Not nanoscale
Both nanotechnologies and nuclear reactions involve interactions between small things, but so far as I can see, they won’t have much interaction with each other at a really basic level. Nanotechnologies have potential applications to processing materials and making devices that are useful in nuclear technologies, but the nuclear interactions themselves are in an almost independent realm.
Most of the reasons for this stem from mismatches in scale: the enormous difference between the sizes of atoms and their nuclei (~105), between the characteristic energies of molecular and nuclear phenomena (typically ~106), and between the energies of molecular phenomena and the energies required to bring about fusion or other short-range interactions between nuclei (~105). There are several consequences of these mismatches.
Regarding fusion, nanomachines of course can’t directly manipulate anything at the nuclear size scale, and aiming one nucleus at another doesn’t look promising: even stiffly constrained (~1000 N/m), high-mass (~100 Dalton) atoms have a zero K, quantum-mechanical uncertainty of >10–12 m, which suggests that the smallest target that can be hit reliably is >104 times the area of a large nucleus.
Considering fission, critical masses are macroscopic (even for exotic isotopes and nuclear isomers), and nanostructures can’t influence the flow of fission neutrons enough to change this.
Aside from the lower bound on positional uncertainty, the above arguments are essentially classical, but I don’t know of a relevant phenomenon involving quantum coherence or resonance, or a good reason to expect one. (This of course indicates my opinion of “cold fusion”.)
This seems to leave little scope for any nanotechnology-based change in the fundamentals of nuclear energy technology. At a practical but less fundamental level, there is a challenge in mixing nano- and nuclear technologies: Atomically precise systems are highly sensitive to radiation damage. The higher the damage rate, the shorter the lifetime of devices and the greater the requirement for fault tolerance and replacement.
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I did a similar calculation once based on Heisenberg: even assuming (which is not the case) that you could get two nuclei aimed *exactly* at each other one nanometer away from the collision point, the minimal uncertainty in their position by the time they reached the collision point would be many times the capture radius.
One place where *advanced* molecular manufacturing will make a big difference is in Big Physics, perhaps including conventional fusion R&D. If construction of complicated physics equipment gets down to $1/kg, and blueprint-to-device takes days instead of years, we could build as many Tokamaks (or whatever) as we want, and spend less time optimizing each design. Thus, research cycles should go a lot faster.
Similar arguments can be made for aerospace technologies. If you can build and test a rocket a day for not much more than the cost of fuel, you can develop an advanced aerospace capability (including testing advanced propulsion concepts) very quickly. The country with the least oppressive regulatory regime (among the countries that have molecular manufacturing) will win that race.
Chris
Thank you – this is one of the succinct arguments against cold fusion that I’ve seen. It’s been difficult for me to quantify, to explain to non-technical, interested, friends and aquaintances why I’m so skeptical.
They will go nicely together as space probes. Eric, I bet if you try hard enough you can figure out a way to integrate radioactive isotopes as a heat source in your solar sail designs.
Basically agreed but
- nanotech is an enabling technology for cheap isotope separation for weakly radioactive isotopes, notably U235.
- if fission-free ICF fusion can be made to work, then the high power density available from nanotech would be a natural match for the pulsed power sources needed.
@ Phillip — A problem with any tight integration would be that the structures in sails are extremely thin compared to those that would stop even an alpha particle (~0.1 micron v. >10 microns).
BTW, there’s an interesting but little known (and probably impractical) propulsion concept that would make direct use of asymmetrically escaping fission fragments as exhaust. From the abstract of 1977 paper [pdf]:
“Thin” here means “very thick” in the present context.
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