CdTe and CdZnTe spectrometers for astrophysical and medical applications

1. CdTe and CdZnTe spectrometers for astrophysical and medical applications AstroMed09 "The Inaugural Sydney International Workshop on Synergies in Astronomy and Medicine" S. Del Sordo1, L. Abbene1,2, E. Caroli1, R.M. Curado Da Silva3, L. Natalucci1, E. Quadrini1, A. Zappettini4 and P. Ubertini1 1IASF-INAF, Italy 2DiFTeR Università di Palermo, Palermo, Italy 3Departmentode Física, Universidade de Coimbra, Coimbra, Portugal 4IMEM-CNR, Parma, Italy

2. 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 Outline

3. 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) The Italian collaboration 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 • ESRF Grenoble • Leicester University • DTU Space Copenaghen • Coimbra University • CEA Saclay Paris • ICE-CSIC Barcelona

4. 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.

5. 1 mm 1 mm CdTe and CdZnTe II Critical Issues Poor transport properties of the charge carriers: hh ~ 10-5-10-6 cm2/ V ee ~ 10-2-10-3 cm2/V) Small electrical signals at the electrodes Small crystal size: typically < 2 cm3 Development of single charge carrier sensing detectors (pixel, strip, Frisch grid, multiple electrodes) to overcome the poor transport properties of the holes is mandatory. L. Abbene et al., NIM A 583 (2007) 324-331.

6. 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

7. 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.

8. 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

9. Science Drivers : Astrophysics Driver 1: Understanding the physics of supernova explosions Supernovae are among the brightest source of light in the Universe. Gamma-ray 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.

10. 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 acceleratedtorelativisticenergies. 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.

11. 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 Pixel size: 0.6mm 155Eu energy spectrum taken with CZT detector, developed for NuSTAR NuSTAR DM: ~4x4 cm2 Ref: Rana et al. 2009, SPIE

12. 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 EXIST DM: 16x32 cm2 128 crystals, each crystal has 32x32 pixels Ref: Hong et al. 2009

13. 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

14. 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

15. CdZnTe detector prototypes CZT pixel detectors focal plane detector prototypes for Hard X-ray multilayer telescopes (10-100 keV)

16. CdZnTe pixel detectors CZT pixel detectors performance L. Abbene et al., JAP, Vol. 105, 2009.

17. CdZnTe detector prototypes CZT pixel detector for the POLCA II Experiment (POLarimetry with CdZnTe Arrays) The POLCA quick look S/W user interface (LABVIEW)

18. CZT pixel detector for the POLCA II Experiment Polca experiment: Set-up at ESRF beam line ID15B and Results Counts maps (scattered events) pixel 186, Energy 200 keV, Angle 0, 45 degree

19. 100 keV 200 keV 300 keV 400 keV 500 keV 600 keV 700 keV 800 keV 900 keV 1 MeV Polarization direction CZT pixel detector for the POLCA II Experiment Double interactions

20. Future Developments The POLCaliste experiment CdTe Schottky detector Caliste Module Low noise readout electronics r.m.s. 80 e-

21. 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

22. 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) (classical configuration) PTF (planar transverse field)

23. 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.

24. 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

25. Small 3D CZT position sensitive spectrometer Front end electronics board Linear modules with the mechanical assembly Read-out electronics Data handling and logic board

26. 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.

27. CdTe detector prototype : Medical applications The detector and the FET are cooled by a Peltier cell The detector with the collimation system

28. 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

29. Digital Signal Processing Techniques The detector signals are digitized immediately after the preamplifier, filtered and optimized using digital processing algorithms. Block diagram of the digital system

30. 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

31. Digital Signal Processing Techniques Performance Tailing reduction pile-up reduction Flexibility and easy optimization on shaping operation corrected uncorrected counts channel

32. Conclusions (I) Italian CZT detector development (crystal growth and detectors assembly) activities are in progress with quite good expectations. Experimental activities devoted to characterize imaging spectrometer operative in the 10 -100 keV energy band are in progress. 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.

33. 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.