Alpha Particle Flux Research Articles

Proton and alpha particle fluxes in the solar wind: Results of a three‐fluid model

A three‐fluid model for the solar wind, with continuity, momentum, and energy equations for the three species protons, alpha particles, and electrons, including electron heat conduction and a parameterized coronal heat source, is used to study the behavior of the resulting proton and alpha fluxes as a function of coronal energy input and the proton‐to‐alpha density ratio at the coronal base. While in model solutions without alpha particles the proton flux is a strongly increasing function of coronal temperature, quite opposite to the observed near constancy of the proton flux in the solar wind, solutions with alpha particle abundances of the order of a few percent at the coronal base have a reduced proton flux and much less variation of the proton flux. The mechanism by which the proton flux is reduced is a pileup of the alpha particle abundance in the region of the coronal temperature maximum and the increased frictional drag on the protons resulting therefrom. We find a range of model solutions in which the resulting proton flux is almost independent of coronal energy input or coronal temperature, and we conclude that proton‐alpha friction and dynamic accumulation of alphas in the corona can provide an explanation for the near constancy of the proton flux which is observed in the solar wind.

A precision facility for measuring alpha-particle energies and flux density

A precision facility for measuring alpha-particle energies and flux density

Control of Alpha-Particle Transport by Ion Cyclotron Resonance Heating

Control of radial alpha-particle transport by using ion cyclotron range of frequency (ICRF) waves is investigated in a large-aspect-ratio tokamak geometry. Spatially inhomogeneous ICRF wave energy with properly selected frequencies and wave numbers can induce fast convective transports of alpha particles at the speed of order υalpha ∼ (PRF/nαε0)ρp, where PRF is the ICRF wave power density, nα is the alpha-particle density, ε0 is the alpha-particle birth energy, and ρp is the poloidal gyroradius of alpha particles at the birth energy. Application to International Thermonuclear Experimental Reactor (ITER) plasma is studied and possible antenna designs to control alpha-particle flux are discussed.

Angular distribution of high energy alpha particle flux on the first wall of a tokamak

The angular distribution of a ripple induced flux of high energy alpha particles on the first wall of a circular tokamak reactor is considered. The authors show that the distribution is highly non-uniform in the poloidal angle and that its peaking factor reaches values of 10 to 15 for typical tokamak reactor parameters. The distribution does not depend on the energy of the escaping particles and is therefore practically equivalent to the distribution of the energy load produced by these particles on the surface of the chamber. Furthermore, it is only weakly dependent on the system parameters over the relevant range of practical interest.

Ultrapure materials for alpha particle-sensitive applications

Materials used in applications where alpha particle radiation can produce “soft” or transitory errors are commonly specified and characterized in terms of uranium and thorium content, often by glow discharge mass spectrographic analysis. Analytical results indicate that low levels of uranium and thorium do not adequately reflect the alpha flux potential of some materials, especially in cases where radioactive isotopes are not in equilibrium or where a dominant decay parent other than uranium or thorium is present. An additional characterization technique—highly sensitive, surface alpha particle flux measurement—has been developed. Alpha particle counting, when used in conjunction with trace metal analysis, allows more optimum selection of low-alpha-radiation materials.

Erratum: ‘‘Slowing down tail enhanced, neoclassical and classical alpha particle fluxes in tokamak reactors’’ [Phys. Fluids 3 1, 2292 (1988)

Erratum: ‘‘Slowing down tail enhanced, neoclassical and classical alpha particle fluxes in tokamak reactors’’ [Phys. Fluids <b>3</b> <b>1</b>, 2292 (1988)

Slowing down tail enhanced, neoclassical and classical alpha particle fluxes in tokamak reactors

The classical and neoclassical particle and energy fluxes associated with a slowing down tail, alpha particle distribution function are evaluated for arbitrary aspect ratio ε−1, cross section, and poloidal magnetic field. The retention of both electron and ion drag and pitch angle scattering by the background ions results in a large diffusive neoclassical heat flux in the plasma core. This flux remains substantial at larger radii only if the characteristic speed associated with pitch angle scattering, vb, is close enough to the alpha birth speed v0 so that ε(v0/vb)3 remains less than some order unity critical value which is not determined by the methods herein. The enhanced neoclassical losses would only have a serious impact on ignition if the critical value of ε(v0/vb)3 is found to be somewhat larger than unity.

