Measuring radioactivity

Radioactivity : a natural phenomenon

Although it usually evokes danger, radioactivity still remains a natural and omnipresent process, to which all matter is permanently exposed. In practice, everything is radioactive and the radionuclides responsible of this radioactivity are for the most part measurable.

Radioactivity originates from the desintegration of instable atomic cores. These desintegrations are followed by highly energetic particles and electromagnetic rays emissions that may interract with the surrounding matter by converting stable atoms into ions. These are ionising radiations.

Ionising radiations

There are 3 types of ionising radiations :

  • Alpha (α): It consists in the emission of a helium (He) core. These are very high energy and high mass particles. They cannot travel in the air toward more than 7 cm, and they can be easily stopped with a sheet of paper or by skin surface. Their radiologic toxicity is very important in the case of internal exposure (ingestion or inhalation).
  • Beta (β): It is an electron (β) or positron (β+) emission. These are low mass and medium energy particles. They may travel in the air toward a few meters. Beta particles are not higlhy penetrative and can be stopped by a thin aluminum layer or a few mm of steel.
  • Gamma (γ): These radiations are very highly energetic (10 keV to 3 MeV) photons that follow most of the time alpha and beta desintegrations. It is a highly penetrative electromagnetic radiation that can be mitigated by very dense materials, such as lead or gold.

What we measure

It is the gamma phtons that are measured at LAFARA lab. Each photon has a specific energy related to the atom that generated it. The principle of gamma spectrometry is thus based on a statistical counting of gamma photons, discriminated by their energy.

LAFARA is specialised in measuring radioactive isotopes such as : 7Be, 40K, 60Co, 131I, 134Cs, 137Cs, 210Pb, 226Ra, 228Ra, 228Th, 234Th, 241Am, etc…

How we measure it

It is quite simple : we put a sample close to a germanium crystal and we wait! Every single gamma ray that comes out from the sample and goes through the Ge crystal can be recorded. Eventually, we obtain a total count for each radioisotope. This count is related to both the analysis time and the sample mass, which lead us to obtain a mass activity, usually given in Becquerel per kg (Bq/ kg). Such a measurement is non destructive and the sample can be shipped back to his/her owner after analysis, if needed.