Defocusing characteristics of auroral X-ray images observed at balloon altitudes.

Kodama, Masashi

doi:10.5636/jgg.41.389

Cited by 4 publications

(4 citation statements)

References 11 publications

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“…In order to investigate the basic characteristics of defocusing of the X ray image viewed by a directional telescope at balloon altitudes, Monte Carlo calculations for the omnidirectional detector have been tried first, assuming a single beam photon source whose energy and zenith angle of incidence are varied [Kodama and Ogura, 1989]. As a result, the dispersion can be as small as 3 km for the photons within incident zenith angles of 30 ø but can go beyond 10 km for 60 ø zenith angle.…”

Section: Discussionmentioning

confidence: 99%

Ghost images of auroral X ray sources observed by directional balloon‐borne detectors

Kodama¹

1989

J. Geophys. Res.

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Diffusion characteristics of auroral X rays propagating through the atmosphere have been investigated by means of a Monte Carlo simulation. The results are used to estimate the defocusing effect of multiple photon scatterings on auroral X ray images detected at balloon altitudes. It is predicted that the auroral X ray image at an atmospheric depth of 6–14 g/cm2 is occasionally accompanied by a spurious ghost image in the zenith when an auroral X ray source near the zenith is viewed by a collimated detector inclined with respect to the zenith. The ghost image is enhanced with increasing zenith angle of the collimator axis. The maximum spurious contribution occurs for a collimator with ±20° opening angle and 40° zenith angle. The magnitude of the spurious contribution also depends on the atmospheric depth and the threshold energy of the detector.

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Section: Discussionmentioning

confidence: 99%

Ghost images of auroral X ray sources observed by directional balloon‐borne detectors

Kodama¹

1989

J. Geophys. Res.

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“…The simulations were carried out under the assumption of an isotropic point source with an exponential-law energy spectrum (the e-folding energy was fixed to 30 keV), as described by KODAMA and OGURA (1989). To quantitatively demonstrate the degree of the ghost contribution, a ratio of the maximum photon count in the ghost image to that of the real image was taken as a function of the collimation steps, where the ghost background was subtracted from the peak count of the real image.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…Several simulation studies have been carried out to investigate propagation procedures of bremsstrahlung X-rays through the atmosphere, in terms of the scattering and energy degradation of photons (PILKINGTON and ANGER, 1971;BERGER and SELTZER, 1972;LAZUTIN,1979;OGURA and KODAMA, 1980;KODAMA and OGURA, 1989). OGURA and KODAMA (1989) first pointed out the possibility of ghost images being superposed on the real image when using a directional X-ray detector at balloon altitudes.…”

Section: Introductionmentioning

confidence: 99%

Ghost image simulation of auroral X-ray sources at balloon altitudes.

Yoneda

Kodama

1990

J. geomagn. geoelec

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Quantitative contributions of the ghost images associated with aurora! X-ray image formings at balloon altitudes have been investigated by a Monte Carlo simulation. Contour maps of the ratios of the ghost peak count to real images are shown as functions of the detectors' specifications, collimation angle, the zenith angle of the collimator axis and threshold energy and balloon altitude. As a result, the count ratio decreases for smaller collimation angle and zenith angle, but is occasionally beyond unity even at a conventional balloon altitude of 10 g/cm2.

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“…A simulation calculation method was presented by Kodama and Ogura (1989). Figure 9 shows the fractional count depression in the channel No.…”

Section: Discussion and Summarymentioning

confidence: 99%

Circumpolar Observation of Bremsstrahlung X-Rays by a Polar Patrol Balloon over Antarctica.

Kodama

Suzuki

Hirasima

et al. 1995

J. geomagn. geoelec

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This is a preliminary report of the first Polar Patrol Balloon (PPB) observation for auroral X-rays arose widely in the south polar region. The PPB No. 6 was launched from Syowa Station, Antarctica, on 5 January 1993, and flew along one and a half circumpolar paths, covering 6-13 g/cm2 atmospheric depth and 49°-81 ° invariant latitude. Distinct enhancements ofbremsstrahlung X-rays (E=30-120 keV) measured by an omni-directional NaI(Tl) scintillation counter were often observed during the entire flight period of 27 days with low to moderate geomagnetic activity. Ninety-three percent of the enhancements of greater than 3000 counts/30 s, being about twice the atmospheric X-ray background flux, were observed in 60°-70° invariant latitude, and 71 percent in the magnetic local dayside sector. Thirty-four percent of the dayside enhancements occurred at low latitudes below 600, suggesting a large-scale expansion of the X-ray auroral oval to lower latitudes. Auroral X-ray enhancements observed at >65° invariant latitude exhibit that their energy spectra progressively harden in the time interval from 6 to 18 h MLT, consisting with the statistical summary of Bewersdorff et al. (1966). A double exponent spectrum in which the exponent E0 becomes smaller in the low energy end below 50 keV is also found. Time profiles of the enhancements are well characterized by the systematic Eo-flux relation that Eos are held within a definite range during the enhancement, otherwise they vary taking a minimum (or maximum) at the peak flux. These may suggest two different modes of energetic electron precipitations accompanying by stationary or variational spectrum from onset to recovery of the enhancement.

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Defocusing characteristics of auroral X-ray images observed at balloon altitudes.

Cited by 4 publications

References 11 publications

Ghost images of auroral X ray sources observed by directional balloon‐borne detectors

Ghost images of auroral X ray sources observed by directional balloon‐borne detectors

Ghost image simulation of auroral X-ray sources at balloon altitudes.

Circumpolar Observation of Bremsstrahlung X-Rays by a Polar Patrol Balloon over Antarctica.

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