No abstract

The public reporting burden for this collection of information i2 estinated to averege 1 hour per response includOing the time for reviewinlg ontructognz. newctmng **isting data sources gothermlg and meainta"'kng thne dole needed. end completing and reviewing the collection Of information. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORIMONITOR'S ACRONYM(S)USAF, AFRL AF Office of Scientific Research 875 N. Randolph St. Roomn 3112 SPONSORIMONITOR'S REPORT NUMBERIS)Arlingtoll. VA '))')3& Jl__ -^__1_.Iq 8 DISTRIBUTION/AVAILABILITY STATEMENT j AFRL-SR-AR-TR-07-0442Approved for public release; distribution unlimited. SUPPLEMENTARY NOTES ABSTRACTPopulations of nuclear spin isomiers of 1781 Ifm2 can be triggered to release their stored energies by the absorption of x-rays having energies in the range 9-13 keV. We have found the basic absorption spectrum for triggrering to be approximately 0.16d/ of the cross section for photoionization of the L-shell electrons surrounding the isomneric nuclei. The maximum effect is induced by X-rays with energies exceeding the threshold for the pholoionization of L3 electrons by amounts less than 10 eV. Absorption of a photon of that energy. around 9567 eV triggers the release of 2.446 MeV, thus producing a gain of radiative energy of'256 times for each event. Confidence ill the observations of such triggering is better than 10 followed by 1823 zeros to I. SUBJECT TERMSNuclear spin isomers. FHigh energy density materials.

Photoexcitation of the isomers of 19 nuclides was examined in this work. Four accelerators were used as sources of bremsstrahlung to expose the samples and end-point energies covered the range from 0.5 to 11 MeV. No evidence was found for nonresonant processes of excitation. However, more than half the cases showed enhanced channels for the resonant photoexcitation of isomers with integrated cross sections approaching 10 ' cm keV. These results are three to four orders of magnitude larger than values usually characterizing {y, y') reactions.

No abstract

No abstract