BRAGG EDGE TRANSMISSION ANALYSIS AT A MEDIUM INTENSITY PULSED NEUTRON SOURCE Part II of IAEA Research Contract No. 14161 Javier Santisteban Neutron Physics Laboratory Centro Atómico Bariloche ARGENTINA
OBJECTIVES 1- To implement the technique of Bragg edge neutron transmission analysis at a medium-intensity pulsed neutron source, namely the 25 MeV LINAC at the Neutron Physics Laboratory, Centro Atómico Bariloche, Argentina. 2- The development and maintenance of a freely- distributable computer code for least-squares analysis of Bragg edge transmission experiments, mostly oriented towards medium intensity neutron sources.
New ‘cool’ moderator for the Bariloche LINAC
Montecarlo simulations (MCNP) 100 Neutron flux density [a.u.] 10 PREMODERATOR THICKNESS 1 premoderator moderator moderator coupled 36 mm source decoupled 36 mm coupled 18 mm decoupled 18 mm 0.1 1 10 100 1000 Neutron energy (meV) PREMODERATOR THICKNESS 4 coupled 36mm Neutron flux density [a.u.] decoupled 36mm coupled 18mm benzene decoupled 18mm 3 zircaloy-4 10 mm polyethylene stainless steel (a) 2 liquid nitrogen cadmium 1 0 0 100 200 300 400 500 600 Time of emission ( µ sec)
Experimental tests to validate simulations premoderator moderator moderator source benzene zircaloy-4 10 mm polyethylene stainless steel (a) liquid nitrogen cadmium
Implementation of transmission beamline •New Data Acquisition Electronics •New Data Acquisition Software •Montecarlo simulation of beam optics (McStas)
Figures of merit for Bragg edge transmission Detector Moderator A d = area A m = area ε = efficiency µ = pulse width ∆ t = time bin n 0 = neutron flux density •Time required to define the edge height with precision R height = ( ∆ H / H ) •Time required to define the edge position with precision R pos = ( ∆ t hkl / t hkl ) A low-cost moderator for Bragg Edge Transmission analysis at small pulsed sources , J R Santisteban , A Tartaglione, L Torres, J R Granada and J J Blostein, Journal of Physics: Conference Series (in press)
Implementation of new beamline: tasks • Commissioning of the recently-built cold moderator and associated cryogenic device. • Installation of a new neutron beam monitor for this beamline. • Installation of a transmission detection bank optimized for Bragg edge transmission on small samples. • Implementation of Nexus-compatible file formats within the data acquisition software
BETMan software: Quantitative Phase Analysis Molybdenum powder (measured at our laboratory)
Open Genie: Single-edge fitting Molybdenum powder (measured at our laboratory) Transmission Mo (211) Transmission Mo (110) Actual application to strain analysis experiments is waiting for the final optimization of our Bragg edge transmission beamline
Standardization: Nexus What is NeXus? (www.nexusformat.org) The NeXus data format has four components: A set of subroutines to make it easy to read and write NeXus files. A set of design principles to help people understand what is in them. A set of instrument definitions to allow the development of more portable analysis software. A set of low-level file formats to actually store NeXus files on physical media.
Total cross section of textured materials ND TD Weld line LD 8.75 Along ND Along TD Total cross section (barns) 7.50 Intermediate direction Isotropic 6.25 5.00 3.75 2.50 1.25 (311) (111) (220) (200) 0.00 2 3 4 5 Neutron wavelength (Å) Characterization of textured materials by time-of-flight transmission , J. R. Santisteban, L. Edwards, V. Stelmukh, Physica B 385–386 (2006) pp. 636–638.
Total cross section of inhomogeneous objects ND TD Weld line 6 LD Total cross section (barns) Distance from weld centre 5 x=10.0mm x=7.5mm 4 x=5.0mm x=2.5mm x=0mm 3 2 (111) (200) (311) (220) 1 2 3 4 Neutron wavelength (Å) Characterization of textured materials by time-of-flight transmission , J. R. Santisteban, L. Edwards, V. Stelmukh, Physica B 385–386 (2006) pp. 636–638.
Energy-selective neutron radiography 3.89Å 4.06 Å 4.23 Å Energy-selective neutron transmission imaging at a pulsed source , W. Kockelmann, G. Frei, E.H. Lehmann, P. Vontobel, J.R. Santisteban, Nucl. Instr. Meth. A 578 (2007) pp 421-434.
Total cross section of Al polycrystals 2.5 Thermal diffuse Total cross section (barns) scattering (TDS): Total 2.0 incoh incoh coh σ + σ + σ el inel inel 1.5 1.0 Bragg diffraction 0.5 Absorption 0.0 TDS 0 1 2 3 4 5 6 7 Neutron wavelength (Å) d λ 2 2 < hkl λ coh 2 el Bragg diffraction: ( ) σ σ λ ∑ F d = el coh hkl hkl V 4 hkl 0
Total cross section of textured materials • The correction factor R is an integral around a circle in the ( hkl ) pole figure • The neutron beam direction defines the centre of the circle • The neutron wavelength defines the radius of integration 2 2 d λ < hkl λ 2 el ( ) σ λ F d ∑ = coh hkl hkl 4 V hkl 0 2 d λ 2 < hkl λ 2 el ( ) ( ) F d R d σ λ ∑ λ , = coh hkl hkl hkl V 4 hkl 0 2 π ( ) λ ( ) R λ , d ∫ P α , π 2 arcsin d α = − hkl hkl 2 d hkl 0
Total cross section of textured materials 5 Total elastci cross section (barns) Calculated Along TD 4 Along ND Isotropic � � � � � � � � � � 3 2 1 (311) (200) (220) (111) 0 min: max: min: max: 0.039 4.4 0.042 4.2 2 3 4 5 � � � � � � � � � � Neutron wavelength (Å) 8.75 Total cross section (barns) Along ND Experimental 7.50 Along TD Isotropic 6.25 min: max: min: max: 5.00 0.063 5.4 0.3 2 3.75 Pole figures measured by X-rays 2.50 1.25 (220) (311) (200) (111) 0.00 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Neutron wavelength (Å)
Bragg edge analysis code: tasks • Definition of input/output routines using the Nexus format • Definition of a “TOF transmission” instrument within the Nexus format. • Creation of a Matlab library for single-Bragg edge fitting analysis. • Creation of a Matlab library for the calculation of total cross section of textured materials. • Publication of the software via a dedicated webpage
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