Solar flare protons and alpha particles during the last three solar cycles

Event‐integrated fluxes of protons and alpha particles in solar‐flare‐associated particle events during solar cycle 21 (1976–1986) are determined from data obtained by detectors on board the IMP‐7 and IMP‐8 satellites. Sixty‐three solar particle events with proton fluence (E &gt; 10 MeV) &gt; 107 cm−2 were identified from October 1972 to March 1987. The average omnidirectional flux of protons with kinetic energy &gt; 10 MeV for cycle 21, 64 cm−2s−1, is lower than the corresponding number for cycle 20 (92 cm−2s−1) based on satellite data and for the cycle 19 (378 cm−2s−1) based on lunar sample data. Six large events contributed 70% of the total proton fluence during solar cycle 21. Several events in early 1981 with high proton fluences could account for much of the high 56Co radioactivities observed in the small‐sized Salem meteorite. The event‐averaged alpha‐particle to proton ratio in the energy interval 1–10 MeV/nucleon varies from 0.006 to 0.05, with an average value of 0.02 for the whole cycle. The events during solar cycle 21 are characterized by softer spectra for both protons and alpha particles compared to those in earlier solar cycles. No definitive correlation exists between cycle‐averaged solar flare proton fluxes and peak sunspot numbers. A comparison with long‐term (million year) averaged data for these parameters, obtained from lunar sample data, shows that the contemporary solar flare proton spectra are characterized by softer spectra (lower R0 values). A similar comparison cannot be made for the mean long‐term averaged flux, as the contemporary average suffers from uncertainty due to statistics of single events. For this reason, the solar energetic particle activity for the last two solar cycles cannot be considered as representative of average solar particle activity over longer time periods.

Quiet time mass composition at near‐geosynchronous altitudes

Mass composition data acquired from the near‐geosynchronous SCATHA spacecraft during magnetically quiet times are analyzed. The time intervals over which data were included in the study span some 4 months in the spring and summer of 1979. This allows a reasonable coverage in both L shell and magnetic local time. At the higher L shells, L &gt; 6.5, the mass composition data are consistent with sunward convection of plasma sheet particles. Protons and alpha particle fluxes peak near 90° pitch angle. There is evidence that the alpha particle spatial distribution has a sharp inner edge near L = 6.5. At lower L values, the proton characteristics change. The density of protons above 1 keV decreases, while the lower‐energy protons show an increase in density. The oxygen ions show a similar change, in that there is a large increase in the lower‐energy oxygen ions from high L to low L, especially in the dusk and midnight local time sectors. This suggests that the ionosphere may be continuously supplying plasma to the inner magnetosphere even during magnetically quiet times.

Some theoretical aspects of charged fusion product plasma diagnostics

The inverse problem for drift losses of fusion alpha particles in a tokamak – the problem of calculating plasma parameters from known distributions of the alpha particle flux over the wall surface – is analysed. As the PLT experiments have shown, the energy spectrum of fusion charged particles escaping from the plasma can give an idea on the plasma temperature. The paper demonstrates that from a known spatial distribution of the particle flux it is possible also to determine the distributions of plasma density, ion temperature and plasma current. – The results of numerical modelling are given for some particular cases in which the aim was to establish the current density and the fusion alpha particle source profiles.

Processing of Low Alpha-Particle Emitting Ceramics

AbstractThe raw materials and clean-room processing techniques required to produce a low alpha-particle emitting insulating material have been investigated with the goal of producing a dense fired alumina ceramic with a reproducible, low alpha-particle flux (≤ 0.01 α/cm2hr). Various sources of A12 O3, MgO, and SiO2, the primary constituents of the alumina body, were tested for the alpha-particle emitting elements, U and Th, and for total alpha-particle flux. Many materials contain U concentrations with corresponding alpha-particle fluxes of 0.01α/cm2hr. Die pressing, filter casting and isopressing have been used under class 100 clean-room conditions to process powder compacts and the benefits and problems of each were evaluated. Analysis of the material before, at various stages during processing, and after firing has shown that dense fired Al2O3 ceramics can be produced with no detectable increase above that of the source powder in the U and Th contents, or the alpha-particle flux.

