Characterization of (252Cf-ZrH2) Monte Carlo model for detection of nitrogen and chlorine by thermal neutron-capture PGNAA

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) Cf-252-based Prompt Gamma Neutron Activation Analysis (PGNAA) assembly. The thickness of moderators was optimized against thermal neutron flux (phi(th)) as well as the ratio of (thermal/fast) neutron flux (phi(th)/phi(fast)), calculated at the sample cavity. The capabilities of moderating 252Cf source neutrons and minimizing the gamma-background due to Cf-2525 fission gamma-rays, H-1(n(th),gamma)H-2 gamma-rays originates in the moderator as well as other (n(th),gamma) capture reactions from surroundings were investigated. The optimal selected moderator with sufficient (phi(th)) at the sample cavity and minimum gamma-contamination was selected as ZrH2 for use in a(252)Cf-PGNAA for detection of nitrogen and chlorine in bulk sample simulants of melamine (C3H6N6) and sodium chloride (NaCl). The prompt gamma-rays spectra were analyzed to detect the 10.83 MeV and 6.11 MeV prompt gamma-peaks released by N-14(n(th),gamma)N-15 and Cl-35(n(th),gamma)Cl-36, respectively. The results showed that the (Cf-252-ZrH2)-PGNAA model has positively identified nitrogen with net counts (1.25 x 10(5) n.cm(-2) .s(-1)) and Chlorine with net counts of (4.19 x 10(6) 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.

Automated summary

Monte Carlo calculations were used to investigate the potential of zirconium hydride as a moderator in Cf-252-based PGNAA, with optimized thickness for thermal neutron flux and minimizing gamma contamination. ZrH2 was selected as the optimal moderator for detecting nitrogen and chlorine in large sample simulants, achieving low minimum detectable concentrations.