Time-integrated Flux Research Articles

The effects of irradiation temperature on the registration and annealing properties of nuclear tracks in crystals

Abstract It is now well-established that some plastic nuclear track detectors exhibit a dependence of registration sensitivity on their temperature during charged-particle irradiation. Meteoritic crystals possess a track record of the time-integrated flux of cosmic rays prevailing over the last 10 7 to 10 8 years. Any temperature dependence of the track registration sensitivity in crystals, analogous to that observed in plastic detectors, would clearly be important for the correct interpretation, in terms of charge and energy spectra, of cosmic-ray tracks in meteorites, most of which spend the majority of their cosmic-ray exposure ages at temperatures of ∼100–150 K. We have therefore irradiated several crystals, held at one of a number of different temperatures, with ∼2 MeV/amu 81 Br ions, and then etched them. In general, the minerals tend to have a reduced sensitivity (i.e. lower track-etch velocity) for registration temperatures below room temperature, i.e. the reverse of the trend observed in plastics. The strongest effect of registration temperature is observed in apatite crystals. The initial stages of track etching appear to be particularly sensitive to changes in registration temperature. The track-annealing sensitivity of apatite also appears to be affected by the registration temperature. These temperature dependences have important implications not only for cosmic-ray particle identification but also for fission-track dating and closure temperature studies of meteoritic crystals, which spent early parts of their histories (> 4 Ga ago) at elevated temperatures.

The frequency and intensity of comet showers from the Oort cloud

We simulate the Oort comet cloud to study the rate and properties of new comets and the intensity and frequency of comet showers. An ensemble of ∼10 6 comets is perturbed at random times by a population of main sequence stars and white dwarfs that is described by the Bahcall-Soneira Galaxy model. A cloning procedure allows us to model a large ensemble of comets efficiently, without wasting computer time following a large number of low eccentricity orbits. For comets at semimajor axis a = 20,000 AU, about every 100 myr a star with mass in the range 1 M ⊙−2 M ⊙ passes within ∼10,000 AU of the Sun and triggers a shower that enhances the flux of new comets by more than a factor of 10. The time-integrated flux is dominated by the showers for comets with semimajor axes less than ∼30,000 AU. For semimajor axes greater than ∼30,000 AU the comet loss rate is roughly constant and strong showers do not occur. In some of our simulations, comets are also perturbed by the Galactic tidal field. The inclusion of tidal effects increases the loss rate of comets with semimajor axes between 10,000 and 20,000 AU by about a factor of 4. Thus the Galactic tide, rather than individual stellar perturbations, is the dominant mechanism which drives the evolution of the Oort cloud.

Evidence for time and directional enhancements of multimuon cosmic-ray events.

We have observed 1.05\ifmmode\times\else\texttimes\fi{}${10}^{6}$ single-muon and 6869 multimuon events deep underground with the Soudan 1 nucleon-decay detector. The single-muon flux is consistent with isotropy and with results of previous experiments. We have found indications of bursts of multimuon events, particularly from a direction near Cygnus X-3. These bursts arrive from an extended angular region of 30\ifmmode^\circ\else\textdegree\fi{}\ifmmode\times\else\texttimes\fi{}30\ifmmode^\circ\else\textdegree\fi{}. The size of the angular region and the lack of a corresponding effect in the single-muon events are difficult to understand. In addition, there is weaker evidence for an excess in the time-integrated multimuon flux near the north galactic pole. We have evaluated the possibility that these effects are caused by random or systematic errors.

Uptake of gaseous sulphur dioxide by the lichen Cladina rangiferina

Samples of the lichen Cladina rangiferina were exposed to various concentrations of sulphur dioxide in a fumigation cuvette system for time periods ranging from 1 to 18 h. The cuvette system provided airstreams which, within the limits of measurement, had identical flow rates, temperatures, and relative humidities. Sulphur dioxide was added to one airstream as a treatment, while the other remained free of sulphur dioxide for control purposes. In some experiments, wind speed could be varied from 8 to 250 cm∙s−1 in a small wind tunnel placed in the fumigation cuvette. The system allowed for the calculation of sulphur dioxide uptake by the lichen sample. Potassium release was shown to increase with an increasing uptake of sulphur dioxide (time-integrated flux), but was not uniquely related to sulphur dioxide concentration alone. Extrapolation of a linear transformation of the potassium release curve to zero potassium efflux resulted in a threshold uptake value of 240 μg SO2∙g lichen−1. Internal lichen resistance and lichen boundary-layer resistance were experimentally determined for later use in an electrical analog model for the calculation of sulphur dioxide uptake.

