I. Certain thyroid treatments involve large doses of the radioactive isotope lod

Question

I. Certain thyroid treatments involve large doses of the radioactive isotope lodine-131. Interestingly, very large doses are less dangerous than low doses, as the treatment kills thyroid tissue that would otherwise likely become cancerous. Iodine-131 undergoes beta decay with a half life of 8.0 days. Calculate the rate constant for the decay of this radioisotope. [2 sf A prescribed dose for a hypothetical patient has an initial activity of 100 MBg. A Becquerel (Bq) is one decay per second, thus the initial activity is 100 million decays per second. Cakculate the remaining activity after 4 half-lives (32 days 1 month). Assume that none of the iodine is excreted. [2 sf] 2. 3. If a prescribed dose is 185 MBa, calculate the activity after 90 days. [2 sf] 4. Express the remaining activity after 90 days as a fraction (ppm) of the original 185 MBq dose. [2 sf s. Before the becquerel was adopted as the Si unit of radioactivity, the curie (Ci) was used. One curie equals the activity of 1 gram of radium-226. If it is known that 100 MBq 2.7 ma, convert the activity of 1 gram of radium-226 to becquerels. [2 sf] Units / Sig fgs Cakculations Other

Explanation / Answer

1. Radioactive decay is the first order reaction.

For first order reaction, rate constant (k) = 0.693 / half-life(t1/2).

Rate constant (k) = 0.693 / 8.0 days = 0.087 days-1

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