The Gamma-Scout is equipped with a sophisticated counter tube from the USA that captures all forms of ionizing radiation (>30 KeV), regardless of radiation source.
Independent of the measuring device, there are nevertheless issues relating to the laws of physics that must be taken into consideration:
- An exact measurement of ionizing radiation from a source requires the measuring facility to be organized in a way that separates the source’s radiation from ambient radiation, and that the distance between the source and sensing element be exactly defined. This CANNOT be achieved with a mobile Geiger counter. However, Gamma-Scout will certainly detect significant radiation (e.g. 1.0 µSv/h at 0.15 µSv/h ambient radiation). The limit set for occupational health and safety is 20 millisievert per year, i.e. an average of approx. 2.2 µSv/h, although radiation does not occur as an average. The 20 mSv/a relate to 50 weeks * 5 days * 8 hours, adding up to 2000 hours/year. This would equate to 10 µSv/h per working hour. If you divide by 8760 (calendar hours), you reach a limit of 2.2 µSv/h. Based on this, you can say that all measurements below 1.0 µSv/h are “background noise”.
- It is important not to confuse dose in µSv/h with activity (scaled in Becquerel). Gamma-Scout calculates the dosage rate from a non-linear correlation of the pulse rate from the counter tube. The basis for the calculation inside the measurement device is a certified cesium-137 emitter (budget Geiger counters work with a simple conversion factor). The activity is defined as 1 decay per second = 1 Becquerel. Because the conversion of an atom into its following atom (via decay) is not necessarily accompanied by the emission of ionizing radiation, the virtually infinite decay patterns make this correlation extremely complex.
- The dose (and the associated limits) “measures” the external radiation to which people and the measuring device are exposed. The effect of radiation sources within the human body (from build-up inside the body in organs, blood, etc.) is a wide-ranging and complex medical topic that can only be diagnosed and treated with specialist medical training. It is investigated in very large clinic facilities using different measuring procedures and processes.
Is irradiated fruit contaminated? Or to put it another way: Does irradiation activate foodstuffs and turn them into radiation sources?
No, because the energy used by such irradiation equipment is considerably below 7 MeV, the lowest level at which activation can occur.
Can the Gamma-Scout measure contaminated foodstuffs?
Gamma-Scout measures ambient radiation and radiation caused by contamination. However, identification of the specific gamma energy of the respective isotope is only possible via gamma spectroscopy.
Ambient radiation is comprised of cosmic radiation and environmental radiation (rock, earth, construction materials, plants, animals and people). Cosmic radiation is dependent upon the altitude above sea level and consists of electrons/photons, hadrons (subatomic particles) and myones (heavy electrons). Radiation from the surroundings is largely determined by the proportion of potassium in rock, construction materials, etc. Further contributors are the radioactive isotopes from the uranium and thorium radioactive series. Airborne contamination comes mainly from radon-222 gas (alpha emitter) from the uranium-238 radioactive series.
Furthermore, successful measurement of contamination requires pulse rates to be considerably above the statistical variations of ambient radiation.
Example: Measurement of the subsoil and a food sample with a mass of 1 kg leads to an hourly figure of 1000 pulses. Further measurements with two sensors deliver one result of 1090 pulses/hour and 1200 pulses/hour. Statistical variations in radiation mean that deviations approximately in the order of 3 times the root of the measurement value (3* root 1000 = 95), i.e. >1095 pulses are notable. The first measurement value of 1090 pulses/hour is thus within the statistic, while the second measurement value of 1200 pulses/hour could have been caused by contamination.