MeV Gamma Ray Nuclear Astrophysics Yesterday: Science and Observations Today: Instrumentation (Krause 2004) Steven Boggs UC Berkeley Department of Physics
Nuclear Gamma-Rays Atmosphere is opaque at these energies.
Gamma-ray interactions Index of refraction ~1.0000 Penetration ≥ cm into materials Standard mirrors & lenses don’t work
Gamma Ray Detectors • Solid State • good/excellent resolution (<2%) • may require cooling • finer position resolution • more channels/power Liquid Xe NaI, CsI, BGO • Scintillators • high Z • large volume • room temperature • moderate/poor resolution (3-10%) Si Semiconductor CZT Semiconductor Ge Semiconductor
The Space Radiation Environment Sun through solar flares: photons, charged particles Radiation belts: Trapped protons (SAA) & resulting activation, electrons • Cosmic rays: • Photons • Protons (& activation) • Alphas • Ions • Electrons • Positrons Secondaries induced by cosmic-ray interaction with upper atmosphere: Albedo photons, neutrons, electrons, positrons The radiation environment
Compton Gamma-Ray Observatory (1991-2000) COMPTEL (0.8-30 MeV) OSSE (50 keV – 10 MeV) BATSE (20-600 keV) EGRET (20 MeV – 30 GeV)
Spectroscopy, no Imaging “light bucket” Galactic Center Positrons (Purcell et al., 1993)
(from P. von Ballmoos)
Coded Aperture Imaging pinhole camera…. with lots of pinholes • Good for: • point sources • photons that stop in the mask (<0.2 MeV)
INTErnational Gamma-Ray Astrophysics Laboratory (launched October 2002) IBIS (15 keV-10 MeV) JEM-X (3-35 keV) E/DE ~ 10, Df ~ 20’ E/DE ~ 500, Df ~ 2º SPI (30 keV-8 MeV) OMC (500-600 nm)
IBIS/INTEGRAL ISGRI: 128x128 CdTe array (4x4x2 mm3) PICsIT: 64x64 CsI array (8.4x8.4x30 mm3)
IBIS Galactic Plane Survey (Bird & Walter 2004)
SPI/INTEGRAL 19 Ge detectors
SPI Positron Map (Weidenspointner et al., 2008)
Compton Gamma-Ray Observatory (1991-2000) COMPTEL (0.8-30 MeV) OSSE (50 keV – 10 MeV) BATSE (20-600 keV) EGRET (20 MeV – 30 GeV)
COMPTEL - Compton Imaging cos = 1+mc2(1/E2-1/E) COMPTEL Detectors D1: 4188 cm2 liq. scint. D2: 8620 cm2 NaI DE: 5-8% (FWHM) DX ~ DY ~ 2 cm (1s) DZ ~ 3 cm (1s) Dt ~ 0.25ns COMPTEL Performance 0.8-30 MeV E/DE ~ 9-14 (FWHM) Df ~3º Aeff < 20 cm2 FOV ~ 1str (Schoenfelder et al., 1993, ApJS 86, 657)
26Al (1.809 MeV), ~1Myr (Oberlack et al., 1996; Pluschke et al., 2001)
Compton Telescopes: Then & Now • ACT Enabling Detectors • 1 mm3 resolution • DE/E ~ 0.2-1% • 10-20% efficiency • background rejection • polarization 3 decades… • CGRO/COMPTEL • ~40 cm3 resolution • DE/E ~ 10% • 0.1% efficiency
Overview of the Nuclear Compton Telescope A balloon-borne g-ray spectrometer, polarimeter & imager Steven Boggs, UCB NCT Collaboration: Berkeley, NTHU, NCU, NSPO, NUU, LBNL, CESR
Nuclear Compton Telescope balloon payload • Heart of NCT: • Cross Strip 3-D GeDs • 37x37 strips • 2-mm pitch • 15-mm thickness • 81000 mm3 volume • 1.6 mm3 localization • ~2.1-keV noise resolution
3D GeD Design (Luke et al. 1992, 1994)
Single-Pixel Spectra (56Co) • excellent GeD Spectroscopy • plus full 3-D positioning
60Co Laboratory Tests 1.173, 1.333 MeV 1.173 MeV processed image
Next flight, May 2009 • northern hemisphere • primarily compact objects
The 2005 balloon flight from Fort Sumner Impressions from the NCT 2009 Balloon flight
BGO shield Pre-Amps lN2 dewar
Rotor Differential GPS Solar Panels Electronics Bay Detector CSBF SIP
4D sin = n • Alternate layers of high/low Z materials • ex. W/Si • D ~ 25 Å (technological limit) • < 1 Å (0.18 Å @ 68 keV) • ~ 30’ f ~ 10 m
SN 1987A in the LMC ~110-4 M (Suntzeff et al.1992; Diehl & Timmes 1998) Blue supergiant (~20 M, 6 M He core) (Arnett et al., 1989) Spherical models predict 44Ti < 1000 km/s 56Ni mixed out to ~3000 km/s (0.7 keV at 68 keV) (Motizuki & Kumagai 2004)
Bragg Scattering • 2D sin = n • Use a crystal to bend (“focus”) the -rays • D ~ 1 Å (crystal spacing) • < 1 Å (0.014 Å @ 0.847 MeV) • ~ 10’ f ~ 60 m
Laue Lens: Focusing g-rays von Ballmoos et al., CESR, Toulouse