Radiation from Burning Hydrocarbon Clouds

Abstract This paper reports on the measurement and analysis of time resolved thermal radiation from combustion of methane, ethane, and propane clouds formed from laboratory scale vapor samples initially contained within a soap bubble. The time scale of the radiant heat pulse was found to be the same as that of the fluid mechanical motion (Fay and Lewis, 1976). The time-integrated radiant energy flux, expressed as a fraction of the initial fuel heating value, was between 0.09 and 0.15 for these fuels, with some dependence on initial fuel volume. The radiation was correlated by a grey gas model, which assumed a uniform time-dependent temperature in a spherical cloud and a time-independent absorption coefficient. The grey gas temperature decreased monotonically during and after the period of combustion. The absorption coefficient was found to be a function of the initial fuel volume and fuel type; it was between 10−3 and 10−2 cm−1 and decreased slightly with increasing initial fuel volume.

Simultaneous radio and X-ray observations of the X-ray burst source MXB 1636 - 53

On June 17, 1977, the X-ray burst source MXB 1636-53 was simultaneously monitored for about 4 hr with the Parkes 64-m radio telescope at a frequency of 14.7 GHz and the SAS 3 X-ray satellite (1.3-12 keV). One X-ray burst was observed; an upper limit (2 sigmas) of 200 mJy is reported for any radio burst coincident with the X-ray event. During the X-ray burst the radio/X-ray time-integrated flux ratio was no more than 375 with a 90 percent confidence. An upper limit (2 sigmas) of 22 mJy was determined for any steady 14.7-GHz source coincident with the X-ray position.

More mysteries from Pandora's box?: Samarium isotopic anomalies in the Allende inclusions.

An alternative interpretation is presented for the Sm isotopic anomalies observed by MCCULLOCH et al. (1978) and LUGMAIR (1978) in the Allende mineral inclusions. The Allende inclusions appear to have received a smaller time-integrated neutron flux than the average earth material during an ‘early’ irradiation period.

Observations of cosmic gamma-ray bursts

The occasional occurrence of brief but intense bursts of cosmic gamma-rays was disclosed through a systematic search of data acquired from the Vela satellites. Confirmation of the nature of the events and additional detail of their characteristics has subsequently been provided by 15 other groups of experimenters with instruments on 13 spacecraft. Thirty-nine such events have been identified from data spanning a period of four and a half years. The record of intensity as a function of time varies considerably for different events, with total durations ranging from 0.1 to ∼ 60s. Time-integrated flux density ranges from ∼10−6 to 10−3 erg cm−2. Spectral measurements have been accomplished by several groups of experimenters, showing a broad maximum in the energy distribution at about 150 keV. The distribution of source directions implies either near galactic or extragalactic locations. The existing data are not sufficient to distinguish between the various models proposed to explain the phenomenon; no model is completely consistent with all observed characteristics.

Use of an infrared scanning thermometer for calorimetric measurement of a pulsed high current electron beam

The time-integrated flux of a pulsed high-current electron beam was measured using a total-adsorption graphite calorimeter array, edge supported and of approximately 20*20 elements. Spatial distribution of the electron flux in the plane of the nominally 150 mm*150 mm array was determined from the heating of the individual calorimeters. Instead of measuring the calorimeter temperatures with thermocouples and recorders, their rear face temperatures were monitored using an AWRE infrared scanning thermometer which displayed the temperature in the form of a digitally coded matrix. The number of flux data points in the calorimeter plane was increased by an order of magnitude with this technique.

Observations of Gamma-Ray Bursts of Cosmic Origin

view Abstract Citations (1022) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Gamma-Ray Bursts of Cosmic Origin Klebesadel, Ray W. ; Strong, Ian B. ; Olson, Roy A. Abstract Sixteen short bursts of photons in the energy range O.2-l.S MeV have been observed between 1969 July and 1972 July using widely separated spacecraft. Burst durations ranged from less than 0.1 5 to 30 5, and time-integrated flux densities from 1O- ergs cm-2 to 2 X 10- ergs cm-2 in the energy range given. Significant time structure within bursts was observed. Directional information eliminates the Earth and Sun as sources. Subject headings:gamma rays - X-rays - variable stars Publication: The Astrophysical Journal Pub Date: June 1973 DOI: 10.1086/181225 Bibcode: 1973ApJ...182L..85K full text sources ADS | Related Materials (1) Commentary: 1999ApJ...525C1218W

