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 Scintillators 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 radiation environment The Space Radiation Environment Sun through solar flares: photons, charged particles The radiation environment Radiation belts: Trapped protons (SAA) & resulting activation, electrons Secondaries induced by cosmic-ray interaction with upper atmosphere: Albedo photons, neutrons, electrons, positrons Cosmic rays: Photons Protons (& activation) Alphas Ions Electrons Positrons In space our little detector is exposed to a very unfriendly 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 Steven Boggs, UCB A balloon-borne g-ray spectrometer, polarimeter & imager Steven Boggs, UCB NCT Collaboration: Berkeley, NTHU, NCU, NSPO, NUU, LBNL, CESR
Nuclear Compton Telescope Heart of NCT: Cross Strip 3-D GeDs 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
(Suntzeff et al.1992; Diehl & Timmes 1998) 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