Authors:R. Wainerdi, R. Zeisler, and E. Schweikert
Capabilities of 14 MeV neutron activation analysis with a high output generator are evaluated and found to be comparable with
conventional activation analysis regarding sensitivity and precision; additional elements are instrumentally accessible at
trace levels. Nuclear reactions featuring higher selectivity are listed and their sensitivity is compared to the present state
of 14 MeV activation. Quasi-promt activation (T<1 sec) expands the scope of the technique to rapid nondestructive assays of
trace species in bulk samples.
Nuclear Analytical Chemistry at Texas A&M University is based in large part on the facilities of the Center for Chemical Characterization and Analysis and the Nuclear Science Center. This paper describes the capabilities of these two centers for instrumental and fast neutron activation analysis, neutron depth profiling, prompt gamma activation analysis, neutron radiography and the unique features of the large volume irradiation cell and reactor pulsing operation.
Both7Li and10B induced radioactivation were applied to trace determination of hydrogen via the1H(7Li,n)7Be and1H(10B, )7Be reactions. In both cases, boron and magnesium present nuclear interferences, but their extent does not exceed 0.5%. At the bombarding energies used, 21 MeV7Li++ and 27 MeV10B++ the detection limits are respectively 2 and 0.5 ppm for an iron matrix irradiated for two hours. Due to the recoil of7Be, the samples were carefully prepared to avoid superficial hydrogen contamination. A series of samples which hydrogen content ranges from 15 to 120 ppm was examined, and the results obtained with the two beams were compared.
10B induced radioactivation was used for the trace determination of hydrogen via the1H(10B )7Be reaction. At 27 MeV10B++, only boron and magnesium present small nuclear interferences. An activation curve has been established by bombarding stacks of thin mylar foils. The comparison of this curve with the excitation function for the forward reaction, namely10B(p, )7Be, shows that the recoil range from superficial hydrogen atoms is small. Hydrogen has been determined in titanium and lead bronze at the 100 ppm level. Studies of 21 potential interfering elements suggest that10B activation might be suitable for the trace determination of lithium [6Li(10b,n)15O and7Li(10B, 2n)15O] and oxygen [18O(10B,)24Na].
9Be induced radioactivation was used to study the trace determination of 19 elements at 3 different ion beam energies (Elab=14, 32 and 63 MeV9Be2+). Nine nuclear reactions, yielding radionuclides with half-lives longer than 2.5 m, present potential analytical features. Beside the very sensitive detection of B and N, the multielemental determination of Na, Si, Ca, Sc, and Zn is possible with a9Be ion beam of appropriate incident energy. Nuclear interferences have also been investigated and quantified.
Authors:S. Kormali, W. James, J. Poland, and E. Schweikert
The application of charged particle activation analysis to the determination of phosphorus in a variety of sample materials is discussed. The activity produced via the31P(, n)34mCl reaction is quantitated either nondestructively or using postirradiation radiochemical separations depending on the characteristics of the sample matrices. Corrections which are necessary for the determination of phosphorus in pure tantalum metal due to spectral interferences are discussed.
Authors:J. Welsh, W. James, E. Schweikert, and H. McWhinney
This paper describes first the application of neutron depth profiling (NDP) for measuring the distribution of6Li in LiAlO2 ceramics. Using a surface barrier detector for detecting3H produced in6Li(n, )3H,6Li was profiled to a depth of 14 m in the ceramics. Secondly, a new methodology is presented for NDP with enhanced capabilities based on measuring the energy of recoiling nuclei from (n, p) and (n, ) reactions by time-of-flight mass spectrometry. The scope of recoil nucleus time-of-flight mass spectrometry (RN-TOF-MS) includes profiling of10B,14N,17O,33S,35Cl,40K. Probe depths may be of a few tens nanometers. RN-TOF-MS complements and refines NDP based on charged particle (p or ) spectrometry.
Authors:A. Sanni, N. Roché, H. Dowell, E. Schweikert, and T. Ramsey
Carbon and oxygen impurities in silicon have been determined by 7.00 MeV3He activation analysis. The detection limits obtained for interference-free conditions are 0.1 ppb (wt) for carbon and 1.0 ppb (wt) for oxygen in silicon.
Authors:J. Poland, S. Kormali, W. James, and E. Schweikert
The feasibility of charged particle activation analysis for phosphorus measurements was evaluated. Several nuclear reactions were studied with respect to pertinent activation data, thick target yields for calibration, relative excitation functions, and quantitative importances of interferences. Determination of phosphorus by the reaction31P(,n)34mCl was determined to be most advantagous with sensitivity competitive with other techniques.
Authors:E. Schweikert, J. McGinley, G. Francis, and D. Swindle
On décrit l'application de l'analyse par activation aux particules chargées (AAPC) avec mesure après irradiation à la détection
de traces d'oxygène, de bore et de lithium. On utilise l'activation aux protens, aux alpha et aux3He pour le dosage non-destructif de l'oxygene dans le silicium. Les limites de détection expérimentale sont respectivement
de 0,06 ppm, 0,05 ppm et 5 ppb. L'activation aux3He, couplée à une séparation radiochimique après irradiation, a été employée pour les analyses de l'oxygène dans le germanium
avec une limite de détection de 10 ppb. De nouvelles techniques ont été développées pour le dosage du bore et du lithium,
basées sur la mesure du8Li (T: 850 msec) et de12B (T: 20 msec), respectivement et utilisant une technique de mesure β en coïncidence avec deux scintillateurs minces de plastique.
Les possibilités de cette méthode presque “prompte” sont illustrées avec des résultats concernant le silicium, le germanium
et des échantillons de verre.