The application of uranium fission track autoradiography as a method of investigating the problem of soft errors in VLSI silicon memory devices

ABSTRACT Soft errors in VLSI random access dynamic memory devices are caused by the passage of ionising alpha-particles, which temporarily alter the contents of a bit location. These alpha-particles are emitted by minute amounts of naturally occurring uranium and thorium, which may be present as trace impurities in the silicon chip, metallic connects, plastic moulds or ceramic packaging, comprising the finished RAM. A method of fission track autoradiography (FTA) has been developed for detecting and measuring the presence of uranium in the various component materials used in the memory device. The technique is described, and involves the irradiation of the specimens with thermal neutrons, and the detection of the fission particles produced from the fission of the 0.72% abundant 235U. A specially prepared film of polyimide is used as the SSNTD, and the fission tracks are observed by optical microscopy and counted on the Quantimet 720 Image Analyser. Extremely small amounts of uranium can be measured equivalent to an alpha-particle flux of 0.001 α/cm2 /hour, arising from the 238U and 234U isotopes in the natural uranium present. The results obtained on a variety of specimens, from standards consisting of ion implanted 235U in silicon wafers, and standard NBS glasses are evaluated. The significance of the FTA method in relation to alternative methods of estimating the alpha-flux is also assessed.

Plastic film detectors for light and heavy element fission studies

Thin (5 μm) polycarbonate plastic films can be used as large solid angle heavy-ion spectrometers. The molecular damage along the track of a heavy ion, that penetrates or nearly peńetrates the thin film, can be enhanced by chemical etching methods and detected with various techniques. A new technique is described in some detail that makes possible the discrimination between ions such as carbon and fission fragments in the presence of a large flux of electrons, gamma rays, neutrons, protons and alpha particles. The advantages and disadvantages of these detectors are discussed.

Characteristics of sunward flowing proton and alpha particle fluxes of moderate intensity

The diffusive streaming of 1.3‐ to 2.3‐MeV per nucleon protons has been found to be predominantly toward the sun during periods between prompt solar particle events. This sunward streaming occurs for essentially all proton intensities from &lt;0.012 to 1.2 (cm² s sr MeV)−1 and for all solar wind velocities. The average radial component (16% ± 3%) of the diffusive anisotropy of 1.4‐ to 2.4‐MeV per nucleon alpha particles is very similar to that observed for protons (14% ± 1%), a finding suggesting a common origin. These periods are characterized by a limited variance in the proton intensities (10−1.2±1.1 cm−2 s−1 sr−1 MeV−1), in the proton spectra (E−3.0±0.8), and in the α/p ratio (3% ± 2%). The sunward diffusion of protons and alpha particles indicates that a positive radial gradient is characteristic of these modestly enhanced fluxes. A steady state propagation model which includes adiabatic energy loss and a source of particles beyond 1 AU produces the average radial anisotropy and its dependence on the solar wind velocity for κrr ∼ 4 × 1020 cm² s−1. The direction of the diffusive anisotropy is strongly dependent on the magnetic field direction, a situation indicating κ⊥ &lt; κ∥. However, the two directions are not identical, a condition indicating nonnegligible flow perpendicular to the average field direction when averaged over a 6‐hour interval.

Acceleration of protons at 32 Jovian radii in the outer magnetosphere of Jupiter

During the inbound pass of Pioneer 10 a rapid tenfold increase of the 0.2‐ to 5‐MeV proton flux was observed at 32 RJ (Jovian radii). The total event lasted for 30 min and was made up of a number of superimposed individual events. At the time the spacecraft was in the outer magnetosphere about 7 RJ below the magnetic equator. Before and after the event the proton flux was characteristic of the low flux level normally encountered between crossings of the magnetic equator. Flux changes at different energies were coherent within 1 min, a time comparable to the time resolution of the data. Differential travel time would have led to a greater time difference if the sources had been further than 5–10 RJ from the spacecraft. The angular distributions were highly anisotropic with protons streaming toward Jupiter. A field‐aligned dumbbell distribution was observed initially, and a pancake distribution just before the flux decayed to its preevent value. The alpha particle flux changed as rapidly as the proton flux but peaked at different times. The energetic electron flux behaved differently; it increased gradually throughout the period. This acceleration event was associated with a double crossing of a current sheet, most of the acceleration being coincident with the first crossing. The average shape of the proton energy spectrum (0.3–5 MeV) remained unchanged during the event and resembled the spectrum observed in the magneto‐disk. A superposition of acceleration processes of this type is probably responsible for maintaining the energetic particle population around 30 RJ in the magnetosphere. Random fluctuations in the occurrence of acceleration events would explain the 10–50% flux changes during less than 15 min which were observed most of the time the Pioneer 10 and 11 spacecraft were in the outer Jovian magnetosphere.

