91Ó°ÊÓ

Where does fusion occur naturally?$(5.6)$

Why are scientists continuing to try to build a fusion reactor even though the very high temperatures it requires have been difficult to reach and maintain?$(5.6)$

The activity of $\mathrm{K}-40$in a$70.-\mathrm{kg}$human body is estimated to be $120\mathrm{nCi}$. What is this activity in becquerels?$(5.3)$

The activity of$\mathrm{C}-14$in a $70$-kg human body is estimated to be$3.7\mathrm{kBq}$. What is this activity in microcuries? (5.3)

The activity of C-14 in a 70kg human body is estimated to be 3.7 kBq. What is this activity in microcuries?

If the amount of radioactive phosphorus-$32$, used to treat leukemia, in a sample decreases from $1.2\mathrm{mg}$to $0.30\mathrm{mg}$in$28.6$days, what is the half-life of phosphorus-$32$?$(5.4)$

If the amount of radioactive iodine-$123$, used to treat thyroid cancer, in a sample decreases from $0.4$ my to$0.1\mathrm{mg}$ in $26.4\mathrm{h}$, what is the half-life of iodinc-$123$? (5.4)

If the amount of radioactive iodine-123, used to treat thyroid cancer, in a sample decreases from 0.4 mg to 0.1 mg in 26.4 h, what is the half-life of iodine-123?

Calcium-$47$, used to evaluate bone metabolism, has a half-life of $4.5$days. $(5.2,5.4)$

a. Write the balanced nuclear equation for the beta decay of calcium-$47$.

b. How many milligrams of a $16-mg$sample of calcium- $47$remain after $18$days?

c. How many days have passed if$4.8\mathrm{mg}$of calcium- $47$decayed to $1.2\mathrm{mg}$of calcium-$47$?

Cesium-$137$, used in cancer treatment, has a half-life of $30yr.(5.2,5.4)$

a. Write the balanced nuclear equation for the beta decay of cesium-$137$.

b. How many milligrams of a $16-mg$sample of cesium-$137$remain after $90yr$?

c. How many years are required for $28\mathrm{mg}$of cesium- $137$to decay to $3.5\mathrm{mg}$of cesium- $137$?