Find in Library

This paper explores the prospect of CMOS devices to assay lead in drinking water, using calorimetry. Lead occurs together with traces of radioisotopes, e.g., <inline-formula><math display="inline"><semantics><mrow><msup><mrow></mrow><mn>210</mn></msup><mi>Pb</mi></mrow></semantics></math></inline-formula>, producing <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula>-emissions with energies ranging from 10 <inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula> to several 100 <inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula> when they decay; this range is detectable in silicon sensors. In this paper we test a CMOS camera (O<span style="font-variant: small-caps;">xford</span> I<span style="font-variant: small-caps;">nstruments</span> Neo 5.5) for its general performance as a detector of X-rays and low energy <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula>-rays and assess its sensitivity relative to the World Health Organization upper limit on lead in drinking water. Energies from 6 <inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula> to 60 <inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula> are examined. The CMOS camera has a linear energy response over this range and its energy resolution is for the most part slightly better than 2%. The Neo sCMOS is not sensitive to X-rays with energies below <inline-formula><math display="inline"><semantics><mrow><mo>∼</mo><mspace width="-0.166667em"></mspace><mspace width="-0.166667em"></mspace><mn>10</mn><mtext> </mtext><mrow><mi mathvariant="normal">k</mi><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></mrow></semantics></math></inline-formula>. The smallest detectable rate is <inline-formula><math display="inline"><semantics><mrow><mn>40</mn><mo>±</mo><mn>3</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi>Hz</mi></semantics></math></inline-formula>, corresponding to an incident activity on the chip of <inline-formula><math display="inline"><semantics><mrow><mn>7</mn><mo>±</mo><mn>4</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi>Bq</mi></semantics></math></inline-formula>. The estimation of the incident activity sensitivity from the detected activity relies on geometric acceptance and the measured efficiency vs. energy. We report the efficiency measurement, which is 0.08(2)% (0.0011(2)%) at <inline-formula><math display="inline"><semantics><mrow><mn>26.3</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula> (<inline-formula><math display="inline"><semantics><mrow><mn>59.5</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula>). Taking calorimetric information into account we measure a minimal detectable rate of <inline-formula><math display="inline"><semantics><mrow><mn>4</mn><mo>±</mo><mn>1</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi>Hz</mi></semantics></math></inline-formula> (<inline-formula><math display="inline"><semantics><mrow><mn>1.5</mn><mo>±</mo><mn>1</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi>Hz</mi></semantics></math></inline-formula>) for <inline-formula><math display="inline"><semantics><mrow><mn>26.3</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula> (<inline-formula><math display="inline"><semantics><mrow><mn>59.5</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mrow><mi mathvariant="normal">e</mi><mspace width="-0.21251pt"></mspace><mi mathvariant="normal">V</mi></mrow></semantics></math></inline-formula>) <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula>-rays, which corresponds to an incident activity of <inline-formula><math display="inline"><semantics><mrow><mn>1.0</mn><mo>±</mo><mn>6</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi>Bq</mi></semantics></math></inline-formula> (<inline-formula><math display="inline"><semantics><mrow><mn>57</mn><mo>±</mo><mn>33</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi>Bq</mi></semantics></math></inline-formula>). Toy Monte Carlo and Geant4 simulations agree with these results. These results show this CMOS sensor is well-suited as a <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula>- and X-ray detector with sensitivity at the few to 100 ppb level for <inline-formula><math display="inline"><semantics><mrow><msup><mrow></mrow><mn>210</mn></msup><mi>Pb</mi></mrow></semantics></math></inline-formula> in a sample.