56 research outputs found
GRAPE - A Balloon-Borne Gamma-Ray Polarimeter Experiment
This paper reviews the development status of GRAPE (the Gamma-Ray Polarimeter
Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to
measure the polarization of hard X-rays in the 50-300 keV energy range. We are
particularly interested in X-rays that are emitted from solar flares and
gamma-ray bursts (GRBs), although GRAPE could also be employed in the study of
other astrophysical sources. Accurately measuring the polarization of the
emitted radiation will lead to a better understating of both emission
mechanisms and source geometries. The GRAPE design consists of an array of
plastic scintillators surrounding a central high-Z crystal scintillator. The
azimuthal distribution of photon scatters from the plastic array into the
central calorimeter provides a measure of the polarization fraction and
polarization angle of the incident radiation. The design of the detector
provides sensitivity over a large field-of-view (>pi steradian). The design
facilitates the fabrication of large area arrays with minimal deadspace. This
paper presents the latest design concept and the most recent results from
laboratory tests of a GRAPE science model.Comment: 6 pages; paper presented at the FRASCATI Workshop 2005 on
Multifrequency Behaviour of High Energy Cosmic Sources; submitted to Chinese
Journal of Astronomy and Astrophysic
Developing a Compton Polarimeter to Measure Polarization of Hard X-Rays in the 50-300 keV Energy Range
This paper discusses the latest progress in the development of GRAPE
(Gamma-Ray Polarimeter Experiment), a hard X-ray Compton Polarimeter. The
purpose of GRAPE is to measure the polarization of hard X-rays in the 50-300
keV energy range. We are particularly interested in X-rays that are emitted
from solar flares and gamma-ray bursts (GRBs). Accurately measuring the
polarization of the emitted radiation from these sources will lead, to a better
understating of both the emission mechanisms and source geometries. The GRAPE
design consists of an array of plastic scintillators surrounding a central
high-Z crystal scintillator. We can monitor individual Compton scatters that
occur in the plastics and determine whether the photon is photo absorbed by the
high-Z crystal or not. A Compton scattered photon that is immediately photo
absorbed by the high-Z crystal constitutes a valid event. These valid events
provide us with the interaction locations of each incident photon and
ultimately produces a modulation pattern for the Compton scattering of the
polarized radiation. Comparing with Monte Carlo simulations of a 100% polarized
beam, the level of polarization of the measured beam can then be determined.
The complete array is mounted on a flat-panel multi-anode photomultiplier tube
(MAPMT) that can measure the deposited energies resulting from the photon
interactions. The design of the detector allows for a large field-of-view (>pi
steradian), at the same time offering the ability to be close-packed with
multiple modules in order to reduce deadspace. We plan to present in this paper
the latest laboratory results obtained from GRAPE using partially polarized
radiation sources.Comment: 10 pages; conference paper presented at the SPIE conference "UV,
X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XIV." To be
published in SPIE Conference Proceedings, vol. 589
A laser based accelerator for ultracold atoms
We present first results on our implementation of a laser based accelerator
for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and
accelerated by means of laser tweezer beams and the atomic scattering is
directly observed in laser absorption imaging. The optical collider has been
characterized using Rb87 atoms in the |F=2,mF=2> state, but the scheme is not
restricted to atoms in any particular magnetic substates and can readily be
extended to other atomic species as well.Comment: (c) 2012 The Optical Society, 3 pages, 4 figures, 1 movie lin
Design optimization and performance capabilities of the fast neutron imaging telescope (FNIT)
