Developments of high energy resolution Developments of high energy resolution cryogenic detectors for Xcryogenic detectors for X--ray ray
spectroscopy.spectroscopy.
Ezio Previtali INFN Sezione Milano Bicocca
Short history of cryogenic particle detectorsShort history of cryogenic particle detectors
Workshop on Metastable Superconductor in Particle Physics Paris 14/15 April 1983
In 1984 two important papers were published: E. Fiorini and T. Niinikoski NIM 224 (1984) 83 S. H. Moseley, J. C. Mather, D. McCammon J. Appl. Phys. 56 (1984) 1257
history begin ~30 years ago
Cryogenic Detector Basic IdeaCryogenic Detector Basic Idea
DT = E/C
Incoming Particle
Thermometer
Absorber Crystal
Thermal Conductance
C
G
E
Thermal bath Particle interaction in absorber produce
Using a suitable thermometer
DV/V ~ A (DT/T)
Where A is the thermometer sensitivity
Tlogd
)T(RlogdA
(in case of resistive sensors)
t = C/G
Ultimate energy resolution for a CalorimeterUltimate energy resolution for a Calorimeter
Thermodynamic fluctuation noise C a Tg (1 < g < 3) Poisson fluctuation give N = (C T) / (kB T) energy fluctuation rms DUrms = √(N) (kB T) = √(C kB T2)
We need to consider the thermal sensor: DUrms = x √(C kB T2) where x = 2 √(6/A) for A > 6 A = 6 – 10 for semiconductor thermistor A = 20 – 100 for TES and other sensors
With 1 g Si crystal absorber @ 10 mK Thermometer sensitivity A = 10 We obtain DUrms < 1 eV
In reality there are contributions from: Johnson noise of sensors and polarization networks Phonon noise due to possible temperature gradients Electronic noise of amplifier Microphonism ...........
Phonons: cL a (T/ TD)3 Debye law (TD - Debye temperature) Electrons: ce a (T/TF)
(TF - Fermi temperature) for superconductor @ T<Tc cs a exp(-2 Tc/T) (Tc - critical temperature) Paramagnetic components Spins Tunneling states Quasi particles
Heat Capacity contributionHeat Capacity contribution
To obtain large DT
We need small C
We must work at low T
Temperature range for Cryogenic Particle detectors
5 mK < T < 1 K
Thermometers: ThermistorsThermometers: Thermistors
@ low temperature conduction in hopping regime R(T) = R0 exp (T0/T)g
realized in Si or Ge Read-out with standard FET front-end electronics
Temperature dependance of R Working point selection for signal maximization
film operated near superconductor-conductor transition - strong variation in resistance after a particle interaction very high sensitivity: A ~ 100
Thermometer: Transition Edge Sensors (TES)Thermometer: Transition Edge Sensors (TES)
Read-out of low impedance sensors needs SQUID
Thermometer: Metallic Magnetic Calorimeter (MMC)Thermometer: Metallic Magnetic Calorimeter (MMC)
Paramagnetic sensor placed in a weak external magnetic field. Particle absorption increases the temperature and thus decreases the sensor magnetization Change is read out by a low noise high-bandwidth SQUID magnetometer
Thermometer: Superconducting Tunnel Thermometer: Superconducting Tunnel JuctionJuction STJSTJ
Al 2 O 3
200×200 μm2
Nb
Ta Absorber Al
SiO 2 Al Ta
X-ray Photon
Si Substrate
SiO 2
Signal = Current pulse
Al Al Ta Ta AlOx
ΔAl
ΔTa
Energy resolution ∆EFWHM = 2.355√(εE(F+1+1/<n>)
X-ray Photon interactions break cooper pairs -> electrons travel to barrier
Small energy gap (Δ ≈ 1meV) -> high energy resolution (<10 eV FWHM)
Thermometer: Microwave Kinetics Inductance DetectorThermometer: Microwave Kinetics Inductance Detector
A simple comparisonA simple comparison
Ionization detectors - Measure energy that goes into ionization (1/3 of energy) - Statistical fluctuation limits resolution (115 eV @ 6 keV for silicon) - Require good electron transport properties only few materials are suitable need strong control on impurities - Very well known technology electronic industries
Thermal detectors - Superconducting Tunnel Junction Analog of semiconductor ionization detector Smaller gap (>30 better energy resolution) More material (some transport problems) - Non Equilibrium phonon detector Wide selection of material Sensitivity to non ionizing events - Near equilibrium thermal detectors No energy branching Few material restriction High tolerance for impurities - Necessary complicated apparatus refrigerators LHe and LN gas liquefiers
FWHM(ID)~120 eV FWHM(TD)<10eV
NTD
High energy resolution X rays spectroscopy IHigh energy resolution X rays spectroscopy I
Using 2 Neutron Transmutation Doped Thermistors with Tin absorbers
~5 eV FWHM energy resolution@ ~ 6 keV First separation of Kα lines of 55Mn using an energy dispersive detector
High energy resolution X rays spectroscopy IIHigh energy resolution X rays spectroscopy II
Using MMC
Energy resolution of energy dispersive detectors match the energy resolution of wave dispersive detectors
Results obtained by ECHO experiment
High energy resolution X rays spectroscopy IIHigh energy resolution X rays spectroscopy II
Results obtained by ECHO experiment
With specific MMC sensors it is also possible very fast signal responses This make such devices also suitable for high event rates
High energy resolution X rays spectroscopy IIIHigh energy resolution X rays spectroscopy III
TES: Mo/Au=35/100 nm, RN=7 mohm, Tc=95 mK Au/Bi Absorber with stripes and stem ΔE= 1.8 eV @ 5.9 keV (in-suti:1.5 eV) (S. Bandler et al. 2007, Iyomoto et al. 2007, C. Kilbourne et al. 2007, etc...)
