C. Borghi, C. Giori, and A. Dall'Olio published an article entitled "Experimental evidence of emission of neutrons from cold hydrogen plasma" appearing in Yad. Fiz. 56, 147-156 (July 1993) and Phys. At. Nucl. 56 (7), July 1993, ©1993 American Institute of Physics.
The abstract of Borgi et al. reads:
We have tried to see experimentally whether there is some interaction between electric charges, other than the Coulombic one, and whether it may produce some kind of bound states between a proton and an electron, electrically neutral but different from a hydrogen-atom state. This requires that the stronger, and quicker, Coulombic interaction may be avoided by means of a high-frequency ionizing e.m. field. This field succeeds in maintaining a "cold" plasma i.e., a considerable number of protons mixed and colliding with an equal number of free electrons, for a time much larger than $10^{-8}$ sec. This limit is suggested by the known average recombination time of the ionized hydrogen atom.
This arXiv.org article summarizes Borgi et al. as follows:
Following Rutherford's 1920 historical hypothesis of the neutron as a compressed hydrogen atom in the core of stars, the laboratory synthesis of the neutron from protons and electrons was claimed in the late 1960 by the Italian priest-physicist Don Carlo Borghi and his associates via a metal chamber containing a partially ionized hydrogen gas at a fraction of $1$ bar pressure traversed by an electric arc with $5 J$ energy and microwaves with $10^{10} s^{-1}$ frequency. The experiment remained unverified for decades due to the lack of theoretical understanding of the results.
Did Borghi's experiment show that neutrons can be synthesized purely from protons and electrons?