From Steam to Stars to the Early Universe

Much of what follows was first published in Les Prix Nobel en 1983 (Fowler 1984). I have updated the autobiographical material to the summer of 1991. I was born in 1911 in Pittsburgh, Pennsylvania, the son of John MacLeod Fowler and Jennie Summers Watson Fowler. My parents had two other children, my younger brother, Arthur Watson Fowler and my still younger sister, Nelda Fowler Wood. My paternal grandfather, William Fowler, was a coal miner in Slammannan, near Falkirk, Scotland who emigrated to Pittsburgh to find work as a coal miner around 1880. My maternal grandfather, Alfred Watson, was a grocer. He emigrated to Pittsburgh, also around 1880, from Taniokey, near Clare in County Armagh, Northern Ireland. His parents taught in the National School, the local grammar school for children, in Taniokey, for sixty years. The family lived in the central part of the school building; my great grandfather taught the boys in one wing of the building and my great grandmother taught the girls in the other wing. The school is still there and I have been to see it. Ihave also visited Slammannan

From Steam to Stars to the Early Universe

Much of what follows was first published in Les Prix Nobel en 1983 (Fowler 1984). I have updated the autobiographical material to the summer of 1991. I was born in 1911 in Pittsburgh, Pennsylvania, the son of John MacLeod Fowler and Jennie Summers Watson Fowler. My parents had two other children, my younger brother, Arthur Watson Fowler and my still younger sister, Nelda Fowler Wood. My paternal grandfather, William Fowler, was a coal miner in Slammannan, near Falkirk, Scotland who emigrated to Pittsburgh to find work as a coal miner around 1880. My maternal grandfather, Alfred Watson, was a grocer. He emigrated to Pittsburgh, also around 1880, from Taniokey, near Clare in County Armagh, Northern Ireland. His parents taught in the National School, the local grammar school for children, in Taniokey, for sixty years. The family lived in the central part of the school building; my great grandfather taught the boys in one wing of the building and my great grandmother taught the girls in the other wing. The school is still there and I have been to see it. Ihave also visited Slammannan

The disintegration of N15 by protons

The absolute cross sections of the reactions (1) N15(p,α)C12, (2) N15(p,αγ)C12, and (3) N15(p,γ)O16 have been measured from 0.2 to 1.6 Mev. The thick target yield of reaction (1) was also measured at 0.100 Mev. Resonances were found at 0.338, 1.05, and 1.210 Mev for reaction (1); at 0.429, 0.898, 1.210, and possibly 1.05 Mev for reaction (2); and at 1.05 Mev for reaction (3). Most of the resonances follow closely the shape of the single level dispersion formula. The 1.05-Mev resonance is asymmetric and cannot be explained as easily. The cross section of reaction (1) has been extrapolated to stellar energies and is given by σ=(110 / E)×exp(-6.95E-1 / 2) barns for E in Mev in the energy region near 0.030 Mev

