Cosmic ray nuclear interactions and EAS-triggered families observed by the Chacaltaya hybrid experiment

Longitudinal and lateral characteristics of the families detected by emulsion chambers in the hybrid experiment with AS-array at Mt. Chacaltaya are studied in detail. Although many groups discuss about an increase of the heavy component in primary cosmic-rays beyond the knee region, it is shown that the observed characteristics of the families accompanied by large shower size, Ne>106, can not be explained by an increase of heavy primaries alone. It is necessary to assume some changes of nuclear interaction in order to explain the observed characteristics of the air-showers accompanied by families.