Is $ud$ matter more dangerous than strange matter? I have seen videos online about how dangerous strange matter is... which is something I have never understood since strange matter created in a lab always disappears very quickly.   However I watched a video today about the continent of stability at around 300 daltons.  At 315, the protons and neutrons break down into $u$ and $d$ quarks, making the nucleus free quarks...  Supposedly any matter that touches this atom breaks down into $u$ and $d$ quarks and is added to the nucleus.  Also supposedly this matter is stable at room temps and pressures.
I cannot find the paper online to support this....  Has anyone read this paper and if so, what are your thoughts?
 A: A basic search on "Stable quark matter" turns up a reputable non-specialist (but not exactly layman) article: https://phys.org/news/2018-06-periodic-table.html
Per the article, the idea is that at around $A=300$, nucleons no longer remain separate and the matter becomes up and down quarks, contained within some volume ($\approx \pm 5\,$)fm.
A: Once formed, the danger of $ud$ Quark Matter ($ud$QM) is probably comparable to that of strange quark matter (SQM). Quoting from the original paper on "Quark Matter May Not Be Strange":

As with SQM, the further injection of neutrons (or heavy ions) can cause the piece of udQM to grow with the release of an indefinite amount of energy.

What might be potentially riskier is that it may be easier to create $ud$ quark matter than strange quark matter. As noted in the article, with $ud$QM:

A faster catastrophic conversion could occur …


it raises the hope to produce this new form of stable matter by the fusion of heavy elements. With no strangeness to produce, this may be an easier task than producing SQM.

If produced, however, it is thought that either SQM or $ud$QM would likely be positively charged.  This is safer since the quark matter would electrostatically repel atomic nuclei making runaway absorption of normal matter unlikely.  The "Review of the Safety of LHC Collisions"
discusses how the risks of quark matter production (or other catastrophes) are negligible for current accelerators.
