Hubertus Giefers

Radiation-Induced Decomposition of PETN and TATB under Extreme Conditions

We conducted a series of experiments investigating decomposition of secondary explosives PETN and TATB at varying static pressures and temperatures using synchrotron radiation. As seen in our earlier work, the decomposition rate of TATB at ambient temperature slows systematically with increasing pressure up to at least 26 GPa but varies little with pressure in PETN at ambient temperature up to 15.7 GPa, yielding important information pertaining to the activation complex volume in both cases. We also investigated the radiation-induced decomposition rate as a function of temperature at ambient pressure and 26 GPa for TATB up to 403 K, observing that the decomposition rate increases with increasing temperature as expected. The activation energy for the TATB reaction at ambient temperature was experimentally determined to be 16 +/- 3 kJ/mol.

Characteristic temperature dependence of the4foccupancy in the Kondo systemCeSi2

We have used temperature dependent x-ray absorption at the Ce-L3 edge to investigate the recently discovered Kondo compound Ce2Rh3Al9. The systematic changes of the spectral lineshape with decreasing temperature are analyzed and found to be related to a change in the

Novel rhenium gasket design for nuclear resonant inelastic x-ray scattering at high pressure

4f

High pressure X-ray diffraction study of all Fe-Sn intermetallic compounds and one Fe-Sn solid solution

occupation number, n_f, as the system undergoes a transition into a Kondo state. The temperature dependence of

Phonon density of states of metallic Sn at high pressure.

n_f

Structural study of SnO at high pressure

indicates a characteristic temperature of 150K, which is clearly related with the high temperature anomaly observed in the magnetic susceptibility of the same system. The further anomaly observed in the resistivity of this system at low temperature (ca. 20K) has no effect on n_f and is thus not of Kondo origin.

Radiation-induced decomposition of PETN and TATB under pressure

For the first time, a highly absorbing element, rhenium, has been proven to be a strong, reliable, and safe gasket material for achieving high pressure in nuclear resonant inelastic x-ray scattering (NRIXS) experiments. Rhenium foil was cut into rectangular slices and in order to reduce absorption, the elevated imprint due to preindenting of the gasket is removed using electrical discharge machining. By utilizing this novel gasket design, transmission losses were mitigated while performing NRIXS experiments conducted on the 119Sn and 57Fe Mössbauer isotopes.