Summary
The key to whether The Urantia Book statement (below) on production of new elements of atomic number greater than 100 is the word "naturally." New elements are formed "naturally" under conditions of high temperature and pressure. Laboratory conditions may be quite different. To date mendelevium 258 is the only artificially produced element having a reasonable degree of stability--half-life 54 days. But if you were hoping to build a dwelling place out of mendelevium, within two years, almost all your new home would have decayed to something else. All other "artificials" have miniscule life times.
However most new, knowledgeable readers will know about the production of new elements but will have little information on stability. So will probably consider the Urantia Book comment to be wrong.
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"In Orvonton it has never been possible naturally to assemble over one hundred orbital electrons in one atomic system. When one hundred and one have been artificially introduced into the orbital field, the result has always been the instantaneous disruption....(478)
The text above is from the first printing, someone having taken the liberty of adding the words "well-nigh" before "instantaneous" in subsequent printings. The important word to keep in mind is "naturally."
It had been known since the 1930's that new elements should be produced by neutron bombardment of an element which would be followed by a beta decay process in which an atomic nucleus with a captured neutron loses an electron. In doing so, one of the nuclear neutrons becomes a proton. Such an element moves to be the next element upwards in the periodic table.
In the 1940's Bohr made a prediction (that turned out to be true) that the beta decay process would cease with element 100. Thus no element above this atomic number could be produced by the neutron capture, beta decay process. This appears to be the process that the revelators regard as natural.
Elements as high as 112 have been produced by other means and all are highly unstable. Element 101, (mendelevium-256) was produced in 1955 by helium ion bombardment of einsteinium-253. Element 102 (nobelium) was produced by bombarding element 96 (curium) with carbon atoms.
It is doubtful whether this type of reaction occurs "naturally" even in supernova explosions. That it can be done in the laboratory is a tribute to the ingenuity of the people involved. In a recent publication, it was stated that new elements with half lives less than 10 microseconds can be identified even if, out of 10 billion trials, only two nuclei fuse together once to form a superheavy new element. The single atom so produced will be both detected and identified!1
The possibility for these superheavy elements occurring naturally in novae explosions may be remote. And even if they were produced, the product would usually decay in an instant.
The Urantia papers use that word "instant" and its derivatives in many different contexts. For example, they say that human beings, "from a cosmic perspective, are born, live, and die in a relative instant of time." In terms of a cosmic perspective, elements above 100, and quite a few below, can exist for only a relative instant of time and many scarcely or not at all.
The important point about the 100 elements comment is that, when made, it was "prophetic." The Fermi theory about neutron capture and beta decay had been established in 1937 with the production of technetium from molybdenum. However its cessation at element 100 was not empirically established until the mid-1950's. Hence there was only very meager evidence to use the concept in the Papers.
So although, technically speaking, the authors' statement can be defended as correct, a major section of new readers will probably see it as erroneous.
Reference
1. Armbruster, P., and F.P. Hessberger, "Making New Elements." Scientific American 279 (3) 50. (1998)
