Focusing gamma rays for sub-MeV astrophysics:state of the art of Laue lenses
Nicolas Barrière, Lorenzo NatalucciINAF - IASF Roma
ESAC - Madrid - March 26th 2009
N. Barrière - ESAC Seminar - 03/26/2009
Outlines
! Introduction! Interests of the sub-MeV gamma-ray astrophysics! Laue lens: why and how?! The Gamma Ray Imager - performances
! Laue lens state of the art! Theoretical and experimental study of crystals for a Laue lens! Still challenging: accurate orientation of crystals! Laue lens design study: general considerations
! Current projects! Laue lens + Compton telescope! A techno-scientific balloon borne mission to pave the way?
! Conclusion
N. Barrière - ESAC Seminar - 03/26/2009
Soft gamma rays and associated science themes
! Gamma rays probe non-thermal processes
! Particle acceleration, particle interactions, nuclear physics
! Gamma rays are penetrating
! Probe deep in the central engine, e.g. Supernovae or compact objects
! Gamma rays are produced in a large diversity of emission sites
! Sun, Compact binaries, pulsars, SNR, Galaxy/ISM, AGNs, GRBs, CB
Pulsars SNR AGN - µQSO
SN
NovaeSN
Physics of supernovae, Novae, Xand gamma ray bursts
Physics of pulsars, compact objects,supernova remnants, Sun
Cosmic explosions Cosmic accelerator
N. Barrière - ESAC Seminar - 03/26/2009
Type 1a Supernova explosion mechanism?
Commonly accepted scenario,But what is the physics behind?
SN1998bu (Gorgie et al. 2002)
847 keV line light curve (11.3 Mpc)847 keV line profile (1Mpc, 120 days after explosion)
(Gòmez-Gomar et al. 1998)
Comptel
1) Standard candles: characterize the 56Ni production, relation to optical2) Explosion physics: uniquely distinguish explosion physics3) Variety: Origin of the intrinsic variety (sub-super luminous)
N. Barrière - ESAC Seminar - 03/26/2009
Origin of Galactic positrons?
Jean et al., 2006
Weidenspointner et al. 2008
Spectroscopy of emission coming from the bulge:! Positrons annihilates in the warm and partiallyionized phase
Unique spatial distribution…
Bulge: - Unresolved point sources? (LMXBs??, microquasar??) - Central black hole (Sgr A*) + diffusion?
Disk: - Combination of LMXBs + 26Al & 44Ti
! Need for more sensitivity, spectroscopy, and better angular resolution
N. Barrière - ESAC Seminar - 03/26/2009
Origin of the soft gamma-ray cosmic background radiation?
! Cut-off distribution of accretion-dominated AGNs! Fraction of Compton thick sources among obscured AGN! Contribution of blazars with breaks in MeV regime! ++ AGN physics and geometry probed through polarization measurement
[Comastri et al, 1999]
Blazar?
AGN, resolved in X-rays
Blazar
N. Barrière - ESAC Seminar - 03/26/2009
Sensitivity of gamma-ray telescopes
Nuclearastrophysicsdomain
Energy (MeV)
Courtesy: S. Boggs
N. Barrière - ESAC Seminar - 03/26/2009
Principle of existing gamma-ray telescopes
! Aim:! Determine the original incidence
direction! Spectroscopy
!
n" =S
S + N#
S
N$
S
Vdet
Detection significance:
! Sensitivity only increases
as the square root of the
detector's surface
Aperturemodulation
Comptonkinematics
! Problem:!Very intense instrumental background!Sources fluxes are weak
N. Barrière - ESAC Seminar - 03/26/2009
Alternative solution
! Depth-graded multilayers mirrors [Jensen et al., 2007]
! Outstanding imaging capabilities
! Emax !300 keV (today Emax = 80 keV)
! Phase Fresnel lens [Skinner, 2005]
! Chromatic
! Very long focal length 106 km (500 keV)
! Laue lens
! How to make a sizeable sensitivity leap in the softgamma ray domain?! Decoupling the sensitive area from the collecting area
N. Barrière - ESAC Seminar - 03/26/2009
Laue lens principle
!
dhkl
!
T0
!
"B
!