We describe the design optimization process and performance characterization of a next generation neutron telescope, with imaging and energy measurement capabilities, sensitive to neutrons in the 1-20 MeV energy range. The response of the Fast Neutron Imaging Telescope (FNIT), its efficiency in neutron detection, energy resolution and imaging capabilities were characterized through a combination of lab tests and Monte Carlo simulations. Monte Carlo simulations, together with experimental data, are also being used in the development and testing of the image reconstruction algorithm. FNIT was initially conceived to study solar neutrons as a candidate instrument for the Inner Heliosphere Sentinel (IHS) spacecraft. However, the design of this detector was eventually adapted to locate Special Nuclear Material (SNM) sources for homeland security purposes, by detecting fission neutrons. In either case, the detection principle is based on multiple elastic neutron-proton scatterings in organic scintillator. By reconstructing event locations and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources identified. This paper presents the most recent results arising from our efforts and outlines the performance of the FNIT detector
A Quantum Scattering Interferometer
The collision of two ultra-cold atoms results in a quantum-mechanical
superposition of two outcomes: each atom continues without scattering and each
atom scatters as a spherically outgoing wave with an s-wave phase shift. The
magnitude of the s-wave phase shift depends very sensitively on the interaction
between the atoms. Quantum scattering and the underlying phase shifts are
vitally important in many areas of contemporary atomic physics, including
Bose-Einstein condensates, degenerate Fermi gases, frequency shifts in atomic
clocks, and magnetically-tuned Feshbach resonances. Precise measurements of
quantum scattering phase shifts have not been possible until now because, in
scattering experiments, the number of scattered atoms depends on the s-wave
phase shifts as well as the atomic density, which cannot be measured precisely.
Here we demonstrate a fundamentally new type of scattering experiment that
interferometrically detects the quantum scattering phase shifts of individual
atoms. By performing an atomic clock measurement using only the scattered part
of each atom, we directly and precisely measure the difference of the s-wave
phase shifts for the two clock states in a density independent manner. Our
method will give the most direct and precise measurements of ultracold
atom-atom interactions and will place stringent limits on the time variations
of fundamental constants.Comment: Corrected formatting and typo
POET: POlarimeters for Energetic Transients
POET (Polarimeters for Energetic Transients) is a Small Explorer mission
concept proposed to NASA in January 2008. The principal scientific goal of POET
is to measure GRB polarization between 2 and 500 keV. The payload consists of
two wide FoV instruments: a Low Energy Polarimeter (LEP) capable of
polarization measurements in the energy range from 2-15 keV and a high energy
polarimeter (Gamma-Ray Polarimeter Experiment -- GRAPE) that will measure
polarization in the 60-500 keV energy range. Spectra will be measured from 2
keV up to 1 MeV. The POET spacecraft provides a zenith-pointed platform for
maximizing the exposure to deep space. Spacecraft rotation will provide a means
of effectively dealing with systematics in the polarization response. POET will
provide sufficient sensitivity and sky coverage to measure statistically
significant polarization for up to 100 GRBs in a two-year mission. Polarization
data will also be obtained for solar flares, pulsars and other sources of
astronomical interest
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
A Model of Polarized X-ray Emission from Twinkling Synchrotron Supernova Shells
Synchrotron X-ray emission components were recently detected in many young
supernova remnants (SNRs). There is even an emerging class - SN1006,
RXJ1713.72-3946, Vela Jr, and others - that is dominated by non-thermal
emission in X-rays, also probably of synchrotron origin. Such emission results
from electrons/positrons accelerated well above TeV energies in the spectral
cut-off regime. In the case of diffusive shock acceleration, which is the most
promising acceleration mechanism in SNRs, very strong magnetic fluctuations
with amplitudes well above the mean magnetic field must be present. Starting
from such a fluctuating field, we have simulated images of polarized X-ray
emission of SNR shells and show that these are highly clumpy with high
polarizations up to 50%. Another distinct characteristic of this emission is
the strong intermittency, resulting from the fluctuating field amplifications.
The details of this "twinkling" polarized X-ray emission of SNRs depend
strongly on the magnetic-field fluctuation spectra, providing a potentially
sensitive diagnostic tool. We demonstrate that the predicted characteristics
can be studied with instruments that are currently being considered. These can
give unique information on magnetic-field characteristics and high-energy
particle acceleration in SNRs.Comment: 7 pages, 8 figures, MNRAS (in press
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