An apparatus includes a support and a radioactive source on the support. The radioactive source includes nuclei. An excitation element is coupled to the support. Upon activation of the excitation element, radiation emission from the radioactive source is reduced. The excitation element includes a vibration source. Excitation is transferred from nuclei of the radioactive source to nuclei of the support. The excitation transfer occurs in bulk from multiple nuclei of the radioactive source. The excitation transfer causes emissions from the support.