FIG 2.> Resulting energy spectrum obtained, specific
for cobalt alone:
FIG.3> Setup using small piece of indium solder as the sample
under test (note in corner is the cadmium filter mentioned next)
FIG. 4> Results of the scan for indium element, note position
of unique peak at the energy of indium K-Lines:
Historically, one of the nifty lab items we use for selective
energy filtering is a metal disc, 2 3/4" diameter and 0.85mm thick, removed from
an old Ludlum made uranium enrichment analyzer. The material it was made from
was never specified, nor could Ludlum identify it after so many years. I assumed
it was either tin or cadmium, since its qualities were similar to either.
Weight/density and hardness testing leaned more towards cadmium. Since cadmium
is a somewhat toxic metal and this filter never had a warning label or anything
else to alert an operator, tin would be a more likely choice. Anyhow to be safe
I labeled it as Cd and always handled it accordingly. Still it has bugged me not
knowing for sure.
Today I know for sure. It is cadmium, nearly pure the
best we can tell. We have metallographic samples of 0.9999 pure elements, one of
which is cadmium. By shining the rays and particles from the Kr-85 source onto
the various metals, a signature is developed using the Scionix probe into an
MCA, for each element. The filter- "Device Under Test" or DUT matches perfectly
the 0.9999 Cd metal sample.
FIG.5> Results of .999 pure cadmium element test showing
unique energy lines of cadmium:
FIG.6> Results of unknown metal filter test, peaks
coincide exactly with pure cadmium element:
FIG. 7> Setup using old US dime coin to test for
FIG. 8> Results of a test of pure tin element (Sn) showing
unique energy lines for Sn:
Observe the specially made periodic charts of the elements we
had made (Thanks AtomicDave!). Instead of protons and neutrons these charts give
the characteristic XRF energies of the two K shell and two L shell electrons.
Our method of beta excitement works mostly on the K shell, so the energy
read with our probe is roughly an average of both the K shell energies together.
Each element can therefore be identified very easily by comparing it to a known
sample. Furthermore, some alloys, like Bronze can be identified by a double
peak, one from copper the other from tin. Two elements that are right next to
one another on the chart will merge usually, but either in pure form can easily
More advanced experiments following this same basic technique
will be shown soon, with which we have identified all the elements from Calcium