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Wefel, J. P.

Publications and source records attributed to Wefel, J. P..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Supernova and cosmic rays

A general overview of supernova astronomy is presented, followed by a discussion of the relationship between SN and galactic cosmic rays. Pre-supernova evolution is traced to core collapse, explosion, and mass ejection. The two types of SN light curves are discussed in terms of their causes, and the different nucleosynthetic processes inside SNs are reviewed. Physical events in SN remnants are discussed. The three main connections between cosmic rays and SNs, the energy requirement, the acceleration mechanism, and the detailed composition of CR, are detailed.

Wefel, J. P.↗
NASA NTRS1980

The energy dependence of the ratios of secondary to primary elements in the cosmic radiation

The secondary to primary ratios B/C, N/O and (Sc-Mn)/Fe in the galactic cosmic rays have been measured in the overall energy interval 30-180 MeV/n with the University of Chicago cosmic ray telescope on board the satellite IMP-8 during the period 1974-1978. These results, together with the values of the same ratios measured at higher energies, have been compared to the results of cosmic ray propagation calculations using different pathlength distributions (PLD) and different levels of solar modulation, in order to select a single set of parameters consistent with all the measured ratios.

Garcia-Munoz, M.↗
NASA NTRS1980

Carbon, nitrogen and oxygen isotopes in the low energy galactic cosmic rays

The isotopes of C, N, and O in the galactic cosmic rays were measured in the 45-106 Mev/nucleon range with data collected during 1973-77 by the cosmic-ray telescope onboard the IMP-7 spacecraft. The ratios of (N-15)/N, (C-13)/C, and ((O-18)/O agreed with previous measurements. Cosmic ray propagation and solar modulation indicate that the measured N isotopic ratio is in agreement with a source ratio of (N-14)/O = 0.03, which is much lower than the solar system abundance ratio.

Guzik, T. G.↗
NASA NTRS1980

The isotopic composition of neon and magnesium in the low energy cosmic rays

The ratios Ne-22/Ne-20 and Mg-26/Mg-24 were measured in galactic cosmic rays by the IMP-7 satellite in the 60 to 230 MeV/nucleon range. The neon cosmic ray source ratio Ne-22/Ne-20 is about 0.38, which is much larger than the current solar system relationship; the Mg data agrees with the solar system isotopic ratio of 0.14 at the cosmic ray source. The Ne and Mg source ratios are explained by supernova models, and become a new constraint which should be satisfied by any model of cosmic ray origin.

Garcia-Munoz, M.↗
NASA NTRS1980

Actinide cosmic ray chronometers - Relative abundances and the cosmic ray lifetime

Measurements of ultraheavy cosmic rays will provide radioactive chronometers, including the actinides, which are expected to be present in the source. These primary chronometers differ from the Be-10 secondary chronometer in total inelastic cross-section and decay half-life. A propagation code, which includes nuclear fragmentation, radioactive decay, and ionization energy-loss of cosmic rays is being used to investigate the variations in the fluxes and mean ages which would be expected for various models of cosmic ray propagation. Some preliminary results in the actinide region are presented here which indicate that measurements of the relative abundances of the actinides in the cosmic rays will be very useful for understanding source abundances but less useful for studying propagation effects.

Margolis, S. H.↗
NASA NTRS1979

Isotopic anomalies from neutron reactions during explosive carbon burning

The heavy isotopic anomalies observed recently in the fractionation and unknown nuclear inclusions from the Allende meteorite are explained by neutron reactions during the explosive carbon burning (ECB). This model produces heavy anomalies in the same zone where Al-26 and O-16 are produced, thus reducing the number of source zones required for the isotopic anomalies. Unlike the classical r-process, the ECB n-process avoids the problem with the Sr anomaly and may resolve the problem of conflicting time scales between Al-26 and the r-process isotopes I-129 and Pu-244. Experimental studies of Zr and Ce isotopic composition are proposed to test this model.

