A certain isotope has a half-life of 32.4 hr and a relative biological effective

Question

A certain isotope has a half-life of 32.4 hr and a relative biological effectiveness of 3.50. A sample of this isotope initially delivers an absorbed dose of 0.240 Gy to 250 g of tissue.

(a)        What was the initial equivalent dose to the tissue in rem and in sieverts?

(b)        How many joules of energy did the 250-g sample initially receive from the isotope?

The radioactive nuclei 60Co is widely used in medical applications. It undergoes beta decay, and the total energy of the decay process is 2.82 MeV per decay event. The half-life of this nucleus is 272 days. Suppose that a patient is given a dose of 6.9 pCi of 60Co. If all of this material decayed while in the patient's body, what would be the total energy deposited there? (1 Ci = 3.70 x 10^10 decay's/sec)

Explanation / Answer

a) Dose equivalent = dose*weight

= 0.240 Gy*3.5

= 0.24*100 rad*3.5 (because 1 rad = 1/100 Gy)

= 84 rem

Since 1rem = 1/100 sieverts

84 rem = 84/100 sieverts = 0.84 sieverts

b) Energy = dose * mass

=0.240 J/kg * 0.250kg

=0.060 J

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