Michael Jentschel Institut Laue-Langevin ELI-NP, March 2011, Bucharest.
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Transcript of Michael Jentschel Institut Laue-Langevin ELI-NP, March 2011, Bucharest.
Monochromatisation of g-rays with ppm resolution via Crystal
DiffractionMichael Jentschel
Institut Laue-Langevin
ELI-NP, March 2011, Bucharest
Monochromatisation via Laue - Diffraction
sin2dE
hcn
22
d
d
E
E Good Resolution:• Perfect crystals• Angle measurement
Perfect crystals Gradientcrystals
Good for highresolution
Good as high efficiencyband pass filter
Laue-Diffraction at a perfect crystal
Dynamical Diffraction theory:
Each el. cell is scattering center
Scattering from indiv. Atoms is summarized via structure factor
interference of forward/backward reflected partial waves from periodically arranged scattering centers
E
hcFWHM
hcEAy
y
yAI
B
2
,,
1
1sin)(
2
22
E
hcn
E
hcnd
B
B
)sin(2
Line profile
Diffraction Angle
Resolution is independent of Gamma Ray Energy
Zachariasen, 1967
Estimate of possible resolution
qB~10-2 rad
DqB ~ 10-8 rad
Diffraction process allows to have ppm resolution!
Double crystal Geometry
L
lRIR
LhaL
lhI BB
4)/sin(42
02
20
ILL geometry: 4 source
ELI case:
10-6
DIVERGENCE
BRI
20 ~10-7 I0
1016 10-5 10-2 103
Diffraction efficiency of perfect crystals
22%3rd order
How does a crystal reflect, if the beam divergence fits its acceptance width ?
Adapting divergence via refractive optics
M. Wegener Karlsruhe Institute of Technology
A. Sinigrev, ESRF, Grenoble
www.X-ray-optics.com
To be tested for gamma rays in 2011
Layout and Functioning of the ILL Double Crystal Spectrometer GAMS
Source
Spectrometer Table with angle interferometers
Detector
1.Crystal
2.Crystal
Beam Collimation Movable Collimation
These beams need to be separated
Large distances needed
21 m 0.7 m 3 m
0.002 m
Interferometer of GAMS6: realisation
All fixations free of epoxy:• optical bonding• silica bonding• mechanical clemping
Crystal Spectrometers GAMS
GAMS 5
GAMS 6 (comissioning)
200 prad resolution
20 prad resolution
What can you get from high resolution
(n,g) of 188Re
Complete spectrat=220+180
-30
Dynamic range of 106
Broadening due to:• Atomic motion• Lifetime• Zero Point Fluctuation
…
1.1MeV
Physics with ppm resolution
Nuclear Structure Physics:Complete SpectroscopyLevel Density/Chaos,n), (,f), (,) reactions
Fundamental PhysicsFine structure constantDiffraction process
Solid state PhysicsAtomic interaction Phase transitions
Many others