june 2 2004x-ray spectroscopy with microcalorimeters1 x-ray spectrometry with microcalorimeters

June 2 2004 X-Ray Spectroscopy with Microcalorimeters 1

X-Ray Spectrometry with Microcalorimeters


Electromagnetic Spectrum


Cassiopeia A in the Optical and the X-Ray Bands


Cas A

(soft) red (medium) green (hard) blue X-rays


1 eV

100 eV

10 eV

Energy (keV)

The need for high resolutionX-ray spectroscopy

Astrophysical Plasmas:

Simulation of the emission froma gas at T = 107 K with normalabundances of elements.

An energy resolution of ~ 10 eVis required to begin seriousX-ray spectroscopy and a resolutionof ~ 1 eV is required for completeplasma diagnostics and velocitymeasurements.


Energy-Selected X-ray Imaging

Cassiopeia A ACIS spectrum

4-6 keV


Cassiopeia A: Ejecta Knots

• Temperatures are comparable ~ 2 keV

• Si-rich knots have low ionization age (electron density x time)

• Fe-rich knots have ionization ages that are higher by ~50-100

SiS

Ar

Fe L Fe K

Ca

SiS

Ar

Ca


Physical Conditions Through X-Ray SpectroscopyFe-K lines provide very clean diagnostics.

One such diagnostic: excellent density-independent temperature sensitivity in the range 107–108 Kelvin.

x

y z

w

He-like Fe “triplet”

Energy (keV)

Coun

ts

Expectedwith XRS(12 eV)

ChandraHEG(~ 60 eV)

w

y, x

zNeutral Fe

He-like Fe

H-like Fe


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


Simple Energy Resolution Argument

• δT = E/C (temperature rise for E deposition)

• C ≈ Nk (N = # of phonons with <kT>)

• N ≈ C/k (fluctuation in N is the “noise”)

• ΔN = √N (Poisson statistics)

• R = E/(ΔE) = N/(ΔN) (resolving power)

• ΔE ≈ kT √N ≈ kT √(C/k) ≈ √(kT2C)

• More carefully, ΔE = 2.35 ζ √(kT2C)


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

SuperconductingTransition

E 2.35 kT 2C

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 (

ohm

s)R

(o

hms)

Temperature

Temperature


Types of thermometers:• resistive• capacitive• inductive• paramagnetic• electron tunneling

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


Silicon Pixel

Silicon Support Beams

X-Ray Absorber (HgTe)

Implanted Traces

Implanted Thermistor

Silicon Spacer

.

.

.

Microcalorimeter Arrays

XQC Array: 36 array of 0.5 2 mm pixels.


X-Ray Quantum Calorimeter Dewar


Astro-E2Astro-E2 is a powerful X-ray observatory developed jointly by the US

and Japan (Institute of Space and Astronautical Science).

High x-ray spectral resolution throughout energy band where bulk of astrophysically abundant elements exist (O - Ni)

Non-dispersive spectrometers enable imaging spectroscopy of extended sources

Large collecting area for high sensitivity

Very large simultaneous bandwidth

Complementary to Chandra and XMM-Newton X-ray Observatories


XRT (GSFC & ISAS)XIS

(ISAS & MIT)

HXD(ISAS)

Astro-E2

GSFC/ISASXRS

Focal LengthsXRS - 4.5 m

XIS - 4.75 m

CCDResponse

He-like Fe K Z = 0.01(3000 km/sec)

X-Ray Image

Astro-E2/XRS Simulation of the Centaurus Cluster

Astro-E2 ideal for for obtaining x-ray spectra of extended sources.

Ar

S

Ca

Si

Mg

O

Fe-LNe

Ni


Developed process to make ion-implanted Si thermistors with deeper profiles using silicon-on-insulator wafers.

Essentially eliminated 1/f noise higher resolution!

Appropriate thermal conductance achieved with thinner Si; no need to perform texturing etch to beams to make them diffusive.

DRIE to form pixels with good mechanical properties.

Ion beam

1.5 m

~ 6 times deeper thermometer

(after anneal)

New Microcalorimeter Design


E

200

150

100

50

0C

ount

s

5890588058705860Energy [eV]

40

20

0

-20

-40

Res

idua

l

Fit Parameters FWHM: 6.40 ± 0.15 eV E_shift: -19.95 ± 0.069 eV Amplitude: 208.8 ± 4 countsy0: 0.0 ± 0 counts 2: 1.43

Energy (keV)

6.4 eV FWHM

Ion beam

1.5 m

~ 6 times deeper thermometer

(after anneal)

Deep implants using silicon-on-insulator wafers.

625 m pixels

Mn K

Mn K

GSFC


RTS – Rotating Target Source

continuum X-ray source

X-ray continuum

X-ray lines

targets (one is open for continuum)

rotating target wheel


target wheel

motor


NTD Calorimeter with Sn Absorbers

SAOSilver et al.


1480 1485 1490 1495 1500 15050

20

40

60

80

100

120

Energy (eV)

Cou

nts

per

0.25

eV

bin Instrument Resolution:

2.0 0.1 eV FWHM

Al K1,2

Al K3,4

Toward higher spectral resolution and large arrays: Transition edge microcalorimeters

4.5 eV

SRON, 4.5 eV, 100 s time constant, 30 min acquisition time


Microcalorimeter Arrays based on Mo/Au TES

Bi

Sharp photolithography

Array of identical 150 micron devices. Soon will make these with 250 and 400 micron “mushroom” absorbers. The Bi absorbers shown are the size of the stem in the mushroom.

Array of identical devices

GSFC


Energy (keV)

Cou

nts

Energy Resolution = 2.5 eV (FWHM)

Mo/Au TESCompact pixel design (300 m)Continuous membrane thermal isolation

Results from Compact TES Pixels

Paves the way for faster, more robust pixels for the Constellation-X Mission.

GSFC 1024 pixel absorber array

june 2 2004x-ray spectroscopy with microcalorimeters1 x-ray spectrometry with microcalorimeters

Documents

xray spectroscopy fe

serious xray spectroscopy

xray bands slide

xray microcalorimeter

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kev slide

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