Method and system for detecting an explosive
A method and system for detecting at least one explosive in a vehicle using a neutron generator and a plurality of NaI detectors. Spectra read from the detectors is calibrated by performing Gaussian peak fitting to define peak regions, locating a Na peak and an annihilation peak doublet, assigning a predetermined energy level to one peak in the doublet, and predicting a hydrogen peak location based on a location of at least one peak of the doublet. The spectra are gain shifted to a common calibration, summed for respective groups of NaI detectors, and nitrogen detection analysis performed on the summed spectra for each group.
1. A method of determining a presence of at least one explosive in a vehicle, the method comprising:
directing energy at a vehicle using a neutron generator;
reading spectra from a plurality of NaI detectors arranged adjacent the vehicle in a plurality of groups comprising different combination of NaI detectors;
calibrating the spectra, comprising:
performing Gaussian peak fitting to define peak regions;
locating a Na peak and an annihilation peak doublet;
assigning a predetermined energy level to one peak in the doublet; and
predicting a hydrogen peak location based on a location of at least one peak of the doublet;
gain shifting the spectra to a common calibration;
summing the spectra for respective groups of NaI detectors; and
performing Nitrogen detection analysis on the summed spectra for each group.
2. The method of claim 1 , further comprising performing Gaussian peak fitting to find a peak in a region surrounding the predicted hydrogen peak location.
3. The method of claim 2 , further comprising predicting a Na peak location based on the location of the annihilation peak and the peak found in the region surrounding the predicted hydrogen peak.
4. The method of claim 2 , further comprising predicting a Na peak location using a linear fit to the location of the annihilation peak and the location of the hydrogen peak.
5. The method of claim 2 , further comprising predicting a Na peak location using a linear fit to the location of the annihilation peak and the location of the hydrogen peak and then applying a nonlinearity adjustment.
6. The method of claim 5 , further comprising providing a library of spectra with known calibrations and using the library to develop a prediction equation for locating the hydrogen peak and developing the nonlinearity adjustment.
7. The method of claim 5 , further comprising providing a library of spectra with known calibrations and using the library to develop the nonlinearity adjustment.
8. The method of claim 5 , further comprising performing Gaussian peak fitting to find a peak in a region surrounding the predicted Na peak location.
9. The method of claim 8 , further comprising fitting a quadratic equation to the annihilation peak, the hydrogen peak, and the Na peak to produce an energy calibration equation.
10. A system for determining a presence of at least one explosive in a vehicle, the system comprising:
a neutron generator located and oriented to direct energy at a vehicle location;
a plurality of NaI detectors adjacent the vehicle location, comprising a plurality of groups containing different combinations of the NaI detectors; and
a control system configured to:
read spectra from the plurality of NaI detectors;
calibrate the spectra, comprising:
performing Gaussian peak fitting to define peak regions;
locating a Na peak and an annihilation peak doublet;
assigning a predetermined energy level to one peak in the doublet; and
predicting a hydrogen peak location based on the location of at least one peak of the doublet;
gain shift the spectra to a common calibration;
sum the spectra for respective groups of NaI detectors; and
perform nitrogen detection analysis on the summed spectra for each group.
11. The system of claim 10 , wherein the control system is further configured to perform Gaussian peak fitting to find a peak in a region surrounding the predicted hydrogen peak location.
12. The system of claim 11 , wherein the control system is further configured to predict a Na peak location based on the location of the annihilation peak and the peak found in the region surrounding the predicted hydrogen peak location.
13. The system of claim 11 , wherein the control system is further configured to predict a Na peak location using a linear fit to the location of the annihilation peak and the location of the hydrogen peak.
14. The system of claim 11 , wherein the control system is further configured to predict a Na peak location using a linear fit to the location of the annihilation peak and the location of the hydrogen peak and then applying a nonlinearity adjustment.
15. The system of claim 14 , further comprising a library of spectra with known calibrations, and wherein the control system is configured to use the library to develop a prediction equation for locating the hydrogen peak and to develop the nonlinearity adjustment.
16. The system of claim 14 , further comprising a library of spectra with known calibrations, and wherein the control system is configured to use the library to develop the nonlinearity adjustment.
17. The system of claim 14 , wherein the control system is further configured to perform Gaussian peak fitting to find a peak in a region surrounding the predicted Na peak location.
18. The system of claim 17 , wherein the control system is further configured to fit a quadratic equation to the annihilation peak, the hydrogen peak, and the Na peak to produce an energy calibration equation.