Propagation of Structural Information in Optical Wave Fields*

A wave field of finite cross section and angular spread has, in effect, a finite number of degrees of freedom. A knowledge of the degrees of freedom provides structural information. This paper is concerned with the propagation of structural information in optical wave fields. The fields considered are those that arise in the diffraction and scattering of quasimonochromatic and polychromatic light by fixed objects. In all cases, the light originates at a point source. To each point of a wave field we assign an information-flow vector J, so defined that its time-integrated flux through a surface of observation yields the number of degrees of freedom of the wave field incident on that surface. Thus J represents the number of independent real data that can be found in unit time on a unit area whose normal is oriented in the direction of information flow. The set of all J values comprises a vector field, which we call the structure field. The structure field can be represented by field lines; these are lines of structural-information flow. The structure field has the following additional properties. (1) In a homogeneous transparent medium, the structure field is solenoidal. Hence structural information behaves like an incompressible fluid. Elementary tubes of flow may be defined such that each tube corresponds to one spatial degree of freedom. (2) The structure field is not, in general, irrotational. However, since J and its curl are orthogonal, there exists a family of surfaces orthogonal to the lines of J. These are surfaces of maximum structural-information density. (3) The normal component of the field vector J is continuous across a smooth boundary separating homogeneous transparent media. Examples of field lines are presented. Applications of the theory include information-density mapping of holographic and conventional image-wave fields, and the determination of minimum sampling intervals.

Calculation of Neutron Fluence-to-Kerma Factors for the Human Body

Fluence-to-kerma factors (where fluence is the time-integrated neutron flux and kerma is equal to the total kinetic energy released in materials resulting from direct neutron interaction per unit mass of the irradiated medium) were calculated at discrete neutron energies from 0.025 eV to 15 MeV for various compositions of the human body—tissue, muscle, bone, lung, brain, red marrow, and the “standard man” composition. The 11 most common elements in man were considered and the latest cross sections used. An attempt was made to include all significant reactions, namely elastic scattering with an anisotropic correction, inelastic scattering, neutron capture, (n, 2n) reactions, (n, charged particle) reactions, and beta or positron emissions from these reactions. These calculations show improvements in the entire energy range over previously reported neutron kerma factors.

Radiative Recombination in Annealed Electron-Irradiated GaAs

Broad-band emission peaking near 1.39 eV appears in Zn-doped GaAs in addition to the narrow bound-exciton emission at 1.49 eV. Electron irradiations at energies between 0.6 and 2.0 MeV for time-integrated fluxes of 1.3\ifmmode\times\else\texttimes\fi{}${10}^{18}$ e/${\mathrm{cm}}^{2}$ quench all luminescence. For bombardment energies below a critical value, which lies between 1.0 and 1.5 MeV, isochronal annealing near 190\ifmmode^\circ\else\textdegree\fi{}C causes the reappearance of the broad-band emission, which now is found to possess structure. The structure consists of three no-phonon lines at 1.4433, 1.4415, and 1.4402 eV which are repeated at intervals of the transverse acoustic phonon energy. The emission intensity is greatest for temperatures near 220\ifmmode^\circ\else\textdegree\fi{}C. Further annealing at higher temperatures diminishes the intensity of the fine structure and the associated broad-band emission; complete disappearance occurs above 260\ifmmode^\circ\else\textdegree\fi{}C. The emission is not regained upon annealing when the bombardment energy exceeds the critical value. It is suggested that direct lattice displacement occurs at the critical bombarding energy. This would correspond to a threshold displacement energy of 50-60 eV. It is also suggested that previous measurements of threshold energy (10-20 eV) in GaAs and other experimental observations may be due to known large concentrations (\ensuremath{\approx}${10}^{19}$ ${\mathrm{cm}}^{3}$) of defects in as-grown GaAs, in the form of Ga-As interstitial pairs.

Radiation from cosmic ray air showers

Cosmic ray showers passing through the atmosphere produce electromagnetic disturbances. It has been suggested that these can be detected by means of a radio telescope. We set up a simple model for a shower and find that the time-integrated energy flux in its radiation field, at say 45M c/s, is of the order of 60000 flux units x microseconds, when the show er contains 10 6 electrons and 10 6 positrons. The radiation pattern depends on the decay rate of the shower. We have done this calculation in order to give some guidance to experimentalists who are planning to observe cosmic ray showers by radio means.

The challenge of chromospheric physics : Athay, R. Grant, High Altitude Observatory Lab, Boulder, Colorado, Reprint, Science, 143, No. 3611, March, 1964, 11 p. illus.

