Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Over the past several years, major changes have been made to the toolkit in order to accommodate the needs of these user communities, and to efficiently exploit the growth of computing power made available by advances in technology. The adaptation of Geant4 to multithreading, advances in physics, detector modeling and visualization, extensions to the toolkit, including biasing and reverse Monte Carlo, and tools for physics and release validation are discussed here.

/pdf/recent-developments-in-geant4-3pgbpf1ko3.pdf

Recent developments in GEANT4

ENDF/B-VII.1 Nuclear Data for Science and Technology: Cross Sections, Covariances, Fission Product Yields and Decay Data

https://digital.library.unt.edu/ark:/67531/metadc888955/m2/1/high_res_d/900147.pdf

ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology

The fourth version of the Japanese Evaluated Nuclear Data Library has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the impro...

https://www.tandfonline.com/doi/pdf/10.1080/18811248.2011.9711675

JENDL-4.0: A New Library for Nuclear Science and Engineering

Cooling a 1 l BaF2 crystal to 243 K yielded the same or even better gamma-ray energy resolution as is obtained NaI(Tl) detectors of comparable efficiency.

Gamma-ray spectroscopy with a cooled barium fluoride crystal

We have made improved measurements of the neutron capture and total cross sections for {sup 137}Ba over a sufficiently wide range of energies so that the reaction rate at s-process temperatures (kT=6{endash}23 keV) can be determined solely from the data. These rates are crucial for the interpretation of recently discovered anomalies of Ba isotopes in silicon carbide grains from the Murchison meteorite. Recent stellar models of the s process are in agreement with the meteoric anomaly data for Ba only if the {sup 137}Ba(n,{gamma}) reaction rate is 20{percent} larger than the previously accepted rate. Our reaction rates at s-process temperatures are in agreement with the extrapolated reaction rate from the most recent previous measurement. Hence, our results uphold, and place on much firmer footing, the discrepancy between recent stellar models of the s-process and the meteoric anomaly data. {copyright} {ital 1998} {ital The American Physical Society}

High resolution neutron capture and transmission measurements on 137 Ba and their impact on the interpretation of meteoric barium anomalies

High Resolution Neutron Capture and Transmission Measurements on ^137Ba and Their Impact on the Interpretation of Meteoric Barium Anomalies

For the first time, high-resolution transmission data of {sup 233}U have been obtained using a cooled sample. The samples were cooled to T = 11 K using a cryogenic device, which reduced the Doppler broadening of resonances by 50% compared to room-temperature measurements. The measurements were carried out at the Oak Ridge Electron Linear Accelerator over the energy range from 0.6 eV to 300 keV at the 80-m flight path station. Corrections were made for experimental effects, and the average total cross section in this energy range was determined. Results are compared to previous measurements.

High-Resolution Transmission Measurements of 233U Using a Cooled Sample at the Temperature T=11 K

We demonstrate that high-quality total radiation width ( γ ) data are a virtually untapped resource for testing and improving nuclear models. To this end, we obtained unprecedentedly large sets of γ values for all six sand p-wave J π values for 95Mo neutron resonances. We show that γ distributions simulated in the framework of the nuclear statistical model are in sharp disagreement with the data. Simulations modified to include doorway effects resulted in much better agreement. These results call into question the reliability of the nuclear statistical model.

/pdf/extreme-nonstatistical-effects-in-g-decay-of-95mo-neutron-2qmouo585x.pdf

Klaus H Guber

Papers

Gamma-ray spectroscopy with a cooled barium fluoride crystal

High resolution neutron capture and transmission measurements on 137 Ba and their impact on the interpretation of meteoric barium anomalies

High Resolution Neutron Capture and Transmission Measurements on ^137Ba and Their Impact on the Interpretation of Meteoric Barium Anomalies

High-Resolution Transmission Measurements of 233U Using a Cooled Sample at the Temperature T=11 K

Extreme nonstatistical effects in γ decay of 95Mo neutron resonances