AstroMed09
" The Inaugural Sydney International Workshop on Synergies in
Astronomy and Medicine "
CdTe and CdZnTe spectrometers for astrophysical
and medical applications
S. Del Sordo1, L. Abbene1,2, E. Caroli1, R.M. Curado Da Silva3,
L. Natalucci1, E. Quadrini1, A. Zappettini4 and P. Ubertini1
1IASF-INAF,
2DiFTeR
3Departmento
Italy
Università di Palermo, Palermo, Italy
de Física, Universidade de Coimbra, Coimbra, Portugal
4IMEM-CNR,
Parma, Italy
Outline
 Framework: Projects and collaborations
 CdTe / CdZnTe X-ray and gamma ray detectors
 Science drivers and international scenario
 Detector prototypes for astrophysical applications
 Detector prototypes for medical applications
 Conclusions
15th December 2009
AstroMed09, Sydney
Framework:
Projects and Collaborations
Progetto ASI Alte Energie (Study for the Gamma Ray Imager mission)
Progetto PRIN INAF SGRIP (funded by INAF)
Development of an high efficiency wide band 3D CZT detector prototype for Laue
telescope focal plane
Progetto PRIN (funded by MIUR)
Growth technologies and spectroscopic optimization for X and Gamma ray
detectors based on CdTe/CdZnTe.
LAUE – A Lens for gamma ray (Technological project funded by ASI)
International collaborations
The Italian collaboration





IASF-INAF (Bologna, Milano, Palermo, Roma)
IMEM-CNR di Parma (crystal growth)
Università di Lecce (crystal growth and bonding)
IMM-CNR di Lecce (bonding and electrical characterization)
DIFTER Università di Palermo (medical applications)
15th December 2009
•
ESRF Grenoble
•
Leicester University
•
DTU Space Copenaghen
•
Coimbra University
•
CEA Saclay Paris
•
ICE-CSIC Barcelona
AstroMed09, Sydney
CdTe and CdZnTe
I
High Z semiconductors
(Zmax = 52)
Wide band gap semiconductors
(room temperature operation)
Del Sordo S. et al., Sensors, Vol. 9, 3491-3526, 2009.
15th December 2009
AstroMed09, Sydney
CdTe and CdZnTe II
Critical Issues
Small crystal size:
Poor transport properties of the charge
carriers:
hh ~ 10-5-10-6 cm2/ V
typically < 2 cm3
ee ~ 10-2-10-3 cm2/V)
Small electrical signals at the electrodes
Development of single charge carrier sensing detectors (pixel, strip, Frisch grid,
multiple electrodes) to overcome the poor transport properties of the holes is
mandatory.
1 mm
1 mm
L. Abbene et al., NIM A 583 (2007) 324-331.
15th December 2009
AstroMed09, Sydney
CdTe and CdZnTe III
Suppliers of
Spectrometer
grade crystals
Italian group at IMEM-CNR :
CdZnTe crystals grown by the boron oxide
encapsulated vertical Bridgman technique
1.1 mm
A. Zappettini et al., IEEE Nucl. Sci.
Symp. Conf. Rec. 2008, 118-121.
2-inch CdZnTe crystal
15th December 2009
AstroMed09, Sydney
Science Drivers : Astrophysics
Most radiation that we receive from the Universe emerges from
thermal emission processes that occur during relatively quiet phases of
the cosmic evolution. Part of this radiation, however, originates in
explosive events or non-thermal processes, capable of accelerating
particles to the most extreme energies, and that provide the conditions
to synthesize the elements from which the Universe is made of.
15th December 2009
AstroMed09, Sydney
Science Drivers : Astrophysics
The observation of gamma-rays allows the exploration of the most violent
places in the Universe.
Gamma-ray observations unveil the most extreme conditions known, where
the densest objects heat matter to temperatures of billions of degrees,
where the strongest magnetic fields accelerate particles to the most
extreme energies, and where the most energetic radiation fields are able
to create matter from pure light.
