1. MeV Gamma Ray Nuclear Astrophysics Yesterday: Science and Observations
Today: Instrumentation
(Krause 2004)
Steven Boggs
UC Berkeley
Department of Physics

2. Nuclear Gamma-Rays
Atmosphere is opaque at these energies.

3. Gamma-ray interactions
Index of refraction ~1.0000
Penetration ≥ cm into materials
Standard mirrors & lenses don’t work

4. 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

6. 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

7. Compton Gamma-Ray Observatory
( )
COMPTEL
( MeV)
OSSE
(50 keV – 10 MeV)
BATSE
( keV)
EGRET
(20 MeV – 30 GeV)

8. Spectroscopy, no Imaging
“light bucket”
Galactic Center Positrons
(Purcell et al., 1993)

9. (from P. von Ballmoos)

10. Coded Aperture Imaging
pinhole camera….
with lots of pinholes
Good for:
point sources
photons that stop in the mask (<0.2 MeV)

11. 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
( nm)

12. IBIS/INTEGRAL ISGRI: 128x128 CdTe array (4x4x2 mm3)
PICsIT: 64x64 CsI array (8.4x8.4x30 mm3)

13. IBIS Galactic Plane Survey
(Bird & Walter 2004)

14. SPI/INTEGRAL
19 Ge detectors

15. SPI Positron Map
(Weidenspointner et al., 2008)

16. Compton Gamma-Ray Observatory (1991-2000)
COMPTEL
( MeV)
OSSE
(50 keV – 10 MeV)
BATSE
( keV)
EGRET
(20 MeV – 30 GeV)

17. 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
MeV
E/DE ~ 9-14 (FWHM)
Df ~3º
Aeff < 20 cm2
FOV ~ 1str
(Schoenfelder et al., 1993, ApJS 86, 657)

18. 26Al (1.809 MeV), ~1Myr
(Oberlack et al., 1996; Pluschke et al., 2001)

19. 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

20. 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

21. 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

22. 3D GeD Design
(Luke et al. 1992, 1994)

23. Single-Pixel Spectra (56Co)
excellent GeD Spectroscopy
plus full 3-D positioning

25. 60Co Laboratory Tests
1.173, MeV
1.173 MeV processed image

26. Next flight, May 2009
northern hemisphere
primarily compact objects

27. The 2005 balloon flight from Fort Sumner
Impressions from the NCT 2009 Balloon flight

29. BGO shield
Pre-Amps
lN2 dewar

31. Rotor
Differential GPS
Solar Panels
Electronics Bay
Detector
CSBF SIP

34. 4D sin  = n 
Alternate layers of high/low Z materials
ex. W/Si
D ~ 25 Å (technological limit)
< 1 Å ( keV)
~ 30’
f ~ 10 m

38. (Suntzeff et al.1992; Diehl & Timmes 1998)
SN 1987A in the LMC
~110-4 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)

39. Bragg Scattering
2D sin  = n 
Use a crystal to bend (“focus”) the -rays
D ~ 1 Å (crystal spacing)
< 1 Å ( MeV)
~ 10’
f ~ 60 m

40. Laue Lens: Focusing g-rays
von Ballmoos et al., CESR, Toulouse