• S Biswas

      Articles written in Proceedings – Section A

    • An improved method for determining the mass of particles from scatteringversus range and its application to the mass ofK-mesons

      S Biswas E C George B Peters

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      A new method is developed for determining the mass of particles coming to rest in nuclear emulsions. Multiple coulomb scattering is measured with cells whose lengths vary along the trajectory in such a manner as to compensate for the momentum loss of the particle and keep the mean deviation between adjacent cells constant over the entire track. It is shown that this procedure is more convenient and inherently more accurate than that based on scattering measurements with constant cellsize. The method has been applied toK-mesons which at the end of their range either decay into a single charged relativistic particle (K+-mesons) or into 3π-mesons (τ-mesons) or give rise to capture stars (K-mesons). The results are within experimental error consistent with the assumption that the mass of these three classes of particles are identical and equal to the well established mass of theτ-mesons. The average mass of a group of 9 longK-mesons determined with our scattering procedure is MK=974±42me.

    • Scattering measurements in nuclear emulsions and their application to measuring the charge of primary cosmic ray nuclei

      S Biswas B Peters Rama

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      Small local dislocations in processed emulsions give rise to spurious scattering whose effect on tracks is indistinguishable from the multiple scattering produced by coulomb interaction. Because of this effect the atomic number of fast primary cosmic ray nuclei will be underestimated in more than 50% of the cases in experiments where multiple scattering of tracks and ionization measurements are employed for charge determination. The spurious scattering was investigated by measuring the track contours of 100 very long tracks due to energetic primary particles; the effect was present in comparable strength in all plates and all types of emulsions which have been investigated. It is too small to affect measurements on medium energy particle tracks (protons with energy below 600 MeV and heavy nuclei with energy below 300 MeV/ nucleon). It dominates, however, other sources or error and noise for tracks of energetic particles although it does not preclude occasional observations of very low scattering values. New methods for measuring various forms of noise have also been developed in the course of this work and the noise level for scattering measurements has been reduced below previously accepted values.

      Spurious scattering is presumably largely responsible for the discrepancies which appear when one compares the primary charge and energy spectra derived from experiments involving scattering measurements with the corresponding spectra derived from numerous other experiments which employ different techniques.

      If the experiments based on scattering measurements are omitted, the remaining evidence strongly favours a spectrum in which the energy per nucleon is nearly independent of atomic number for all primaries. It also favours a charge distribution which has a pronounced minimum for charges 3≤ Z≤ 5 and, therefore, yields a fairly low upper limit for the amount of interstellar matter traversed by primary cosmic ray nuclei.

    • Multiple scattering measurements on high energy protons with long cell lengths

      S Biswas N Durga Rasad S Mitra

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      Scattering measurements on individual tracks and relative scattering measurements on pairs of tracks have been made in two stacks exposed to 6·2 and 5·7 BeV protons respectively from the Berkeley Bevatron. Spurious scattering was determined in these two stacks for cell lengths ranging from 1 mm. to 8 mm. In one stack the magnitude of spurious scattering was very low while in the other it was fairly high. Our results indicate that:

      Spurious scattering varies with cell lengtht, as tx, wherex is about 0·8 fort = 1 mm. to 3 mm. and about 0·5 fort = 3 mm. to 8 mm.

      The spurious scattering is lowest near the glass surface of the emulsion and increases towards the air surface.

      The small-scale dislocations which give rise to spurious scattering extend in the plane of the emulsion at least over distances of 200 µ, but vary rapidly in size and direction with depth. Therefore, reliable relative scattering measurements require that the separation between the tracks in the depth of emulsion should be as small as possible (≤50 µ) whereas the separation in the plane of the emulsion may be as large as 200 µ.

      The scattering constant for cell lengths of 1 mm. to 8 mm. has been determined. Our values are about 10% higher than the theoretical values, on the assumption that the proton energy in the Bevatron was known accurately at the time the plates were exposed.

    • He3 nuclei in the low energy primary cosmic radiation

      S Biswas P J Lavakare S Ramadurai N Sreenivasan

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      The flux of He3 nuclei and the ratio He3/(He3+He4) in the low energy primary cosmic radiation have been determined using a stack of nuclear emulsions exposed at 3·1 g. cm.−2 of atmospheric depth from Fort Churchill, Canada, in June 1963. The grain-densityversus residual range method was used to determine the masses of the helium nuclei. Using a sample of 146 helium nuclei whose masses could be identified, the ratio He3/(He3+He4) is obtained as 0·14±0·04 for the kinetic energy interval 115–210 MeV per nucleon and 0·43±0·11 for the rigidity interval 0·85–1·05 BV. The differential fluxes of He3 nuclei are determined as 0·017±0·006, 0·045±0·015, and 0·054±0·017 particles/M2. Sr. Sec. MeV/nucleon, in the kinetic energy intervals of 117–183, 183–217, and 217–250 MeV/nucleon respectively. These results are compared with those of other investigators. From the results of the present work the amount of matter traversed in space by the primary cosmic ray helium nuclei of energy 115–210 MeV/nucleon is obtained as 4·7±1·8 gm. cm.−2 of hydrogen.

    • Cosmic ray nuclei of chargeZ⩾3 during the period of low solar activity

      K C Anand S Biswas P J Lavakare S Ramadurai N Sreenivasan V S Bhatia V S Chohan S D Pabbi

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      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 Rβ dependence and that the modulation parameter Δη between 1965 and 1957 was about 1·1.

      The implications of these results are discussed.


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