Analysis Of Underwater Neutron Activation By Monte Carlo

A preliminary research shows that the ocean contains a lot of mineral resources A new exploration method, underwater neutron activation analysis, may develop the seabed metal mineral resources. The topic of this paper was mainly comes from “863 Project” resources and environment technology subject” High-Precision Spectrum Detection Instruments Development”, Project Number: 2012AA061803 and the National Natural Science Foundation program of China named application of radiation field in geology on the surface of earth and moon(No.41374136). The element analyzer of underwater neutron activation with inserted and dragged model is the main part of the paper, using MCNP5 software to sludge the object at 4000 m under the sea. Through changing the internal parameters of the instrument by simulation of Monte Carlo method, the detector count in two different models have regularity with the porosity and distance from source. Furthermore, The relationship between γ ray induced by Na, Al, Si, Mn after activation and count sensitivity from porosity is discussed. Lastly, the entire inserted model inducing particular γ-ray is also a task in the paper.The main research in the paper is as follows:(1) The current situation of controllable neutron tube is investigated and the excitation source which is suitable to underwater neutron activation elemental analyzer is selected as an ideal point in the process of MC simulation.(2)Based on the research of domestic and foreign scholars, a overall structure of underwater neutron activation elemental analyzer is established by using MC software, using NaI(Tl) as detector. The peripheral of Na I coated with gadolinium by 0.5cm for preventing thermal neutrons into the detector, playing a role to protect it. There are three-layer composite shielding structure between the source and the detector. The first layer aims at W and alloy of W and Ni. The second layer is paraffin and 20% of boron-polyethylene material. The third layer is Pb which is usually used to shielded γ-ray. The purpose of the three structure is to obtain the best shielding thickness.(3) The regulation between the total induced γ-ray and the distance and porosity in inserted and dragged model is simulated by MC. The particular γ-ray from Na, Al,Si, Mn, detected by the detector varies with the sensitivity of porosity is also analyzed.(4) The sludge below the waterline 4000 m contains 65 kinds of elements. Twelve kinds of 65 elements are selected due to the high percentage. The particular γ-ray of the 12 elements are simulated by MC. On this basis, the sludge with aqueous porosity of 35% is activated called neutron activation by the inserted model with 54 cm from the source and produces the particular γ-ray spectrum.