Radioactivity measurements involve counting the characteristic atomic disintegrations of an isotope followed by complex statistical calculations. Each measurement has its own minimum detectable concentration (also known as minimum detectable activity – MDA), or MDC, which varies depending upon sample amount and elapsed time of the measurement. Therefore, each sample result consists of three different values – the calculated activity, the total propagated uncertainty (TPU), and the MDC, reported as: Activity, +/- TPU, MDC. For example, Radium-228 = 6.2 +/- 1.8, 0.95 pCi/L.
Unlike environmental chemistry, radiochemistry measurements are not limited by the Method Detection Limits (MDLs). Lower MDCs and uncertainties may be obtained through increased sample volumes or count times. Based on experience, the laboratory targets standard MDCs that are below most common regulatory requirements. It is always a good idea to know the concentration targets or regulatory requirements for radioisotopes of concern prior to requesting a quote.