Lee, T.↗
NASA NTRS1979

The isotopes of neon in the galactic cosmic rays

The paper examines the results obtained by the University of Chicago instrument on board the IMP 7 satellite used to measure the abundances of Ne-20 and Ne-22 in the galactic cosmic rays during 1973-1977, over the general energy range of 60-230 MeV per nucleon. It is reported that the instrument shows a mass resolution of 0.7 amu(sigma) which was confirmed by calibrating a backup instrument at the LBL Bevalac with separated beams of neon isotopes. Through the use of standard solar modulation and cosmic-ray propagation models, the cosmic-ray source ratio inferred is Ne-22/Ne-20 = 0.38 = or -0.07 which is significantly greater than the present solar system ratio. It is concluded that propagation effects or cross-section uncertainties cannot account for such a large abundance of Ne-22, and thus this measurement provides evidence that the cosmic rays come from a source region where the Ne-22 abundance is substantially greater than in solar system material.

Garcia-Munoz, M.↗
NASA NTRS1978

Isotopic anomalies from neutron reactions during explosive carbon burning

The possibility that the newly discovered correlated isotopic anomalies for heavy elements in the Allende meteorite were synthesized in the secondary neutron capture episode during the explosive carbon burning, the possible source of the O-16 and Al-26 anomalies, is examined. Explosive carbon burning calculations under typical conditions were first performed to generate time profiles of temperature, density, and free particle concentrations. These quantities were inputted into a general neutron capture code which calculates the resulting isotopic pattern from exposing the preexisting heavy seed nuclei to these free particles during the explosive carbon burning conditions. The interpretation avoids the problem of the Sr isotopic data and may resolve the conflict between the time scales inferred from 1-129, Pu-244, and Al-26.

Lee, T.↗
NASA NTRS1978

Charge and energy spectra of heavy cosmic rays at intermediate energies

The energy spectra and the charge composition of the primary elements C, O, Ne, Mg, and Si have been measured in both the low-energy and high-energy modes of the University of Chicago telescope on board the IMP 8 spacecraft. Combining both modes of analysis yields differential energy spectra for each element from about 50 MeV/nucleon to about 1 GeV/nucleon. The charge ratios with respect to oxygen are found to be energy independent over this interval and are consistent with the results of cosmic-ray propagation and solar-modulation calculations. The relative abundances obtained are in substantial agreement with previous investigations in this energy regime.

Garcia-Munoz, M.↗
NASA NTRS1978

UH cosmic rays - Possible origin in massive stars

The origin of the Z greater than 28, ultraheavy (UH) cosmic rays in supernova explosions of massive stars, at least about 10 solar masses, is considered. For Z greater than 70, the UH data are dominated by an r-process source distribution, but for the elements just beyond iron, Z from 29 to 36, the data cannot be explained by any single process of nucleosynthesis. This problem is solved naturally in a massive-star model by secondary neutron-capture reactions occurring during core helium burning (a limited s-process) and during explosive carbon burning. Interstellar-propagation calculations have been performed with these episodes of synthesis as source distributions, and the results offer an explanation for the current UH cosmic-ray data. Further, the heavy-element synthesis during explosive carbon burning is re-examined by using more realistic initial conditions given by the post-helium-burning configuration of the star. These results are compared with earlier work and the UH cosmic-ray data. Some effects of preferential acceleration, based upon ionization potential, are considered, and experimental tests for this model are discussed.

Wefel, J. P.↗
NASA NTRS1977

UH cosmic rays: Possible origin in massive stars

The origin of the Z greater than 28, ultraheavy, cosmic rays in supernova explosions of massive stars is considered. For Z greater than 70, the UH data is dominated by an r-process source distribution, but for the elements just beyond iron, 29 or = Z less than 36, the data cannot be explained by any single process of nucleosynthesis. This problem is solved naturally in a massive star model by secondary neutron capture reactions occuring during core helium burning and during explosive carbon burning. Interstellar propagation calculations were performed with these episodes of synthesis as source distributions, and the results offer an explanation for the current UH cosmic-ray data. The heavy element synthesis during explosive carbon burning is reexamined using more realistic initial conditions given by the post-helium-burning configuration of the star. Effects of preferential acceleration are considered, and experimental tests are discussed.

