That value, 2200m/s, is pretty slow--there are some bullets that go faster than that, I think...
JPK On Fri, Sep 23, 2011 at 11:59 AM, Andreas Ostermann <andreas.osterm...@frm2.tum.de> wrote: > Jacob Keller wrote: >> Wow, neutrons are pretty cool! No radiation damage--and time >> resolution? I guess this is since they have much higher energy, and >> are measurable individually? What are the numbers for fluxes >> (neutrons/sec)? Are the neutrons all at one energy, or is there a >> bandwidth? > > The energy of neutrons is even lower when compared to X-rays. > A neutron with a wavelength of 1.8A has an energy of about 25 meV. > The flux at neutron sources compared to synchrotrons is unfortunately low: > > Diffractometer "LADI III" reactor ILL/France: > 3 x 10^7 neutrons/sec/cm^2 (quasi-Laue, delta L / L = 20%) > > Diffractometer "BioDiff" reactor FRM II / Germany: > 1 x 10^7 neutrons/sec/cm^2 (monochromatic, delta L / L = 2.5%) > > Diffractometer "BIX4" reactor JRR3M / Japan: > 4 x 10^6 neutrons/sec/cm^2 (monochromatic, delta L / L = 2.0%) > > BUT you can detect hydrogen atoms even at a moderate resolution of > about 2A ! With neutrons the scattering power of hydrogen/deuterium > is "comparable" to the scattering power of carbon. You can even distinguish > between isotopes. Since the nucleus is a point scatterer the "form factor" > -for neutrons called scattering length- is not scattering angle depended. > A typical measurement time is about 2-3 weeks for a crystal of 1 mm^3. > I know...of course not every protein can be crystallized up to 1 mm^3 but > if you have such a system and you are interested in the protonation states > of amino acids in the active centre for example, than neutrons are worth a > try > for sure! If you fully deuterate your protein (which gets more and more > routine > work for example at the D-LAB at ILL/EMBL) you can even work with smaller > crystals. > > Because of the relative low flux most reactor based neutron diffractometers > for > proteins uses large cylindrical neutron image plate detector, which cover a > solid angle > of about 2 Pi. At spallation sources (which are pulsed neutron sources) > detectors > with time resolution are used. This instruments (PCS in Los Alamos; iBIX in > Japan > and MANDI in Oak Ridge) are time of flight instruments. They uses the fact > that > neutrons with different energy/wavelength show different velocities ( a 1.8A > neutron > has a velocity of about 2200 m/s). They measure different wavelength > neutrons at > different time at the detector. > > Hope to see some of you as new "neutron users" in the future, > cheers, > > Andreas > > -- > Dr. Andreas Ostermann > Technische Universität München > Research reactor FRM II > Instrument "BioDiff" > Lichtenbergstr. 1 > D-85747 Garching > Tel.: +49-89-289-14702 > Fax.: +49-89-289-14666 > Email: andreas.osterm...@frm2.tum.de > Web: http://www.frm2.tum.de/en/science/index.html > -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program cel: 773.608.9185 email: j-kell...@northwestern.edu *******************************************
