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AbstractNeutron cross sections of the stable lithium isotopes 6Li and 7Li were of interest in the 1940s and 1950s in part because of their reactions, which form tritium using moderated neutrons on 6Li and higher-energy neutrons on either isotope. Lithium remains of interest today for use as a blanket and shielding material in fusion reactors, where it can be used to breed tritium for a self-sustaining fuel cycle. During the Manhattan Project, the resonance in the 6Li(n,t) reaction was discovered and later became important for enhancing tritium production for nuclear technologies. The dominant natural isotope 7Li was and remains of interest because of the expense of enriching 6Li. It has been oft reported that the 1954 Castle Bravo nuclear test had a yield twice as large as expected because the nuclear explosive device designers had not properly accounted for the benefits from the 7Li isotope in the fuel; we note that this explanation is false.

AbstractWhile studying d(d,n)3He fusion in 1938, Ruhlig observed protons with energies larger than 15 MeV. Ruhlig suggested that these high-energy protons were generated by tritium-on-deuterium fusion neutrons scattering protons out of a thin cellophane foil placed inside a cloud chamber. This led Ruhlig to hypothesize that he was observing secondary (in-flight) tritium-on-deuterium fusions and conclude that the d(t,n) reaction “must be an exceedingly probable one.” This was the first attempt to quantify the probability of d(t,n) fusion, using the ~1-MeV tritons generated by d(d,p)t fusion. This caused some Manhattan Project scientists to suggest that the d(t,n) cross sections are significantly higher than those for deuteron-on-deuterium fusion and led to the first measurement of d(3He,p) and d(t,n) cross sections in 1943. Here, we have used modern cross sections and stopping powers to estimate the expected numbers of high-energy protons associated with in-flight d(t,n) reactions in Ruhlig’s experiment. Our estimate is four orders of magnitude lower than Ruhlig’s observed rate. However, the number of high-energy protons in Ruhlig’s experiment can be obtained via simulation if the protons are assumed to have been emitted by secondary in-flight d(3He,p) reactions, with various plausible assumptions about the experimental geometry and target-backing thickness. Our calculations demonstrate that quantitative information about the fusion of A = 3 ions with deuterium could have been obtained via experiments similar to Ruhlig’s well in advance of the advent of 3He ion and triton beams in 1943. This opportunity seems to have been missed.

The introduction of cytological methods for the early diagnosis of uterine cancer has been a significant modern development in spite of waning emphasis on the morphological approach to clinical problems. The emergence of the method was the logical outcome of two separate series of investigations—the introduction of the concept of noninvasive carcinoma by Rubin1 and the perfection by Papanicolaou2 of technical methods for studying cells exfoliated from the female genital tract. The principle on which the method rests derives from phenomena implicit in the observations of Coman,3 namely, that the force required mutually to separate normal cervical cells is some 10 times that required to separate the cells of squamous carcinoma of the cervix. The usefulness of exfoliative cytologic studies in the early diagnosis of uterine cancer has been extensively studied during the past eight years. Several investigators4 have convincingly documented its relative reliability, and L'Esperance