"B
! Based on Bragg diffraction in the volume of crystals: Laue Geometry
! Crystal slabs arranged on concentric rings: Photons are diffractedfrom every ring towards a common focal point
! Beam deviated of 2 "B ! long focal length: - Formation flying
- Extensible boom
Small angle of deviation= conservation of thepolarisation of incident radiation
!
!
2 dhkl
sin"B
= n #
[Curado da Silva et al.,IEEE 2007]
Experimentally confirmed
N. Barrière - ESAC Seminar - 03/26/2009
Broad band Laue lens
! Same crystal using same reflexion on several adjacent rings
! diffracted wavelength is shifted from one ring to another
1234
Energie
Su
rfa
ce
eff
ica
ce 4
"1#
1
"2
"3
"4
#2
#3
#4
f
3
2
1
# variable
dhkl constant
MAX GRI
N. Barrière - ESAC Seminar - 03/26/2009
Narrow band Laue lens: CLAIRE
[Halloin, 2003; von Ballmoos et al., 2004]
Surf
ace e
ffic
ace (
cm
2)
Energie (keV)170 175165160
0
10
20
30
!
dhkl
sin"B
= const # dhkl,i
ri= const $i
! Example of the CLAIRE lens built at CESR (Toulouse,France) in 2001
! 556 Ge1-xSix crystals focusing at 170 keV
! 8 rings:
Ge (111) (220) (311) (400) (331) (422) (333) (440)
# constant
dhkl variable4
"1#
1
"2
"3
"4
#2
#3
#4
f
3
2
1
N. Barrière - ESAC Seminar - 03/26/2009
The Gamma Ray Imager
! 100m focal distance ! Composed of 2 satellites flying in formation
! Optics spacecraft:! Grazing incidence mirrors (simple reflection): 20 keV - 300 keV! Laue lens: 220 keV - 1300 keV
! Detectors spacecraft:! Option 1: CZT pixellated detector! Option 2: Stack of stripped planar germanium detectors
[Knödlseder et al, (2006; 2007)]
http://gri.iasf-roma.inaf.it
N. Barrière - ESAC Seminar - 03/26/2009
Example of lens conception: GRI
Rayon (
cm
)
Energie (keV)
N. Barrière - ESAC Seminar - 03/26/2009
GRI: Effective area
• Crystals mass: 250 kg• Crystals: Cu: 18465; Si: 7757; Ge: 1315• Mosaicity: 26 - 40 arcsec
• Radii: 65.50 cm - 179.80 cm• Crystals' size: 10.0 - 15.0 mm• Geometrical area: 27537 cm2
• Lens' structure: 1.5 mm eq. Al
Surf
ace e
ffic
ace (
cm
2) Point source on-axis
N. Barrière - ESAC Seminar - 03/26/2009
GRI's sensitivity
[knödlseder et al., 2007]
N. Barrière - ESAC Seminar - 03/26/2009
Imaging? Point source off-axis PSF
55% in Ø 24 mm
15 arcsec
30 arcsec
60 arcsec
90 arcsec
120 arcsec
150 arcsec
GRI:Angular resolution: 30 arcsecField of view: 5 arcmin FWHM
N. Barrière - ESAC Seminar - 03/26/2009
Outlines
! Introduction! Interests of the sub-MeV gamma-ray astrophysics! Laue lens: why and how?! The Gamma Ray Imager - performances
! Laue lens state of the art! Theoretical and experimental study of crystals for a Laue lens! Still challenging: accurate orientation of crystals! Laue lens design study: general considerations
! Current projects! Laue lens + Compton telescope! A techno-scientific balloon borne mission to pave the way?
! Conclusion
N. Barrière - ESAC Seminar - 03/26/2009
Definitions
! Rocking curve: Plot of the intensity (diffracted or transmitted) whilethe crystal is rotated in a parallel and monochromatic beam
! Diffraction efficiency: Ratio of the diffracted intensity over thetransmitted intensity
! Reflectivity: Ratio of the diffracted intensity over the incidentintensity => includes the absorption
!
dhkl!
T0
!
"B
!
2"B
Incidentbeam
Diffractedbeam
Transmittedbeam
Crystals characterization:Rocking curve
Angle d'incidence
!
