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One of the figures they cite is 2.5 electrons per um^2, which I think means once the whole bunch has gone through. That struck me as being pretty far from where one needs to be to get structures. Do you know off hand a comparable figure for the FEL experiment? I assume it would be many orders of magnitude greater. For example, how many total photons were in each bunch with the FEL? JPK On Thu, Apr 14, 2011 at 5:24 PM, Colin Nave <[log in to unmask]> wrote: > Petr > Well, not sure - are we doing imaging or diffraction/scattering? What energy are the electrons in these sources? The idea of pulsed sources is to put more electrons/A^2 and still beat radiation damage. Can one do this when there are only around 10^6 electrons in perhaps a rather divergent beam? > Shall we discuss off line (with Jacob) and present our conclusions when/if we get agreement? > Regards > Colin > > > >> -----Original Message----- >> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of >> Petr Leiman >> Sent: 14 April 2011 22:59 >> To: [log in to unmask] >> Subject: Re: [ccp4bb] Femtosecond Electron Beam >> >> Colin, >> >> We know that with a dose of 20-30 electrons per A^2, a lot of image >> processing, and insane amount of luck, one can reconstruct cryoEM >> images to 3 A resolution or better. A typical protein molecule is say >> 100 A in diameter, which is ~8000 A^2 in projection. So, in an ideal >> case one needs only 240,000 electrons to record an image of a protein >> molecule with a signal extending to 3A resolution. >> >> Jacob, >> >> Yes, you are correct. Jom et al. manipulate electron bunches of 1+ Mln >> electrons, which should be enough to record an image of a protein >> molecule. >> >> Best, >> >> Petr >> >> >> On Apr 14, 2011, at 11:13 PM, Colin Nave wrote: >> >> > Petr >> > Yes, I saw the figure. Similar ones appear in the Hastings et. al. >> paper (the SLAC one I referenced). They use a much higher energy beam >> to get the short pulse length. >> > >> > I still believe the issues are >> > >> > 1. For diffraction, can you get a low enough electron beam divergence >> to resolve larger unit cells? The peaks appear rather broad in the foil >> experiments. Luiten et. al. believe they can extend the technique to >> resolve cells of a few tens of nm which would be fine. Their ideas for >> doing this appear to be quite novel. I don't know if they have >> demonstrated this though. >> > 2. Given the above, will there be enough electrons in one of the >> short pulses to get enough statistics for a biological molecule or >> protein nano-crystal? I have not seen calculations for this for >> electron beams (as has been done for the FEL x-ray beams). Actually it >> should be quite easy to do as the cross sections are all available. >> > 3. For imaging (i.e. using an objective lens) is the blurring I >> mention going to be a fundamental limitation and what will this >> limitation be? >> > >> > These instruments would be useful for material science applications >> and fast chemistry investigations where some of the above issues would >> not be relevant. Not sure for imaging biological molecules. We will >> see. >> > >> > Finally saying Phys Rev Let is not a high impact journal would >> probably upset my physicist colleagues - that's fine though! >> > >> > Regards >> > Colin >> > >> >> -----Original Message----- >> >> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf >> Of >> >> Petr Leiman >> >> Sent: 14 April 2011 21:07 >> >> To: [log in to unmask] >> >> Subject: Re: [ccp4bb] Femtosecond Electron Beam >> >> >> >> Dear Colin and all interested in the FEL development. >> >> >> >> Please look at the figures in the first link I mentioned. Jom Luiten >> et >> >> al. are able to record a 1.25 A resolution diffraction pattern of a >> >> gold foil using a pulse compressed to 50 fs. Ahmed Zewail is a >> pioneer >> >> of the technique but as far as I know his instrumentation is nowhere >> >> near Jom's amazing machine. >> >> >> >> Why Jom's paper was not published in one of the high profile >> journals, >> >> ahem, magazines, is a mystery to me. >> >> >> >> Petr >> >> >> >> On Apr 14, 2011, at 9:11 PM, Colin Nave wrote: >> >> >> >>> Petr has provided the Eindhoven links. >> >>> >> >>> For more details on fast electron imaging (as opposed to >> diffraction) >> >> see https://e-reports-ext.llnl.gov/pdf/343044.pdf >> >>> >> >>> Apparently stochastic scattering of the electrons at the high >> current >> >> densities necessary for short pulsed sources result in blurring in >> the >> >> image. The paper says that 10nm spatial and 10ps temporal