on the isotopic composition of primary cosmic ray nuclei

Volume 31B, number 8 PHYSICS LETTERS 13 April 1970 ON THE ISOTOPIC COMPOSITION OF PRIMARY COSMIC RAY NUCLEI N. LUND and B. PETERS Danish Soace Research Institute, Copenhagen, Denmark and R. COWSIK and Y. PAL TATA Institute of Fundamental Research, Bombay, India Received 5 March 1970 A table showing the relative abundance of chemical elements in the primary cosmic radiation, when constructed by measuring the flux of particles which exceed a given magnetic rigidity, differs from a table constructed by measuring the flux of particles which exceed a given velocity; the difference is a known function of the charge to mass ratio of the various components. Using this effect we have obtained information on the isotopic composition of the elements Be, B, C, N, 0, Ne, Mg and Si in the rigidity region above - 5 GV. We have obtained some information on the isotopic composition of primary cosmic ray nuclei with momenta of a few (GeV/c)/nucleon. The study covers the elements between lithium and iron, but conclusions can as yet be drawn only for Be, B, C, N, 0, Ne, Mg and Si. These conclusions are based on - 6000 particles with atomic number Z> 3 observed in two balloon flights at a latitude corresponding to a verical cut-off rigidity of 5 GV (Aire-sur-1’Adour). The instrument which consists of two flat sheets of Cerenkov radiators with different indices of refraction and three digitized single-gap spark chambers accepts particles incident with zenith angles up to 55O; a full description of its con- struction and performance is given in ref. 1. DANISH SPACE RESEARCH . . .. . . I. . INSTITUTE . .. .. . . . . . FLIGHT II 3600 EVENTS /. . . . . , . . .. . . .. . .. .I. ..,.. . . . . . . . . . .. . I . . .. .. . . . . . . .. . . . . . . .... . . . .. .. . .. IS . . . . . . . . . :. , : . . ., . . . . . .. . *, ... . . . . .I.. . . .,.. . . . . .... I . . . .,I# . ., . . . . . .. . , . .. , . . . . . . . . , ,.. .. . .. . . . . . . ,.. II . . . . I .. . . I: . . . ,.. .. ,. . . .. . ..‘ 1.1 . . .. . . .. I.,. . . . ‘ . . . .. . . .., . . . . . . . . I. .. . . . . . . . . I . .. . I . Li BC B C N 0- F Nc N.3 &I Al SI Fig. 1. The figure illustrates the charge resolution for particles on which the isotope study was carried out. The ordinate is the ratio of pulse heights in the Cerenkov counters and is therefore a measure of particle velocity. 553

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Volume 31B, number 8 PHYSICS LETTERS 13 April 1970

ON THE ISOTOPIC COMPOSITION OF PRIMARY COSMIC RAY NUCLEI

N. LUND and B. PETERS Danish Soace Research Institute, Copenhagen, Denmark

and

R. COWSIK and Y. PAL TATA Institute of Fundamental Research, Bombay, India

Received 5 March 1970

A table showing the relative abundance of chemical elements in the primary cosmic radiation, when constructed by measuring the flux of particles which exceed a given magnetic rigidity, differs from a table constructed by measuring the flux of particles which exceed a given velocity; the difference is a known function of the charge to mass ratio of the various components. Using this effect we have obtained information on the isotopic composition of the elements Be, B, C, N, 0, Ne, Mg and Si in the rigidity region above - 5 GV.

We have obtained some information on the isotopic composition of primary cosmic ray nuclei with momenta of a few (GeV/c)/nucleon. The study covers the elements between lithium and iron, but conclusions can as yet be drawn only for Be, B, C, N, 0, Ne, Mg and Si.

These conclusions are based on - 6000 particles with atomic number Z> 3 observed in two

balloon flights at a latitude corresponding to a verical cut-off rigidity of 5 GV (Aire-sur-1’Adour). The instrument which consists of two flat sheets of Cerenkov radiators with different indices of refraction and three digitized single-gap spark chambers accepts particles incident with zenith angles up to 55O; a full description of its con- struction and performance is given in ref. 1.

DANISH SPACE RESEARCH . . . . . . I. . INSTITUTE . . . . . . . . . . FLIGHT II 3600 EVENTS

/. . . . . , . . . . . . . . . . .

.I. ..,.. . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IS . . . . . . . . . :. , : . . . , . . . . . . . . *, . . . . . . . .I.. . . .,.. . . . . . . . . I . . . .,I# . . , . . . . . . . . , . . . , . . . . . .

. . , , . . . . . . . . . . . . . , . . I I . . .

I . . . . I: . . . , . . . . ,. . . . . . ..‘ 1.1 . . . . . . . . I. , . . . . ‘ . . . . . . . . ., . . . . . . . . I. . . . . . . . . . . I . . . . I . Li BC B C N 0- F Nc N.3 &I Al SI

Fig. 1. The figure illustrates the charge resolution for particles on which the isotope study was carried out. The ordinate is the ratio of pulse heights in the Cerenkov counters and is therefore a measure of particle velocity.

553