On the possible existence of cosmological cosmic rays. I - The framework for light-element and gamma-ray production

view Abstract Citations (21) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the possible existence of cosmological cosmic rays. I. The framework for light-element and gamma-ray production. Montmerle, T. Abstract The possible existence of cosmological cosmic rays (CCR) is considered in the context of an expanding universe. A model accounting for CCR production, composition and spectrum is given. This version assumes that CCR were formed in a burst (Stecker, 1971) at some starting redshift. CCR are interpreted as consisting of protons and alpha particles only; the high-energy sector of the CCR spectrum produces pi-mesons (and thence gamma rays) by collision with matter, while the low-energy sector collides with intergalactic hydrogen, heating the ambient and ionizing the gaseous component. Also, light element production involving alpha-alpha reactions that give rise to isotopes of elements such as lithium is assumed to take place. Cosmological parameters and transport equations for photons as well as for nuclei are discussed; the relevant source functions are also studied, and analytical solutions to the transport equations are derived. Procedures for obtaining quantitative results for the CCR alpha-particle flux are given, as well as methods for determining the gamma ray background spectrum and accounting for an abundance of the isotope Li-7. Publication: The Astrophysical Journal Pub Date: August 1977 DOI: 10.1086/155459 Bibcode: 1977ApJ...216..177M Keywords: Abundance; Astronomical Models; Cosmic Rays; Cosmology; Gamma Rays; Light Elements; Alpha Particles; Astrodynamics; High Energy Interactions; Hydrogen Clouds; Intergalactic Media; Lithium Isotopes; Nuclear Fusion; Universe; Astrophysics full text sources ADS |

Plasma modeling and first wall interaction phenomena in Tokamaks

Fluxes of neutral hydrogenic particles, alpha particles and electromagnetic radiation to the liner or first wall of both two component tokamaks and large ignited tokamak fusion reactors are estimated using space and time dependent models of tokamak plasmas. Data requirements and the effects of uncertainties in the areas of first wall interaction phenomenon and plasma transport coefficients are described.

Observation and analysis of low-energy solar particle propagation from discrete flare events

The proton, alpha particle, and electron fluxes measured following two west limb solar flare events are analyzed by using numerical solutions to the complete particle transport equation, including considerations of particle convection and energy loss. The values of the obtained mean free paths lambda/subr/ suggest that interplanetary propagation conditions were different during these two events. During the November 4, 1968, event the derived values of lambda/subr/ were approx.0.2--0.3 AU, while during the November 1969 event the derived values of lambda/subr/ were approx.0.1 AU for particles with energies as low as a few MeV. For these events the rise and decay of the alpha and proton flux profiles can be reasonably reproduced with a distant (10 AU) free escape boundary. (AIP)

Abundances of Solar Cosmic Ray Protons and Alpha Particles for 1969-1972

Hsieh and Simpson have given the abundance ratio of alpha particles and protons for seven solar proton events in 1967. In addition, Lanzerotti and Maclennan have analyzed seven events that occurred during the December 1967 to November 1969 period, which includes the maximum of solar cycle 20. Herein a similar analysis is reported based on OV5-6 satellite data for eight events during the November 1969 to November 1972 period after the cycle maximum. The flare-averaged alpha particle to proton ratio reported here varies as 0.032E$sup - 0$.$sup 3$ in the particle energy range from 2.7 to 8.0 MeV/nucleon. Following the precedent of Lanzerotti and Robbins the alpha particle to proton ratios are determined for equal energy/nucleon, equal rigidity, and equal energy/charge. Finally, a comparison of the yearly average of the total integrated proton and alpha particle fluxes is made for the maximum and descending periods of solar cycle 20. (AIP)

ATS-6 Energetic Particle Radiation Measurement at Synchronous Altitude

The Aerospace Corporation energetic electron-proton spectrometer operating on Applications Technology Satellite-6 (ATS-6) detects energetic electrons in four channels between 140 keV and greater than 32 MeV, and measures energetic protons in five energy channels between 2.3 and 80 MeV and energetic alpha particles in three channels between 9.4 and 94 MeV. After more than a year of operation in orbit, the experiment continues to return excellent data on the behavior of energetic magnetospheric electrons as well as information regarding the fluxes of solar protons and alpha particles.