NEUTRON DETECTOR

PURPOSE:To extremely lower the probability of the generation of crevice corrosion in the top end part of a spring housing by butt-welding a spring housing cylindrical body part and spring housing cap part. CONSTITUTION:The spring housing cap part 17B is constituted of the cylindrical part having the wall thickness of the spring housing cylindrical part 17A and a ring part which is provided to the top end of the cylindrical part and has an aperture 18 of the diameter smaller than the inside diameter of the spring housing cylindrical part 17A. The bottom end of the spring housing cylindrical part is butt-welded to the top end of the spring housing cylindrical part 17A. The clearance which is heretofore formed between the spring housing 3 and a guide plug 4 and the clearance which is formed between the spring housing 3 and an end plug 2 do not exist in this case and, therefore, the probability at which the crevice corrosion generates in the top end part and bottom end part of the spring housing 17 is extremely lowered.