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A Comparative Study to Optimize the In-Vivo Neutron Activation Analysis System

S Tabbassum1*, H Nie2 , (1) PURDUE UNIVERSITY, W Lafayette, IN, (2) Purdue Univ, West Lafayette, IN


(Wednesday, 7/17/2019) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 6

Purpose: To develop a highly sensitive in-vivo neutron activation analysis system with a neutron fusion source, to quantify trace elements in human.

Methods: In this work, we have developed an irradiation assembly for in-vivo measurement of trace elements in the human hand using FLUKA, and compare the results with similar model in Monte Carlo N-Particle (MCNP). Design of irradiation assembly include: 3.5 cm high density polyethylene moderator, neutron multiplier made of Beryllium, a fast neutron filter based on single crystal Sapphire (Al2O3) and reflectors. In order to assess the sensitivity of in-vivo system for thermal neutron activation analysis, we have maximized thermal neutron flux inside the irradiation cave (i.e. where the sample is placed), minimized the fast neutrons flux to reduce the dose, without substantial decrease in total flux. The thermal neutron flux and thermal neutron spectrum inside the irradiation cave and dose was calculated.

Results: For an irradiation cave of dimension 20x10x20 cm, thermal neutron yield is maximized to 6.71x10^5 n /s for DD fast neutron yield of 1X10^9 n/s. Fast neutron yield inside the irradiation cave is 3.8X10^4 n/s. Comparison between MCNP and FLUKA shows a good general agreement. Thermal neutron flux (below 0.1ev) inside radiation cave is 3 times more than fast neutron (above 0.1ev). However, FLUKA shows higher total of flux 9x10^5 n/s inside the cave as compared with MCNP of 6.9x10^5 n/s, mainly due to different physics models. Radiation dose rate inside the irradiation cave is 3.3mSv/hr. from the neutrons.

Conclusion: Optimized assembly for the in-vivo neutron activation analysis showed a high thermal flux resulting in higher sensitivity and low fast neutron flux. Results from both FLUKA and MCNP validates the feasibility of designed irradiation assembly, however differences between two simulation codes require experimental validation to benchmark a reference system.


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