Wefel, J. P.↗
NASA NTRS1977

UH cosmic rays and solar system material - The elements just beyond iron

The nucleosynthesis of cosmic-ray elements between the iron peak and the rare-earth region is examined, and compositional changes introduced by propagation in interstellar space are calculated. Theories on the origin of elements heavier than iron are reviewed, a supernova model of explosive nucleosynthesis is adopted for the ultraheavy (UH) cosmic rays, and computational results for different source distributions are compared with experimental data. It is shown that both the cosmic-ray data and the nucleosynthesis calculations are not yet of sufficient precision to pinpoint the processes occurring in cosmic-ray source regions, that the available data do provide boundary conditions for cosmic-ray nucleosynthesis, and that these limits may apply to the origin of elements in the solar system. Specifically, it is concluded that solar-system abundances appear to be consistent with a superposition of the massive-star core-helium-burning s-process plus explosive-carbon-burning synthesis for the elements from Cu to As and are explained adequately by the s- and r-processes for heavier elements.

Wefel, J. P.↗
NASA NTRS1974

Primary cosmic ray particles with Z greater than 35 /VVH particles/

Large areas of nuclear emulsions and plastic detectors were exposed to the primary cosmic radiation during high-altitude balloon flights. From an analysis of 141 particle tracks recorded during a total exposure of 13,000,000 sq m-ster-sec, a charge spectrum of the VVH particles has been derived.

Blanford, G. E., Jr.↗
NASA NTRS1974

Testing of models of VVH particle sources and propagation

For comparisons between theoretical and observed charge spectra of VVH particles to be meaningful, at least two conditions must be met. First, charge resolution must be adequate to separate important groups of nuclei, and there should be no significant systematic errors in the charge scale developed. Second, there must be adequate rejection of slower particles of smaller Z, which have been observed in several flights. Within these conditions, it has been shown that observed features of the charge spectrum are not accidents of the analysis but reflect real variations in the relative abundances that must be explained by any successful model.

Blanford, G. E., Jr.↗
NASA NTRS1974

The origin and propagation of VVH primary cosmic ray particles

In an attempt to match the observed charge spectrum of VVH particles, several source spectra have been constructed from combinations of r- and s-process nuclei. Their propagation has then been followed, allowing for interactions and decay, and comparisons have been made between the calculated near-earth spectra and those observed during high-altitude balloon flights. None of the models yet used leads to good agreement with observation, suggesting either that more complicated models need to be examined, or that different components (for instance the r- and s-process nuclei) have different histories.

Blanford, G. E., Jr.↗
NASA NTRS1973

Observation of cosmic-ray particles with Z greater than 35.

The results of two flights conducted in Texas in September 1968 are reported, giving attention to experimental details, the charge spectrum, and the primary flux of very very heavy cosmic rays. Considerable interest is attached to the observation of uranium, thorium, and transuranic nuclei in the cosmic radiation. It is found that the relative abundances of the charge groups in the ranges from 35 to 40 and from 41 to 50 deviate significantly from solar system abundances.

Blanford, G. E., Jr.↗
NASA NTRS1973

Observation of cosmic-ray particles with Z of 50 or greater and interpretation of the charge spectrum.

Large areas of plastic detectors and nuclear emulsions were exposed to the primary cosmic radiation on two high-altitude balloon flights in May 1968 and September 1969. From measurements on the tracks found in the scanning of the plastic detectors, events with charges Z greater than 50 were selected, and these data were consolidated with those from our earlier flights. Several conclusions can be drawn from the observed charge spectrum. The detection of trans-bismuth nuclei confirms earlier observations of these particles in the cosmic rays. However, no trans-uranium particles were observed. Detailed features of the charge spectrum cannot be explained by nuclei from r-process nucleosynthesis alone. Although the addition of particles following s-process abundances yields improved agreement, the spectrum appears more complicated than would result from a simple combination of r- and s-process abundances with identical propagation histories.

Blanford, G. E., Jr.↗