"B
Laue geometry of diffraction
N. Barrière - ESAC Seminar - 03/26/2009
Getting a bandpass diffracted: Mosaic crystals
! Juxtaposition of tiny perfect crystal blocks (the crystallites)slightly disoriented the ones with respect to the others (Darwinmodel)
! Gaussian angular distribution of crystallites which FWHM is called'mosaïcity' $
" Gaussian energy bandpass
# Gaussian profile of the diffracted beam
! mosaic difocusing
# Diffraction efficiency ! 50 %
" As-grown mosaic structure for alot of different crystals :
- Copper- Silver- GaAs- Gold- …
Meanorientation
t0 T0
[Darwin, 1914; 1922]
N. Barrière - ESAC Seminar - 03/26/2009
Mosaic crystals
Ø 80 mm
180 m
m
Cu (ILL, Grenoble, France)Au (Mateck Gmbh)
Rh & Ag (Mateck)
GaAs (IMEM, Parme, Italy)
Cellular structure asrevealed by DSLetching in GaAs
[Ferrari et al, 2008]
[Courtois et al., 2005]
N. Barrière - ESAC Seminar - 03/26/2009
Alternative solution: crystals with curved diffracting plans
! Qualitative view: assembly of fine slices disposed in 'fan'
! Rectangular-shaped angular distribution of crystalline plans
d
$ Rectangular shaped energy bandpass
" rectangular shaped diffracted beam
profile
! Better focusing
" Diffraction efficiency ! 100 %
# Hard to obtain such crystals- Temperature gradient- Elastic bending- Concentration gardient
d: distance over which the orientation of plans vary from more than a Darwin Width
[Smither et al. 2001; Malgrange et al., 2002]
N. Barrière - ESAC Seminar - 03/26/2009
Crystals with curved diffracting plans
Curved
diffractingplanes
Ge c
oncentr
ation
Example: Si1-xGex, x increasingalong the growth axis
Composition gradient crystal Elastic bending by surface treatment
Example: Si wafer curved by grooves
N. Barrière - ESAC Seminar - 03/26/2009
Search of efficient diffracting materials
1) Calculate the reflectivity of various potentially interesting materialsª Available in large quantities,ª not toxic, radioactive, too expensiveª (melting point under 3000 K)ª Relatively good crystal quality mosaicity around a few arcmin
2) Find crystal producers, and get some representative samples
3) X-ray diffraction:! Measure the actual mosaicity, check the homogeneity and of the
selected samples! Calculate reflectivity and check the accordance with theoretical
predictions
N. Barrière - ESAC Seminar - 03/26/2009
What are the best materials?
Increasing mean Z
Hypothesis:- Mosaic crystals- Mosaicity = 30 arcsec- Thickness optimized
but " 2 mm- Kinematical theory of
diffraction
Scope of the theoretical study:- every pure-element crystal satisfying Laue lens requirements- a selection of 'commonly produced' two-component crystals
[Barriere et al., 2009]
N. Barrière - ESAC Seminar - 03/26/2009
ESRF & ILL: High-energy X- and gamma-ray beams
ILL: GAMS(184 keV < E < 2 MeV)ESRF: beamline ID 15A
(100 keV < E < 750 keV)
Cu
Ge
SiGe
Ag
Au
Pt
Pb
Rh
GaAs
InP
Al2O3
CaF2
CdTe
Crystals investigated / developped since 2005:
Grenoble, France
Accretion physics
Cosmic explosions
N. Barrière - ESAC Seminar - 03/26/2009
% 100 keV # E # 750 keV (tuneable)
% Beam cross section: from 10 x 10 µm2 up to 4 x 4 mm2
% Beam div. = < 1 arcsec
ESRF experimental setup
"B
Monochromators:
2 bent Ge (711)
SlitsBeam stop
Collimators:
2 tunable slits
Ge detector
Diffracte
d beam
Detector in transmitted beam
position
Sample on its
rotation tower
Experimental hutch
57.5 m 1.89 m 1.19 m1.775 m
White
beam
Optical hutch
&x
y
z
N. Barrière - ESAC Seminar - 03/26/2009
ESRF, beamline ID15A experimental Setup
Crystal
Ge
detector
Cryostat for
