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