The Study of High Energy Heavy Nucleus Interactions in Nuclear Emulsion Chambers Using Digital Image Processing.

Nuclear emulsion chambers with lead targets have been exposed to a 158 GeV per nucleon beam of \sp{208}pb nuclei, by far the heaviest ion accelerated to such a high energy to date. These interactions frequently produce more than 1000 charged particles. In order to measure multiplicities and secondary particle trajectories in these extremely large events, an automatic CCD-based microscope system has been developed to analyze images, count secondary tracks, measure their trajectories, and estimate their charge. Based on the analysis of 40 high-multiplicity Pb-Pb events measured using this system, we assess the degree to which these interactions can be described as a superposition of individual nucleon-nucleon interactions. The measured pseudorapidity distributions agree very well with the superposition-based FRITIOF parton model, although the actual multiplicities are somewhat lower than the calculated ones. The Pb-Pb pseudorapidity distributions are compared to those from emulsion exposures to other beams. At energies of 158-200 GeV per nucleon, the target and projectile tails of the pseudorapidity distributions are consistent with limiting fragmentation of the target and beam nucleons, supporting the wounded nucleon description of superposition. The variations in the central pseudorapidity regions can also be described as the sum of production from wounded target and projectile nucleons. In agreement with previous studies, we find that multiplicities of heavy nucleus interactions increase more rapidly with energy than in nucleon-nucleon interactions. However, the produced multiplicity per wounded nucleon in central Pb-Pb interactions is no greater than in central interactions of protons, oxygen, or sulfur on silver-bromine targets. This suggests that the increase in multiplicity may not be the effect of re-interaction of particles in large nuclei, as previously conjectured

A burst chasing x-ray polarimeter

Gamma-ray bursts are one of the most powerful explosions in the universe and have been detected out to distances of almost 13 billion light years. The exact origin of these energetic explosions is still unknown but the resulting huge release of energy is thought to create a highly relativistic jet of material and a power-law distribution of electrons. There are several theories describing the origin of the prompt GRB emission that currently cannot be distinguished. Measurements of the linear polarization would provide unique and important constraints on the mechanisms thought to drive these powerful explosions. We present the design of a sensitive, and extremely versatile gamma-ray burst polarimeter. The instrument is a photoelectric polarimeter based on a time-projection chamber. The photoelectric time-projection technique combines high sensitivity with broad band-pass and is potentially the most powerful method between 2 and 100 keV where the photoelectric effect is the dominant interaction process. We present measurements of polarized and unpolarized X-rays obtained with a prototype detector and describe the two mission concepts; the Gamma-Ray Burst Polarimeter (GRBP) for the U.S. Naval Academy satellite MidSTAR-2, and the Low Energy Polarimeter (LEP) onboard POET, a broadband polarimetry concept for a small explorer mission

Imaging X-Ray Polarimeter for Solar Flares (IXPS)

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IX PS). This novel instrument, a Time Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level in the 20-50 keV energy range during an M- or X class flare, and will provide imaging information at the approx.10 arcsec level. The primary objective of such observations is to determine the directivity of nonthermal high-energy electrons producing solar hard X-rays, and hence to learn about the particle acceleration and energy release processes in solar flares. Secondary objectives include the separation of the thermal and nonthermal components of the flare X-ray emissions and the separation of photospheric albedo fluxes from direct emissions