Development of high flux thermal neutron generator for neutron activation analysis
Introduction
The deuteron–deuteron fusion reaction (D–D) has been a utilized extensively in recent years in various Adelphi Technology neutron generators [17], [19], [4] to produce neutrons without using radioactive material. Without the need for tritium, the design and maintenance of D–D generators are much more simple and flexible, ultimately driving down the cost of very high flux neutron generators. The DD110MB manufactured by Adelphi Technology creates high intensity thermal neutron flux to irradiate samples for neutron-activation analysis (NAA).
The neutron generator consists of four radial deuteron ion sources surrounding a central target cavity. Deuteron ions are generated by electron cyclotron resonance (ECR) [2], [6], [12] which are then accelerated to 120 keV and bombard a titanium target. Fast neutrons (2.45 MeV) are produced via the D–D reaction (Eq. (1)) at the rectangular cavity walls and then thermalized immediately by an integrated polyethylene moderator on the back of the target. To further enhance the thermal neutron flux at the sample area, the target cavity is surrounded by a neutron reflector. The moderator is designed such that the thermal flux peaks at the center of the target cavity where the radiated sample is located. A sample rabbit transfer system was implemented to minimize the time between irradiation and counting.
The DD110MB (Fig. 1) pushes the boundary of achievable neutron fluxes from compact D–D neutron generators. Thermal neutron flux on the order of 0.5–1·108 n/cm2/s with less than 12 kW of beam power have not been available on compact D–D fusion based neutron generator systems. DD110MB provides compact and simple solution with minimal regulatory burden for NAA applications that previous required reactor-based or traditional accelerator-based systems.
Section snippets
Generator design
The DD110MB is considered a low energy beam transport (LEBT) system because of the low energy ion acceleration needed to achieve neutron production, the following considerations are critical in order to design a neutron generator that has stable operation and high neutron production efficiency [2], [11], [14], [8], [9], [18]:
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Ion beam envelope steers clear of contact with the puller electrode.
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Electric field gradients remain below design limit of 5 MV/m on the extraction gap [11].
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Power density and
Characteristic curves
The characteristic curves are a set of curves that relates the current and voltage at various neutron generator operating parameters. These curves are invaluable for determining the operable range of the neutron generator. Normally, the ion current stays relatively constant as the voltage is decreased. When the voltage is low enough such that the ion beam begins to make contact with the puller electrode, the current-voltage relationship begins to exhibit a sharp inverse proportionality. As seen
High voltage arcing
One of the most challenging issue for compact, high flux neutron generators is the problem of high voltage arcing. Such arcing behavior not only reduces the average neutron flux by decreasing the uptime, but also causes instability and potential damage to the high voltage insulation. The most common form of arcing for compact generators is surface flashover on the insulator surface between the high voltage electrode and ground. The flashover strength across this insulator-bridged gap can be up
References (19)
- J.F. Briesmeister, MCNP-A general Monte Carlo code for neutron and photon transport, LA-7396-M...
The Physics and Technology of Ion Sources
(2004)- et al.
Model of positive ion sources for neutral beam injection
J. Appl. Phys.
(1983) - M.K. Fuller, M.A. Piestrup, C.K. Gary, J.L. Harris, G. Jones, J.H. Vainionpaa, D.L. Williams, J.T. Cremer, Adam Bell,...
- Gamma Ray Spectroscopy Using NaI(Tl), Ortec Application Note, AN34,...
ECR Ion sources and ECR Plasmas
(1996)- S. Hahto, Development of negative ion sources for accelerator, fusion and semiconductor manufacturing applications,...
Charged Particle Beams
(1990)Principles of Charged Particle Acceleration
(1999)
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