Nuclear Instruments and Methods in Physics Research A 580 (2007) 286–288 Micro-Hole and Strip Plate (MHSP) operation in CF 4 H. Natal da Luz a,b,Ã , J.A. Mir c , J.F.C.A. Veloso a , J.M.F. dos Santos b , N.J. Rhodes c , E.M. Schooneveld c a Departmento de Fı´sica, Universidade de Aveiro, P-3810-193 Aveiro, Portugal b Departmento de Fı´sica, Universidade de Coimbra, P-3004-516 Coimbra, Portugal c CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK Available online 18 May 2007 Abstract The Micro-Hole and Strip Plate (MHSP) is a hybrid electron multiplier which combines the working principles of a Gas Electron Multiplier (GEM) and a Micro-Strip Gas Counter (MSGC). The compact double stage electron multiplication processes found in the MHSP enables the realisation of higher gas gain than the lone GEM operation. Thermal neutron detection using gas detectors involves the use of 3 He gas with another suitable stopping gas, operated at elevated pressure to confine the products of the neutron- 3 He reaction. It is, however, well known that the gain of GEMs drops too sharply with increasing chamber pressure. We have pursued experimental work using the MHSP to infer the upper limits of thermal neutron position resolution. The stopping gas used during the present studies was Tetrafluoromethane ðCF 4 Þ chosen due to its low X-ray and g-ray efficiency, requiring only 2.6 bar to yield a position resolution of 1 mm. In the present studies, systematic measurements were taken to establish the gain versus CF 4 pressure characteristics of the MHSP, in the 1 to 2.65 bar range. These studies demonstrated that it was possible to sustain gains above 10 4 and 300 with pressures of 1 and 2.65 bar, respectively. The advantage of having two multiplication stages in the MHSP separated by only few tens of microns, results in a less pronounced gain reduction with pressure, presenting higher gains than single or multiple GEMs. The energy resolution at 1 bar was 29% FWHM for the 5.9 keV Mn K a line from a 55 Fe source, which is a typical value for micro-patterned gas detectors operating in CF 4 . r 2007 Elsevier B.V. All rights reserved. PACS: 29.40.Cs; 29.40.Gx; 85.60.Gz Keywords: Micro-hole and strip plate; Thermal neutrons; Effective gain 1. Introduction The Micro-Hole and Strip Plate (MHSP) [1] is a hybrid detector combining a Micro Strip Gas Chamber (MSGC) [2] and a Gas Electron Multiplier (GEM) [3] in opposite sides of the same substrate, having the advantage of two multiplication stages. The MHSP has been intensely investigated, showing very good detection capabilities, providing high gains and good energy resolutions when compared to other micro-pattern devices, including its operation under high pressure [4,5]. Imaging capability can be achieved by reading the anodes either individually or in groups on the MSGC side, for one dimension and structuring the GEM side for the second dimension. The aim of this work is to infer the ability of the MHSP for thermal neutron detection and evaluating an upper position resolution limit using 3 He =CF 4 mixtures. From several possible nuclear reactions for neutron capture and subsequent detection, one of the most common is the reaction of thermal neutron with 3 He nucleus yielding a 573 keV proton and a 192 keV tritium: 3 He ðn; pÞT. For position detection capability, the centre of mass of the avalanches originated by the proton and the tritium is measured, which means that there is always a systematic error associated with the measurement. This error is dependent on the range of the two particles in the medium. The range of 573 keV protons in 3 He at 1 bar is too long [6], which imposes the need for a high pressure operation as ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2007.05.157 Ã Corresponding author. Tel.: +351 234 378 108; fax: +351 234 424 965. E-mail address: hugo@gian.fis.uc.pt (H. Natal da Luz).