resolution >> >> could be achieved with 5MeV electrons and annular dark field >> imaging. >> >>> >> >>> Of course more recent developments at Eindhoven and elsewhere might >> >> get round some of the limitations. >> >>> >> >>> >> >>> Colin >> >>> >> >>>> -----Original Message----- >> >>>> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf >> >> Of >> >>>> Petr Leiman >> >>>> Sent: 14 April 2011 16:23 >> >>>> To: [log in to unmask] >> >>>> Subject: Re: [ccp4bb] Femtosecond Electron Beam >> >>>> >> >>>> People are looking into how to fit the old retired MeV microscopes >> >> with >> >>>> pulsed electron guns (problem is there are very few of those >> beasts >> >>>> left). If this works, such a machine will produce equivalent >> results >> >> to >> >>>> FEL but at a fraction of the cost. >> >>>> >> >>>> The group at Eindhoven, which Colin had mentioned, has already >> made >> >> a >> >>>> significant progress in achieving both time and spatial coherence. >> >> They >> >>>> are able to manipulate electrons in ultrashort electron bunches >> akin >> >> to >> >>>> spins in an NMR machine: >> >>>> http://prl.aps.org/abstract/PRL/v105/i26/e264801 >> >>>> http://jap.aip.org/resource/1/japiau/v109/i3/p033302_s1 >> >>>> And this is due to the fact that electrons can be focused with >> >> lenses. >> >>>> Amazing stuff. We will hear more about this for sure. >> >>>> >> >>>> Sincerely, >> >>>> >> >>>> Petr >> >>>> >> >>>> ________________________________________ >> >>>> From: CCP4 bulletin board [[log in to unmask]] on behalf of >> Colin >> >>>> Nave [[log in to unmask]] >> >>>> Sent: Thursday, April 14, 2011 16:50 >> >>>> To: [log in to unmask] >> >>>> Subject: Re: [ccp4bb] Femtosecond Electron Beam >> >>>> >> >>>> Jacob >> >>>> Very good question. >> >>>> >> >>>> People are considering this sort of thing. See for example >> >>>> http://www-spires.slac.stanford.edu/cgi-wrap/getdoc/slac-pub- >> >> 12162.pdf >> >>>> >> >>>> Due to coulomb explosion one normally needs MeV beams to get the >> >> short >> >>>> bunch length. MeV beams also give a more reasonable penetration >> >> depth >> >>>> (not relevant for single molecules). I think the problem is that >> the >> >>>> divergence is too high to resolve diffraction spots from protein >> >>>> crystals (or in other words insufficient coherence). Probably fine >> >> for >> >>>> many small molecule crystals though. You mentioned single >> molecules, >> >>>> presumably protein molecules and I think the same would apply if >> >> trying >> >>>> to observe the scattering. >> >>>> >> >>>> One could try imaging (i.e. with an electron lens) rather than do >> >>>> diffraction. I presume this is what you mean by "focussed to solve >> >> the >> >>>> phase problem". However, I understand that there are problems with >> >> this >> >>>> as well for MeV beams but I can't remember the exact details. Can >> >> look >> >>>> it up if you are interested. >> >>>> >> >>>> There could of course be technical advances which would make some >> of >> >>>> these ideas possible. I think a group at Eindhoven have plans to >> get >> >>>> round some of the problems. Again I would have to look up the >> >> details. >> >>>> >> >>>> Regards >> >>>> Colin >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>>> -----Original Message----- >> >>>>> From: CCP4 bulletin board [mailto:[log in to unmask]] On >> Behalf >> >> Of >> >>>>> Jacob Keller >> >>>>> Sent: 14 April 2011 14:39 >> >>>>> To: [log in to unmask] >> >>>>> Subject: [ccp4bb] Femtosecond Electron Beam >> >>>>> >> >>>>> Dear Crystallographers, >> >>>>> >> >>>>> is there any reason why we are not considering using super- >> intense >> >>>>> femtosecond electron bursts, instead of photons? Since the >> >> scattering >> >>>>> of electrons is much more efficient, and because they can be >> >> focussed >> >>>>> to solve the phase problem, it seems that it might be worthwhile >> to >> >>>>> explore that route of single-molecule structure solution by using >> >>>>> electrospray techniques similar to the recently-reported results >> >>>> using >> >>>>> the FEL. Is there some technical limitation which would hinder >> this >> >>>>> possibility? >> >>>>> >> >>>>> JPK >> >>>>> >> >>>>> -- >> >>>>> ******************************************* >> >>>>> Jacob Pearson Keller >> >>>>> Northwestern University >> >>>>> Medical Scientist Training Program >> >>>>> cel: 773.608.9185 >> >>>>> email: [log in to unmask] >> >>>>> ******************************************* > -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program cel: 773.608.9185 email: [log in to unmask] *******************************************