The table shows five different radioactive isotopes. Which isotopes would be suitable for use in gamma-ray beam therapy?
Looking at the table, we see these five isotopes listed, iridium-192, neodymium-144, Cesium-137, uranium-238, and polonium-218. Even if these names aren’t familiar, that’s alright. All we need to know is that these are radioactive isotopes. And then in the table, we see what kind of radiation they emit. That information is covered in the row called decay type. And then below that, we’re told the half-life of each of these isotopes. Half-life recall is the time it takes for a radioactive sample to decay to half its original amount.
So for example, if we were considering a sample of uranium-238, an isotope that has a half-life of 4.5 times 10 to the ninth years, as four-and-a-half billion years. This means that if we had a 100-gram sample of uranium-238, then if we waited 4.5 of billion years, then that sample would have decayed to a 50-gram sample of uranium-238. And by the way, that 50 grams of mass which is decayed wouldn’t have disappeared. It would have just transferred to another element.
Anyway, so that’s half-life, the time it takes for a radioactive sample to decay to half its original amount. But in this question, we’re not so concerned about time lines as we are about which isotopes would be suitable for a certain type of beam therapy, 𝛾-ray beam therapy. To answer this question, we’ll need to look at the second row of our table, the one which shows us the decay type of each of the isotopes. The first isotope, iridium-192, and its 𝛽 radiation as well as 𝛾 radiation. Since it emits 𝛾 rays, that means it is a candidate for 𝛾-ray beam therapy.
Moving on, neodymium-144 only emits α particles and, therefore, isn’t useful as a 𝛾-ray beam. Cesium-137, on the other hand, emits 𝛽 particles as well as 𝛾 rays. So this isotope also would be suitable for this type of application. Uranium-238, just like neodymium-144, only emits α particles. And polonium-218 emits α as well as 𝛽 particles but no 𝛾 rays. It is the isotopes that emit 𝛾 rays which would be suitable for use in 𝛾-ray beam therapy. We saw that these two isotopes are iridium-192 and Cesium-137. Since they’re both emit 𝛾 rays, they’re both useful for this type of beam therapy.