2018 Impact factor 2.481
Hadrons and Nuclei
Eur. Phys. J. A 17, 285-296 (2003)
DOI: 10.1140/epja/i2002-10152-3

Precise measurement of the $\chem{^{27}Al}(n,2n)\chem{^{26g}Al}$ excitation function near threshold and its relevance for fusion-plasma technology

A. Wallner1, S.V. Chuvaev2, A.A. Filatenkov2, Y. Ikeda3, W. Kutschera1, G. Mertens4, A. Priller1, W. Rochow4, P. Steier1 and H. Vonach1

1  Institut für Isotopenforschung und Kernphysik, University of Vienna, Währinger Str. 17, A-1090 Wien, Austria
2  V.G. Khlopin Radium Institute, 2nd Murinski ave. 28, 194021 St. Petersburg, Russia
3  Fusion Neutronics Laboratory (FNS), Department of Reactor Engineering, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken 319-1195, Japan
4  Physikalisches Institut, University of Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany

anton.wallner@physik.tu-muenchen.de

(Received: 26 November 2002 / Revised version: 28 February 2003 / Published online: 27 May 2003)

Abstract
A new accurate measurement of the $\chem{^{27}Al}$(n,2n) $\chem{^{26}Al}$ excitation function leading to the ground state of $\chem{^{26}Al}$ ( $t_{1 / 2} =7.1 \times 10^{5}$ years) in the near-threshold region ( $E_{\rm th} =13.55$ MeV) was performed, with the goal to achieve relative cross-sections with the highest accuracy possible using proven methods. In addition, the measurements were also designed to provide good absolute cross-section values, since absolute cross-sections are important for radioactive waste predictions in future fusion reactor materials. Samples of Al metal were irradiated with neutrons in the energy range near threshold ( $E_{\rm n} =13.5$-14.8 MeV) in Vienna and St. Petersburg, and at 14.8 MeV in Tokai-mura. In addition, irradiations with neutrons of higher energies (17 and 19 MeV) were performed in Tübingen, to obtain also cross-section values well above threshold. The amount of $\chem{^{26}Al}$ produced during the irradiations was measured via accelerator mass spectrometry (AMS). With this system, a background as low as $3 \times 10^{-15}$ for $\chem{^{26}Al}$/ $\chem{^{27}Al}$ isotope ratios was obtained, corresponding to a (n,2n) cross-section of 0.04 mb. Utilizing AMS, cross-sections with much higher precision and considerably closer to the threshold than in previous investigations were measured. A substantial improvement in the knowledge of this excitation function was obtained. Its expected strongly non-linear behaviour near threshold makes the production of $\chem{^{26}Al}$ sensitive to temperature changes in a deuterium-tritium (D-T) fusion plasma. The prerequisite for such an application as a temperature monitor, namely a very well-known shape of the excitation function, was met. A quantitative prediction of the sensitivity of this method for monitoring the temperature in a D-T fusion plasma was therefore possible.

PACS
07.75.+h - Mass spectrometers.
28.20.+v - Neutron physics.
28.52.-s - Fusion reactors.
52.70.Nc - Plasma diagnostic techniques and instrumentation: Particle measurements.

© Società Italiana di Fisica, Springer-Verlag 2003