Preferential Acceleration Research Articles

Ultraheavy cosmic rays - Theoretical implications of recent observations

The recent extreme ultraheavy cosmic-ray observations (Z greater than or equal to 70) are compared with r-process models. A detailed cosmic ray propagation calculation is used to transform the calculated source distributions to those observed at the earth. The r-process production abundances are calculated using different mass formulae and beta-rate formulae; an empirical estimate based on the observed solar-system abundances is also used. There is the continued strong indication of an r-process dominance in the extreme ultraheavy cosmic rays. It is shown that the observed high actinide/Pt ratio in the cosmic rays cannot be fitted with the same r-process calculation which also fits the solar-system material. This result suggests that the cosmic rays probably undergo some preferential acceleration in addition to the apparent general enrichment in heavy (r-process) material. An estimate is also made of the expected relative abundance of superheavy elements in the cosmic rays if the anomalous heavy xenon in carbonaceous chondrites is due to a fissioning superheavy element.

Charge and energy spectra of cosmic rays with Z greater than or approximately equal to 60 - The SKYLAB experiment

A 1.2 m/sup 2/ array of Lexan track detectors, 1 g cm/sup -2/ thick, inside a 1 g cm/sup -2/ aluminum wall of the Skylab workshop, detected 104 cosmic-ray nuclei with Z> or =65, seven nuclei with Z> or approx. =88, three nuclei with Z> or approx. =94, and no superheavy nuclei (Z> or approx. =110). The shape of the energy spectrum for events with Z> or =65 is consistent with that for Fe, and the abundance ratio is (Z> or =65/Fe)approx. =1.3 x 10/sup -5/. Other abundance ratios are (74 or =65)approx. =0.38; (Z> or =88)/(74 or =94)/(74< or =Z< or =87)=0.043. The world limit for superheavy nuclei is none out of 204 with 74< or =Z< or =87. The median error in charge for the Skylab experiment is 3.1%. The charge distribution is inconsistent with a source of solar-system composition (even with preferential acceleration of elements with low ionization potential) and is quite consistent with a source of predominantly r-process material.

The role of Coulomb collisions in limiting differential flow and temperature differences in the solar wind

Analysis of data obtained by Ogo 5 confirms the Imp 6 observations of the inverse dependence of the helium to hydrogen temperature ratio THe/TH on τe/τc, the ratio of the solar wind expansion time to the Coulomb collision equipartition time. The difference between the absolute values of the averages of THe/TH as observed by Imp and Ogo is probably due to the difference of the weights given to high- and low-velocity periods by the two experiments. The magnitude of the differential flow vector Δυ = |vHe - vH| varies inversely with τe/τs (where τs is the Coulomb collision slowing-down time) when τe/τs is small and approaches zero when τe/τs is large. The data suggest a model of continuous preferential acceleration and heating of helium (or deceleration and cooling of hydrogen) which is opposed and limited by Coulomb collisions. Since the average dependence of Δυ on τe/τs cannot explain all of the systematic variations of Δυ observed in corotating high-velocity streams, extra helium acceleration (or hydrogen deceleration) probably occurs on the leading edge of such streams.

Enrichment of heavy nuclei in He-3-rich flares

Five ^3He-rich solar-flare particle events were observed in 1973-1974 with ^3He/^4He ranging from 0.2 to ~8 at 2.9-12.7 MeV per nucleon. In all five events the (Z ≥ 6)/^1H ratio at ~3 MeV per nucleon was enriched by ~10 to ~100 times and the (Z ~ 6)/^4He ratio was enriched by ~3 to ~30 times, when compared with average solar-particle abundances measured over this 2-year period. It is suggested that the simultaneous enhancement of Z ≥ 6 and ^3He nuclei and the absence of ^2H and ^3H may be partly due to a preferential acceleration process which depends on the Z^2/A of the nuclei.

Multispacecraft study of the solar wind velocity at interplanetary sector boundaries

The sector structure of the interplanetary magnetic field and the solar wind velocity at the sector boundaries are compared at separations of up to 0.3 AU, 50 deg in heliocentric longitude, and 7 deg in heliographic latitude, using data from Mariner 5 en route to Venus and from the near-earth Explorer 33, 34, and 35 satellites. The polarity pattern of the magnetic sectors is found to be very similar at the two locations, and 18 pairs of corresponding sector boundaries are identified. One-hour averages of solar wind velocities near the boundaries show that the velocities near earth exceed those measured by Mariner 5 by as much as 30%. Two possible explanations of the observed velocity differences are discussed: a preferential acceleration of sector boundaries with distance, possibly caused by stream-stream interactions; and a dependence of the solar wind velocity on heliographic latitude.

