S. E. Koonin

Solar fusion cross-sections

We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates.

Proton pictures of high-energy nuclear collisions

Abstract Correlations between protons emitted with nearly equal momenta are shown to be sensitive to the space-time structure of high-energy heavy-ion collisions. A quantal estimate indicates that final-state interactions and the exclusion principle result in a rich, experimentally accessible correlation structure for relative-photon-proton momenta ⪅50 MeV/c which can be used to determine the size, velocity, and lifetime of the collision volume.

Shell model Monte Carlo methods

We review quantum Monte Carlo methods for dealing with large shell model problems. These methods reduce the imaginary-time many-body evolution operator to a coherent superposition of one-body evolutions in fluctuating one-body fields; resultant path integral is evaluated stochastically. We first discuss the motivation, formalism, and implementation of such Shell Model Monte Carlo methods. There then follows a sampler of results and insights obtained from a number of applications. These include the ground state and thermal properties of pf-shell nuclei, thermal behavior of {gamma}-soft nuclei, and calculation of double beta-decay matrix elements. Finally, prospects for further progress in such calculations are discussed. 87 refs.

The Disassembly of Nuclear Matter

A statistical model is applied for multi-fragment final states in nuclear collisions with bombarding energies E/A ≈ 100 MeV. A portion of the intermediate system formed is assumed to decay according to the available classical non-relativistic phase space, calculated in a grand canonical ensemble. The model correlates and predicts many experimental observables in terms of three parameters: the available energy per nucleon, the isospin asymmetry, and the effective interaction volume.

Earthshine observations of the Earth's reflectance

Regular photometric observations of the moons “ashen light” (earthshine) from the Big Bear Solar Observatory (BBSO) since December 1998 have quantified the earths optical reflectance. We find large (∼5%) daily variations in the reflectance due to large-scale weather changes on the other side of the globe. Separately, we find comparable hourly variations during the course of many nights as the earths rotation changes that portion of the earth in view. Our data imply an average terrestrial albedo of 0.297±0.005, which agrees with that from simulations based upon both changing snow and ice cover and satellite-derived cloud cover (0.296±0.002). However, we find seasonal variations roughly twice those of the simulation, with the earth being brightest in the spring. Our results suggest that long-term earthshine observations are a useful monitor of the earths albedo. Comparison with more limited earthshine observations during 1994–1995 show a marginally higher albedo then.

MICROCANONICAL SIMULATION OF NUCLEAR DISASSEMBLY

Abstract We formulate a model for the disassembly of a highly excited finite nuclear source into interacting nuclear fragments. Monte Carlo sampling of the exact microcanonical and canonical ensemble provides many-fragment configurations at the effective freeze-out stage. The effect of including the interaction between the fragments is significant and an elaboration of the model that allows for a nucleon vapor suggests the existence of a first-order phase transition.

Climate engineering responses to climate emergencies

Despite efforts to stabilize CO_2 concentrations, it is possible that the climate system could respond abruptly with catastrophic consequences. Intentional intervention in the climate system to avoid or ameliorate such consequences has been proposed as one possible response, should such a scenario arise. In a one-week study, the authors of this report conducted a technical review and evaluation of proposed climate engineering concepts that might serve as a rapid palliative response to such climate emergency scenarios. Because of their potential to induce a prompt (less than one year) global cooling, this study concentrated on Shortwave Climate Engineering (SWCE) methods for moderately reducing the amount of shortwave solar radiation reaching the Earth. The studys main objective was to outline a decade-long agenda of technical research that would maximally reduce the uncertainty surrounding the benefits and risks associated with SWCE. For rigor of technical analysis, the study focused the research agenda on one particular SWCE concept--stratospheric aerosol injection--and in doing so developed several conceptual frameworks and methods valuable for assessing any SWCE proposal.

Shell-model Monte Carlo studies of fp-shell nuclei

We study the gross properties of even-even and {ital N}={ital Z} nuclei with {ital A}=48--64 using shell-model Monte Carlo methods. Our calculations account for all 0{h_bar}{omega} configurations in the {ital fp} shell and employ the modified Kuo-Brown interaction {ital KB}3. We find good agreement with data for masses and total {ital B}({ital E}2) strengths, the latter employing effective charges {ital e}{sub {ital p}}=1.35{ital e} and {ital e}{sub {ital n}}=0.35{ital e}. The calculated total Gamow-Teller strengths agree consistently with the {ital B}({ital GT}{sub +}) values deduced from ({ital n},{ital p}) data if the shell-model results are renormalized by 0.64, as has already been established for {ital sd}-shell nuclei. The present calculations therefore suggest that this renormalization (i.e., {ital g}{sub {ital A}}=1 in the nuclear medium) is universal.

Auxiliary field Monte-Carlo for quantum many-body ground states

Abstract We develop an algorithm for determining the exact ground state properties of quantum many-body systems which is equally applicable to bosons and fermions. The Schroedinger eigenvalue equation for the ground state energy is recast as a many-dimensional integral using the Hubbard-Stratonovitch representation of the imaginary-time many-body evolution operator. The integral is then evaluated stochastically. We test the algorithm for an exactly soluble boson system with an attractive potential and then extend it to fermions and repulsive potentials. Importance sampling is crucial to the success of the method, particularly for more complex systems. Computational efficiency is improved by performing the calculations in Fourier space.

Determining pion source parameters in relativistic heavy-ion collisions

Abstract Two-pion inclusive spectra from relativistic heavy-ion collisions are related to single-particle inclusive measurements in a Lorentz-invariant formulation of the Hanbury-Brown-Twiss effect. A thermal pion source with a gaussian space-time distribution is assumed. The angular anisotropy and moments of the correlation function are computed to facilitate the determination of pion source parameters from the ratios of the two-pion to single-pion inclusive data.