Stellar explosions of all kinds and particle acceleration processes play a
key role in this evolution, providing the conditions to synthesize new
elements and providing kinetic energy to the interstellar and intergalactic
media that are the seeds for new generations of stars and galaxies.
Image of 44Ti (68 keV) in Cas A SNR
15th December 2009
AstroMed09, Sydney
Science Drivers : Astrophysics
Driver 1: Understanding the physics of supernova explosions
Supernovae are among the brightest source of light in the Universe. Gammaray burst have been recognized to constitute one variety of massive-star
supernovae, the collapsars, at least for the long duration GRBs.
Consequently, supernovae and GRBs are prominent tools to probe the early
Universe
Driver 2: The origin of the soft gamma-ray cosmic background radiation
The extragalactic cosmic background radiation encodes within its spectral
and spatial distribution the history of the formation and growth of galaxies
and stars. The high energy extragalactic background which covers an
extremely wide range from about 1 keV to 100 GeV is believed to originate
from many contributions.
15th December 2009
AstroMed09, Sydney
Science Drivers : Astrophysics
Driver 3: Linking jet ejection to accretion in compact binary systems
At the endpoint of stellar evolution, neutron stars and black holes present the
densest objects known in the Universe. Black holes become observable when
they accrete gas, a common source of which is a close stellar companion. In
contrast to X-rays, which trace the inflow of matter via a hot accretion disk,
gamma-rays probe the ultimate flow of matter beyond the innermost stable
orbit, where time and space is governed by general relativity, and where
collimated jets are accelerated to relativistic energies.
Driver 4: Particle acceleration in extreme magnetic fields
The incredibly strong gravitational and magnetic fields of a pulsar make it an
excellent laboratory for the study of physical processes in extreme conditions.
The huge electric field generated by the rotating pulsar is able to accelerate
particles to extreme energies, providing a wind of relativistic particles that
shapes its environment. In the strongest magnetic fields, quantum
electrodynamic (QED) effects profoundly change the characteristics of
continuum radiation processes such as synchrotron emission and Compton
scattering.
15th December 2009
AstroMed09, Sydney
International Missions Scenario
NuSTAR Focal Plane Detector
(focusing multilayer, deep studies of single objects)
• NASA Explorer Mission, scheduled for launch in 2011
• Detector Plane composed by 2 modules
155Eu
energy spectrum taken with
CZT detector, developed for NuSTAR
15th December 2009
Ref: Rana et al. 2009, SPIE
Pixel size: 0.6mm
NuSTAR DM: ~4x4 cm2
AstroMed09, Sydney
International Missions Scenario
High Energy Telescope on EXIST
(coded mask, astronomical surveys)
Coded Mask
• EXIST ia a mission proposed
to ASTRO2010 Decadal Survey
• Scheduled for launch in 2017
when fully funded
• 6 tons satellite in Low Earth Orbit
CZT Detection Plane, 4.5m2,
88 Detector Modules (DM)
Pixel size: 0.6mm
128 crystals,
each crystal has
32x32 pixels
Ref: Hong et al. 2009
15th December 2009
EXIST DM: 16x32 cm2
AstroMed09, Sydney
Science Drivers :
Medical applications
CZT and CdTe detectors for nuclear
gamma cameras
(140 keV gamma emission of 99mTc)
Energy resolution < 10% (140 keV)
Spatial resolution ~ 3-4 mm
CZT and CdTe detectors for PET
(511 keV)
Energy resolution < 10% (511 keV)
Time resolution < 3ns
15th December 2009
AstroMed09, Sydney
Science Drivers :
Medical applications
CdTe and CZT detectors for
mammographic X-ray spectroscopy
(1- 40 keV); Mo target
Measurements of the X-ray spectra are
very important in quality assurances and
quality
controls
of
mammographic
systems,
especially
for
radiation
protection calculation, patient dosimetry
and optimization of imaging properties.
