Uranium Mössbauer Array Spectroscopy: A Non-destructive Method for Detecting Traces of High Enriched Uranium in Environmental Samples
Open Access
- Author:
- De Morais, Matheus
- Graduate Program:
- Nuclear Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 24, 2025
- Committee Members:
- Jon Michael Schwantes, Thesis Advisor/Co-Advisor
Federico Scurti, Committee Member
Dipanjan Pan, Professor in Charge/Director of Graduate Studies - Keywords:
- Mössbauer
Spectroscopy
Gamma-ray
Uranium
Plutonium
Enrichment
Detection - Abstract:
- This thesis presents the development of a computational model using Python to simulate the Mössbauer effect. This model was used to test and theoretically demonstrate the viability of a new approach, based upon Mössbauer Spectroscopy, to non-destructively detect trace High Enriched Uranium in environmental samples, an approach coined as Uranium Mössbauer Array Spectroscopy (UxMAS). This approach relies on simultaneously measuring U-234 and U-238 by Mössbauer Spectroscopy. While U-235 is not Mossbauer active, U-235 abundance can be estimated indirectly via the ratio of U-234/U-238. Resonance gammas for the two isotopes are less than 1 keV separated in energy, however, so resolving these gamma lines is key to validating this approach. Model simulations were used here to simulate the simultaneous emission and absorption of resonant gamma rays from excited state U-234 and U-238, created by the decay of their radiogenic parents, isotopes Pu-238Pu and Pu-242, respectively. Attempts to simulate the separation of the two gamma lines was approximated by measuring activities across a low (representing U-234) and a high band region of the gamma energy spectra. The model simulated the effect of varying the speed of the velocity transducer, the resolution of the detector, the isotopic abundance of the sample, and the activities of the sources. Simulations indicate that detection of traces of HEU are possible with the UxMAS approach, but that detector resolution was a critical design feature of the system. Specifically, employing a detector with a 1% energy resolution was capable of detecting traces of 20% enriched U with a 67% uncertainty. That uncertainty decreased significantly with an increasing level of enrichment. Uranium with an enrichment level of 35%, for instance, could be differentiated from Low Enriched Uranium at High Confidence. Simulations indicated detection could be optimized by adjusting the location of the low and high band regions to coincide with the resonance gamma energy at peak activity for U-234 and U-238. Further optimization was created by adjusting the ratio of the activities of the Pu-238 and Pu-242 sources to favor that of Pu-238 in order to compensate for the large difference in abundance levels between the 234U and 238U. Additional advantages may be possible by altering the form of the Pu-242 relative to Pu-238.