Storage of Nuclear Excitation Energy through Magnetic Switching

The decay rate of {sup 57}Fe nuclei in an {sup 57}FeBO{sub 3} crystal excited by 14.4keV synchrotron radiation pulses was controlled by switching the direction of the crystal magnetization. Abrupt switching some nanoseconds after excitation suppresses the coherent nuclear decay. Switching back at later times restores it, starting with an intense radiation spike. The enhanced delayed reemission is due to the release of the energy stored during the period of suppression. Suppression and restoration originate from drastic changes of the nuclear states and of the interference within the nuclear transitions. {copyright} {ital 1996 The American Physical Society.}