32.3 Therapeutic Uses of Ionizing Radiation

A beam of 168-MeV nitrogen nuclei is used for cancer therapy. If this beam is directed onto a 0.200-kg tumor and gives it a 2.00-Sv dose, how many nitrogen nuclei were stopped? (Use an RBE of 20 for heavy ions.)

Calculate the dose in Sv to the chest of a patient given an x-ray under the following conditions. The x-ray beam intensity is $\text{1}.\text{50 W} /\text{m}^{2}$, the area of the chest exposed is $\text{0}.\text{0750} \text{m}^{2}$, 35.0% of the x-rays are absorbed in 20.0 kg of tissue, and the exposure time is 0.250 s.

What is the mass of $^{60} \text{Co}$ in a cancer therapy transillumination unit containing 5.00 kCi of $^{60} \text{Co}$?

Naturally occurring $^{\text{40}} \text{K}$ is listed as responsible for 16 mrem/y of background radiation. Calculate the mass of $^{\text{40}} \text{K}$ that must be inside the 55-kg body of a woman to produce this dose. Each $^{\text{40}} \text{K}$ decay emits a 1.32-MeV $\beta$, and 50% of the energy is absorbed inside the body.

The annual radiation dose from $^{14} \text{C}$ in our bodies is 0.01 mSv/y. Each $^{14} \text{C}$ decay emits a $\beta^{–}$ averaging 0.0750 MeV. Taking the fraction of $^{14} \text{C}$ to be $1.3 \times 10^{–12} \text{N}$ of normal $^{12} \text{C}$, and assuming the body is 13% carbon, estimate the fraction of the decay energy absorbed. (The rest escapes, exposing those close to you.)