Jacob We should not be comparing the Xray and electron beam fluxes in terms of particle density as the scattering cross sections are very different. I have to admit I did not see the number you are quoting, which is very low. One needs 20-30 electrons per A^2 to acheive 3A resolution. Presumably the beam can be focused to this density at the specimen plane, but I do not know for sure.
Fabrizio Carbone has just sent me his latest estimates for the numbers we are discussing. But let's do as Colin suggested and discuss this further off the board and post a summary later. Cheers, Petr Sent from my iPhone On 15 Apr 2011, at 03:40, "Jacob Keller" <j- kell...@fsm.northwestern.edu> wrote: > 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 > <colin.n...@diamond.ac.uk> 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:CCP4BB@JISCMAIL.AC.UK] On Behalf >>> Of >>> Petr Leiman >>> Sent: 14 April 2011 22:59 >>> To: CCP4BB@JISCMAIL.AC.UK >>> 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:CCP4BB@JISCMAIL.AC.UK] On Behalf >>> Of >>>>> Petr Leiman >>>>> Sent: 14 April 2011 21:07 >>>>> To: CCP4BB@JISCMAIL.AC.UK >>>>> 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:CCP4BB@JISCMAIL.AC.UK] On >>>>>>> Behalf >>>>> Of >>>>>>> Petr Leiman >>>>>>> Sent: 14 April 2011 16:23 >>>>>>> To: CCP4BB@JISCMAIL.AC.UK >>>>>>> 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 [CCP4BB@JISCMAIL.AC.UK] on behalf of >>> Colin >>>>>>> Nave [colin.n...@diamond.ac.uk] >>>>>>> Sent: Thursday, April 14, 2011 16:50 >>>>>>> To: CCP4BB@JISCMAIL.AC.UK >>>>>>> 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:CCP4BB@JISCMAIL.AC.UK] On >>> Behalf >>>>> Of >>>>>>>> Jacob Keller >>>>>>>> Sent: 14 April 2011 14:39 >>>>>>>> To: CCP4BB@JISCMAIL.AC.UK >>>>>>>> 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: j-kell...@northwestern.edu >>>>>>>> ******************************************* >> > > > > -- > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > cel: 773.608.9185 > email: j-kell...@northwestern.edu > *******************************************
