Logo of the Physikalisch-Technische Bundesanstalt

Neutron cross sections

The time-of-flight spectrometer installed at the cyclotron allows the measurements of differential neutron scattering cross sections, neutron emission spectra, and neutron activation cross in the energy range between 2.7 MeV and 15 MeV. The neutrons are produced by means of the 15N(p,n) and the 2H(d,n) reaction. The facility has been optimized to the energy range from 6 MeV to 15 MeV, in which no mono-energetic neutrons can be produced by nuclear reactions. This energy range is relevant in particular to the design of experiments for controlled nuclear fusion, e. g., for the Opens external link in new windowITER project.

The times of flight of the scattered neutrons and, thus, their kinetic energies, are measured on a flight path of 12 m. Due to the massive collimation system, only neutrons in five different directions are detected. In order to increase the number of scattering angles, the cyclotron can be rotated on a circular rail. A suitable selection of the cyclotron position allows measurements with scattering angles between 12.5° and 160° to be performed.

The nuclear data measured on the time-of-flight spectrometer are transferred to the international Opens external link in new windowdatabases for experimental nuclear data (Opens external link in new windowEXFOR) and are taken into account in the establishment of libraries of evaluated nuclear data such as Opens external link in new windowJEFF (Joint European File for Fission and Fusion) or Opens external link in new windowENDF (Evaluated Nuclear Data File).

Left: Time-of-flight spectrum of the neutrons scattered on a lead sample. The structures on the left are generated by inelastic scattering, in the case of which the lead nucleus is left in an excited state. The high maximum on the right corresponds to the elastic scattering, in the case of which the atomic nucleus remains in the ground state.
Right: Cross section for inelastic scattering for the first excited state of the lead isotope 206Pb. The data marked by the red symbols were measured within the scope of a PhD thesis at the time-of-flight spectrometer. For the first time, the 15N(p,n) reaction was used as a neutron source.


  • D. Schmidt:
    Determination of Neutron Scattering Cross Sections with High Precision at PTB in the Energy Region 8 MeV to 14 MeV
    Nucl. Sci. Eng. 160 (2008) 349 - 362