Energy resolution < 5% (22.1 keV)
High time resolution
15th December 2009
AstroMed09, Sydney
CdZnTe detector prototypes
DETECTORS CHARACTERISTICS
CZT pixel detectors
Pixel detectors
CZT (eV Products)
Geometric surface
10×10 mm2
Active area
8×8 mm2
Thickness
1 mm and 2 mm
Number of pixels
256
Pitch
0.5 mm
(0.45 mm anodes, 0.05 mm
gap)
focal plane detector prototypes
for Hard X-ray multilayer
telescopes (10-100 keV)
15th December 2009
AstroMed09, Sydney
CdZnTe pixel detectors
CZT pixel detectors
performance
Energy
(keV)
Energy resolution
(%)
Peak to valley ratio (2 x FWHM)
59.5
5.80 ± 0.16
28.1 ± 1.1
88,1
3.9 ± 0.2
19.5 ± 1.1
L. Abbene et al., JAP, Vol. 105,
2009.
15th December 2009
AstroMed09, Sydney
CdZnTe detector prototypes
CZT pixel detector for the POLCA II Experiment
(POLarimetry with CdZnTe Arrays)
Detector
CZT Imarad
4x4 cm2, 5 mm thick
HV = -600 V
16x16 pix with 2.5 mm pitch
11x11 + 7 pix used
Readout
Electronics
8 eV products ASIC
16 channels/chip
33/50/100/200 sel. Gain
0.6/1.2/2.4/4 μs shaping
time
The POLCA quick look S/W user interface (LABVIEW)
15th December 2009
AstroMed09, Sydney
CZT pixel detector for the POLCA II Experiment
Polca experiment: Set-up at ESRF beam line ID15B and Results
2 mm
2 mm
Polarised Beam
Energy range:
100 keV to ~1 MeV
10 mm
E
CdTe Pixel Dimensions
E
ring
catte
S
n
o
pt
Com

Counts maps (scattered events)
CdTe Pixel Matrix
Q
pixel 186, Energy 200 keV, Angle 0, 45 degree
15th December 2009
Nx  N y
Nx  N y
AstroMed09, Sydney
CZT pixel detector for the POLCA II Experiment
Double interactions
100
200
300
400
500
600
700
800
900
1
MeV
keV
Polarization direction
15th December 2009
AstroMed09, Sydney
Future Developments The POLCaliste experiment
CdTe Schottky detector
Low noise readout
electronics r.m.s. 80 e-
15th December 2009
Caliste Module
AstroMed09, Sydney
Future Developments The POLCaliste experiment
POLCaliste Experiment (POLarimetry with Caliste)
Caliste module performance
Energy resolution 1.5 % (FWHM) @ 59.5 keV
T = -15 °C
Polarimetric measurements at ESRF with the PolCaliste prototype are
foreseen in 2010. We foresee to use in a first run the 64 ch device and
in a next step the new 256 ch device. The device thickness will be 0.5,
1, 2 mm
15th December 2009
AstroMed09, Sydney
CdZnTe detector prototypes
Small 3D CZT position sensitive spectrometer
(SmallGRIPrototype)
High energy measurements require an increase of the detector thickness up
to 10 mm. PTF irradiation configuration allows to increase the energy range
and to minimize the well known trapping effects
cathode
anode
cathode
anode
PPF (planar parallel field)
PTF (planar transverse field)
(classical configuration)
15th December 2009
AstroMed09, Sydney
Small 3D CZT position sensitive spectrometer
Basic sensitive CZT unit
External Dimensions: 10×10×2.5 mm3
Anode side: 4 anodes strips 0.15 mm
wide (pitch=2.5 mm) correcting field
strips 0.15 mm wide gap between
strips=0.15 mm
Cathode side: 4 cathodes strips 2.4
mm widegap between strips=0.10 mm
The basic CZT sensitive units; (left) anode side with microstrip pattern: the
brown strips are the collecting anodes (0.10 mm wide), while the others are the
drift strips (0.15 mm wide); (right) cathode side with the four horizontal strip for
the reconstruction of the interaction position.
