Shielded Scintillator for Neutron Characterization

The High Energy Density Physics group is studying the basic science of a novel neutron and gamma ray source for the Defense Threat Reduction Agency to probe nuclear material nondestructively. The neutrons and gamma rays are produced by accelerating ions via a laser into a target and creating fusion neutrons and gamma rays. A scintillator will be used as a time of flight detector to characterize the neutron source. Neutrons and photons produce ionizing radiation in the scintillator which then activates metastable states. These metastable states have both short and long decay rates. The initial photon count is orders of magnitude higher than the neutron count and poses problems for accurately detecting the neutrons due to the long decay state that is activated by the photons. Shielding the scintillator with lead will attenuate the photons but could also delay and scatter the neutrons. A Monte Carlo transport code was used to determine the feasibility of using a shielded scintillator as a time of flight detector. It was found that shielding the scintillator with 5-7 cm of lead is optimal.No embarg

Modeling of torsion stress giant magnetoimpedance in amorphous wires with negative magnetostriction

A model describing the influence of torsion stress on the giant magnetoimpedance in amorphous wires with negative magnetostriction is proposed. The wire impedance is found by means of the solution of Maxwell equations together with the Landau-Lifshitz equation, assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsion stress. The impedance is analyzed as a function of the external magnetic field, torsion stress and frequency. It is shown that the magnetoimpedance ratio torsion dependence has an asymmetric shape, with a sharp peak at some value of the torsion stress. The calculated field and stress dependences of the impedance are in qualitative agreement with results of the experimental study of the torsion stress giant magnetoimpedance in Co-based amorphous wires.Comment: 17 pages, 5 figure

Conceptual Design of an Experiment to Study Dust Destruction by Astrophysical Shock Waves

A novel laboratory experimental design is described that will investigate the processing of dust grains in astrophysical shocks. Dust is a ubiquitous ingredient in the interstellar medium (ISM) of galaxies; however, its evolutionary cycle is still poorly understood. Especially shrouded in mystery is the efficiency of grain destruction by astrophysical shocks generated by expanding supernova remnants. While the evolution of these remnants is fairly well understood, the grain destruction efficiency in these shocks is largely unknown. The experiments described herein will fill this knowledge gap by studying the dust destruction efficiencies for shock velocities in the range of approximately 10-30 kilometers per second (microns per nanosecond), at which most of the grain destruction and processing in the ISM takes place. The experiments focus on the study of grain-grain collisions by accelerating small (1 millimeter) dust particles into a large (approximately 5-10 millimeter diameter) population; this simulates the astrophysical system well in that the more numerous, small grains impact and collide with the large population. Facilities that combine the versatility of high-power optical lasers with the diagnostic capabilities of X-ray free-electron lasers, e.g., the Matter in Extreme Conditions instrument at the SLAC (originally named Stanford Linear Accelerator Center) National Accelerator Laboratory, provide an ideal laboratory environment to create and diagnose dust destruction by astrophysically relevant shocks at the micron scale

Strong Shock Waves in Highly Porous Materials

Strong shock waves traversing through porous materials occur in a broad range of applications. Foamed plastics are a popular material in many high-energy-density physics (HEDP) experiment due to the low, tunable density, and being easily machinable. Shocked foams are also of interest in equation of state (EOS) studies due to the ability to change the initial density to obtain different shocked states. Finally, the effect of porosity on asteroid collisions is needed to understand the cratering mechanism. This dissertation presents experimental and theoretical work related to strong shock waves in highly porous materials. A platform to study shocked foams on the OMEGA EP laser system was developed in the first of a series of shot days. The imaging x-ray Thomson spectrometer (IXTS) was the main diagnostic and the measurement provided information on the compression, shock front location, temperature, and ionization, making it a potentially powerful diagnostic for equation of state measurements. The first shot day demonstrated the ability to perform the x-ray Thomson scattering technique on OMEGA EP. A second shot day improved the target design and obtained good quality data with a 150 mg/cc carbon foam. The experimental data was compared to Rankine-Hugoniot calculations of commonly used carbon EOS tables. The findings from this experiment suggest that the carbon EOS table over predicts the compression of the shocked carbon foam. The theoretical aspect of this dissertation describes the pore closure in highly porous materials due to a strong shock wave. Many previous models of pore collapse due to shock waves are in the low-pressure regime where the pore is crushed as a response to the shock wave. This dissertation presents a simple 1-D pore heating model where thermal radiation from the shock can penetrate deep into the porous material and cause heating of the pore walls. As the pore walls heat up, they start to expand and fill in the pores. This work suggests that there may be enough time for the pores to close prior to the arrival of the shock in conditions of interest to HEDP experiments.PHDAtmospheric, Oceanic & Space ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/151496/1/pxb_1.pd

Balanç i comprovants de l'any 1863-1864

El dossier conté: balanç econòmic de la Societat i balanç econòmic dels balls de màscares, així com també rebuts. Entre d'altres, es conserven els rebuts de pagament del copiat de les músiques dels balls. El balanç dels comptes de la Societat està signat pel comptable J.Damians i el dels balls és una signatura il·legibl