Towards a Compton Telescope for Gamma-Ray Astronomy in the MeV range

1. Towards a Compton Telescope for Gamma-Ray Astronomy in the MeV range CSNSM-Orsay, AIM/CEA-Saclay, APC-Paris, MPE-Garching, NSI-Copenhagen • The 0.110 MeV photon energy range is the domain of nuclear line spectroscopy • Interaction of low-energy CRs with the ISM • Gamma-ray emissions of SN Ia and classical novae • Radioactive line emission from the solar atmosphere • … • We seek a gain in sensitivity of 2 orders of magnitude as compared to INTEGRAL AHEAD meeting, 9-10 February 2009, Roma

2. Tracker. Low-Z material for optimizing Compton scattering and minimizing Doppler broadening  Si Calorimeter. High-Z material for an efficient absorption of the scattered photon e- Anticoincidence detector to veto charged-particle induced background Compton telescope constitution • To optimize background rejection (=sensitivity), Compton imaging and polarization studies: • Fine 3-D position resolution (~1 mm3) • Good energy resolution (better than 12 %) • Tracking of the initial recoil electron • Very fast timing of interactions (<1 ns) to allow ToF selection with a compact instrument Refs: ACT Study Report (Boggs et al. 2006); GRIPS proposal (Greiner et al. 2007)

3. Thanks to INTEGRAL and SWIFT, CdTe and CZT semiconductors are already qualified for space applications • New development: Caliste 64 for the HED (8-100 keV) of SIMBOL-X R&D of pixelated CdTe detector technology CdTe detector(64 pixels, 1mm pitch, 1mm thick, guard ring) 10 mm Front-end electronics (4 IDeF-X 1.1 ASIC of 16 analogue channels) 18 mm Rear interface(7x7 pin grid array, 1.27 mm pitch) X radiography

4. Promising technology for the calorimeter: high efficiency, excellent position and energyresolutions (alternative to Ge for hard X-ray spectroscopy) • R&D challenge: extension of the bandpass beyond 1 MeV Caliste 64 Sum of 64 spectra -10°C, -400 V, 241Am: 805 eV FWHM @ 60 keV (1.35%) R&D of pixelated CdTe detector technology • Multi-layers of pixelated detectors • Extension of the dynamics of the IDeF-X ASIC up to 1 MeV/layer • Detector substrate with high transparency • Bigger CdTe crystals: 256 pixel detectors, 1 mm pitch, 6 mm thick

5. 0.66% FWHM @ 662 keV Relevant X- and Gamma ray detector Activities for AHEAD at NSI 1) CZT pixel detectors for the ESA ASIM mission CZT test crystals :10 mm x 10 mm Pixel pitch : 2.5 mm Thickness : 5 – 10 mm Normalized depth (μτ)e >10-2 cm2/V, (μτ)h <10-4 cm2/V 3D CZT-pixel detector configuration for the calorimeter 3D position information, high energy resolution, high efficiency DTU Space, Technical University of Denmark

6. 0.70% FWHM @ 356 keV Relevant X- and Gamma ray detector Activities for AHEAD at NSI 2) 3D CZT drift strip detectors PTF = Photon Transverse Field: the field is perpendicular to ‘optical’ axis CZT crystal units 10×10×2.5 mm3 E. Caroli et al. (2008), Proc. SPIE, Vol. 7011, 70113G DTU Space, Technical University of Denmark

7. R&D of LaBr3:Ce technology • The new LaBr3:Ce scintillator could be an alternative for the calorimeter • High stopping power (comparable to CZT) and can be fabricated in large volumes • Good energy resolution above a few hundreds of keV • Very fast response (CRT ~ 0.2 ns  light transit distance of 6 cm in vacuum) Saint Gobain Technical Note on BrilLanCeTM Scintillators “A good choice for a -ray spectrometer for future space applications” (Drozdowski et al. 2007, program “Gamma Ray Scintillator Development” of ESA, Cosine Research BV, St Gobain and Delft University of Technology)

8. X=0.73 mm @ 302 keV (Pani et al. 2007) LaBr3:Ce  3D position resolution • Coupling of a LaBr3 crystal (55 cm2, 2 cm thick) to a 1616 multianode PMT (Hamamatsu H9500) to form an Anger camera • In addition to the X-Y position of the -ray interaction, depth Z from the signaldistribution within the sensor plane • New ASICs (coll. LAL/CSNSM). Duplication of each outputsignal with 2 different integration times to optimize the energy and position resolutions • Specific data acquisition system for a real-time -ray tracking (multi-hit events ?) from a library of scintillation signal distributions • Note: the effect of the intrinsic background of LaBr3 (EC and - decay of 138La, 0.09% nat. ab.) should be suppressed

9. Case et al., NIM A 563 (2006) 355 LaBr3:Ce + fibres design • Coupling of the scintillation crystal to waveshifting optical fibres • Ex: design proposed for the CASTER mission (McConnell et al. 2006) • The position X, Y could be measured by using orthogonal optical fibre grids on each side of a LaBr3 scintillator to convey the light to a MAPMT.Z-coordinate from the distribution of scintillation signals • The measure of the deposit energy E could be done by looking through the system with larger PMT • Less electronics channels • Reduction in the power requirements

10. n 7Li p beam neutron detector  n shield LaBr3 Ge LaBr3:Ce  Neutron irradiation • LaBr3 has a satisfactory radiation tolerance to irradiation by 60-200 MeV protons(Owens et al. 2007; Drozdowski et al. 2007a)and MeV -rays(Normand et al. 2007; Drozdowski et al. 2007b) • Neutron irradiation using the 7Li(p,n)7Be reaction at the - CENBG/Van de Graaff @ Ebeam=3 MeV - IPNO/Tandem @ Ebeam=57 MeV  quasi-monoenergetic neutron beams between 0.5 and 5 MeV • Online measurements of the prompt-ray emission + offline analyses of the activation  radioisotope production yields • Calculations with the nuclear reaction code TALYS

11. Monte-Carlo simulations and accelerator tests • Simulation of the full chain from the spatial environment to the data treatment using : • Cosmic environment simulators, for given period and orbits. • Detector simulators (Geant 4). • On-board data treatment simulators (C++). • On-ground data reduction simulators (C++). • Test of mock-ups in “real” conditions in particle accelerators in order to check the estimates we derived from simulations • Optimization of the anticoincidence detector • Full performances of the Compton telescope