How can I use the Inspector USB to detect radiation in food and water?
A Geiger counter is a "Yes or no and how much" type of detector. They cannot determine the
distribution of the incident radiation energy, so they cannot identify which potential isotopes are
present. To identify specific isotopes, a radiation spectrum analyzer with a sensitive enough scintillation
detector for the application would be necessary. Geiger counters are ideal for basic screening, especially
if you do long timed counts and, in most instances, will give you an indication regarding foods that are
significantly contaminated.
When using a Geiger counter to test food, you should take into consideration that the meter is likely
missing a bit of the radiation. This is due to the shielding of the radiation by the density of food, and the
limitations posed by the detection range of the meter. Alpha radiation can be detected on the food's
surface, but can be blocked if there is internal contamination. You can better test food by grinding it into
a paste and taking a timed count. This may give an indication that you have contamination in your food,
though it will not qualify what type of radiation may be present in the sample.
Water and food can also be a shield for radiation, so unless there is gamma radiation our instruments
are not the most ideal without a little processing of the material in question (beta and alpha will not
move very far in water and will be shielded by it). You can take a sample of the water and run it through
a filter and test the filter or you can evaporate it down and test the swipe on an Inspector USB with a
Wipe Test Plate, however, the URSA-II with the appropriate detector would be much more efficient for
this application, but scintillation based instruments are more expensive than the handheld GM based
alternatives. Regardless, most of the higher energy betas and gamma radiation that falls within the
sensitivity of the detector will be measured.
It is important to remember to establish a background count prior to surveying your samples. To do this,
use your Inspector in the Timed Count mode and take a background count of at least 10 minutes. Then,
divide the total counts displayed on the unit by the number of minutes of your count. For instance, if
you take a 10 minute timed count, divide the total counts by 10. If you're taking a 24 hour background
count, then divide the total by 1440 (the number of minutes in a 24 hour period) to get your Counts Per
Minute background level. The longer you take a timed count, the more statistically accurate your
reading will be. You will then subtract that amount from the readings of your sample.