Ge det
N. Barrière - ESAC Seminar - 03/26/2009
Experimental results: "Well known" crystals
E = 589 keV Copper mosaic crystal(produced by ILL, Grenoble, France)
8.6 mm thick => Reflectivity = 0.24
Today: ' Crystal quality
' Mosaicity range' Reproducibility
( Cutting procedure
! We are confident
Si1-xGex gradient crystal(produced by IKZ, Berlin, Germany)
23 mm thick => Reflectivity = 0.26
E = 299 keV
' First time with large ingots
' First time that "mosaicity" reaches30 arcsec
! Development still ongoing, very
successful so far
FWHM =30 arcsec
FWHM =15 arcsec
[Barrière et al. 2007; 2009]
N. Barrière - ESAC Seminar - 03/26/2009
Experimental results: "New" promising materials
E = 589 keVGold mosaic crystal
(produced by Mateck, Germany)
2 mm thick => Reflectivity = 0.31
Very promising results
Firsts attempts with 3 pieces:
' 10 arcsec < mosaicity < 60 arcsec
' Reflectivity > 30% at E > 500 keV
E = 184 keV Silver mosaic crystal(produced by Mateck, Germany)
2 mm thick => Reflectivity = 0.23
Very promising results
First attempt with 1 pieces:
' Mosaicity range! Need to be investigated at higher energy
FWHM =16 arcsec
FWHM =
50 arcsec
N. Barrière - ESAC Seminar - 03/26/2009
Laue lens prototypes
[von Ballmoos et al., ExpA 2008] [Frontera et al., SPIE 2008]
• 556 Ge mosaic crystals• Ground tests, 2 balloons flights ! Crab nebula detection
20 Cu mosaic crystalsglued on a carbon fibersupport
• Setup of an assembling and testing facility• Development of a mounting method without
orienting device ! High packing factor
20072001
N. Barrière - ESAC Seminar - 03/26/2009
Main issue: orientation precision
! Problems:! most of crystals does not cleave (split along diffracting plans)! Some of them are too smooth to be polished => not possible to
make a plan of reference)
! Crystals cutting precision is about 2 arcmin! Good enough for two angles but not for Bragg's Angle! no external reference for Bragg's angle
! Crystals have to be oriented in an X-ray beam
%x
%*
%x
N. Barrière - ESAC Seminar - 03/26/2009
Crystals orientation: CLAIRE's method
N. Barrière - ESAC Seminar - 03/26/2009
Current R&D in France (CNES Founded, CESR + TAS)
2nd step: Eachcrystal has itsdedicated spot, withpins machined to setthe diffracting planesat the rightorientation
Aluminium unit cellwith 3 accuratemachined pins foreach crystal
3 pins
%x1st step: Characterization of the assymetryangle with respect to a reference surface onthe crystal
Prototype due for the end of 2009
N. Barrière - ESAC Seminar - 03/26/2009
Current R&D in Itaty (Univ. of Ferrara, ASI Founded)
Courtesy: F. Frontera
First try
Accuracy around 1.5 arcmin
Error budget analysis
1) Orientation of crystals: 2 pins are glued to keep theorientation for the crystal assembly2) Pins are inserted in a counter mask, which holes havebeen drilled at the Bragg angle3) Counter mask is put on the lens frame and crystals areglued4) Pins are chemically separated, and counter maskremoved.
New prototype for summer 2009
N. Barrière - ESAC Seminar - 03/26/2009
Lens design: Factor of merit definition
! Most important criterion? Sensitivity!
!
fn =n N
c1X=
n b "E h (1+#)
1+# $#
%sf
&
' ( (
)
* + + %det%S tobs
Aon
Al%sf
!
" =Aon
Aoff
For an off-axis source, the focal spot issymmetrical:
!
Aon
Al"sf#
rPSF
Signalin
A unique criterion for the optimization of every parameter:mosaicity, size of crystals, focal distance, materials, …
PSF must be computed fastly to be able to test a large range of parameters
GRI: PSF for a point source on axis
Ropt = 12 mm
&sf = 0.55
!
