Curved crystals as high-reflectivity components of a Laue lens ... - Cesr

Curved crystals as high-reflectivitycomponents of a Laue lens to focusthe 511-keV annihilation lineV. Guidi,V. Bellucci, R. Camattari, I. NeriUniversity of Ferrara, INFN and CNRFerrara - ItalyMürren, March 23, 2012

Bragg geometry

Neutron beamdetectorCurved crystalin Bragg geometrySampleCurved crystals can be used as neutron monochromatorsover a wide energy band to analyze magnetic structure of materials

Channeling is confinement of charged particles travellingthrough a crystal by atomic planes or strings (planar oraxial mode)0.52Channeled particles in a bent crystal follow the curvatureof the crystal thereby they are diverted like an equivalentmagnetic filed of thousands of Tesla would do!!!

Crystals fabricated atFerrara andexperimented at SPS(CERN)Phys Lett. B 692 (2010) 78

• Space-borne telescope toconcentrate radiation overselected energy bands in thehard x-ray/soft γ domains.• Crystals are arranged asconcentric rings to diffractradiation in Laue geometry fromcelestial sources to the focus.• Mosaic crystals are normallyconsidered for applicationCurved crystals allow focusing and concentratinghigh-energy x-rays at high diffraction efficiencyand increasing the energy bandwidth of the lens

Curved crystals for a Laue lensvs.

Scientific motivationsSources of positrons in galactic centerLow Mass x-ray binaries (LMXRB)?Dark Matter?

Imaging in nuclear medicine: SPECTCurved crystalOptics in LAUEgeometryDetectorGamma-raysourceDecay of 99m Tc to140 keV photons--99Mo 99m Tc + + e99mTc 99 Tc + Curved crystals would improve gamma-ray detection inSPECT with better resolution and lower radioactive doseto the patient than for the standard case with a gammacamerasystem.

A Laue lens made of curvedcrystals would concentrate511-keV photons due toannihilationproviding higher resolutionwith respect to existinginstruments.Positron Emission Tomography schemeIt can work under eitherstandard radial or innovativeaxial geometry.

Self-standing bent crystals throughsurface groovingGrooved Si crystalOptical profilometry ofthe surface without grooves

Principles and featuresN. Barrière, V. Guidi et al J. Appl. Cryst. 43 (2010) 1519

Measurements at ESRF Grooved crystals were tested by x-ray diffraction of (111)planes in Laue geometry. Aim of the experiment was to assess the performance of suchcrystalsA quasi-parallel and highlymonochromatic pencil beamwas set at energy rangingfrom 150 to 700 keV.Measurement consisted inRocking Curves.European Synchrotron Radiation Facility(Grenoble, France)V. Bellucci et al. Exp. Astron. 31 (2011) 45–58

Silicon samples(a)Beam quasi-parallel to the grooves(b)Beam perpendicular to the grooves

Rocking Curves at 150 keVNormalized countsParallel configurationPerpendicular configurationz=0.4 mmz=0.15 mm13 ”z=0.8 mm93 %Angle of incidence (arcsec)53 %60 ”z=0.85 mmNormalized counts15 ”94 %54 ”71 %Angle of incidence (arcsec)

Discussion

Insight into the method ofsurface grooving

Efficiency vs. energybeam parallel to the grooves200 keV300 keVNormalized counts92 %84 %Normalized counts400 keVAngle of incidence (arcsec)68 %500 keV54 %Angle of incidence (arcsec)

Efficiency vs. energybeam perpendicular to the groovesNormalized countsNormalized counts200 keV400 keV300 keV59% 35%Angle of incidence (arcsec)500 keV24% 17%Angle of incidence (arcsec)

Parallel configurationPerpendicular configurationModel for a curved Si crystalModel for a mosaic Si crystal

Samples of germaniumzy xBeam quasi-parallel to the grooves

Rocking curves at 300 keVNormalized countsz=0.25 mmz=0.85 mmz=1.25 mmAngle of incidence (arcsec)Normalized countsAngle of incidence (arcsec)Diffraction efficiencyaveraged 58%Passband is determinedby the curvature

Possible configuration for a Laue lensx-ray beam[111]V. Bellucci et al. Exp. Astron. 31 (2011) 45–58See also poster presentation P20 by R. Camattari

Experimental results on Sistack at ILLAnalyzed at different y(110)y => 45 mm(111)x => 3 mm(110)y => 45 mm(111) x => 3 mm(211)z => 10 mm(211)z => 10 mmBeam set quasi-parallel to the (220) planesBeam size: 10 x 1 mm 2Red arrow => X-ray beam

1) No misalignment 2) Critical misalignment3) Less important misalignment 4) Indifferent misalignment

Count450040003500300025002000150010005000Horizontal Average Cross Section176190204218232246260274288302316330344358372386400414428442456470484498512Pixels(111)x => 3 mm(110)y => 45 mm(211)z => 10 mmy=0mm(edgeofthemul0‐crystal)(220)planesarecoplanar,thuscri0calandindifferentmisalignmentscanbeexcluded

Count40003500300025002000150010005000Horizontal Average Cross Section176190204218232246260274288302316330344358372386400414428442456470484498512Pixels(111)x => 3 mm(110)y => 45 mm(211)z => 10 mmy=21mm(220)planesarecoplanar,thuscri0calandindifferentmisalignmentscanbeexcluded

Count300025002000150010005000Horizontal Average Cross Section176189202215228241254267280293306319332345358371384397410423436449462475488501Pixels(111)x => 3 mm(211)z => 10 mm(110)y => 45 mmy=38mmBeCerweldingofneighbouringplatesmustbedonenearthemul0‐crystaledge

Horizontal Average Cross SectionCount25002000150010005000176190204218232246260274288302316330344358372386400414428442456470484498512Pixels(111)x => 3 mm(110)y => 45 mm(211)z => 10 mmy=42mmBeCerweldingofneighbouringplatesmustbedonenearthemul0‐crystaledge

Count800070006000500040003000200010000Horizontal Average Cross Section182197212227242257272287302317332347362377392407422437452467482497Pixels(111) x => 3 mm(110)y => 45 mm(211)z => 10 mm Slitwidth:10x10mm 2Thebeamimpingesonthewholevolumeofthemul0‐crystalAlignmentof(111)crystallineplanesbutmisalignmentof(211)planes.Cri0calmisalignmentisexcluded

Configuration with focusingPhotonsV. Guidi et al. J. Appl. Cryst. 44 (2011) 1255-1258Angularspread

Quasi-Mosaic crystals for high-resolution focusing of hard x-rays_________ R (QM) ≈ 2.4 for GeR (primary)_________R (QM)R (primary)≈ 2.6 for SiPrimary curvature: allows focalizationSecondary curvature (QM): increases the energy pass-bandavoids the factor 1/2

Laue lens – Quasi Mosaic CrystalsOne ringFocal plane

Laue lens – Quasi Mosaic CrystalsOne ringFocal plane

Photons distributionon the focal plane – QM caseCounts normalized to themosaic caseFocal plane(meter)

Conclusions

Thank you foryour attention