Quoting Ethan Merritt <[email protected]>:
On Wednesday 22 April 2009 09:23:19 Jacob Keller wrote:
Hello All,
What is the reason that x-ray fluorescence is neglected in our experiments?
Obviously it is measureable, as in EXAFS experiments to determine
anomalous edges,
but should it not play a role in the intensities as well? What am I missing?
Fluorescence is directly proportional to f", so in one sense we do account
for it in any calculation that includes the anomalous scattering terms.
If you were thinking of direct contribution of the fluorescent X-rays to the
measured Bragg peak - that is negligible. Those photons do not retain the
momentum vector of the original incident photon, and are emitted in all
I am not sure whether this is a good explanation. The elastically
scattered photons (which make up the Bragg peaks) also do not not
retain the momentum of the incident photon.
directions. I.e., they contribute even less to the diffraction image than
air-scatter from the direct beam or from the diffracted beam.
Well, this clearly depends on the sample content and on the X-ray
wavelength. There are many examples of data collected at an absorption
edge, where fluorescence is the dominating contributor to the
background, i.e. it is much larger than air-scatter from the direct
beam or from the diffracted beams. For an extreme case, see fig. 4 in
Shepard et al.(2000). Acta Cryst. D56, 1288-1303.
Marc
Ethan
Jacob
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: [email protected]
*******************************************
----- Original Message -----
From: rui
To: [email protected]
Sent: Wednesday, April 22, 2009 11:06 AM
Subject: [ccp4bb] microbatch vs hanging drop
Hi,
I have a question about the method for crystallization. With
traditional hanging drop(24 wells), one slide can also hold for
multiple drops but it requires the buffer quite a lot, > 600uL?
Microbatch can save buffers,only 100uL is required, and also can
hold up to three samples in the sitting well. Other than saving the
buffer, what's the advantage of microbatch? Which method will be
easier to get crystals or no big difference? Thanks for sharing.
R
--
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle 98195-7742
