I don't claim to know much about quantum physics but I do know the masses involved are almost infinitesimally small and any measurement of them is likely to be incorrect as our methods of measuring are far from perfect.
The mass defect is the basis of both nuclear fission and nuclear fusion power generation, and the atomic masses are known to quite a high accuracy these days. Go look at NIST, their physical reference data has the electron, proton, neutron and various atomic masses with the uncertainties, with references to the data sources.
*sigh* Yes, the madrid group is a reciprocal-space-using helium atom scattering group. The lead surface they've made is for real-space imaging using one of the several helium *microscopes* being developed in the EU.
Yep, the idea is to use neutral atoms. Actually people tend to get a bit hung up on the resolution issue - it is true that it is an absolute pain to both focus and detect neutral helium, and other microscopies offer better ultimate resolution.
However, what things like helium ion microscopy and scanning electron microscopy don't offer is absolute surface sensitivity, with almost no damage. An SEM can only be used with conducting samples (yes, you can gold or graphite coat stuff but if you're interested in the surface you're still stuffed) and the beam penetrates a good 30-100 atomic layers so the *surface* resolution is quite limited. Helium ion microscopy is better in that regard but still penetrates quite a few atomic layers and will still damage the surface.
In short, if you're interested in delicate or reactive surfaces, neutral helium is probably the only way to go. The initial resolution won't be great (I believe they're still aiming initially for sub-optical, rather than atomic;o) ) but that's not really the point.
It's not already done at all - the techniques are quite distinct, they just have the word helium in them. All the work on helium ion microscopes I've seen uses ions well into the kV range. The resolution is definitely improved...but you're still firing things at a surface with thousands of times more energy than a chemical bond, and helium ions have a lot more mass than electrons. What does spewing electrons even mean anyway? They get focussed the same way as helium ions, after all...
The neutral atom microscope projects work with beams in the meV (that's *milli* eV) range. The atoms rebound a few angstroms from the 'surface', the beam is produced using a supersonic free jet expansion, the focussing is done differently...it's a completely different microscopy technique.
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I don't claim to know much about quantum physics but I do know the masses involved are almost infinitesimally small and any measurement of them is likely to be incorrect as our methods of measuring are far from perfect.
The mass defect is the basis of both nuclear fission and nuclear fusion power generation, and the atomic masses are known to quite a high accuracy these days. Go look at NIST, their physical reference data has the electron, proton, neutron and various atomic masses with the uncertainties, with references to the data sources.
*sigh* Yes, the madrid group is a reciprocal-space-using helium atom scattering group. The lead surface they've made is for real-space imaging using one of the several helium *microscopes* being developed in the EU.
Same beam source, different technique.
Yep, the idea is to use neutral atoms. Actually people tend to get a bit hung up on the resolution issue - it is true that it is an absolute pain to both focus and detect neutral helium, and other microscopies offer better ultimate resolution. ;o) ) but that's not really the point.
However, what things like helium ion microscopy and scanning electron microscopy don't offer is absolute surface sensitivity, with almost no damage. An SEM can only be used with conducting samples (yes, you can gold or graphite coat stuff but if you're interested in the surface you're still stuffed) and the beam penetrates a good 30-100 atomic layers so the *surface* resolution is quite limited. Helium ion microscopy is better in that regard but still penetrates quite a few atomic layers and will still damage the surface.
In short, if you're interested in delicate or reactive surfaces, neutral helium is probably the only way to go. The initial resolution won't be great (I believe they're still aiming initially for sub-optical, rather than atomic
It's not already done at all - the techniques are quite distinct, they just have the word helium in them. All the work on helium ion microscopes I've seen uses ions well into the kV range. The resolution is definitely improved...but you're still firing things at a surface with thousands of times more energy than a chemical bond, and helium ions have a lot more mass than electrons. What does spewing electrons even mean anyway? They get focussed the same way as helium ions, after all...
The neutral atom microscope projects work with beams in the meV (that's *milli* eV) range. The atoms rebound a few angstroms from the 'surface', the beam is produced using a supersonic free jet expansion, the focussing is done differently...it's a completely different microscopy technique.