Interview with Hans A. Bethe

Two interviews conducted at Caltech in 1982 and 1993 with theoretical physicist Hans Bethe. The recipient of the Nobel Prize in physics in 1967 for his work on nuclear reactions in stars, Bethe was born in Strasbourg and educated at the University of Frankfurt and at the University of Munich, where he earned a PhD in 1928 under A. Sommerfeld at the Institute for Theoretical Physics. From 1928 to 1933, Bethe held a variety of teaching positions in Germany, also visiting the Physics Institute of the University of Rome in Via Panisperna 89A in 1931 and 1932. Hitler's rise to power forced Bethe from the University of Tubingen in 1933. Two years later he became an assistant professor at Cornell University, garnering a full professorship there in 1937. In the 1982 interview Bethe speaks principally about his contacts at Caltech, including L. Pauling, R. Millikan, T. von Karman, F. Zwicky, C. C. Lauritsen, W. A. Fowler, R. Feynman and R. F. Bacher. He discusses his relations with other prominent physicists, including E. Teller, N. Bohr and J. R. Oppenheimer. He also describes his first impressions of nuclear physics, the political climate in Italy in the 1930s, and the Rome school of physics, including E. Fermi, F. Rasetti, and E. Segre. The 1993 interview concerns R. Bacher at Cornell and at work on the Manhattan Project at Los Alamos during World War II

Nuclear Level Densities in the Constant-Spacing Model

A new method to calculate level densities for non-interacting Fermions within the constant-spacing model with a finite number of states is developed. We show that asymptotically (for large numbers of particles or holes) the densities have Gaussian form. We improve on the Gaussian distribution by using analytical expressions for moments higher than the second. Comparison with numerical results shows that the resulting sixth-moment approximation is excellent except near the boundaries of the spectra and works globally for all particle/hole numbers and all excitation energies.Comment: 14 pages, 4 figures; v2 updated to the published version - extended the motivation; results unchange

Nucleon Spin Fluctuations and the Supernova Emission of Neutrinos and Axions

In the hot and dense medium of a supernova (SN) core, the nucleon spins fluctuate so fast that the axial-vector neutrino opacity and the axion emissivity are expected to be significantly modified. Axions with m_a\alt10^{-2}\,{\rm eV} are not excluded by SN~1987A. A substantial transfer of energy in neutrino-nucleon ($\nu N$) collisions is enabled which may alter the spectra of SN neutrinos relative to calculations where energy-conserving $\nu N$ collisions had been assumed near the neutrinosphere.Comment: 8 pages. REVTeX. 2 postscript figures, can be included with epsf. Small modifications of the text, a new "Note Added", and three new references. To be published in Phys. Rev. Let

Mesons with Beauty and Charm: Spectroscopy

Applying knowledge of the interaction between heavy quarks derived from the study of $c\overline{c}$ and $b\overline{b}$ bound states, we calculate the spectrum of $c\overline{b}$ mesons. We compute transition rates for the electromagnetic and hadronic cascades that lead from excited states to the $^1\text{S}_0$ ground state, and briefly consider the prospects for experimental observation of the spectrum.Comment: 32 pages + 2 uuencoded PostScript figures Fermilab-Pub-94/032-

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

Pauli letter collection: letter to Wolfgang Pauli

Bethe talks about mathematical difficulties in his calculations (maybe on the scattering of light)

Teoria elementare del nucleo

La presente opera mira a dare allo studente di fisica un quadro ben delineato ed essenzialmente concreto dei principi e dei concetti più importanti che stanno a base della fisica dei nuclei