J. Phys. IV France 127 (2005) 163-168
DOI: 10.1051/jp4:2005127025

The use of selected monochromatic X-rays to induce a cascade of gamma transitions from the 31-year nuclear isomer to the 4 second isomeric state of Hf-178

N.C. Zoita¹, F. Davanloo¹, C.B. Collins¹, J.M. Pouvesle², S. Emura³, I.I. Popescu⁴, V.I. Kirischuk⁵, N.V. Strilchuk⁵, T. Uruga⁶ and Y. Yoda<sup>6

1</sup>  Center for Quantum Electronics, University of Texas, Dallas, PO Box 830688, Richardson, TX 75083-0688, USA
²  GREMI, CNRS, Université d'Orléans, Orléans, France
³  Institute of Scientific and Industrial Research, University of Osaka, Osaka 567-0047, Japan
⁴  IGE Foundation, Bucharest, Romania
⁵  Institute for Nuclear Research, Kiev, Ukraine
⁶  SPring-8/JASRI, Sayo-gun, Hyogo 679-5198, Japan

Abstract
The Hf-178m2 nuclear spin isomer stores 2.45 MeV of energy for a half life of 31 years. Unperturbed, such nuclei radiate away the stored energy through the emission of gamma photons from electromagnetic (EM) transitions occurring within the nuclei. It has been shown that the irradiation of samples containing such nuclei with pulsed X-rays can accelerate the rate of the EM transitions by relaxing the selection rules upon changes of angular momenta. To date, most work has been done with incident X-ray energies between 9 and 10 keV, and in such cases the acceleration of the rate of gamma emission is immediate. Reported here is a channel for deexcitation excited by more energetic X-rays that results in a cascade of gamma transitions that includes a 4 second statistical time lag. This more protracted release of the energy stored in samples of the Hf-178m2 nuclear isomers encourages consideration of potential mechanical and thermal applications.

© EDP Sciences 2005