  Chinese Spallation Neutron Source (CSNS), one project of the 12th
five-year-plan scheme of China, is under construction in Guangdong province.
Three neutron spectrometers will be installed at the first phase of the
project, where two-dimensional position sensitive thermal neutron detectors are
required. Before the construction of the neutron detector, a prototype of
two-dimensional 200 mmx200 mm Multi-wire Proportional Chamber (MWPC) with the
flowing gas of Ar/CO2 (90/10) has been constructed and tested with the 55Fe
X-Ray using part of the electronics in 2009, which showed a good performance.
Following the test in 2009, the neutron detector has been constructed with the
complete electronics and filled with the 6atm.3He + 2.5atm.C3H8 gas mixture in
2010. The neutron detector has been primarily tested with an Am/Be source. In
this paper, some new developments of the neutron detector including the design
of the high pressure chamber, the optimization of the gas purifying system and
the gas filling process will be reported. The results and discussion are also
presented in this paper.
