On 15 Feb 2012, at 23:55, Bart Hazes wrote:
Diffracted intensity goes up by the cube of the wavelength, but so
does absorption and I don't know exactly about radiation damage. One
interesting point is that on image plate and CCD detectors the
signal is also proportional to photon energy, so doubling the
wavelength gives 8 times diffraction intensity, but only 4 times the
signal on integrating detectors (assuming the full photon energy is
captured). So it would be interesting to see how the equation works
out on the new counting detectors where the signal does not depend
on photon energy.
You make a good point about the variation in efficiency of the
detectors, but I don't think your comment about the "new counting
detectors" (assuming this refers to hybrid pixel detectors) is
correct. The efficiency of the Pilatus detector, for example, falls
off significantly at higher energies simply because the photons are
not absorbed by the silicon (320 microns thick). The DQE for the
Pilatus is quoted as 80% at 12KeV but only 50% at 16KeV and I think
this variation is entirely (or at least mainly) due to the efficiency
of absorption by the silicon.
Andrew
Another point to take into account is that beamlines can have
different optimal wavelength ranges. Typically, your beamline guy/
gal should be the one to ask. Maybe James Holton will chime in on
this.
Bart
On 12-02-15 04:21 PM, Jacob Keller wrote:
Well, but there is more scattering with lower energy as well. The
salient parameter should probably be scattering per damage. I
remember
reading some systematic studies a while back in which wavelength
choice ended up being insignificant, but perhaps there is more info
now, or perhaps I am remembering wrong?
Jacob
On Wed, Feb 15, 2012 at 5:14 PM, Bosch, Juergen<[email protected]>
wrote:
No impact ? Longer wavelength more absorption more damage. But
between the choices given no problem.
Spread of spots might be better with 1.0 versus 0.9 but that
depends on your cell and also how big your detector is. Given your
current resolution none of the mentioned issues are deal breakers.
Jürgen
......................
Jürgen Bosch
Johns Hopkins Bloomberg School of Public Health
Department of Biochemistry& Molecular Biology
Johns Hopkins Malaria Research Institute
615 North Wolfe Street, W8708
Baltimore, MD 21205
Phone: +1-410-614-4742
Lab: +1-410-614-4894
Fax: +1-410-955-3655
http://web.mac.com/bosch_lab/
On Feb 15, 2012, at 18:08, "Jacob Keller"<[email protected]
> wrote:
I would say the better practice would be to collect higher
multiplicity/completeness, which should have a great impact on
maps.
Just watch out for radiation damage though. I think the wavelength
will have no impact whatsoever.
JPK
On Wed, Feb 15, 2012 at 4:23 PM, Seungil
Han<[email protected]> wrote:
All,
I am curious to hear what our CCP4 community thoughts are....
I have a marginally diffracting protein crystal (3-3.5 Angstrom
resolution)
and would like to squeeze in a few tenth of angstrom.
Given that I am working on crystal quality improvement, would
different
wavelengths make any difference in resolution, for example 0.9
vs. 1.0
Angstrom at synchrotron?
Thanks.
Seungil
--------------------------------------------
Seungil Han, Ph.D.
Pfizer Inc.
Eastern Point Road, MS8118W-228
Groton, CT 06340
Tel: 860-686-1788, Fax: 860-686-2095
Email: [email protected]
--
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
email: [email protected]
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