CONVERSION ELECTRON SPECTROSCOPY FOR ISOTOPIC ANALYSIS OF SPECIAL NUCLEAR MATERIAL

• Published in: Health physics (1958) Vol. 115; p. S112
• Main Authors: Watson, MW, DeVol, TA
• Format: Journal Article
• Language: English
• Published: Baltimore Lippincott Williams & Wilkins Ovid Technologies 01-07-2018
• Subjects: Alpha decay; Alpha particles; Alpha rays; Conversion; Deconvolution; Electron spectroscopy; Electrons; Emission measurements; Energy; Energy measurement; Energy resolution; Evacuation systems; Forensic science; Isotopes; Nuclear accidents & safety; Nuclear physics; Nuclear safety; Particle decay; Particle emission; Safety regulations; Spectroscopy; Spectrum analysis; Turbine pumps; Vacuum; Vacuum chambers; X ray spectra
• ISSN: 0017-9078; 1538-5159

Special nuclear material (SNM) isotopes primarily decay via alpha particle emission, making alpha spectroscopy the most common measurement technique. However, alpha spectroscopy cannot distinguish Pu-239 and Pu-240 peaks or Pu-241 and Am-241 peaks without peak deconvolution techniques. Conversion electron spectroscopy offers complimentary information relative to alpha spectroscopy by allowing SNM isotope quantification without peak deconvolution techniques if there is sufficient energy resolution. Conversion electron spectra were collected using a silicon drift detector (SDD) mounted in a conflat vacuum chamber. The chamber was evacuated to 10-6 Torr using a turbo pump system. Conversion electron plus x-ray spectra were collected for approximately 24 h with a source placed 13 mm from the face of the detector. X-ray only spectra are then acquired using the same setup with a conversion electron parafilm shield between the source and detector to shield conversion electrons. The x-ray only spectrum is subtracted from the conversion electron plus x-ray spectrum to obtain a conversion electron only spectrum. The energy resolution was measured to be 0.2 keV (FWHM) for Am-241 x rays at 13.9 keV. The energy resolution of the conversion electrons can be degraded because of self-absorption. Besides the nuclear safeguards and forensics applications, these data indicate that an SDD provides adequate resolution to experimentally define conversion electron coefficients for SNM isotopes; data currently available are derived using theoretical models.