Characterization of the graphite pile as a source of thermal neutrons

• Published in: Radiation physics and chemistry (Oxford, England : 1993) Vol. 116; pp. 65 - 68
• Main Authors: Vykydal, Zdenek, Králík, Miloslav, Jančář, Aleš, Kopecký, Zdeněk, Dressler, Jan, Veškrna, Martin
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2015
• Subjects: 3He proportional detectors; Cadmium ratio; Calibration; Channels; Detectors; Fluence; Foils; Graphite pile; Piles; Placement; Thermal neutrons; Graphite pile; Thermal neutrons; Cadmium ratio; 3He proportional detectors
• ISSN: 0969-806X; 1879-0895
• DOI: 10.1016/j.radphyschem.2015.01.028

A new graphite pile designed to serve as a standard source of thermal neutrons has been built at the Czech Metrology Institute. Actual dimensions of the pile are 1.95m (W)×1.95m (L)×2.0m (H). At its center, there is a measurement channel whose dimensions are 0.4m×0.4m×1.25m (depth). The channel is equipped with a calibration bench, which allows reproducible placement of the tested/calibrated device. At a distance of 80cm from the channel axis, six holes are symmetrically located allowing the placement of radionuclide neutron sources of Pu–Be and/or Am–Be type. Spatial distribution of thermal neutron fluence in the cavity was calculated in detail with the MCNP neutron transport code. Experimentally, it was measured with two active detectors: a small 3He proportional detector by the French company LMT, type 0.5NH 1/1KF, and a silicon pixel detector Timepix with 10B converter foil. The relative values of thermal neutron fluence rate obtained with active detectors were converted to absolute ones using thermal neutron fluence rates measured by means of gold foil activation. The quality of thermal neutron field was characterized by the cadmium ratio. •We built a graphite pile as a source of thermal neutrons.•We measure the thermal neutron fluence rate with different detectors.•We model and verify the thermal neutron field homogeneity.