By "That's" I presume Bob means "the 0.01% bandwidth figure is" approximately the intrinsic bandwidth of a Si (111) monochromator.
The 0.1% bandwidth in the title of the email is the standard bandwidth often used to define the output of synchrotron sources.
When defining flux within a certain bandwidth, the term spectral flux is useful. See also
Journal of Synchrotron Radiation Volume 12, Part 3 (May 2005) http://scripts.iucr.org/cgi-bin/paper?es0344
This article ends with a plea to retain 0.1% bandwidth (and mm^2 etc.) as this is ensconced in the literature. This gets difficult if the source emits its radiation in to a bandwidth smaller than this. John gives an example in his response.
When describing the output of a particular beamline with a monochromator then it is reasonable to give the flux in to a bandwidth relevant to the monochromator e.g. approx 0.01% for Si (111). However, this too has its complications as it might not correspond to the bandwidth one actually gets on the beamline.
Colin
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> -----Original Message-----
> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
> Robert Sweet
> Sent: 09 February 2011 13:47
> To: [log in to unmask]
> Subject: Re: [ccp4bb] Why 0.1% bandwidth?
>
> That's approximately the bandwidth of a Si (111) monochromator.
>
>
> On Wed, 9 Feb 2011, Andre Luis Berteli Ambrosio wrote:
>
> >
> > Dear ccp4bb,
> >
> >
> >
> > I sometimes find the flux of x-ray sources reported in units of
> “photons/s/0.1% bandwidth”
> > instead of simply “photons/s”.
> >
> > Where does the “1/0.1% bandwidth” unit come from? I have also seen
> other percentages like 0.01%
> > bw or 0.02% bw…
> >
> > Is it simply defining some degree of acceptance in energy (for
> example, the flux between 8 KeV
> > +/- 8 eV for a given stored current)? Does it somehow have to do with
> energy resolution?
> >
> > Thank you in advance for your answers,
> >
> >
> >
> > -Andre Ambrosio
> >
> >
> >
> >
> >
>
> --
> =======================================================================
> ==
> Robert M. Sweet E-Dress: [log in to unmask]
> Group Leader, PXRR: Macromolecular ^ (that's L
> Crystallography Research Resource at NSLS not 1)
> http://px.nsls.bnl.gov/
> Biology Dept
> Brookhaven Nat'l Lab. Phones:
> Upton, NY 11973 631 344 3401 (Office)
> U.S.A. 631 344 2741 (Facsimile)
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