How to define instrument radius?

[rowlesmr]

I've been adding PD_INSTR-related output to my TOPAS macros, and I'm a little stumped on how to define the instrument radius.

I've found: _pd_instr.dist_src_mono _pd_instr.dist_mono_spec _pd_instr.dist_src_spec _pd_instr.dist_spec_anal _pd_instr.dist_anal_detc _pd_instr.dist_spec_detc

In the example below, I can specify the distances src_mono, mono_spec, spec_anal, and anal_detc, but I can't see how that allows me to calculate the goniometer radius.

What am I missing?

[briantoby]

I probably did not consider the dual monochromator case. Not very common at all for Bragg-Brentano, but very common for synchrotrons.

On Oct 8, 2022, at 8:32 AM, Matthew Rowles @.**@.>> wrote:

I've been adding PD_INSTR-related output to my TOPAS macros, and I'm a little stumped on how to define the instrument radius.

I've found: _pd_instr.dist_src_mono _pd_instr.dist_mono_spec _pd_instr.dist_src_spec _pd_instr.dist_spec_anal _pd_instr.dist_anal_detc _pd_instr.dist_spec_detc

In the example below, I can specify the distances src_mono, mono_spec, spec_anal, and anal_detc, but I can't see how that allows me to calculate the goniometer radius. [image]https://user-images.githubusercontent.com/14921460/194709714-1b2f3623-6035-4f11-b99c-30eb65a7907e.png

What am I missing?

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[rowlesmr]

How about this as a proposal?

• _pd_instr.dist_vsrc_spec
  • Specifies the distance in millimetres from the virtual source to the specimen. The virtual source is point in space from which the incident radiation can be said to be coming from from the point of view of the specimen.
• _pd_instr.dist_spec_vdetc
  • Specifies the distance in millimetres from the specimen to the virtual detector. The virtual detector is point in space at which the detector is sampling the diffracted radiation from the point of view of the specimen. eg the specimen-receiving slit distance in a point-detector, Bragg-Brentano diffractometer.

.

you need allow both distances, as you could have a parallel or convergent beam instrument where the incident and diffracted radii are different.

[jamesrhester]

Is there a reference work that could be cited in the definition where these concepts are discussed? Volume H maybe even (we don't have access yet)?

[rowlesmr]

Yes.

Vol H, S2.1.4.1, Figs 2.1.3 & 2.1.4

Arnt has some good figures of various setups. He has labelled the relevant dimension as the "detector circle"; I know it as the "goniometer circle".

[rowlesmr]

Arnt also describes a a couple of optics that could be added:

• multilayer mirrors
  • elliptical
  • parabolic
  • K-B
  • Montel
• Capillaries
  • monocapillary
  • polycapillary

[jamesrhester]

I think it makes sense to provide data names for the detector circle and the two virtual distances originally proposed. In the most general case it looks like these virtual distances could vary for each angle at least in Bragg-Brentano, even if most constructions hold them constant. So we could reserve the virtual distances for cases where they vary during measurement (pd_meas loop), and provide a detector circle data name for use where the two virtual distances are identical for every measurement point.

[briantoby]

In a Seeman-Bolin diffractometer the distances do vary to keep the focusing circle at constant curvature.

Brian

Sent from a powerful small device but with weak eyes.

On Oct 16, 2022, at 8:12 PM, James Hester @.***> wrote:



I think it makes sense to provide data names for the detector circle and the two virtual distances originally proposed. In the most general case it looks like these virtual distances could vary for each angle at least in Bragg-Brentano, even if most constructions hold them constant. So we could reserve the virtual distances for cases where they vary during measurement (pd_meas loop), and provide a detector circle data name for use where the two virtual distances are identical for every measurement point.

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