ELI5 How is radioactivity measured in water?
What is the unit that is used? What are the thresholds for drinking water vs say irrigation water?
Posted Dec 19, 2022, 8:16 AM UTC
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Well okay- this is beyond an explain to a 5 year old, but I’ll give it my best shot.
First off- Radioactive water: H2O that’s actually giving off nuclear radiation is exceptionally uncommon. For a water molecule itself to give off radiation it would have to be formed with Tritium (hydrogen-3). For all intents and purposes- Hydrogen 3 water is not tested for except around places like particle accelerators where Hydrogen-3 is actually synthesized.
However I’m assuming you are meaning water as the thing that comes out of the taps of your home.
Generally in this water we concern ourselves with two things- dissolved solids and particulate counts. Practically speaking if you were to receive a radioactive dose from water it would be from radioactive material that’s within the water.
And from the best of my knowledge we measure that kind of radiation as we do any other kind of radiation, of which there are two main measurements we can concern ourself with, those being Activity and Absorbed dose.
Activity (measured in Curies or Becquerels) is the amount of radiation a material gives off in a given time. Basically the flow rate of radiation. This is what we would actively measure radioactivity of a sample of water with.
Absorbed dose is the quantity of radiation something receives- usually measured in Rads or Grays. This is how we’d measure the amount of radiation a sample of water would deliver to a human (or other object) over a given period.
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Thank you for this!
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Radioactivity in water can be measured using a variety of techniques, depending on the specific radioisotopes present and the sensitivity and accuracy required. Some common methods for measuring radioactivity in water include:
Gamma spectrometry: This method involves measuring the energy of gamma rays emitted by radioactive isotopes in the water.
Liquid scintillation counting: In this method, a sample of the water is mixed with a scintillation cocktail, which contains chemicals that emit light when exposed to radiation. The light is then detected and used to measure the radioactivity in the sample.
Alpha spectrometry: This method involves measuring the energy of alpha particles emitted by radioactive isotopes in the water.
Ionizing radiation detectors: These devices, such as Geiger counters, can be used to measure the radiation emitted by radioactive isotopes in the water.
Radiometric dating: In some cases, the age of the water can be determined by measuring the levels of radioactive isotopes present, such as carbon-14 or tritium.
Overall, the choice of method for measuring radioactivity in water will depend on the specific goals of the measurement, the resources available, and the characteristics of the water sample.
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The SI unit for radioactivity is the becquerel, which is 1 decay per second. It's the same in every material. If you mean how is radiation exposure measured or how a dose of radiation is determined, there are several different units for that.
If by "thershold" you mean "safety threshold," different jurisdictions set different limits and they don't all use the same units. Some measure by radioactivity using the becquerel but others measure by absorbed dose or tissue-weighted dose.
Yes, I mean safety threshold. Do you have an example of a safety threshold from anywhere by any chance? Doesn't matter where
It's not always straightforward like just one number. Many places have fractional limits for different isotopes or different types of radiation and the might use different units within that. For example:
The U.S. Environmental Protection Agency standard is 0.185Bq per liter of water for radium 226 and radium 228 combined, 0.555 Bq per liter combined for all alpha emitters excluding radium and uranium, 30 micrograms per liter of uranium, and 4 millirem per year combined for all beta emitters.
For some some context on the beta emitters, 4 millirem is about how much radiation you'd be exposed to on a 5-6 hours flight.
Thank you! This is great