Rebirth of Nucleogenesis

            Among the enormous amount of ‘stuff’ I came across in cleaning out the basement of about 15 file boxes that were shipped up from Huntsville when we moved to Jenkintown was a notice of a seminar that I presented as a graduate student at Purdue University.  It was required that each doctoral candidate in the Chemistry Department present a seminar to the faculty and students on a topic not directly related to their research. The title of my talk was “Nucleogenesis.” For the benefit of my non-scientist readers, what this title implies is the question of how did it come about that we now have about 100 different chemical elements on earth. The “nucleo-” of nucleogenesis refers to the nucleus of an atom that determines the chemical nature of each element. The nucleus consists of varying number of protons and neutrons. It is the number of protons that determines the chemical nature of the element. For example, hydrogen has one proton, oxygen has eight. Hence, as there are different numbers of protons, we have the various chemical elements: carbon, sulfur, iron, lead, gold, etc. The “-genesis” part of nucleogenesis refers to the question of how the elements were created. (The term nucleosynthesis is also used to describe this process.) How did it come about that there are the different chemical elements? At the time of “creation” of the universe was each element created as such, or was there some process of creating each element by adding protons to existing elements thereby growing in size, each one representing a new chemical element?

            Why this seminar notice now attracted my attention and didn’t just get tossed out with the ‘tons’ of other stuff was the fact I have been taking various MOOC courses (Massive Open Online Courses), one being Astronomy and another being From the Big Bang to Dark Energy. The first course, in addition to lectures on the description of the universe in terms of stars, planets, orbits, etc., included a major segment on the evolution of the universe, the formation of stars, galaxies, planets, etc., going back in time to the Big Bang. Very early on, even before the heavenly bodies were formed, it was necessary to create the fundamental particles of matter that make up these bodies and then the chemical elements that we now observe on our planet and distributed throughout the universe. This is nucleogenesis.

            With a degree in physical chemistry and working in industry in the fields of rocketry, plastics, fibers, toxicology, and chemical regulation, I had not paid much attention to the growth in knowledge in the fields of nuclear chemistry and physics. I was able to do my work with the knowledge of the atom as was taught in the late 1950’s; there were just four fundamental particles: electrons, protons, neutrons, and the mysterious neutrino. Those particles along with photons (light rays), and a variety of electromagnetic waves, like x rays, gamma rays, radio waves, were all one needed to pursue chemical research for the rest of one’s career. Today there are 16 known fundamental particles (17 if you count the Higgs boson whose existence was confirmed in 2013); twice that number if you count anti-matter. In fact , two of the fundamental particles in my day, the proton and the neutron, are no longer considered fundamental because they are now known to be made up of two other more fundamental particles, the up and down quark.

            The curious question that I had when I came across the seminar notice was: how was it that I was attracted to the topic of nucleogenesis in 1958 when I had no special interest in nucleo chemistry or physics. Surely at that time there must have been some event or trigger that sparked my interest. Through the marvels of the Internet, I located a paper entitled “Stellar Evolution, Nuclear Astrophysics, and Nucleogenesis” by A.G.W. Cameron. This paper contains the series of lectures given at the Purdue Physics Department in March and April 1957. I am quite sure that I did not attend these lectures, but it is quite likely that I saw some announcement of this series of lectures, and that the title of the talks triggered a curiosity in me that led to my personal pursuit of the topic and eventually the seminar that I presented.

            What shocks me now, having taken the two MOOC courses and also knowing that an understanding the formation of the elements requires a knowledge of what was occurring in the very early moments of the universe, is what did I teach at the seminar?  Nucleogenesis couldn’t be fully understood until the theory of the Big Bang was well developed and the processes that were occurring during the expansion of the universe after the Big Bang were appreciated.   Although the Big Bang was first proposed in 1927, a deep understanding didn’t develop until the 1960’s and beyond. So what did I teach my fellow graduate students and professors how the chemical elements were formed without this understanding? Of course at this point some 56 years later, I have no memory of the details of the seminar. What I can glean from the summary on the seminar notice was that I proposed two approaches that would appeal to chemists: One is that the distribution of the abundance of the elements represents an equilibrium of the energy contained in each element (which is referred to as the grand canonical ensemble). The second is that the distribution of elements that we see now resulted from the kinetics of formation of each element. Today both these concepts are as naïve as Lord Kelvin’s calculation was in 1862 that the sun would burn out in a trivial number of years because he did not know of any process that could release the amount of energy required for what he knew was being released from the sun. Although Lord Kelvin died in 1907, we have no knowledge whether he appreciated the impact of Einstein’s famous E = mc² which was published in 1905.


Postscript: I am certain that I did not know of the existence of a paper entitled “Synthesis of the Elements in Stars” which was published in October of 1957 since it was not listed in my References. Remember in the days (actually decades) before Google, the equivalent in the form of scientific abstract journals weren’t published until a year or more after the original paper was published. To this day, this paper continues to be the definitive paper on the formation of the elements beyond hydrogen and helium despite the fact that the synthesis of the elements is based totally of what was known of nuclear chemistry at that time (roughly twelve years after the explosion of the first atomic bomb) and excludes any notion of the synthesis of the elements in a very early life of the universe. In fact, this paper has become somewhat of a celebrity in the realm of scientific papers by simply being referred to as B2FH which stands for the initials of the authors of the paper, K. Margaret Burbidge, G. R. Burbidge, William A. Fowler, and F. Hoyle. B2FH even has its own website where the original paper can be found along with related material (www.b2fh.org).