The advantages of an underground laboratory for the measurement of activated pure materials are demonstrated. Background spectra and experimentally determined detection limits for the INAA of semiconductor silicon are compared with literature data and interference-free detection limits are calculated.
The energy-dependent range of charged particles in activation analysis according to the reaction12C(d,n)13N permits the method to be applied to carbon determination in model epitaxial layers of sufficient thickness. We investigated
100 μm epitaxial layers of the n-type and undoped 50 μ layers as to p− Czochralski substrates. Deuterons were slowed down with Cu and Ta foils having a limiting energy of 13.5 MeV, to 4.2 MeV
and 2.9 MeV, respectively. In the resulting activation depths of 52 and 102 μm, the sensitivity of the method, which is 3·1014 at ·cm−3C at Ed=10 MeV in silicon, is reduced to 25% and 10%, respectively. An optimal flux of 0.9 μA·cm−2 was maintained. After irradiation, 20 or 10 μm were etched off. The sample was inductively fused at 1500 K in a Pb3O4/B2O3 mixture.13N was passed with He as carrier gas into an absorption vessel kept at 77 K, and its activity was measured in γ, γ-coincidence.
The installation of a multi-sample beta-gamma coincidence spectrometer in an underground laboratory with a rock covering of 47 m yielded further background reduction by factors of between 10 (at 2 MeV) and about 4 (below 1 MeV). In silicon samples Fe can be measured by neutron activation analysis with a detection limit of 40 pg.
Authors:Ursula Niese, W. Smulek, M. Borkowski, and W. Helbig
Low level alpha-spectrometry was applied for the determination of actinides separated from environmental samples. Interference free detection limits of 1.5–2.0 E-5 Bq at a counting interval of 150,000 sec and detection limits of the investigated samples of 0.05–0.005 Bq kg–1 were determined.
Authors:M. Böttger, D. Birnstein, W. Helbig, and S. Niese
A sensitive method of carbon determination in silicon by activation with deuterons and3He particles followed by chemical separation of the measured nuclides13N and11C has been developed. Aside from the etch removal after irradiation, it is essential for a low detection limit to avoid too
much thermal exposure of the target surface during the irradiation process, or else microflaw formation and diffusion on the
surface have to be anticipated. The ion current must have an optimal rather than a maximum value.
Authors:S. Niese, G. Loos, B. Gleisberg, and W. Helbig
Trace elements have been determined by instrumental and radiochemical NAA and the cosmogenic radioactivity of22Na and26Al using gamma spectrometry in the smallsize L-chondrite Hohenlangenbeck. A low condensation temperature is indicated by relatively high contents of Rb and Cs. The low activity ratio of22Na/26Al is due to a relatively low particle flux in the orbit during the last four years.
Authors:M. Böttger, S. Niese, D. Birnstein, and W. Helbig
NAA and CPAA are the most sensitive analytical tools for the determination of residual impurities in semiconductor silicon. Extremely small detection limits are found by measuring the activity in an underground laboratory. The accuracy and reliability of the methods were checked by several comparisons: interlaboratory comparison on NAA, another CPAA with IR-spectrometry as well as comparison of NAA-results, obtained instrumentally and by chemical separation.