"
"r
Sin
rPSF
#
$ %
&
' ( = 0 ) FM =
Sin
rPSF
#
$ %
&
' (
max
N. Barrière - ESAC Seminar - 03/26/2009
Simulation parameters:• Cu 111• Fixed energy band: 500-530 keV
Lens design: focal distance, mosaicity, and disorientation
Ideal orientation Disorientation: ' = 30 arcsec
Factor of merit
• Gaussian angular distribution of crystals orientation• Crystals: 15 x 15 mm2
N. Barrière - ESAC Seminar - 03/26/2009
Lens design study: Mosaicity, Size of Crystals, disorientation
Focal length = 20 mIdeal orientation Disorientation: ' = 30 arcsec
Simulation parameters:• Cu 111• Fixed energy band: 300-400 keV
• Gaussian angular distribution of crystals orientation• Focal distance = 20 m
Factor of merit
N. Barrière - ESAC Seminar - 03/26/2009
Outlines
! Introduction! Interests of the sub-MeV gamma-ray astrophysics! Laue lens: why and how?! The Gamma Ray Imager - performances
! Laue lens state of the art! Theoretical and experimental study of crystals for a Laue lens! Still challenging: accurate orientation of crystals! Laue lens design study: general considerations
! Current projects! Laue lens + Compton telescope! A techno-scientific balloon borne mission to pave the way?
! Conclusion
N. Barrière - ESAC Seminar - 03/26/2009
New mission concept: associate a Laue lens to wide fieldCompton telescope: DUAL
+ point source sensitivity+ High angular resolution(+ polarisation)- Narrow field of view- Narrow energy band- Small number of targets
+ Large number of targets+ Survey sensitivity+ Polarisation- Feasibility (ACT class)- Angular resolution- SN sensitivity
2 complementarytelescopes:
AGNLMXBs (e+ e-?)PulsarsSN
e+ e- (galactic center)26Al60Fe
Point source
Extended sources
Peter von Ballmoos, Tad Takahashi, Steven Boggs
N. Barrière - ESAC Seminar - 03/26/2009
R&D for compact Compton telescopes (examples!)
NCT developped at SSL (Berkeley, USA)
HPGe stripped planar detectors
Developped at ISAS / JAXA (Tokyo, Japan)
N. Barrière - ESAC Seminar - 03/26/2009
DUAL lens design: an interesting option
Based on newly discovered crystals
F = 20 m : extensible boom
Composed of 20100 crystals tiles, 15x15 mm2, mosaicity = 2 arcmin! Relaxed requirements on orientation
Crystals mass: 165 kgColecting area: 4.5 m2
Total lens mass ~ 550 kg
N. Barrière - ESAC Seminar - 03/26/2009
DUAL Laue lens' telescope sensitivity
Low earth orbit, equatorialCZT focal planCompton background rejection Courtesy: L. Natalucci
N. Barrière - ESAC Seminar - 03/26/2009
10m focal length lens for a balloon fligth
Study of e+-e- annihilation line from a balloon borne mission
Focal length = 10 mObjective: - Scan a handful of potential sites of positrons annihilation
- Scientifically exploitable Laue lens demonstrator
Performance summary• Energy range 500 - 520 keV• FoV 12 arcmin• Angular resolution 1 arcmin• Sensitivity: 7x10-6 ph/s/cm2 (3', Tobs 10 ks)
Lens• Crystals: Ge, Cu, Rh, Ag, W• 8x8mm2, 3000 pieces ! 15 kg• 70 cm in diameter
50 times better than INTEGRAL/SPI
150 cm2
concentratedin 1 cm2
6 cmEff
ecti
ve a
rea (
cm
2)
Energy (keV)
N. Barrière - ESAC Seminar - 03/26/2009
Conclusion
With the GRI mission, we established how a focusing telescope could answer
some of the most fundamental questions of modern high energy astrophysics,
thanks to:
• Unprecedented sensitivity in the energy range 200 keV - 1 MeV
• Polarisation measurement (pixellated focal plane + Compton reconstruction)
• (Poor) imaging capabilities
GRI is not going ahead, but the principle of a gamma-ray focusing telescope
remains the only option to increase dramatically the sensitivity in the soft
gamma-ray domain
Thanks to the support from French, Italian and European space agencies,
technological issues are being overcome:
• French and Italian prototype ready in a few months
• Crystals study and development (crystal growth, cutting, gluing)