An important part of the information about the mass and energy of the shower inducing primary particle is transported within the hadronic air shower component to ground level. The hadrons and their interactions are important for the understanding of the shower development within the atmosphere. The measurement of the hadrons allows to study high-energy hadronic interaction models used in the shower simulations. Therefore a calorimeter is one of the main components of KASCADE , located in the center of the scintillator array. The point of incidence, the energy, and the angle of incidence can be measured with this detector for individual hadrons within an air shower.
The detector is an iron sampling calorimeter with liquid ionization chambers as active media. Its size of 16x20 m2 corresponds to the size of the shower core of high-energy air showers. The absorber consists out of several layers of iron slabs with a thickness of 12 cm in the upper part increasing to 24 cm and 36 cm in the lower part, respectively. A 5 cm lead filter on top of the calorimeter serves to suppress the electromagnetic component. The 77 cm concrete ceiling of the detector cellar acts as last absorber layer. The absorber corresponds to 1460 g/cm2 or 11.4 hadronic interaction lengths. Hadrons up to an energy of about 25 TeV can be absorbed in the calorimeter completely.
10000 liquid ionization chambers serve as active components, installed in eight layers between and below the absorber slabs. In addition, the third active layer and the calorimeter roof are equipped with scintillation counters. A homogeneous active area can be achieved due to the special construction of the chambers and their arrangement in the detector. The effective active area is greater than 97%.
The ionization chambers are a new detector technology developed at the Institute for Nuclear Physics of the Forschungszentrum Karlsruhe. The KASCADE hadron calorimeter is the first experiment using warm ionizing liquids for a large detector. The chambers achieve a large dynamic range of about 6x104, only limited due to the amplifier electronic. Therefore signals from a minimum ionizing particle up to hadrons in the shower core up to primary energies of 1016 eV can be measured without saturation. Due to the fine lateral segmentation and the read-out of the calorimeter in 40000 electronic channels, hadrons with an energy EH>20 GeV can be measured in the calorimeter. They can be separated from each other in a distance of more than 40 cm. The spatial resolution is about 11 cm and the angular resolution in the order of 5o. The energy resolution is 30% for hadrons with 100 GeV decreasing to 15 % for EH=25 TeV.