Measurement of the Mean Free Path of Relativistic 12C Nuclei Undergoing Coherent Fragmentation to Three Alpha Particles in a Nuclear Emulsion Filled with Lead Nuclei

Abstract

A stack of track-photoemulsion layers was exposed to a beam of ¹²C ions accelerated to a momentum of 4.5 GeV/c per nucleon at the synchrophasotron of the Laboratory of High Energies at the Joint Institute for Nuclear Research (JINR, Dubna). The mean free path of relativistic ¹²C nuclei was measured for the reaction of their coherent fragmentation to three alpha particles in BR-2 nuclear track photoemulsion filled with lead nuclei in proportion of one lead atom per five silver atoms. The result was λ_(Em+Pb) = (11±3) m. The cross section of σ_(Em+Pb) = (18±3) mb averaged over all track-photoemulsion nuclei corresponds to this value of λ_(Em+Pb). From a comparison of the value obtained in the present study for λ_(Em+Pb) with the mean free path of ¹²C nuclei in a standard BR-2 track photoemulsion, (10.3 ± 1.5) m, it follows that, in this channel, a nuclear fragmentation mechanism is dominant in the fragmentation of ¹²C nuclei both off lead nuclei and off track-photoemulsion nuclei.