than 0, then the target element is present between 0 and X1 and between X1 and X2 ; Case 2 if y(E2)/y(E1) is less than R21 (X1) and y(E1) is greater than 0, then the target element is between 0 and X1 ; Case 3 if y(E2) is greater than 0 and y(E1) is 0, then the target element is between X1, and X2 ; and
then, performing an equivalent mass calculation by the following formulas;
##EQU10## wherein ESmax and ESmin represent the maximum and minimum equivalent mass within the specified ranges;wherein steps a, b, and c are performed with a neutron source, detector and analysis system, respectively, wherein said neutron source, detector and analysis system are maintained outside said interrogation volume and in a non-contacting relation with said target element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification