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Characterisation of a high-resolution diamond detector in neutron reference fields

04.01.2010

A commercially available detector made of a synthetic single-crystal diamond was investigated using PTB’s monoenergetic neutron reference fields in the energy range from 2.5 MeV to 14 MeV. This detector works according to the known principle of semi-conducting detectors, e.g. silicon detectors. For applications in neutron fields, diamond has the advantage of being a semiconductor material which is resistent against radiation-induced damage of the crystal. For high-energy neutrons having an energy of more than approx. 6 MeV, neutrons generate in diamond a measuring signal via the 12C(n,α)9Be reaction, which directly reflects the energy distribution of the neutron field. This is represented in the figure, in which measured pulse height distributions and calculated neutron energy distributions are superimposed for different detector positions relative to the ion beam of the accelerator.

Figure : Pulse height spectrum for neutrons from the T(d,n)4He reaction for different angles of the detector relative to the ion beam of the accelerator. The measurements performed with the diamond detector (colour histograms, lower x-coordinate) are in excellent agreement with the calculated neutron energy distributions (black histograms, upper x-coordinate, code: TARGET). 

Due to its high energy resolution, this detector is well suited for determining the properties of neutron fields and the influence of target properties on the neutron spectrum directly, without using time-of-flight methods. Since the charge collection times lie in the range of a few ns, this detector is, in principle, also well suited as a neutron spectrometer with high energy resolution at high counting rates in high-intensity neutron fields such as those which are encountered in the field of fusion research, e.g. at the ITER experiment which is currently under construction. For this purpose, it is, however, necessary to investigate in more detail the response function which is given by a superposition of signals from (n,n’) and (n,α) reactions, and to model for different neutron energies.