What isotope remains after the I-131decays? Radioactive isotopes are often intro

Question

What isotope remains after the I-131decays?
Radioactive isotopes are often introduced into the body through thebloodstream. Their spread through the body can then be monitored bydetecting the appearance of radiation in different organs.^{131}I, a beta ^ - emitter with a half-lifeof 8.00 {rm d}, is one such tracer. Supposea scientist introduces a sample with an activity of425 {rm Bq} and watches it spread tothe organs. Assuming that the sample all went to the thyroid gland, what willbe the decay rate in that gland 24.0 {rm d} (about 3frac{1}{2} weeks) later? If the decay rate in the thyroid 24.0 {rm d} later is actually measuredto be 17.0 {rm Bq}, what percent of the tracerwent to that gland? What isotope remains after the I-131decays? _{53}^{130}{rm I} _{52}^{131}{rm Te} _{54}^{131}{rm Xe} _{52}^{130}{rm Te}

Explanation / Answer

Not sure if this is how you would actually do this, but this is how I got the answer. There would be 3 decays (8*3 = 24) So divide 300 by 2, three times, or divide by 8 (2^3). This gets you 37.5 Bq.

Because the actual sample is 17, you count upwards three decays, so multiply by 2 three times, or multiple by 8 (2^3). You'll get 136 Bq. To find the percent, you divide 136 by 300, and you get 45.3%.

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