# Conversion of millicuries to Kilograys (?)

Matt Doherty
Is there any conversion between Millicuries (radiation measurement) and Kilograys (absorbed energy)? In other words if there was a radiaition source of 3000 millicuries what would be the equivalent in Kilograys absorbed dose be if a microorganism organism in a saline solution absorbed if a liquid sample of that radiation source were added to the solution. Not sure if this is a conversion that can be done, but wanted to ask anyway. Thank you.

## Answers and Replies

No, not directly, you need to know the specific radioisotope, as well as the activity (disintegrations per second). The curie, ( the current recommended unit is the Becquerel), is a measurement of the rate at which a radioactive material decays ( one Bq is one disintegration per second). The energy released and therefore the energy absorbed depends on the decay products for each disintegration as well as the number of disintegration and the type of radiation emitted, gamma, beta, or alpha.

3.7 x 107 Bq = 1 mCi.

• • berkeman and hutchphd
Staff Emeritus
One would need the decay rate multiplied by the energy per decay (the product proportional to dose rate) and integrated over time to get energy deposited. Of course, one would have to determine how much of the energy of the decay is absorbed locally, as opposed to radiation the escapes from the body of interest.

• • gleem, berkeman and hutchphd
One would need the decay rate multiplied by the energy per decay (the product proportional to dose rate) and integrated over time to get energy deposited. Of course, one would have to determine how much of the energy of the decay is absorbed locally, as opposed to radiation the escapes from the body of interest
This could be a big problem depending on the isotope and the size of the container used for the culture.

I might also add that since the radiation is emitted from a myriad of point sources and since the absorption of radiation is nonuniformly absorbed as it recedes (inverse square law and various absorption processes) one must average the absorption over the path. The Society of Nuclear Medicine's Committee on Medical Internal Radiation Dose (MIRD) had developed methods for calculating the absorbed dose of administered radiopharmaceuticals to human organs which would be similar to the OP situation.

• Astronuc
Staff Emeritus
This could be a big problem depending on the isotope and the size of the container used for the culture.
The OP describes a complicated situation with a microbe, or population of microbes, in a solution. OP
a microorganism organism in a saline solution absorbed if a liquid sample of that radiation source were added to the solution.

A saline solution could contain radioisotopes of Na, Cl or both, or Cs, and other cation or anion. Usually, an external does is applied, which could be electrons or photons (X-ray or gamma), or a mix. We have software for determining the interaction of radiation (electrons and photons) with matter, including solids and liquids. One would usually benchmark an application with distributed dosimeters in order to check the calculated/predicted dose against measured dose.

One would normally use a Monte Carlo (MC) method with a discretized volume. Sources close to surfaces would have some fraction of radiation escape, while sources further in, would have more of their emanations absorbed in the material.

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