Compact DD generator-based neutron activation analysis (NAA) system to determine fluorine in human bonein vivo: a feasibility study

Abstract

The subject of whether fluorine (F) is detrimental to human health has been controversial for many years. Much of the discussion focuses on the known benefits and detriments to dental care and problems that F causes in bone structure at high doses. It is therefore advantageous to have the means to monitor F concentrations in the human body as a method to directly assess exposure. F accumulates in the skeleton making bone a useful biomarker to assess long term cumulative exposure to F. This study presents work in the development of a non-invasive method for the monitoring of F in human bone. The work was based on the technique of in vivo neutron activation analysis (IVNAA). A compact deuterium-deuterium (DD) generator was used to produce neutrons. A moderator/reflector/shielding assembly was designed and built for human hand irradiation. The gamma rays emitted through the (19)F(n,γ)(20)F reaction were measured using a HPGe detector. This study was undertaken to (i) find the feasibility of using DD system to determine F in human bone, (ii) estimate the F minimum detection limit (MDL), and (iii) optimize the system using the Monte Carlo N-Particle eXtended (MCNPX) code in order to improve the MDL of the system. The F MDL was found to be 0.54 g experimentally with a neutron flux of 7 × 10(8) n s(-1) and an optimized irradiation, decay, and measurement time scheme. The numbers of F counts from the experiment were found to be close to the (MCNPX) simulation results with the same irradiation and detection parameters. The equivalent dose to the irradiated hand and the effective dose to the whole body were found to be 0.9 mSv and 0.33 μSv, respectively. Based on these results, it is feasible to develop a compact DD generator based IVNAA system to measure bone F in a population with moderate to high F exposure.

The prototyping of a high-resolution neutron activation analysis system – based on a Pelletron accelerator and fast pneumatic sample-transport

“…NAA is considered non-destructive and is sensitive to at least two thirds of stable nuclei, with detection limits as low as several parts-per-trillion in some cases [7,8]. Traditionally, NAA relies on samples being irradiated in a fission-reactor, but both neutron generators [9,10] and isotopic neutron sources [11,12] can also be used. The high neutron fluxes within reactor cores (on the order of 10 13 n/cm 2 /s) result in excellent detection limits; but, when measurement is undertaken in a separate location, the sample transport time often means that activation products with half-lives of less than a few hours decay away before measurement.…”

Elemental analysis in living human subjects using biomedical devices

“…Timing was the single largest factor in the variation of uncertainty between measurements for different people (Mostafaei et al 2013(Mostafaei et al , 2015a In our opinion, research should be conducted into the use of 2 H, 2 H as a neutron source to allow a transportable system that could study people at both high and low fluoride exposure sites. The main research question is whether such a source could deliver the sufficient number of neutrons in a short time (~10 s) as required by the short half-life of 20 F (Mostafaei et al 2015b).…”

The study ofin vivoquantification of aluminum (Al) in human bone with a compact DD generator-based neutron activation analysis (NAA) system

“…The neutrons emerge from the generator essentially mono-energetically, with 2.45 MeV of kinetic energy. The characteristics of the DD neutron generator are described in our previous studies (Liu et al 2013, 2014, Mostafaei et al 2015a.…”

“…Eight centimeters of graphite was chosen and simulated as a reflector to scatter neutrons back towards the cavity. For shielding, 15 cm of high density polyethylene with 5 cm of borated polyethylene was selected and simulated (Liu et al 2014, Mostafaei et al 2015a. The cross section of the irradiation cavity is shown in figure 2.…”