14.43  The Lens McStas Component

Refractive lens with absorption, incoherent scattering and surface imperfection.

Identification

• Author: C. Monzat/E. Farhi/S. Desert/G. Euzen

• Origin: ILL/LLB

• Date: 2009

Description

Refractive Lens with absorption, incoherent scattering and surface imperfection. Geometry may be: spherical (use r1 and r2 to specify radius of curvature),

planar    (use phiy1 and phiy2 to specify rotation angle of plane w.r.t beam)

parabolic (use focus1 and focus2 as optical focal length).

Optionally, you can specify the ’geometry’ parameter as a OFF/PLY file name. The complex geometry option handles any closed non-convex polyhedra. It computes the intersection points of the neutron ray with the object transparently, so that it can be used like a regular sample object. It supports the PLY, OFF and NOFF file format but not COFF (colored faces). Such files may be generated from XYZ data using: qhull < coordinates.xyz Qx Qv Tv o > geomview.off or powercrust coordinates.xyz and viewed with geomview or java -jar jroff.jar (see below).

The lens cross-section is seen as a 2*radius disk from the beam Z axis, except when a ’geometry’ file is given. Usually, you should stack more than one of these to get a significant effect on the neutron beam, so-called ’compound refractive lens’.

The focal length for N lenses with focal ’f’ is f/N, where f=R/(1-n)

and R = r/2   for a spherical lens with curvature radius ’r’

R = focus for a parabolic lens with focal of the parabola and n = sqrt(1-(lambda*lambda*rho*bc/PI)) with bc = sqrt(fabs(sigma_coh)*100/4/PI)*1e-5 rho = density*6.02214179*1e23*1e-24/weight

Common materials: Should have high coherent, and low incoherent and absorption cross sections

Be:            density=1.85,  weight=9.0121, sigma_coh=7.63,  sigma_inc=0.0018,sigma_abs=0.0076
Pb:            density=11.115,weight=207.2,  sigma_coh=11.115,sigma_inc=0.003, sigma_abs=0.171
Pb206:                                     sigma_coh=10.68, sigma_inc=0    , sigma_abs=0.03
Pb208:                                     sigma_coh=11.34, sigma_inc=0    , sigma_abs=0.00048
Zr:            density=6.52,  weight=91.224, sigma_coh=6.44,  sigma_inc=0.02,  sigma_abs=0.185
Zr90:                                      sigma_coh=5.1,   sigma_inc=0    , sigma_abs=0.011
Zr94:                                      sigma_coh=8.4,   sigma_inc=0    , sigma_abs=0.05
Bi:            density=9.78,  weight=208.98, sigma_coh=9.148, sigma_inc=0.0084,sigma_abs=0.0338
Mg:            density=1.738, weight=24.3,   sigma_coh=3.631, sigma_inc=0.08,  sigma_abs=0.063
MgF2:          density=3.148, weight=62.3018,sigma_coh=11.74, sigma_inc=0.0816,sigma_abs=0.0822
diamond:       density=3.52,  weight=12.01,  sigma_coh=5.551, sigma_inc=0.001, sigma_abs=0.0035

Quartz/silica: density=2.53, weight=60.08, sigma_coh=10.625,sigma_inc=0.0056,sigma_abs=0.1714

Si:            density=2.329, weight=28.0855,sigma_coh=2.1633,sigma_inc=0.004, sigma_abs=0.171
Al:            density=2.7,   weight=26.98,  sigma_coh=1.495, sigma_inc=0.0082,sigma_abs=0.231

perfluoropolymer(PTFE/Teflon/CF2):

density=2.2,   weight=50.007, sigma_coh=13.584,sigma_inc=0.0026,sigma_abs=0.0227

Organic molecules with C,O,H,F

Example: Lens(r1=0.025,r2=0.025, thickness=0.001,radius=0.0150)

%BUGS parabolic shape is not fully validated yet, but should do still...

Input parameters

Parameters in boldface are required; the others are optional.

Links

• Component source code found in file Lens.comp.

• M. L. Goldberger et al, Phys. Rev. 71, 294 - 310 (1947)

• Sears V.F. Neutron optics. An introduction to the theory of neutron optical phenomena and their applications. Oxford University Press, 1989.

• H. Park et al. Measured operationnal neutron energies of compound refractive lenses. Nuclear Instruments and Methods B, 251:507-511, 2006.

• J. Feinstein and R. H. Pantell. Characteristics of the thick, compound refractive lens. Applied Optics, 42 No. 4:719-723, 2001.

• Geomview and Object File Format (OFF)

• Java version of Geomview (display only) jroff.jar

• qhull

• powercrust