During morning output checks, a Cobalt-60 unit reads lower than it did last month, while the linac reads the same as yesterday. The physics group asks the therapists to explain the pattern. Which statement correctly compares how the two beams are produced and how their output changes over time?
Select an answer to reveal the explanation.
Short Explanation
A sealed source is its own engine, so you can’t adjust its scheduled decline. A linac holds no isotope, so its output shifts with tuning and operating conditions. Your half-life clock explains the lower Cobalt-60 reading.
Full Explanation
The correct comparison is that a Cobalt-60 unit emits radiation from a sealed radioactive source, whose activity and output decrease at the isotope’s fixed physical decay rate. A linac produces x-rays or electrons through accelerator operation rather than radioactive decay, so its output can shift with tuning and operating conditions. Monitor-chamber feedback is a real linac feature, but it monitors delivered dose during irradiation; it does not prevent changes in calibrated output or guarantee constancy between calibrations. Dose-rate mode can affect linac operation, but treating it as the main determinant of output and discounting tuning or operating conditions is incorrect. Daily output QA checks constancy, but measurement does not itself keep output at the reference level; investigation and appropriate adjustment or calibration are separate steps. Exam caveat: distinguish radioactive-source decay from machine-output constancy, and do not confuse monitoring or QA with automatic correction. Practical check: compare the Cobalt-60 reading with its decay-corrected expected value, then review the linac’s daily output-constancy results and recent service or tuning history.