Abstract
Monte Carlo calculations were conducted to explore the potentials of zirconium hydride (ZrH2) as possible alternative moderator for high density polyethylene (HDPE) and water (H2O) in a simple (100MBq) 252Cf-based Prompt Gamma Neutron Activation Analysis (PGNAA) assembly. The thickness of moderators was optimized against thermal neutron flux (ϕth) as well as the ratio of (thermal/fast) neutron flux (ϕth/ϕfast), calculated at the sample cavity. The capabilities of moderating 252Cf source neutrons and minimizing the γ-background due to 2525Cf fission γ-rays, 1H(nth,γ)2H γ-rays originates in the moderator as well as other (nth,γ) capture reactions from surroundings were investigated. The optimal selected moderator with sufficient (ϕth) at the sample cavity and minimum γ-contamination was selected as ZrH2 for use in a252Cf-PGNAA for detection of nitrogen and chlorine in bulk sample simulants of melamine (C3H6N6) and sodium chloride (NaCl). The prompt γ-rays spectra were analyzed to detect the 10.83 MeV and 6.11 MeV prompt γ-peaks released by 14N(nth,γ)15N and 35Cl(nth,γ)36Cl, respectively. The results showed that the (252Cf-ZrH2)-PGNAA model has positively identified nitrogen with net counts (1.25 × 105 n.cm−2.s−1) and Chlorine with net counts of (4.19 × 106 n.cm−2.s−1), achieving minimum detectable concentrations of about (350 ppm at 10.83 MeV) and (640 ppm at 6.11 MeV), respectively.
•MCNP simulations were performed to model ZrH2 as alternative moderator for C2H4 and H2O.•ZrH2 was selected due its superior γ-filtering capabilities to model (252Cf-ZrH2) PGNAA analyzer.•The (252Cf-ZrH2) model has positively identified nitrogen in melamine and chlorine in sodium chloride.•The Minimum Detectable Concentrations (MDC) were (350 ppm) for nitrogen and (640 ppm) for chlorine.•The model may operate for 20000h within the requirements of the annual dose limit (20 mSv).