Theoretical Stability of "AB-matter" Alexander Bolonkin has proposed the possibility of manipulating nucleons to produce stable, macroscopic structures of nuclear matter at zero pressure (which he calls "AB-matter"), by analogy with the nanotech ideas of directly manipulating atoms to build high-tech materials. 
The basic claim is that an unbounded number of alternating protons and neutrons can be arranged in a fiber held together by residual nuclear force and a small contribution from magnetism due to the nucleon magnetic moments, and prevented from collapsing and held rigid by electrostatic repulsion. Superstrong macroscopic structures can then be built by combining these basic nuclear matter needles.
Bolonkin is a legitimate scientist (PhD in aerospace engineering), but not a nuclear physicist, and has gotten papers on this stuff published, but not in physics journals (for example, "Femtotechnology: Nuclear AB-Matter with Fantastic Properties" in American Journal of Engineering and Applied Sciences and "Femtotechnology: Design of the Strongest AB Matter for Aerospace" in Journal of Aerospace Engineering). Furthermore, nobody else seems to have published anything on this topic, all of which makes me rather skeptical of his claims.
So, ignoring the issue of how you'd construct it in the first place (assume we find some helpful Cheela to do it for us or something), could a linear arrangement of alternating protons and neutrons at zero pressure (i.e., not confined in a neutron star or something) remain stable and not collapse into one big nucleus, or segment itself into a bunch of individual nucleii? And does it make any difference if the fiber is kept under tension by some external means?
 A: Everything that's physically possible occurs naturally. Atoms arrange themselves naturally into one- and two-dimensional structures (lipid and polymer chains in 1D, graphene and nanotubes from soot in 2D) and so we're able to envision techniques to mass-produce those. But there's no evidence that nucleons form chains in nature (at least outside of neutron stars), and so no reason to believe we could construct such a phase.
In fact we can be a little more quantitative. Different nuclei have different shapes; the sign of their quadrupole moment tells you whether they are primarily cigar-shaped ("prolate") or coin-shape ("oblate"), and octupole and higher moments describe more complicated shapes than ellipsoids. There are a small number of nuclei which are super-deformed in their ground states, with their long elliptical axis two or three times the length of their short axes. But those superdeformed nuclei tend to have masses $A\approx 80\mathrm{-}100$, so an ellipsoid with 3:1:1 axis ratio is a pretty long way away from a one-dimensional chain.
You have to remember the reason that the periodic table has finite size: the nuclear force, which holds nucleons together, is a contact force with a potential like 
$$
V \sim \frac \alpha r e^{-r/r_0}.
$$
For the attractive part of the nuclear interaction the range $r_0$ is set by the pion mass to about 1 fm. If you separate two protons by several femtometers, as in a heavy nucleus, the attractive interaction is exponentially weakened relative to the electrical repulsion. I see no reason to expect this to be any different for nucleons in a hypothetical chain.
A: Sounds like kook material. If his hypothetical material consists only of N neutrons and Z protons, then it has a nonzero net electric charge and can't possibly be a stable form of matter. The electrical potential energy would go like $Z^2$, while the nuclear potential energy would vary linearly with $N+Z$, because the nuclear force has a short range.
A: I am not a nuclear physicist but I have studied these structures. Bolonkin is not a fool. He knows what he is talking about. The claim that "everything possible occurs in nature" is not true. While fullerenes and tetrahedral carbon/diamond does occur, and while you could point to "natural" stainless steels, such as iron-cobalt-nickel meteorites, I can point to unnatural, manmade structures that do not occur in nature. Japanese metallurgists have made an Austenitic Stainless steel called H-1 which uses nitrogen in place of carbon in the iron matrix, and thus it is nearly 100 percent impervious to rust and is used in knife blades by Spyderco knives. Stainless steel does not occur in bone structures and yet steel is ten times stronger than bone. Because something does not occur in nature does not make it impossible.
I guess the two main issues here are stability issues: 1 Could you make subatomic/nuclear femto structures that take forms other than a glob or drop. Well, what if the assumption that the nucleus is a sphere are false? Buckminster Fuller proved the vector equilibrium structure/tensegrity/geodesics are found in nature, from the atom and molecule on up to the galatic level. You are ASSUMING that SUB-Atomic structures are chaotic and cannot have structures like tubes, sheets, bars, rods, and so on and so forth. If we find these structures in the atomic world (fullerenes for example), why wouldn't they exist even at smaller scales, like this: ? https://arxiv.org/abs/hep-ph/0112066
" Motivated by Fullerenes, in this Letter we point out the exis
tence of new ge-
ometric structures in QCD with high spatial symmetry. We det
ermine the
geometric structure and the characteristic “magic numbers
” of these configu-
rations, using analogies with carbon Fullerene structures
. We explore some of
the interesting topological structures that can be created
by QCD networks
and closed cages that may be produced in high energy nuclear r
eactions joining
multiple QCD junctions and anti-junctions. Although the QC
D Lagrangian is
CP even, we point out that the junction and anti-junction bui
lding blocks can
be used construct CP odd configurations that may also serve as
domain walls
between inequivalent (
θ
) QCD vacua."
At least consider it
