New PTB thermal neutron calibration facility: first results

Area of Science:

• Nuclear physics
• Metrology
• Radiation detection

Background:

• Accurate calibration of radiation detection instruments is crucial for reliable measurements.
• Existing facilities may have limitations in terms of neutron energy spectrum or intensity.
• The Physikalisch-Technische Bundesanstalt (PTB) requires a dedicated facility for thermal neutron calibration.

Purpose of the Study:

• To establish and characterize a new thermal neutron calibration facility at PTB.
• To provide a well-defined and stable neutron field for instrument calibration.
• To assess the suitability of the facility for routine calibration tasks.

Main Methods:

• Utilized a moderator assembly with 16 (241)Am-Be radionuclide sources.
• Characterized the neutron field using Monte Carlo simulations.
• Performed measurements with Bonner spheres and gold foil activation.
• Determined the neutron fluence rate and energy spectrum at a reference position.

Main Results:

• The neutron field is highly thermalized, with 99% thermal neutrons by fluence.
• The field exhibits homogeneity within a 20 cm x 20 cm area.
• The ambient dose equivalent rate at the reference position is 3 µSv h⁻¹.
• Initial characterization confirms the facility's potential for calibration.

Conclusions:

• The newly established thermal neutron calibration facility at PTB is operational.
• The characterized neutron field meets the requirements for thermal neutron calibration.
• Further studies may focus on extending the range of calibration capabilities.