Determination of size and distribution of second phases using nuclear microscopy
- PDF / 1,168,598 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 104 Downloads / 186 Views
L. T. Romanoa) and C. J. Salter Materials Department, Parks Road, Oxford University, Oxford OX1 3RJ, United Kingdom
G. W. Grime and F. Watt Nuclear Physics Laboratory, Keble Road, Oxford University, Oxford OX1 3RH, United Kingdom (Received 26 February 1992; accepted 3 June 1992)
Nuclear microscopy combines a range of MeV light ion beam analytical techniques such as Proton Induced X-ray Emission (PIXE), Rutherford Backscattering Spectrometry (RBS), and Scanning Transmission Ion Microscopy (STIM). One of the main advantages of using MeV light ion beams for materials characterization is the large analytical volume due to their high penetration depth. This paper shows how nuclear microscopy is used to determine the size and distribution of Pb precipitates in a 40 /mm thick alloy sample with a nominal composition of A l - 5 wt. % Pb.
I. INTRODUCTION Nuclear microscopy is an imaging and analysis technique that uses a focused MeV ion beam, typically protons or a particles, to generate a range of analytical signals from the sample by interaction with the sample electrons and nuclei. Electron microscopy by comparison relies mainly on the interactions with the sample electrons. Since the range of 3 MeV protons in Al is 82 /mm, and only about 2 /mm for 15 keV electrons, the sample composition and distribution is thus analyzed through a considerably greater depth with nuclear microscopy than with bulk electron techniques, such as electron microprobe analysis (EPMA). The incident MeV ion beam can generate x-rays (PIXE)1 to determine the sample composition. Since MeV ions generate less bremsstrahlung radiation than keV electrons because of their greater mass, PIXE is a much more sensitive technique for measuring trace element distributions than bulk electron techniques. The incident ion beam can also interact with the sample nuclei and backscatter elastically out of the sample, in an analogous manner to electron backscattering. The measurement of the recoiling incident ion energy allows the sample stoichiometry and depth distribution to be measured to within a few % accuracy, which is the basis of RBS. 2 If the sample is of the order of 50 /mm thick, then virtually all the incident MeV ions are transmitted. The measurement of the transmitted beam energy allows variation in the sample areal density to be mapped out, which is the basis of STIM.3 STIM is used typically to image heavy
''Current address: XEROX Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304. J. Mater. Res., Vol. 7, No. 9, Sep 1992
http://journals.cambridge.org
Downloaded: 18 Mar 2015
elements in light element matrices commonly found in biological specimens.4 Some types of MeV light ions can interact inelastically with light element sample nuclei, causing a change in the sample nucleus and reaction products to be emitted. The measurement of the emitted reaction products such as neutrons, y rays, high energy protons, and a particles forms the basis of Nuclear Reaction Analysis (NRA),5 which is used to detect and depth profile the li
Data Loading...
