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 -------------------------------------------------------------------------------- > -----Original Message----- > From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of > Robert Sweet > Sent: 09 February 2011 13:47 > To: CCP4BB@JISCMAIL.AC.UK > 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: sw...@bnl.gov > 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) > ======================================================================= > ==
