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How does californium-252 help start up and calibrate nuclear reactors?

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Californium-252 is a highly effective tool for nuclear reactors because it serves as an intense source of neutrons, with one gram emitting approximately $2.3 \times 10^{12}$ neutrons per second.1

Its primary industrial application in this field is acting as a start-up source for nuclear reactors. Because it undergoes spontaneous fission, it provides a reliable and consistent flux of neutrons necessary to initiate the chain reaction process safely. Additionally, this neutron output is utilized to calibrate reactor instrumentation, ensuring that monitoring systems are accurate before and during operation.21

Beyond its role in reactors, californium-252 is used in various other fields, including neutron-activation analysis for mineral prospecting, oil-well monitoring, neutron radiography, and the detection of explosives at airports. It is also employed in medical settings for the irradiation of tumors that do not respond well to traditional gamma-ray treatments.1