X-Ray Spectroscopy

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X-Ray Spectroscopy
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The need for high resolution X-ray
spectroscopy Astrophysical Plasmas Simulation
of the emission from a gas at T 107 K with
normal abundances of elements. An energy
resolution of 10 eV is required to begin
serious X-ray spectroscopy and a resolution of
1 eV is required for complete plasma diagnostics
and velocity measurements.
1 eV
10 eV
100 eV
Energy (keV)
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Whats a milliCrab?

• The second brightest X-ray (1-10 keV) source in
  the sky is the Crab nebula
• Its photon intensity at the top of the atmosphere
  of the Earth is 10 cm-2 s-1
• There are about 1000 AGN (quasars) at a level
  of about .01 cm-2 s-1 1 mC

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Oxygen Shock-Heated to kT 0.3 keV
ionized
H-like
He-like
Ionization age
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X-Ray Spectrum with 100 eV Resolution
4-6 keV
Cassiopeia A ACIS spectrum
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Estimates of H- and He-Like Energies vs Atomic
Number
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X-Ray Spectrometers - I

• Proportional counters have
• High efficiency
• Imaging capability
• Multiplex spatial/spectral without confusion
• But resolving power E/(dE) 6vE(keV)

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X-Ray Spectrometers - II

• Bragg crystal spectrometers
• Dispersive, so they can use any detectors
• Can achieve R gt 103
• Can have high efficiency (at one E at a time)
• But no imaging or multiplexing capabilities
• (i.e. can look at only one E at a time)

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X-Ray Spectrometers - III

• Gratings
• Dispersive
• Can have moderate (few ) efficiencies
• Can multiplex (all E at the same time)
• Can have R gt 103/vE(keV) (better for low E)
• But image and spectral orders are mixed

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Capella Chandra HETG
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X-Ray Spectrometers - IV

• Solid State (including CCDs)
• High efficiency (gt90)
• Non-dispersive, can multiplex all E
• Imaging capability without confusion with E
• But cannot achieve better than R 25vE(keV)
• (Resolution 40vE(keV) eV)

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The need for high resolution X-ray
spectroscopy Astrophysical Plasmas Simulation
of the emission from a gas at T 107 K with
normal abundances of elements. An energy
resolution of 10 eV is required to begin
serious X-ray spectroscopy and a resolution of
1 eV is required for complete plasma diagnostics
and velocity measurements.
1 eV
10 eV
100 eV
Energy (keV)
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X-Ray Spectrometers - V

• Cryogenic Microcalorimeters
• High efficiency (gt90)
• Non-dispersive, can multiplex all E
• Imaging capability without confusion with E
• And can achieve R gt 103 vE(keV)

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Physical Conditions Through X-Ray Spectroscopy
Fe-K lines provide very clean diagnostics.
One such diagnostic excellent density-independent
temperature sensitivity in the range 107108
Kelvin.
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The X-ray Microcalorimeter
Features high resolution, non-dispersive
spectroscopy with high quantum efficiency over K-
and L- atomic transition band.
Moseley, Mather and McCammon 1984
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Simple Energy Resolution Argument

• dT E/C (temperature rise for E deposition)
• C N(kT)/T (N of phonons with ltkTgt)
• N C/k (fluctuation in N is the noise)
• ?N vN (Poisson statistics)
• R E/(?E) (resolving power)
• ?E kTvN kTv(C/k) v(kT2C)
• More carefully, ?E 2.35 ? v(kT2C)

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Spectral Resolving Power Depends on thermometer
technology Temperature-sensitive
resistance Resolution limited by thermal
fluctuations between sensor and heat bath and
Johnson noise.
Doped semiconductor
R (ohms)
Temperature

• T operating temperature (50-100 mK)
• C heat capacity
• 2 - 4 for doped semiconductors
• 0.2 for transition edge sensors
• For both thermometer schemes a spectral
  resolution of few a eV is possible!

R (ohms)
Superconducting Transition
Temperature
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Basic requirements Low temperature Sensitive
thermometer Thermal link weak enough that the
time for restoration of the base temperature is
the slowest time constant in the system yet not
so weak that the device is made too slow to
handle the incident flux. Absorber with high
cross section yet low heat capacity
Reproducible and efficient thermalization
Types of thermometers resistive capacitive
inductive paramagnetic electron tunneling
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Microcalorimeter Arrays
XQC Array 36 array of 0.5 ? 2 mm pixels.
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X-Ray Quantum Calorimeter Dewar
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Deep implants using silicon-on-insulator
wafers. 625 ?m pixels
GSFC
Mn Ka1
Mn Ka2
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RTS Rotating Target Source
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motor
target wheel
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