Spectrum unfolding

Adjust a guess neutron spectrum against measured foil-activation rates with the SAND-II iteration and compare guess vs unfolded.

Foil-activation spectrometry measures a handful of reaction rates — each detector is sensitive to a different energy band — and the spectrum behind those rates must be reconstructed. SAND-II (McElroy et al., AFWL-TR-67-41, 1967) does this iteratively: it folds the current spectrum guess through the response matrix, compares the calculated rates against the measured ones, and multiplies each energy group by a weighted geometric mean of the correction factors, so the spectrum stays positive and a guess that already fits is left unchanged.

The demo below ships a small determined synthetic problem — four detectors, six energy groups, Gaussian response bumps — with editable measured rates. Press Unfold spectrum to watch the adjusted spectrum against the flat guess, the iteration count, and how well the final fold reproduces the rates you entered. The response values are synthetic round numbers, not evaluated detector data.

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