Friends of mine did a lab experiment where they recorded $\gamma$-spectra in the range from 0 to 1500 keV with a soil sample. The data contains some background and a couple sharp peaks at different locations. Their task is to find the isotopes contained in that sample.
There are of course thousands of isotopes with tens to hundreds of decay lines each. My suggestion was to take some database of lines and built up the expected spectrum. Then try to match those spectra to the measurement. So if $m(E)$ is the energy and $s_i(E)$ are the spectral functions generated by $$ s_i(E) = \sum_{j} \sigma(E') \delta(E - E'_{ij}) $$ where $E_{ij}$ are the $j$th spectral line of the $i$th isotope. To match them I suggested to do $$a_i = \frac{\int_0^\infty \mathrm d E \, m(E) s_i(E)}{\int_0^\infty \mathrm d E \, s_i(E)}$$ that would give some measure how well the peaks of the isotope are present in the measurement. In the numerical calculation the $\delta$-peaks are modeled by Lorentz-peaks.
In order to do that they were looking for some machine readable database. They have found this site where you can query for specific energy ranges and get a list of isotopes. That is somewhat interesting, but there are so many lines in every energy range that it does not really help. Also it is not machine readable until you query and parse the whole energy range and store it to a local SQLite database or so. Then they also found another site where you can download plain text files. However they turned out to contain only some isotopes. Some of the lines of the first site are not contained on the second which is a problem.
This is what the best fitting generated spectra and the data looks like at some energy:
http://chaos.stw-bonn.de/users/mu/uploads/2015-11-28/isotopes.png
Is there some machine readable database of $\gamma$-decay lines such that they can programatically check for the best matching lines?
No comments:
Post a Comment