¹⁰B coated multigrid position sensitive neutron detector with zero parallax

¹⁰B as a solid state converter material for neutron detection is being revisited due to its properties such as chemically non reactive, nontoxic and high energy reaction products. The disadvantage is low efficiency as only thin layer can be used for the detection, where coating thickness should be less than range of 0.91 MeV Li. Gain in efficiency can be attained using two strategies: multiple stacking of thin layers or by inclining the converter layer to increase effective neutron penetration depth as in Jalousie detector. Consideration on design of position sensitive detector (PSD) is for the ¹⁰B layer thickness, detection efficiency and transmission of neutron beam to following consecutive ¹⁰B layers. Design of PSD with stacking of multiple ¹⁰B layers, for improvement in efficiency, involves complex anode-cathode geometry. It results in broadening of peak due to parallax. This paper deals with the novel design and fabrication of a PSD based on multilayer ¹⁰B, multiple anode grids and zero parallax. It is essential to handle skilfully hardware design, in addition to complexity of data acquisition electronics. The structure follows the curvature equivalent to sample to detector distance as radius. A PSD consists of four ¹⁰B coated plates and an array of three multiwire grids arranged alternately in curved casing. Incident neutron beam thus intercepts six ¹⁰B coated surfaces. An assembled curvilinear PSD and the layout of teflon holder supporting curved anode-cathode structure is shown. Position readout is carried out using charge division encoding method. An arc length of 0.7 m (detector sensitive length) covers the angular range of 23°. Central anode grid is mounted at radius 2000 mm and other two grids at ± 12 mm radii from central grid position. At constant sensitive length of 700 mm for all three grids, deviation in 2 for other two grids is ± 0.12 ∼ ± 4 mm, when central anode wires on multiwire grids are aligned. This deviation in angular position can be normalized with linear position using a software correction. Presently PSD with single grid is tested and position resolution obtained is 5 mm∼ anode pitch. Overview of these developments with multiple grids is presented.