Design and development of cold neutron guides at the Dhruva reactor

Two curved neutron guides of lengths 21 and 35m (of radii of curvature 1916 and 3452m, respectively) are being set up at the Dhruva reactor, Trombay. These guides will transmit cold neutrons from a liquid methane cold source and will penetrate the double containment wall of the hall on to the guide laboratory where four experimental posts are provided for setting up spectrometers. A brief description of the mechanical design of these guides is given. These guides are made up of 1 m-long guide constituted of nickel coated float glass plates. Summary of the authors' experience is given in respect of: (i)nickel coating of 400 plates and spacers(each one meter long), to the required thickness of approximately 1500 A utilizing an evaporation chamber 2.8 m in diameter loaded with 76 nickel wire carrying tungsten filaments; (ii) measurements of neutron reflectivity on randomly chosen nickel coated plates at various grazing angles using a finely collimated beryllium filtered neutron beam; and (iii) assembly of 100 neutron guide elements to the required precision in parallelism using precision jigs designed and developed in authors' laboratory. (author). 6 refs., 2 tabs., 8 figs