  An estimated 26 million people in low- and middle-income countries are at
risk of lead exposure and there is no safe threshold for lead ingestion. Radio
assay methods are not easily accessible in regions at risk, therefore a low
cost and easy to use sensor is desirable. $\textrm{Pb}$ occurs together with
traces of radioisotopes with decay energies in the range of $10$ to several
\SI{100}{\kilo\electronvolt} and beyond. Such energies are accessible in
silicon sensors. We have tested a scientific CMOS (Neo 5.5 sCMOS), optimised
for optical wavelengths, as $\gamma$ detector for radiation in the range of $0$
to a few 10 keV. We find a minimal detectable $^{241}\textrm{Am}$ decay rate of
20 Bq for a < 1.4h measurement. Optimising our analysis software will
potentially enable detecting lower rates in the same measurement time. We
established that the Neo 5.5 sCMOS allows to measure a spectrum of
$^{241}\textrm{Am}$ decay lines. In addition we show that it is possible to
enhance the concentration of radioisotopes in water when reducing the water's
volume by boiling. The knowledge gained using the scientific CMOS sensor will
be transferred to commercial silicon sensors as the chips in smart phones.
