During the 1995-96 austral summer, a period of solar minimum, we operated a neutron monitor on board the ship Italica of the Italian Antarctic Programme to record cosmic ray neutron intensities in seas from Italy to Antarctica and back. This survey provided a full coverage of cut-off rigidities and the possibility of repeating the measurements at least twice at the same cut-offs. In spite of some problems encountered, mainly due to the unstable AC voltage supplied by the ship, it was possible to get a preliminary latitude curve of the cosmic ray nucleonic intensity . Data corrections for efficiency changes, pressure variations and small primary cosmic ray variations were applied to the raw data recorded along the survey.
The high-energy cosmic ray (CR) nucleonic component intensity was measured with a standard neutron detector (of NM-64 type, extensively used all over the world in several CR stations) made by three large BF3 proportional counters placed, each of them, inside a lead structure, surrounded by a proper layer of polyethylene (N1, N2, N3).
Lead works as a neutron ... multiplier, due to the interactions (single or multiple) between the energetic incoming particles (with energy E>50 MeV) of the secondary nucleonic component and the lead nuclei. The surrounding polyethylene acts as an inner-reflector for particles generated inside the detector and, at the same time, as an outer-reflector for particles generated out of the detector (for instance in high atomic number external structures). Just around each counter a polyethylene tube (2 cm thick) acts as a neutron thermalizer. The thermal neutrons are detected by the proportional counters. Over the high-energy neutron detector, on the extreme left and right sides, two additional BF3 counters without lead and polyethylene (bare counters B1, B2) are utilized for recording the low energy neutrons (thermal background). The instrumentation was installed inside a air-conditioned container capable of maintaining the relative humidity below 55% and temperature between 18° and 25°C along the survey.
The data were recorded at 5-min intervals using a standard VXIbus data acquisition system (the clock was inside the VXI). The following information are obtained: (1) geographic position and universal time provided by a Global Position System (GPS); (2) atmospheric pressure by a high precision device (resolution 0.01 mbar, precision 0.1 mbar, stability 0.1 mbar per year); an additional pressure sensor (0.2 mbar resolution) was also operating; (3) internal temperature and relative humidity and external temperature; (4) the values of high and low voltages; (5) the integral 5-min value of CR intensities measured by each counter of 3NM and of bare counters. A spare acquisition system was foreseen and used with an external computer supplied with a HP-basic co-processor.
To acknowledge the IFSI-CNR/UNIROMATRE collaboration and PNRA