System and method for trace detection using dual ionization sources

1. A dual source ionizer comprising:

a first ionization source configured to generate a first electric field, the first electric field having a first field strength insufficient to form NO x − ions;

a second ionization source configured to generate a second electric field, the second electric field having a second field strength sufficient to form ozone and NO x − ions; and

a controller configured to disable said second ionization source for a period of time while said first ionization source is enabled to screen a chemical substance for a target nitrate-based chemical substance using the first electric field.

2. The dual source ionizer of claim 1 wherein said first ionization source comprises a radioactive ionization source.

3. The dual source ionizer of claim 1 wherein the first ionization source comprises a photoionization source.

4. The dual source ionizer of claim 1 wherein the second ionization source comprises an electrical discharge radiation source.

5. The dual source ionizer of claim 1 wherein the second field strength is at least 12.5 megavolts per meter, and wherein the second electric field is generated in a volume having a pressure of substantially 1 atmosphere.

6. A method of ionizing a gas, the method comprising:

ionizing the gas during a first period of time of a scan duration using a first ionization source configured to generate one of the group consisting of a low-strength electric field and no electric field;

disabling a second ionization source during the first period of time for screening ions of the gas for a nitrate-based chemical substance, the second ionization source configured to generate a high-strength electric field; and

ionizing the gas during a second period of time of the scan duration using the second ionization source to screen the gas for a non-nitrate-based chemical substance.

7. The method of claim 6 , wherein the scan duration is determined according to a vaporization time of a chemical substance sample from which the gas is formed.

8. The method of claim 6 further comprising disabling the first ionization source before ionizing the gas using the second ionization source.

9. The method of claim 6 further comprising performing spectrometry on ions of the gas to screen for a target chemical substance.

10. The method of claim 9 , wherein performing spectrometry comprises performing mass spectrometry.

11. The method of claim 9 , wherein performing spectrometry further comprises screening for a nitrate-based explosive and for a non-nitrate-based explosive.

12. A trace detection system comprising:

a chamber configured to contain a gas composed of at least vapor of a chemical substance sample;

a first ionization source configured to generate a low-strength electric field in said chamber to ionize the gas;

a second ionization source configured to generate a high-strength electric field in said chamber to ionize the gas; and

a controller configured to:

enable said first ionization source and disable said second ionization source during a first period of time of a scan duration to screen the gas for a target nitrate-based chemical substance, and

enable said second ionization source during a second period of time of the scan duration to screen the gas for a target non-nitrate-based chemical substance.

13. The trace detection system of claim 12 further comprising a spectrometer configured to screen ions of the gas for a nitrate-based explosive and for non-nitrate-based explosives.

14. The trace detection system of claim 13 , wherein said chamber comprises a first volume within which said first ionization source operates, and a second volume, distinct from said first volume, within which said second ionization source operates.

15. The trace detection system of claim 14 , wherein said spectrometer is further configured to screen ions from said first volume for the nitrate-based explosives, and to screen ions from said second volume for the non-nitrate-based explosives.

16. The trace detection system of claim 12 , wherein said low-strength electric field is configured to:

liberate a free electron from a molecule of the gas; and

accelerate the free electron to a first kinetic energy level, the first kinetic energy level insufficient to break chemical bonds of diatomic oxygen.

17. The trace detection system of claim 12 , wherein said high-strength electric field is configured to:

liberate a free electron from a molecule of the gas; and

accelerate the free electron to a second kinetic energy level, the second kinetic energy level sufficient to form metastable nitrogen molecules.

18. The dual source ionizer of claim 1 wherein the first ionization source comprises an X-ray source.

19. The dual source ionizer of claim 1 wherein the first field strength is no greater than 10 megavolts per meter, and wherein the first electric field is generated in a volume having a pressure of substantially 1 atmosphere.