Radionuclide neutron source characterization techniques

Abstract

Radionuclide neutron sources are of fundamental importance to neutron metrology. They are the reference standards which allow quantities such as neutron fluence and neutron dose equivalent to be realized in laboratories around the world. In order to do this it is essential that the sources themselves are well characterized in terms of neutron emission rate, emission anisotropy and spectral fluence ΦE of emitted neutrons. A summary of the types of radionuclide neutron sources is given followed by detailed descriptions of the primary standardization techniques in use today, focusing on the manganese bath technique. Methods for determining the anisotropy of emission are discussed, followed by a brief description of the spectral fluence of the different source types. Finally, an overview of international comparison exercises in this area is included.

Assessment of the neutron emission anisotropy factor of a sealed AmBe source by means of measurements and Monte Carlo simulations

“…The aforementioned values of the background and scattering signals are well known by the operators of the metrology laboratory where the measurements were performed. Thus knowing that the emission rate of the source is R¼ 2.20 Â 10 6 neutrons s À 1 , r 0 ¼ 4.5 cm [7] the value of A Á ε int is found to be 3.24 cm 2 , in agreement with values provided in literature [1]. As the acceptance area of the detector is almost circular with a radius of 2 cm, the angular acceptance at 150 cm from the source is 0.81.…”

“…Calibration can be done by means of a primary standard, often relying on the Manganese Sulfate (MnSO 4 ) bath technique [1,2,3] or in a more rapid (although with higher uncertainties) way by a comparison with a calibrated source using a proper neutron detector, such as a long counter (LC).…”

Characterization of neutron fields from bare and heavy water moderated 252Cf spontaneous fission source using Bonner Sphere Spectrometer

“…The anisotropy factor for this particular source was not determined experimentally. However, there is a body of literature (Roberts et al, 2011;ISO, 2001;Eisenhauer and Hunt, 1988;Hawkes et al, 2007;Tsujimura et al, 2007) suggesting anisotropy factor value of 1.02 for a 252 Cf source of dimensions similar to dimensions of the source used in this work. Therefore, this value was adopted.…”

“…5 (a)), multiplied with the expected neutron fluence rate (calculated at the measured distances). The calculation of direct neutron fluence rates were performed using the following equation (Roberts et al, 2011):…”

“…The anisotropy factor is estimated by a multiple fluence measurements of the source, around its cylindrical axis in the horizontal plane, using a long counter (Roberts et al, 2011). These measurements are usually performed at the low scattering, primary standard reference laboratories, such as NPL.…”