Nucleosynthesis during the Early History of the Solar System

Abundances in terrestrial and meteoritic matter indicate that the synthesis of D^2, Li^6, Li^7, Be^9, B^(10) and B^(11) and possibly C^(13) and N^(15) occurred during an intermediate stage in the early history of the solar system. In this intermediate stage, the planetary material had become largely separated, but not completely, from the hydrogen which was the main constituent of primitive solar material. Appropriate physical conditions were satisfied by solid planetesimals of dimensions from 1 to 50 metres consisting of silicates and oxides of the metals embedded in an icy matrix. The synthesis occurred through spallation and neutron reactions simultaneously induced in the outer layers of the planetesimals by the bombardment of high energy charged particles, mostly protons, accelerated in magnetic flares at the surface of the condensing Sun. The total particle energy was approximately 10^(45) ergs while the average energy was close to 500 MeV per nucleon. Recent studies of the abundance of lithium in young T Tauri stars serve as the primary astronomical evidence for this point of view. The observed abundances of lithium and beryllium in the surface of the Sun are discussed in terms of the astronomical and nuclear considerations brought forward. The isotope ratios D^2/H^1 = 1.5 × 10^(−4), Li^6/L^i7 = 0.08, and B^(10)/B^(11) = 0.23 are the basic data leading to the requirement that 10 per cent of terrestrial-meteoritic material was irradiated with a thermal neutron flux of 10^7 n/cm^2 s for an interval of 10^7 years. The importance of the (n, α) reactions on Li^6 and B^(10) is indicated by the relatively low abundances of these two nuclei. It is shown that the neutron flux was sufficient to produce the radioactive Pd^(107) and I^(129) necessary to account for the radiogenic Ag^(107) and Xe^(129) anomalies recently observed in meteorites. The short time interval, ∼ 6 × 10^7 years, required for the radioactive decays to be effective applies to the interval between the end of nucleosynthesis in the solar system and the termination of fractionation processes in the parent bodies of the meteorites. It is not necessary to postulate a short time interval between the last event of galactic nucleosynthesis and the formation of large, solid bodies in the solar nebula

Nucleosynthesis of Heavy Elements by Neutron Capture

Nucleosynthesis of elements heavier than the iron group by neutron capture on both slow and fast time scales is evaluated. The s-process calculations of Clayton, Fowler, Hull, and Zimmerman (1961) have been revised to include more recent experimental results on abundances and neutron capture cross- sections. The solar-system s-process abundances indicate a history of neutron exposure distributions characterized by decreasing probability of high integrated flux; an exponential exposure distribution is extracted. Estimates are made of the s-process contribution to each isotopic abundance; a table gives the amounts of elements produced by each process in the solar-system material. The r-process calculations are carried out using a semi-empirical atomic-mass law to determine neutron-binding energies and betadecay probabilities. The solar-system r-process material has probably been synthesized in two distinct types of environments, e.g., one of about 4 sec duration with temperature 2.4 X 10 K and neutron density 5 X tO , and the other of the same or longer duration with temperature 1.0 X 10 K and neutron density 3 X 1O both of these environments could be found in an object with mass 10 Mo

Nucleosynthesis During Silicon Burning

Silicon burning at temperatures in the neighborhood of 4 × 109 °K has been studied with the aid of a quasiequilibrium model which describes the abundance of the nuclei in the interval 28\u3c~A\u3c~62. It is found that, for a broad range of temperatures and densities, silicon burning leads to nuclear abundance distributions which match important features of the natural solar-system abundance distributions and that a large nuclear energy release accompanies silicon burning

Interview with William A. Fowler

Interview conducted in eight sessions between May 1983 and May 1984 with Willy Fowler, Nobel laureate and Institute Professor of Physics, emeritus. In a career in nuclear physics and nuclear astrophysics that spanned more that sixty years, Fowler was primarily concerned with nucleosynthesis--that is, the creation of the heavy elements by the fusion of the nuclei of lighter elements. In 1957, with Fred Hoyle and Geoffrey and Margaret Burbidge, Fowler coauthored the seminal paper "Synthesis of the Elements in the Stars," now known as B2FH. In it, they showed that all the elements from carbon to uranium could be produced by nuclear processes in stars starting only with the light elements produced in the Big Bang. In the interview, Fowler discusses his early education as a physicist at Ohio State; his work with Charles C. and Tommy Lauritsen at Caltech's Kellogg Radiation Laboratory; the history of nuclear physics and nuclear astrophysics at Caltech; and the evolution of nucleosynthesis. There are recollections of many of his mentors and colleagues, including Robert A. Millikan, Hans Bethe, J. Robert Oppenheimer, the Lauritsens, Fred Hoyle, the Burbidges, Jesse Greenstein, A. G. W. Cameron, Richard P. Feynman, and H. P. Robertson. A 1986 Supplement contains an interview on Fowler's work for the Naval Bureau of Ordnance and the Manhattan Project during the Second World War