Coherent Effect in the Preferential Acceleration of Relativistic Solar Heavy Cosmic Ray Nuclei

(Solar Phys.). The observed enrichment of heavy nuclei in the composition of relativistic cosmic rays including solar, may be explained on the basis of a coherent accelerating mechanism. This mechanism requires the existence of high intensity relativistic electron beams or preferably blobs (with number density ≥1011 electrons cm−3) in the accelerating solar regions. The radius of each blob should be less than its plasma wavelength, i.e. of the order of cm.

Charge Dependence of the Energy Spectra of Cosmic Rays

WHEN the abundance of elements in galactic cosmic rays is compared with the universal abundance1, galactic cosmic rays are found to be very highly enriched in heavier elements. A similar enrichment has been reported recently based on comparisons of solar energetic particles and solar photospheric and coronal abundances (ref. 2 and J. D. Sullivan, P. B. Price and H. J. Crawford at the Solar Physics Division meeting of AAS, Univ. Maryland, April 1972). The high energy universe composed of suprathermal particles is apparently richer in heavy nuclei than the thermal universe. The reason for this has been sought in the possible preferential acceleration of energetic particles of higher atomic number Z (refs 3 and 4). We report new experimental results in the energy range 3 to 50 GeV nucleon−1 which indicate that the well known enrichment of heavy nuclei in cosmic rays is increasing with increasing energy.

The Preferential Acceleration of Heavy Nuclei in Solar Flares

A two-stage model is proposed for the mechanism of heavy nuclei (Z greater than 8) accelerated in solar flares. In the first stage, fully stripped ions are first accelerated to suprathermal energies. In the second stage, a fraction of these ions are Fermi-accelerated to higher energies. Transport to the Fermi-acceleration region involves electron pickup, while injection into Fermi acceleration is rigidity dependent. The degree of enhancement of the abundance of heavy nuclei may be expected to vary for each individual flare.

Enhanced Abundances of Low-Energy Heavy Elements in Solar Cosmic Rays

view Abstract Citations (19) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Enhanced Abundances of Low-Energy Heavy Elements in Solar Cosmic Rays Lanzerotti, L. J. ; Maclennan, C. G. ; Graedel, T. E. Abstract Measurements of solar cosmic-ray 0/He, Si/He, and Fe/He ratios during the onset phase of the 197t January 25 flare event indicate a substantial (2() O times) enhancement of the ratios above the solar photospheric abundances. It is suggested that preferential acceleration of the heavy elements within the solar-flare region is the most likely cause of the increased abundances. Publication: The Astrophysical Journal Pub Date: April 1972 DOI: 10.1086/180913 Bibcode: 1972ApJ...173L..39L full text sources ADS |

Acylarylnitrosamines. Part II. The formation of arynes in the anomalous decompositions of o-t-butyl- and 2,5-di-t-butyl-N-nitrosoacetanilide

Decomposition of o-t-butyl-N-nitrosoacetanilide in benzene gives o- and m-t-butylphenylacetates (55%) rather than the expected high yield of 2-t-butylbiphenyl. The isolation of aryne adducts in the presence of furan, anthracene, and 2,3,4,5-tetraphenylcyclopentadienone and the results of aryne-competition experiments involving anthracene and 9,10-dimethoxyanthracene, establish the participation of 3-t-butylbenzyne. 2,5-Di-t-butyl-N-nitrosoacetanilide similarly decomposes, in part, via 3,6-di-t-butylbenzyne. These abnormal decompositions are considered to arise as a result of preferential steric acceleration of unimolecular decomposition of the o-t-butylaryldiazonium cations to the corresponding carbonium ions, which either are converted into the ortho-acetates or to the aryne, which reacts with acetic acid to give m-acetate. These arynes, in turn, are considered to be less reactive as a result of steric hindrance.

