A new modular cosmic-ray detector

Comparing the mean features of helium propor- tional counters with the ones of the standard boron trifluoride tubes, it appears at glance that, in equal term of efficiency and for the same active length, the 3 He filled counters are char- acterized by a very smaller diameter which optimizes their spectral resolution and minimizes wall effects. Moreover he- lium counters are usually designed in standard diameters and the 2 inch size is commonly available in a wide set of sen- sitive lengths. This manufacturing characteristic suggested us the realization of a modular neutron detector with a vari- able geometry to be adapted to counters of different lengths. At first a small modular detector (length of 80 cm) was as- sembled in Rome at SVIRCO Observatory and TPL during 2006. In March 2010 a second larger modular neutron mon- itor (length of 216 cm) was realized as well to be used for cosmic ray registration with a higher counting rate and better reliability. A short description of both modular cosmic-ray detectors is given.