Jan Batteux

Design of a multichannel ultra-high-resolution superconducting gamma-ray spectrometer

Superconducting Gamma-ray microcalorimeters operated at temperatures around ~0.1 K offer an order of magnitude improvement in energy resolution over conventional high-purity Germanium spectrometers. The calorimeters consist of a ~1 mm3 superconducting or insulating absorber and a sensitive thermistor, which are weakly coupled to a cold bath. Gamma-ray capture increases the absorber temperature in proportion to the Gamma-ray energy, this is measured by the thermistor, and both subsequently cool back down to the base temperature through the weak link. We are developing ultra-high-resolution Gamma-ray spectrometers based on Sn absorbers and superconducting Mo/Cu multilayer thermistors for nuclear non-proliferation applications. They have achieved an energy resolution between 60 and 90 eV for Gamma-rays up to 100 keV. We also build two-stage adiabatic demagnetization refrigerators for user-friendly detector operation at 0.1 K. We present recent results on the performance of single pixel Gamma-ray spectrometers, and discuss the design of a large detector array for increased sensitivity.

TIME-SEQUENCED X-RAY OBSERVATION OF A THERMAL EXPLOSION

The evolution of a thermally‐initiated explosion is studied using a multiple‐image x‐ray system. HMX‐based PBX 9501 is used in this work, enabling direct comparison to recently‐published data obtained with proton radiography [1]. Multiple x‐ray images of the explosion are obtained with image spacing of ten microseconds or more. The explosion is simultaneously characterized with a high‐speed camera using an interframe spacing of 11 μs. X‐ray and camera images were both initiated passively by signals from an embedded thermocouple array, as opposed to being actively triggered by a laser pulse or other external source. X‐ray images show an accelerating reacting front within the explosive, and also show unreacted explosive at the time the containment vessel bursts. High‐speed camera images show debris ejected from the vessel expanding at 800–2100 m/s in the first tens of μs after the container wall failure. The effective center of the initiation volume is about 6 mm from the geometric center of the explosive.

DETAILED COMPARISON OF BLAST EFFECTS IN AIR AND VACUUM

The role of air as an energy transfer medium was examined experimentally by subjecting identical large‐area rectangular witness plates to short‐range blast effects in air and vacuum (∼50 mtorr) at 25 °C. The expanding reactant front of 3 kg C4 charges was observed by fast camera to be cylindrically symmetric in both air and vacuum. The horizontal component of the reactant cloud velocity (perpendicular to the witness plates) was constant in both cases, with values of 3.0 and 5.9 km/s for air and vacuum, respectively. As a result of the blast, witness plates were plastically deformed into a shallow dish geometry, with local maxima 30 and 20 mm deep for air and vacuum, respectively. The average plate deflection from the air blast was 11 mm, ∼10% deeper than the average vacuum plate deflection. Shock pressure estimates were made with a simple impedance‐matching model, and indicate peak values in the 30–50 MPa range are consistent with the reactant cloud density and velocity. However, more detailed analysis is...

Mix and instability growth from oblique shock

We have studied the formation and evolution of shock-induced mix resulting from interface features in a divergent cylindrical geometry. In this research a cylindrical core of high-explosive was detonated to create an oblique shock wave and accelerate the interface. The interfaces studied were between high-explosive/aluminum, aluminum/plastic, and plastic/air. Surface features added to the aluminum were used to modify this interface. Time sequence radiographic imaging quantified the resulting instability formation from the growth phase to over 60 μs post-detonation, thus allowing the study of the onset of mix and evolution to turbulence. The plastic used here was porous polyethylene. Radiographic image data are compared with numerical simulations of the experiment.