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X-Ray
Quantum Calorimeter
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Introduction
Welcome to the XQC sounding rocket experiment. XQC stands for X-Ray
Quantum Calorimeter, a soft x-ray spectrometer used for suborbital
astrophysical observations. The XQC sounding rocket payload is designed
to study the diffuse X-Ray background in the energy range from 0.05 to
1 keV at very high spectral resolution. The diffuse x-ray background is
thought to emanate from a local region of hot interstellar gas.
Previous experiments have implied that this gas is a hot, low density
plasma but did not have the resolving power to distinguish individual
emission lines over a broad spectral range. This experiment is able to
resolve line emission from the hot plasma.
The XQC detector is composed of a 36 pixel microcalorimeter array
attached to an adiabatic demagnetization refrigerator operating at 60
mK. Each pixel measures 0.5 x 2.0 mm to give a total detector area of
36 mm2. The entire detector has a mechanically defined 28 degree field
of view through four infrared blocking filters.
The launch vehicle for the XQC detector is a Nike-Black Brant two stage
sounding rocket. The rocket was assembled at White Sands Missile Range
by NASA's Wallops Flight Facility. Sounding rocket flights are quite
short in duration, approximately 15 minutes, but obtain an altitude
above 220 km. The XQC experiment was designed to have an observing time
of only 240 seconds during the flight, sufficient, however, to obtain a
reasonable spectroscopic observation.
The XQC experiment has been launched three times from White Sands
Missile Range in New Mexico; twice successfully. Successful
observations were made on June 3, 1996 and March 28, 1999. Both times,
the experiment observed a large portion of the northern sky for 240
seconds before landing via parachute about 80 miles up-range in the New
Mexico desert. Preliminary results from these flights show emission
lines from several highly ionized atoms in both the Wisconsin C and M
spectral bands. Analysis of the flight data and calibrations of the
flight detector and filters continue to be performed by the experiment
team.
The sounding rocket program is an inexpensive way to test the
technologies necessary to deploy microcalorimeters in orbital
experiments such as XRS and Constellation-X. In addition, however,
useful astrophysical observations can be performed. In future
experiments, the XQC detector will observe other regions of the soft
x-ray sky and will use new, more advanced microcalorimeter detectors.
The goal is to understand the origin, composition, ionization state and
temperature of the emitting region..
This project is a collaboration between the X-ray Astrophysics and
Detector Development branches at NASA/GSFC and the University of
Wisconsin.
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Further Detail
The XQC experiment is composed of a 36 pixel
microcalorimeter x-ray detector. The entire array is micromachined from
a single piece of silicon with each pixel measuring 0.5 x 2.0 mm. A
HgTe x-ray aborber is epoxied onto the front surface of each pixel.
The
detector system has to be maintained at a temperture of 60mK above
absolute zero during operation. This is achieved using a liquid helium
dewar and an adiabatic demagnetization refrigerator (ADR).
The
adiabatic demagnetization refrigerator is the ultra low temperature
refrigerator for the microcalorimeter detectors. It uses the pumped
liquid helium bath at 1.8K as a heat sink and cools the detectors to 60
mK. The refrigerator works by using a 40 kG superconducting magnet to
align the spins of a paramagnetic salt dumping the heat of
magnetization to the helium bath. A heat switch is then opened and the
field ramped down. The salt then cools adiabatically to the base
temperature. The magnetic field is then controlled (slowly ramped down)
to keep the detectors at constant temperature.
The payload was
launched on its third flight on March 28, 1999 to observe a one
steradian field near the northern galactic pole at 90, +60 in galactic
coordinates. Half-way through the flight the rocket makes a 360 degree
rotation scanning across the earth and then returning to the on-target
position. The reason for scanning across the earth is to obtain a
measure of the in-flight background. Historically, some flights have
seen a high particle background from precipitating electrons in the
upper atmosphere.
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For more information and further detail please try this
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