Performance tests of external moderators of a PGNAA setup

Area of Science:

• Nuclear Physics
• Analytical Chemistry
• Materials Science

Background:

• Accelerator-based prompt gamma-ray neutron activation analysis (PGNAA) is utilized for material analysis.
• External cylindrical moderators are crucial components in PGNAA setups, influencing neutron yield and analytical performance.
• Optimizing moderator geometry is essential for enhancing PGNAA efficiency, particularly for cement sample analysis.

Purpose of the Study:

• To evaluate the performance of two distinct cylindrical moderator geometries for an accelerator-based PGNAA system.
• To investigate the impact of moderator geometry on thermal neutron yield and prompt gamma-ray output for cement analysis.
• To compare the effectiveness of small-sample and large-sample moderator designs in terms of neutron and gamma-ray yields.

Main Methods:

• Performance testing involved measuring thermal neutron and prompt gamma-ray yields using two different cylindrical moderator assemblies.
• Neutron yield measurements were conducted at the King Fahd University of Petroleum and Minerals 350 keV pulsed beam accelerator.
• Nuclear track detectors were employed to measure neutron yields as a function of moderator thickness and sample length, utilizing a 2.8 MeV neutron source produced via the D(d,n) reaction.

Main Results:

• Neutron yield measurements indicated that the large sample moderator produced a lower yield of thermal neutrons compared to the small sample moderator.
• These experimental findings were consistent with Monte Carlo simulations for both thermal and fast neutron yields.
• Despite a reduced thermal neutron yield, the large sample moderator demonstrated a higher prompt gamma-ray yield from a Portland cement sample.

Conclusions:

• The geometry of the cylindrical moderator significantly influences both thermal neutron and prompt gamma-ray yields in PGNAA.
• For cement analysis, the large sample moderator, while yielding fewer thermal neutrons, offers an advantage due to its higher prompt gamma-ray output.
• The study validates the use of Monte Carlo simulations for predicting moderator performance and guides the selection of optimal moderator designs for specific PGNAA applications.