Search for X-Ray Induced Acceleration of the Decay of the 31-yr Isomer 178Hf Using Synchrotron Radiation

Ahmad, I ; Banar, J C ; Becker, J A ; Gemmell, D S ; Kraemer, A ; Mashayekhi, A ; McNabb, D P ; Miller, G G ; Moore, E F ; Pangault, L N ; Rundberg, R S ; Schiffer, J P ; Shastri, S D ; Wang, T F ; Wilhelmy, J B

Lawrence Livermore National Laboratory

关键词: Advanced Photon Source;    Acceleration;    Rotational States;    Decay;    Energy Sources;   

DOI  :  10.2172/15004655
RP-ID  :  UCRL-ID-148266
RP-ID  :  W-7405-ENG-48
RP-ID  :  15004655

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来源: UNT Digital Library

【 摘 要 】

Releasing the energy stored in an isomeric nuclear state in a controlled way with an atomic or electromagnetic trigger is an attractive speculation: the energy gain may be on the order of the ratio of nuclear/atomic energies - MeV/keV. (Nuclear isomers are loosely defined as excited nuclear states with lifetimes longer than 10{sup -9} s.) Nuclear isomers, therefore, represent an opportunity for a stand-alone energy source if suitable schemes for trigger and control of the energy release can be found. Potential applications include space drive, as well as very bright {gamma}-ray sources. The nucleus {sup 178}Hf has a nuclear isomer with excitation energy E{sub x} = 2.447 MeV. The 2.447-MeV isomeric state decays slowly (t{sub 1/2} = 31 y) to the nearby state at 2.433 MeV. The J{sup {pi}} = 13{sup -} state loses energy in a rapid (t {approx} 10{sup -12} s) {gamma}-ray cascade ending at the 8{sup -} rotational band head which in turn decays via the ground-state rotational band cascade. The {gamma}-ray cascade is delayed at the 8{sup -} state at 1.147 MeV, since the 8{sup -} state is also isomeric, with t{sub 1/2} = 4 s. Very scarce quantities of the 16{sup +}, 31-yr isomer are available for research ({approx} 10{sup 15} atoms). Reports of triggered decay of the {sup 178}Hf isomer induced by x-rays delivered by a dental x-ray machine have been made [2,3]. Enhancements of {approx} 1 - 2% in the isomer decay rate (dN/dt = - (1 + {var_epsilon})N/{tau}) had been reported for various {gamma}-rays in the cascade (distinguished by red and vertical lines in Figure 1). The reported integrated cross section for triggering the decay is cm{sup 2} keV, so large as to demand new physics. We have sought to verify these reports taking advantage of the intense photon flux available at the Advanced Photon Source.