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Hidden in the nucleus of a gold atom lies a potential future cancer treatment. When a gold target is struck by a gamma ray with an energy of about 30 megaelectronvolts, one of the nuclei loses a proton and a neutron, transforming into a rare platinum isotope — platinum-195m. This isotope is unstable: as it decays, it releases Auger electrons — tiny particles that travel only a few millionths of a millimeter and tear apart DNA strands. For a cancer cell, such a precise strike is lethal, while surrounding healthy tissue remains largely unharmed.

The challenge is producing enough platinum-195m. Physicists at Duke University irradiated a stack of concentric gold rings at the HIγS facility — a gamma-ray source with precisely tunable energies. After irradiation, they measured the radioactivity of the targets and found that the reaction producing platinum only begins at a threshold of 30 MeV, with a noticeable yield appearing at even higher energies. These are the first experimental data for this reaction near the threshold.

Why are such measurements important? To enable the production of platinum-195m for medical use. Platinum radioisotopes are increasingly used in targeted therapy — treatment that hits the tumor precisely without affecting the rest of the body. But this requires isotopes with high specific activity, meaning a large fraction of radioactive atoms in the sample. Cross-section data are like a recipe for an accelerator: knowing them, you can calculate how much gold to irradiate, at what energy, and for how long, to obtain the desired amount of the drug.

The gold used in jewelry could become a life-saving resource. The experiment showed that the path from a gold ring to radioactive platinum is real, but it requires powerful accelerators. Now physicists and doctors have the first numbers to plan that path.