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Problem

Interventional nuclear medicine is a specialty in medicine that uses radioactive isotopes to treat various medical ailments. These radioactive isotopes, or radioisotopes, are often attached to a specific biomolecular compound that targets a particular organ when injected intravenously or ingested orally. Once these radioisotopes reach their primary site of action, they remain in the targeted tissue until they undergo a radioactive decay process. This radioactive decay produces ionizing radiation that destroys the affected tissue. The short distance through which the radiation acts leaves the distant noninvolved tissues virtually unharmed.
There are various types of radioisotopes that are useful in destroying cancerous or hyperactive cells. Radioisotopes are selected for therapy based on their type and energy emissions, half-life, and chemical behavior.
Most therapeutic radioisotopes are either beta or alpha emitters. Beta emitters release highly energetic electrons that can penetrate several millimeters of tissues depending on their maximal energy emission (Estart subscript, m, a, x, end subscript). Alpha emitters release large helium nuclei into the surrounding tissues. These helium nuclei are roughly 100 to 1000 times more likely to cause significant biological damage than beta particles, but have a small range of action. Alpha emitters are used to deliver radiation in a highly localized manner, as most alpha-particles can only penetrate a few micrometers away from the source of emission. A table of some the most common therapeutic radioisotopes is provided Table 1.
Table 1: Characteristics of Various Therapeutic Radioisotopes
RadioisotopesType of EmissionEstart subscript, m, a, x, end subscript (MeV)Half-life (hrs)
Copper-64Beta decay0.57 and 0.6612.8
Copper-67Beta decay0.5762
Iodine-131Beta decay0.61193
Phosphorus-32Beta decay1.71342
Yttrium-90Beta decay2.2764
Actinium-225Alpha decay5.97.2
Bismuth-213Alpha decay5.8 and 8.40.78
Which of the following graphs correctly illustrates the radioactive decay curve of copper-64, iodine-131, and yttrium-90?