NASA/GSFC TES calorimeter array
TES will show energy resolutions of the order of few eV
High energy resolution X rays spectroscopy IIIHigh energy resolution X rays spectroscopy III
Large arrays need -> Large Read-out system
To reduce the number of SQUIDs a cryogenic multiplexing process for the acquired signal will be used
High energy resolution X rays spectroscopy IVHigh energy resolution X rays spectroscopy IV
112 pixels of 200 x 200 µm2 STJs
100
1000
104
105
200 400 600 800 1000 1200 1400 1600 1800
Counts/eV
Energy[eV]
BK
CK
NK
OK
FK Ni
La,b
AlKa
AlKb
AsLa,b
SeLa,b
CuLa,b
ZnLa,b
TaM
a1NiLi,h
AsLi,h
SeLi,h
WM
a1
FeLa
WM
b
High integration of STJ for large detector arrays For syncotron application it is necessary: increase area/pixels thicker adsorbers (Ta) array read-out systems
STAR Cryoelectronics
FWHM ~ 9 eV Rate ~ 5000 c/(s pixel)
ionisation detectors
2 eV
6 eV
3.4 eV
C. Enss, J. Low Temp. Phys. 124, 353 (2001)
Cryogenic particle detectors show energy resolutions comparable with WDS but: detection efficiency of EDD is few order of magnitude larger then WDD
Eg = 6 keV
X rays spectroscopy evolutionX rays spectroscopy evolution
2.7 eV 2.0 eV
X rays spectroscopy best performancesX rays spectroscopy best performances
maXs: 1d-array for soft x-rays (T=20 mK)
Heidelberg gruop, ECHO collaboration L. Gastaldo presentation
FWHMs obtained with the present generation of high energy resolution cryogenic detectors are at the limits of the intrinsic widths of the measured X-ray lines
Applications: X rays absorption spectroscopy IApplications: X rays absorption spectroscopy I
Applications: X rays absorption spectroscopy IIApplications: X rays absorption spectroscopy II
Microcalorimeters give complementary approach Preliminary test shows perfect compatibility A relative more simple approach will be possible
Applications: X rays absorption spectroscopy IIIApplications: X rays absorption spectroscopy III
The presence of lattice atoms produce an interference pattern for b electrons
The interference pattern modulate the energy distribution of b electrons
AgReO4 crystal
Applications: Beta Environmental Fine StructureApplications: Beta Environmental Fine Structure
Applications: PIXEApplications: PIXE
Proton accelerator + High energy resolution TES
Better spectroscopic energy resolution
Better evaluation of elemental composition
Applications: …….Applications: …….
Microcalorimeters for X ray Astrophysics
X ray fluorescence for material surface characterization
Measurements of radioactive elements with X rays emissions
Others ……………..
ConclusionConclusion
- Cryogenic particle detectors were studied during the last 30 years
- Many thermal sensors were developed and optimized
- Energy resolution is today around 100 lower then semiconductor detectors
- With present performances microcalorimeter is comparable with WDS
- Fast detectors are now available with rise time of the order of 100 nsec
- Large arrays were realized to cover large surface area
- Microcalorimeters can be applied to many different fields of research
