BRAGG EDGE TRANSMISSION ANALYSIS AT A MEDIUM INTENSITY PULSED - - PowerPoint PPT Presentation

BRAGG EDGE TRANSMISSION ANALYSIS AT A MEDIUM INTENSITY PULSED NEUTRON SOURCE

Javier Santisteban Neutron Physics Laboratory Centro Atómico Bariloche ARGENTINA

Part II of IAEA Research Contract No. 14161

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)

benzene source

premoderator moderator moderator

10 mm zircaloy-4 polyethylene stainless steel liquid nitrogen cadmium

(a)

1 10 100 1000 0.1 1 10 100

Neutron flux density [a.u.] Neutron energy (meV)

coupled 36 mm decoupled 36 mm coupled 18 mm decoupled 18 mm

PREMODERATOR THICKNESS

100 200 300 400 500 600 1 2 3 4

PREMODERATOR THICKNESS

coupled 36mm decoupled 36mm coupled 18mm decoupled 18mm

Neutron flux density [a.u.] Time of emission (µsec)

Experimental tests to validate simulations

benzene source

premoderator moderator moderator

10 mm zircaloy-4 polyethylene stainless steel liquid nitrogen cadmium

(a)

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

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)

Moderator Am = area µ = pulse width n0 = neutron flux density Detector Ad = area ε = efficiency ∆t = time bin

• Time required to define the edge

height with precision Rheight= (∆H/H)

• Time required to define the edge position

with precision Rpos= (∆thkl/thkl)

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
• ptimized 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 (110) Transmission Mo (211)

Actual application to strain analysis experiments is waiting for the final optimization of our Bragg edge transmission beamline

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.

Standardization: Nexus

Total cross section of textured materials

2 3 4 5 0.00 1.25 2.50 3.75 5.00 6.25 7.50 8.75

(311) (200) (220) Total cross section (barns) Neutron wavelength (Å) Along ND Along TD Intermediate direction Isotropic (111)

ND LD

Weld line

TD

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 LD

Weld line

TD

2 3 4

1 2 3 4 5 6 (311) (220) (200)

Total cross section (barns)

Distance from weld centre

Neutron wavelength (Å)

x=10.0mm x=7.5mm x=5.0mm x=2.5mm x=0mm (111) 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 4.06Å 4.23Å 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.

1 2 3 4 5 6 7 0.0 0.5 1.0 1.5 2.0 2.5

TDS Bragg diffraction Total

Total cross section (barns) Neutron wavelength (Å)

Absorption

Total cross section of Al polycrystals

coh el

σ

coh inel incoh inel incoh el

σ σ σ + +

Bragg diffraction: Thermal diffuse scattering (TDS):

( )

∑

<

=

λ

λ λ σ

hkl

d hkl hkl hkl el coh

d F V

2 2 2

4

Total cross section of textured materials

( )

( )

∫

− =

π λ

α π α λ

2 2

arcsin 2 , , d P d R

hkl

d hkl hkl

( ) ( )

∑

<

=

λ

λ λ λ σ

hkl

d hkl hkl hkl hkl el coh

d R d F V

2 2 2

, 4

( )

∑

<

=

λ

λ λ σ

hkl

d hkl hkl hkl el coh

d F V

2 2 2

4

• 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

Total cross section of textured materials

min: 0.039 max: 4.4

• min:

0.042 max: 4.2

• min:

0.063 max: 5.4

• min:

0.3 max: 2

• 2

3 4 5 1 2 3 4 5 (311) (200) (220)

Total elastci cross section (barns) Neutron wavelength (Å)

Along TD Along ND Isotropic (111) 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.00 1.25 2.50 3.75 5.00 6.25 7.50 8.75 (311) (200) (220)

Total cross section (barns) Neutron wavelength (Å)

Along ND Along TD Isotropic (111)

Calculated Experimental Pole figures measured by X-rays

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