15th December 2009
AstroMed09, Sydney
Small 3D CZT position sensitive spectrometer
Alumina
support
I/O pads
The detector will be based on 8 basic units
mounted in a side by side configuration
15th December 2009
AstroMed09, Sydney
Small 3D CZT position sensitive spectrometer
Front end electronics board
Linear modules with the
mechanical assembly
Read-out electronics
15th December 2009
Data handling and logic board
AstroMed09, Sydney
Small 3D CZT position sensitive spectrometer
Read-out electronics
The RENA-3 ASIC is a 36-channel charge sensitive amplifier self-triggering. Each
channel includes a low-noise preamplifier, a shaper with sample/hold, and in addition a
fast shaper that gives a trigger signal for coincident event detection. Moreover it can
provide channel-by-channel time difference information.The polarity, peaking time
and gain are selectable channel-by-channel. Further, the comparator thresholds are
individually adjustable through an 8 bit DAC on each channel.
15th December 2009
AstroMed09, Sydney
CdTe detector prototype : Medical applications
material
CdTe
dimensions
2 x 2 x 1 mm3
electrodes
planar
contacts
Anode: In
Cathode: Pt
Schottky diode
The detector and the FET are
cooled by a Peltier cell
The detector with the collimation system
15th December 2009
AstroMed09, Sydney
CdTe detector prototypes
X-ray spectroscopy in mammography
Direct measurements of mammographic spectra (Mo target) with
the portable device based on the CdTe detector. Energy
resolution : 5 % @ 22.1 keV
15th December 2009
AstroMed09, Sydney
Digital Signal Processing Techniques
The detector signals are digitized
preamplifier, filtered and optimized
algorithms.
immediately after the
using digital processing
Block diagram of the digital system
15th December 2009
AstroMed09, Sydney
Digital Signal Processing Techniques
The system
Analog anti-aliasing filter (low-pass filter)
ADC (NI 5122) with a sampling rate up to 100 MS/s
and 14 bit resolution
Digital shaping and MCA (Labview); gaussian shaped
signals and pile-up discrimination
15th December 2009
AstroMed09, Sydney
Digital Signal Processing Techniques
Performance
Flexibility and easy
optimization on
shaping operation
Tailing reduction
pile-up reduction
counts
corrected
uncorrected
channel
15th December 2009
AstroMed09, Sydney
Conclusions (I)
Italian CZT detector development (crystal growth and detectors
assembly) activities are in progress with quite good expectations.
Experimental
spectrometer
progress.
activities
devoted
to
characterize
imaging
operative in the 10 -100 keV energy band are in
The SGRIP experiment is in an advanced realization phase. The
CZT crystal and the read-out electronic are already assembled on
the board. Presently the read-out electronics is under an
intensive characterization phase.The study of the prototype
performances, foreseen in the 2010, will allow the optimization of
the main operative parameters for a detector operative up to 800
keV in stack configuration.
15th December 2009
AstroMed09, Sydney
Conclusions (II)
The polarimetric performances of the POLCAII experiment are
under evaluation. Measurements with the improved POLCaliste
experiment are foreseen in the 2010 at ESRF.
Very recently ASI funded a technological project named :
“LAUE - A Gamma Ray Lens”. In this project our collaboration has
the responsibility of the focal plane detector (4 x 4 cm2 , 0.5 mm
spatial resolution, good energy resolution) for the test of the lens
prototypes. In this framework one of the most appealing
possibilities will be the use of an array of Calliste detectors in the
new 256 channel version.
Experimental tests on digital spectrometers based on CdTe/CZT
detectors are in progress with promising results. We foresee to
carried out activities on the direct measurement of mammographic
spectra under clinical conditions.
15th December 2009
AstroMed09, Sydney