The understanding of the micron-sized populations of natural micrometeoroids and artificial space debris in low Earth orbit has benefited considerably from the post-flight investigations of retrieved surfaces from spacecraft, such as the Long Duration Exposure Facility. The returned solar array from the Hubble Space Telescope has added to this repository and has offered a further opportunity to document these particles. 25 individual solar cells were specially selected on the basis that they contained impact craters (diameter 100–1000 μm) which had the most potential to retain impactor residue chemistry. The solar cells were subject to a detailed investigation using analytical scanning electron microscopy which identified 29 impact craters, the analysis of which identified 3 residues as artificial in origin, 6 unclassified and 20 as natural in origin. The limited number of unclassified residues identified indicates that the methods of analysis employed in this investigation are a significant step forward for such studies and, if employed on a greater number of samples, will improve the calculations of the time-integrated flux rates for micrometeoroids and space debris in the low Earth orbit environment. Notwithstanding the small sample set examined, the observed chemical classification of the impact residues in terms of micrometeoroid to space debris (in the particle size range 8–80 μm) corresponds well to the flux model that predicts the dominance of natural particles.

Nucleosynthesis in the early history of the solar system

This paper revises the model of Fowler, Greenstein and Hoyle (FGH) for the nucleosynthesis of D, Li, Be and B by high energy particles from the Sun during the early history of the solar system. In this model these nuclei are produced by spallation reactions, mainly on O 16, in metric-sized planetesimals. Large numbers of neutrons are also produced. A fraction of these are thermalized and react by B 10( n, α) Li 7, Li( n, α) H 3, to produce the terrestrial Li and B isotopic ratios. Additional D is produced by H 1( n, γ) on hydrogen retained in the planetesimals as H 2O. The total energy required in high energy particles is about 2 × 10 44 ergs. The nuclear calculations have been generalized in an approximate manner to include a dependence on the duration of the irradiation caused by the long lifetime of Be 10. The first stage of the calculation yields the required spallation yields and time-integrated neutron flux to produce the terrestrial Li, Be and B abundances and isotopic ratios. The required flux is 4 × 10 21 n/cm 2, identical with that obtained by FGH, and does not depend significantly on the choice of irradiation time. The predicted spallation yields depend more strongly on the irradiation time. Those are compared with cloud chamber data for O 16 + 300 MeV neutrons. The predicted low spallation yield for Be 9, which merely reflects its low relative abundance, is consistent with the cloud chamber data. Good agreement is not obtained for the B Li spallation ratio; however, for large values of the irradiation time, this could be due to uncertainties in the parameters. This does not seem possible for short irradiation times, however. Tho nuclear processes are less reasonable if C is present in the planetesimals or if higher energy particles are assumed in order to get appreciable amounts of LiBeB from spallation of SiFe as well as from O 16. The second stage of the calculation yields the required hydrogen concentration, H Si ≈ 1 , and “dilution factor,” F d ≈ 20 (approximately the ratio of unirradiated to irradiated material) to give the terrestrial D H ratio. FGH calculated F d = 10 and H Si = 8 . The amount of water is considerably reduced in the present calculations. Although a loss of O during the formation of the Earth still must be postulated, the amount to be lost is much less than in tho FGH case. We point out that the FGH model is compatible with suggestions that the Moon has a high water content and that biotic material has formed in the carbonaceous chondrites and on the lunar surface. The nucleosynthesis of C 13 in its present terrestrial abundance appears quite feasible; however, in this case the solar C 13 C 12 ratio will be much less than that observed terrestrially. Conflicting experimental results exist on this point at the present time. Observed C 13 C 12 variations in meteorites appear to be due to chemical fractionation. The fact that the isotopic composition of Li, Gd, and K in stone meteorites is identical with that found terrestrially requires that both terrestrial and meteoritic material were subjected to the same particle flux and had the same fraction of material irradiated. This implies that the Earth and the meteorites had a common initial history if the basic features of this model are to be retained. A lunar origin for stone meteorites could very well provide the required astrophysical situation to meet this requirement, whereas an asteroidal origin presents many more difficulties.

Photoneutron spectra and cross sections for 12C and 16O

Partial (γ, n) cross sections have been measured for two self-conjugate nuclei 12C and 16O by measuring the spectral intensity of emitted neutrons in conjunction with a determination of the time-integrated absolute photon flux. The maximum-energy photoneutrons which leave the residual nuclei in their ground state were isolated from other transitions, making it possible to study individual excited levels in 12C and 16O. By measuring the neutron spectra at several angles and taking advantage of the use of self-conjugate target nuclei, these isolated levels in 12C and 16O were found to be due to electric dipole photo-absorption with subsequent emission of d-wave neutrons.