Simultaneous Analysis of Light Elements Using Prompt Nuclear Reaction Gamma Rays Robert B. Boulton’ and George T. Ewan* Department of Physics, Stirllng Hail, Queen’s Unlversity, Kingston, Ontario, Canada K7L 3N6
A method Is described for the slmultaneous quantltatlve analysls of the llght elements Ilthlum, boron, fluorine, sodlum, magneslum, and alumlnum, uslng prompt nuclear-reaction y rays emitted when a sample Is bombarded wlth low energy protons. Relatlve peak areas In a y-ray spectrum are measured, and elemental concentrations determined uslng y-ray data obtalned from standards. Factors affectlng the accuracy of analysis are considered; the effect of stopplng-power is dlscussed; on-llne checks for systematlc errors caused by target lnstablllty or target nonunlformlty are described. A range of dlff erent materlals has been analyzed with a mlnlmum of sample preparatlon and selected analytlcal results are presented.
In recent years, prompt nuclear-reaction y rays have been used for elemental analysis in a variety of materials. Examples include nitrogen (1) and carbon (2) in biological materials, carbon in steel (3),oxygen in uranium dioxide ( 4 ) , fluorine in dental enamel (5),aluminum in stainless steel (6),chlorine in aluminum (7), oxygen and nitrogen in gases (8),fluorine, sodium, and aluminum in archaeological samples (9) and carbon, nitrogen, oxygen, aluminum, silicon, sulfur, calcium, and iron in dust samples (10). These applications of nuclear-reaction y-ray analysis have generally been to particular problems, and direct application to other types of sample containing different bulk elements is often not possible. In many cases, a single element was of interest, and no attempt was made to determine several elements simultaneously. In this paper we describe a method for the simultaneous analysis of several light elements in a wide range of materials using charged particles from a small Van de Graaff accelerator and a high-resolution lithium-drifted germanium detector. Protons of 1.8 MeV were selected to allow the simultaneous analysis of lithium, boron, fluorine, sodium, magnesium, and aluminum. Several types of geological material, lithiummagnesium alloys, blood serum, and leaf material have been analyzed by the same experimental procedure, and selected results me presented in this paper. The emphasis of this work has been on the accuracy of the method. Checks for systematic error caused by target instability or target inhomogeneity are described, and the effect of stopping power on the accuracy of results is discussed. Fluorescence x rays produced by the proton beam were detected simultaneously in many cases by a lithium-drifted silicon detector. These fluorescence x rays are useful for the analysis of heavier elements. In this paper we describe the nuclear-reaction y-ray method, and the use of proton-induced fluorescence x rays will not be discussed further.
produced by nuclear reactions in the different elements of the target were detected in a high-resolution lithium-drifted germanium detector. Data were collected and analyzed using a PDP-9 computer. Relative peak areas in a y-ray spectrum were measured and the relative concentration of different elements calculated by using data from standards, and the simple relation
where Yi is the detected yield (peak area) of y ray i and Ni is the atomic density of the element producing that y ray. This equation and the stopping-power approximation involved are discussed in the following sections. Tests were made on the stability of each target under proton bombardment. The y-ray data were used to test for systematic errors caused by nonuniformities in the target, and these tests are described in later sections. The 60 cm3Ge(Li) detector had a resolution of 2.6 keV (at 1332 keV) and an efficiency of 14%. Low energy (