The influence of grain size and stress on the morphology of a 300-grade maraging steel

The effects of austenite grain size and externally applied stress on the morphology of martensite formation for a 300-grade maraging steel were investigated. Austenite grain sizes ranging from ASTM 14 to 5 were examined. The growth pattern of the martensite was revealed by a selective aging treatment that involved heating to 815° C (austenitizing), cooling to 184° C (about 50 pct transformation to martensite), reheating to 400° C (partial aging of the martensite), and finally, cooling to room temperature (balance of austenite transforms). Blocky martensite formed in the fine-grain austenite, whereas for the coarse-grain size, a stringer-like structure developed. Electron transmission studies showed that the individual martensite units (laths or platelets) were similar in size for both types of morphologies. In both cases, the length of these units corresponded closely to the spacing between the twin boundaries or grain boundaries of the fine-grain specimens. Differences in morphology for different grain sizes are explained in terms of the relative ratios between the size of the martensite unit and the distance between boundaries intersecting the path of growing platelets. The application of an external stress to a coarse-grain specimen results in the delineation of the austenite annealing twins that normally cannot be readily detected. It is proposed that the application of a stress causes a preferential acceleration of the transformation in one of the two differently oriented, twin-related regions of an austenite grain. This argument is based on the differences in the maximum resolved shear stress for the most favorable orientation of the (112) {111} shear variants in each of the various possible twin-related austenite crystal orientations. Hardness and tensile data were also obtained. The absence of any significant variation in these properties for the different grain sizes is attributed to the similarity in size of the martensite units.

Preferential acceleration of heavy ions from thermal velocities

The acceleration of ions from thermal velocities is analyzed to determine conditions under which heavy ions can be preferentially accelerated. Two accelerating mechanisms involving high-and low-frequency hydromagnetic waves respectively are considered. Preferential acceleration of heavy ions occurs for high-frequency waves if the frequency spectrum falls off faster than (frequency)−1. For the low-frequency waves heavy ions are less effectively accelerated than lighter ions. However, very heavy ions can be preferentially accelerated, the abundances of the very heavy ions being enhanced by a factor Ai over the thermal abundances. Acceleration of ions in the envelope of the Crab nebula is considered as an example.

ABUNDANCE ANOMALIES PRODUCED BY NUCLEAR REACTIONS IN STELLAR SURFACE LAYERS: II. RESULTS AND COMPARISON WITH ANOMALIES IN PECULIAR A STARS

A normal solar abundance distribution of the elements was subjected to a calculated bombardment by protons and alpha particles having energy spectra of the form E−n, where n was usually taken to be equal to 2.5, and having low-energy cutoffs on the spectra at 1 MeV. Bombardment with protons resulted in breakdown of nuclei to lower mass numbers. Bombardment with alpha particles resulted in buildup of nuclei to higher mass numbers. It is concluded that preferential acceleration of alpha particles to varying total fluxes can produce the abundance anomalies of peculiar A stars in concentrated patches on the surface. Local surface magnetic fields in the range 106–107 G are required to provide the necessary energy sources for the accelerated particles.

Investigations on the multiply charged nuclei of the primary cosmic radiation near the geomagnetic equator using nuclear emulsion

A nuclear emulsion stack was exposed over Hyderabad, India (geomagnetic latitudeλ=7·6° N) under a mean atmospheric depth of 6·8 g./cm.2, on 24 March 1960. The relative and absolute intensities of Be and B nuclei and nuclei of charge Z⩾6 (the S-nuclei) have been determined in this stack. The intensities were extrapolated to the top of the atmosphere using measured fragmentation parameters involved in collisions of cosmic ray nuclei in graphite. The flux values of Be, B and S nuclei at the top of the atmosphere have been determined to be 0·025±0·011, 0·101±0·023 and 1·12±0·10 particles/m.2 sec. sr. respectively. The ratios of intensities B/S, Be/S and Be/B have been found to be 0·09±0·02, 0·022±0·008 and 0·25±0·11 respectively. These ratios of intensities have been used (a) to compute the amount of matter traversed by the radiation before reaching the vicinity of the earth as 2·6±0·6 g./cm.2, (b) to show that the Fermi mechanism of acceleration of particles is not efficient at these energies (1–10 GeV/n.) in interstellar space and (c) to show that preferential acceleration of H1-nuclei (Z⩾20) is not of overwhelming importance. The derived source composition of nuclei of energy ⩾7·5 GeV/n suggests that N, O, F and H3-nuclei (Z=10–15) have similar abundances in the universe and in cosmic rays, and that C and H1-nuclei are overabundant in cosmic rays.