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Pardon for my ignorance in physics; I just want to get some accurate information about the Fukushima accident. According to various sources I can find (such as this article) the total amount of tritium in Fukushima wastewater is about 860 trillion Bq, and the amount of carbon-14 and strontium-90 are 53.7 billion Bq and 37.5 billion Bq respectively (if they succeed in retreating the water).

I know that 1Bq means one decay per second, and 1Bq of tritium probably differs from 1Bq of carbon-14, but how exactly are they different? Can they be compared directly? Wikipedia says the decay energy of tritium and carbon-14 are 0.018590 and 0.156476 MeV. Can I say that 1Bq of carbon-14 is "as harmful as" $\frac{0.156476}{0.018590}\approx 8.42$ Bq of tritium? Or is this even the correct way to calculate the amount of energy emitted?

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    $\begingroup$ Harmful to what? Radiation absorbed dose (rad) and radiation effect man (rem) are two different things. Becquerels just tells you the decay rate, not what it does to you. Decay type (alpha, beta, gamma), energy, and where in the body (external vs internal at the least) all impact the effect on you as a person. Alpha emitter external to the body is not a problem, but inside you is a big problem, for example. $\endgroup$
    – Jon Custer
    Commented Jul 23, 2021 at 20:15
  • $\begingroup$ These are difficult to compare. Alpha radiation, beta radiation, and gamma rays, all come from radioactive materials, but their effects are very different, even when the same radiation rate is present. $\endgroup$
    – David White
    Commented Jul 24, 2021 at 0:00

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Congratulations, you understand the important distinction between activity and dose. This is something that many people (and news people) don't understand.

Activity (measured in Bq) is a measure of how fast something is decaying, but it doesn't say anything about the type of radiation emitted. Tritium and strontium may have the same activity, but they emit different types of radiation, and therefore have different levels of "harm".

Equivalent Dose is a measure of how "harmful" a type of radiation is. Equivalent Dose is going to depend on the:

  1. activity of the radiation (Bq)
  2. time spent with the radiation (exposure)
  3. type of radiation emitted (e.g. alpha, beta, gamma, neutron)
  4. energy of the radiation emitted (for example 1 keV vs. 10 MeV)

The units of dose are usually given in Sievert (modern SI unit) or the rem (older but commonly used unit).

Unfortunately, it isn't straightforward to convert activity to dose. Radioactive almost always emit more than one type of radiation, so you usually use a computer program to do this.

Another thing to consider is the biological hazard of the radiation. Some radiation passes through the body fairly quickly, and some radiation stays in the body for a long time. Strontium as absorbed by your bones and stays in the body a long time. Tritium is bound to water and passes through the body fairly quickly.

If you read about the effects of tritium, you will find out that the radioactivity effects of tritium are very low to humans. The radiation it emits is fairly low and it doesn't accumulate in the body. Most countries can't agree on what a "dangerous level" of tritium is because there are no cases of people being harmed by tritium. Strontium is a different story.

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