AIRBORNE SURVEY OF THE NUCLEONIC COMPONENT OF COSMIC RAYS AND THE MAGNETIC FIELD OF THE EARTH
< < 9 ; 8 9 9 intensity of primary cosmic radiation, as detected through their nucleonic component progeny observed deep within the earth's atmosphere, was measured, covering extensive portions around the globe, with an airborne neutron monitor, installed aboard a Super Constellation aircraft of the U. S. Navy Hydrographic Office. The measurements have extended over a period November, 1958 to October 1960. The data obtained during ascents and descents, as well as periods of level flight at different altitudes, above a fixed station, provided determinations of the atmospheric absorption mean free path at different latitudes. Absorption curves were obtained from the counting rate versus pressurealtitude measurements, recorded at 22 different locations from the Arctic to the Antarctic. The results indicated that the absorption coefficient of the nucleonic component in the lower atmosphere (atmospheric depth > 500 g/cm/sup 2/) is a function of the primary threshold rigidity over the range 2.5 to 15 Bv. The change from equator to high latitude amounts to approximately 10%. For high altitude stations, having threshold rigidity less than 2.5 Bv, the absorption mean free path length tends to become constant. The weighted mean of all the independent determinations at 7 high latitude stations (P/sub c/ < 2.5 Bv) yielded a value for the attenuation length, L = 135.2 plus or minus 0.8 gm/ cm/sup 2/. Repeated measurements of the absorption mean free path made at Washington (D.C.), Kodiak (Aleutian Is.), and Honolulu (Hawaiian Is.), showed that within experimental and statistical uncertainties, the absorption mean free path length, at a given location, remained essentially constant, during the period of the measurements. The analysis of the measurements obtained during the aircraft cruising altitude provided a comparison among geomagnetic threshold rigidity calculations based upon various approximations to the terrestrial magnetic field. A plot of the intensity of the nucleonic component versus threshold rigidity computed in accordance with the theoretical calculations of Quenby and Wenk, who took into account the effects of the dipole and non-dipole parts of the earth's internal field, as well as the penumbral correction at the low and intermediate latitudes, revealed that, except for measurements over one region in the North Atlantic, all the data fall within a narrow band. The contrast with previous rigidity cut-off assignments, based either on the centereddipole theory, or on dipole plus non-dipole formulation of Quenby and Webber, is striking. A contour map of equal intensities (isocosms) was obtained for the entire globe. The isocosmic map shows that the general variations of the lines of equal cosmic-ray intensity coincide with the topography of magnetic rigidity. It was concluded that the Buenby-Wenk representation is essentially correct. The geomagnetic field effective on cosmic particles is due to the geomagnetic field which consists of both the dipole and non-dipole parts of the internal field. Fields of external origin do not significantly influence the trajectories of cosmic-ray primary charged particles. The effect of the main cone at intermediate latitudes is a very important factor in determining the threshold magnetic rigidities. In the region, where significant discrepancy is noted between theory and experiment, the measurements provide an empirical correction and suggest a revision of the interpolation procedure which was used by Quenby and Wenk in their work. Determinations of the location of the cosmicray equator were also made at six points. The results indicated that a very good agreement is achieved with the theoretical cosmic-ray equator computed using all the moments through 26 pole. A plot of the minimum intensity as a function of longitude showed that at the cosmic-ray equator, the magnitude of the longitude effect is substantial. The peak to peak amplitude is approximately 25%. A comparison of the nucleonic intensity measurements obtained
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-17-037928
- OSTI ID:
- 4646425
- Resource Relation:
- Other Information: Thesis. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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A NEW METHOD OF COMPUTING COSMIC-RAY CUTOFF RIGIDITY FOR SEVERAL GEOMAGNETIC FIELD MODELS