Project for modifying the setup for adron-55 to improveitsbackground characteristics and a review of unsolved problems in studies of extensive air showers

The article presents an overview of modern problems in studiesof Extensive Air Showers and works devoted to their investigation. It is demonstrated that over the past decade convincing evidence of the presence of a neutron component has beendemonstrated. When designing experimental facilities aimed at studying the nature of cosmic rays, this must be taken into account, since fast neutrons that arise outside the working volume can adversely affect the interpretation of the obtained data. In particular,if one tries to reveal the nature of penetrating component this effect is at most importance. Studies of biological shielding for thehigh flux research reactorPIKreactor at the Kurchatov Institute have shown that effective shielding from such neutrons can be provided by polyethylene in combination with borated rubber. At the same time, the use of boron-containing polyethylene does not lead to a significant improvement in protection, however, it significantly increases its cost. Based on foregoing, a modification of the hadron calorimeter protection is proposed to improve its protection it from the influence of the fast neutrons.