K C Anand
Articles written in Proceedings – Section A
Volume 67 Issue 3 March 1968 pp 138-154
An experiment has been carried out using an oriented stack of nuclear emulsions to determine the rigidity spectrum of cosmic ray helium nuclei between 12 and 40 GV, by taking advantage of the variation of the geomagnetic cut-off rigidity in the east-west plane over Hyderabad, India. Altotal of 2433 identified helium nuclei recorded in the stack, has been divided into 8 angular intervals in the east-west plane corresponding to 8 different cut-off rigidities. From this the integral fluxes of helium nuclei at the top of the atmosphere have been obtained for all the 8 rigidity intervals. The vertical flux above an effective threshold rigidity of 16·73 GV has been determined with high statistical accuracy and has a value of 15·0±0·5 helium nuclei (m2.sr.sec.)−1. The rigidity spectrum of these nuclei between 12 and 40 GV can be well represented by a power law of the type N (>R) =1990 R−1.74±0.11 (m2.sr.sec.)−1 and is the first direct determination so far made in this rigidity region.
The differential rigidity spectra of protons, helium nuclei and S-nuclei of the cosmic radiation in the vicinity of the earth at solar minimum (1965) have been constructed with the existing world data and it is found that for rigidities ≳ 10 GV, the three spectra have, within experimental errors, the same slope of 2·6. The ratio P/He and He/S of the differential fluxes have been studied as a function of rigidity. It is found that for R>2 GV, the ratio P/He has, within experimental errors, a constant value of 6·3; as for the ratio He/S, it seems that the experimental data above a GV is not inconsistent with a constant value of 14 over the entire rigidity interval considered here.
Volume 67 Issue 5 May 1968 pp 267-283
Extensive data now available on the non-thermal background radio emission from different celestial directions, and recent measurements on the energy spectrum of cosmic ray electrons in the vicinity of the earth permit one to deduce information on the mean magnetic fields and cosmic electron spectra needed to exist in different regions of the Galaxy. It is found that in order to explain quantitatively the background radio brightness distributions from the Galaxy one needs (i) the same or nearly same electron spectrum that exists in the near interstellar space, to exist in almost all regions of Galactic space, (ii) a mean magnetic field close to 6×10−6 Gauss in the Disc in the direction of the Anti-centre, (iii) a mean magnetic field close to 2·5×10−6 Gauss in the radio Halo and (iv) a mean magnetic field probably close to 9·5×10−6 Gauss towards the Galactic Ridge in the direction of the Centre. Some inferences are also drawn on the confinement of cosmic rays in the Galaxy.
Volume 68 Issue 5 November 1968 pp 219-227
Radio astronomical data available on the galactic background radiation has been carefully examined to deduce information on the existence or otherwise of a Galactic Radio Halo. It is shown that, though considerable doubt has been recently expressed by some regarding its existence, no convincing and quantitative reasoning has been so far advanced towards this; on the other hand, there are substantial arguments in its favour.
Volume 70 Issue 5 November 1969 pp 201-220
A detailed study of the composition and energy spectra of heavy nuclei of charge Z⩾3 in the primary cosmic rays has been made during the period of low solar activity, using two stacks of nuclear emulsions exposed in balloon flights from Fort Churchill, Canada, in June 1963. Each of the stacks was composed of 120 nuclear emulsions of three different sensitivities and was exposed at about 3·5 g. cm.−2 of residual air for about 11.1 hr. Reliable resolution of charges of nuclei from lithium to oxygen was obtained; for heavier nuclei, charge groups were determined. From the analysis of 793 tracks of nuclei with Z⩾3, results on the following aspects were obtained:
The differential energy spectra of L (Z=3–5), M (Z=6–9) and H (Z=10–28) nuclei were measured in the energy intervel 150–600 MeV/nucleon; integral fluxes were obtained for energy >600 MeV/nucleon;
The energy dependence of the L/M ratio at the top of the atmosphere was determined; the ratios were obtained as 0·45 ± 0·06 and 0·29 ± 0·03 in the energy intervals of 200–575, and >575 MeV/nucleon respectively;
Relative abundances of individual nuclei of Li, Be, B, C, N and O at the top of the atmosphere were determined as 36, 29, 55, 100, 60 and 106 respectively in the energy interval 150–600 MeV/nucleon; corresponding values were also obtained for energy >600 MeV/nucleon.
The differential fluxes of multiply charged nuclei measured by us and by other investigators were used to determine the solar modulation between solar maximum to solar minimum. It was found that solar modulation of the fluxes of M and He nuclei were consistent with R
The implications of these results are discussed.
Volume 71 Issue 5 May 1970 pp 225-229
Balloon, satellite and other deep space probe observations on the intensity of low energy (0·1–10 MeV) gamma-rays are carefully examined with a view to understand the existing anomalies in their intensities and energy spectra. The observed spectral data is “unfolded” to deduce the true gamma-ray energy spectrum. The recently observed flattening in the spectral shape at about 1 MeV is shown to be likely to arise as a result of the gamma-ray detector response to a simple power law input spectrum.
Volume 72 Issue 2 August 1970 pp 62-66
The high energy gamma-ray flux (energy greater than 1012 eV) resulting from high energy protons interacting with photons of the recently observed sub-millimeter microwave radiation in metagalactic space is calculated. Comparison of the flux of these gamma-rays with experimental observations indicate that the observed sub-millimeter radiation may not be universal.