cQ% __ Nuclear Instruments and Methods in Physics Research B 129 (1997) 423-428 zyxwvutsrqponmlkjihgfedcbaZYXWVU _- !Iz ELSEVIER LMMI B Beam Interactions with Materials & Atoms A Bragg curve spectroscopy detector for ERDA studies A. Tripathi, Samit Mandal, D.O. Kataria, D.K. Avasthi, SK. Datta zyxwvutsrqponmlkjihg Nuclear Science Cemre, P.B. No. 10502, Aruna Asaf Ali Marg, New Delhi 110067, India Received 21 June 1996; revised form received 3 April 1997 zyxwvutsrqponmlkjihgfedcbaZYXWVUT Abstract The design and use of a Bragg curve spectroscopy (BCS) detector for depth profiling of elements in materials using the elastic recoil detection analysis (ERDA) technique is discussed. The detector when used to identify recoils from samples in an ERDA experiment using a 170 MeV Ag beam showed a clear separation between Fe (Z = 26) and Cu (Z - 29) recoils. Measurements near Z = 11 yielded AZ/Z of l/34 showing a Bragg peak resolution of 2.9%. For typical applications, the detector can be effectively used for neighbouring charge identification up to Z - 30. PACS: 81.90. + c; 29.4O.Br Keywords: Bragg curve detector; Energy loss; Elastic recoil detection analysis 0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved P/I SO1 68-583X(97)00290-5 1. Introduction Rutherford backscattering (RBS) [l] and elastic recoil detection analysis (ERDA) 121 are popular ion beam tech- niques for depth profiling of high Z and low Z elements, respectively, in materials. It has been shown by Jaipal et al. [3] and Kabiraj et al. [4] that several light elements with neighbouring masses can be analyzed in a sample with the use of conventional heavy ion ERDA (HlERDA), if the sample is available in the form of a self-supporting thin film. In general it is not feasible to get the sample in the form of a self-supporting film. Avasthi et al. [S] have shown that with the proper choice of stopper foil thickness and substrate of the sample, several elements having well separated masses can be analyzed by HIERDA. However, if the sample is thick and has several neighbouring mass elements, the recoil energies of different elements overlap. Therefore, it becomes difficult to study such samples by conventional ERDA. Some of the popular techniques for the study of such samples are (a) the use of time of flight arrangement [6], (b) the use of detector telescope [7-IO] and (c) the use of Bragg curve spectroscopy (BCS) detec- tor [Ill. The use of gas detectors, such as a BCS detector, for heavy ion studies is preferred over surface barrier detectors because of radiation damage possibility of the latter. The application of various gas detectors for charge identifica- tion is reviewed by Assmann et al. [ 121. The time of flight arrangement generally employs a microchannel plate (MCP) for the timing signal and hence is not very efficient for detection of light elements which have lower efficiency for secondary electron production [ 131. The detector tele- scope arrangement has the disadvantage that the total energy is not directly available and the signals from the two detectors have to be added with proper calibration to obtain the energy spectrum required for the depth profile. The aim of the present work is the design of a BCS detector for studying light and medium heavy elements using the ERDA technique. The detector will be used to simultaneously identify different recoils from the con- stituents of the sample and to obtain their depth profile. 2. Design and fabrication Bragg curve spectroscopy detectors [14-161 are being used widely for identification of charge in heavy ion reactions because of intrinsically high charge resolution, almost independent of energy. As an energetic ion beam passes through a target it loses energy along the path. The specific energy loss along its path is represented by d E/d X. The maximum of this specific energy loss, called Bragg peak energy is found to be directly proportional to the nuclear charge Z of the projectile. Hence the Bragg peak signal can be utilised to identify the Z of the projec- tile. A BCS detector is essentially a parallel plate ioniza- tion chamber where the electric field is parallel to the ion path rather than perpendicular as in conventional ion chambers. The anode signal from the detector is analyzed with two pulse shaping times. The pulse integrated over a