Preliminary Study on Accelerator Based D-D Neutron Generator with Hydrocarbon Liquid Target Jeong-Jeung Dang, Kyoung-Jae Chung, Y. S. Hwang * Department of Nuclear Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea *yhwang@snu.ac.kr Abstract This study proposes a new concept of a beam-target type neutron generator (NG) based on deuteron-deuteron (D-D) fusion reaction. The conceptual design of the neutron generator introduces 10 MeV class accelerator to achieve high neutron yield and energy. Especially, the neutron yield on beam direction significantly increases, because not only a cross section of D-D fusion reaction steadily increases and is sustained up to 10 MeV, but also an anisotropy of the D-D fusion reaction is enhanced on the beam direction. In addition, 10 MeV beam energy allows that the D-D neutron energy reaches over 13 MeV which is similar value of deuteron-triton (D-T) fusion reaction. Furthermore, in order to increase the neutron yield, a cryogenically-cooled hydrocarbon liquid target is adopted. A proof-of-principle experiment for the liquid target was conducted in a vacuum. Advantage of D-D neutron generator with 10 MeV beam High yield and beam power efficiency High neutron energy Forward biased neutron flux Introduction FIG. 5. Forward flux and forward flux/beam power Why high yield and energy compact NG is required ? Application [1,2] - Neutron activation analysis - Neutron radiography - Nuclear data production - Material irradiation test - Transmutation - Medical isotope production Cryogenically Cooled Hydrocarbon Liquid Target Neutron Yield of Hydrocarbon Liquid Target Cryogenically cooled hydrocarbon liquid target - Self-cooling and self healing - Low energy loss rate - Cryo-cooling for reduction of vapor pressure Comparison of neutron sources Materials Deuterium concentration [#/cm3] Triple point (liquid target) Pressure [Pa] Temp. [K] TiD1.6 9.07 × 1022 - D2O (s) 6.12 × 1022 C3D8 (liq.) 4.98 × 1022 1.7 × 10-4 85.5 C2D5OD (liq.) 6.18 × 1022 4.3 × 10-4 150 Neutron sources Fission Reactor Large accelerators Compact neutron sources† Spallation IFMIF Cf-252†† D-T D-D Neutron yield [n/s] ~ 1018 1017 2.3 x 109 ~ 1010 ~ 108 Neutron flux [n/cm2/s] ~ 1015 1016 1015 ~ 106 ~ 107 ~ 105 Neutron energy [MeV] thermal ~ 2 thermal 14 (peak) 2.3 14.1 2.45 Scale [m] ~ 101 ~ 102 < 0.1 < 1 †. Neutron flux of compact neutron source is the flux at 10 cm away from the source. ††. 1 mg Table I: Physical properties of neutron emission target High yield and high energy compact NG should be developed to extend the applications. Numerical Study on Accelerator Based D-D Neutron Generator Neutron Yield of Beam-Target Neutron Generator [1] Ib : Beam current Ct : Hydrogen isotope concentration in target Eb : Incident beam energy dE/dx : Beam energy loss rate of target εX: Stopping cross section of element X Neutron Energy of Beam-Target Neutron Generator θ : Neutron emission angle FIG. 1. Fusion cross section and stopping cross section of target materials FIG. 6. Neutron yield of various target material. FIG. 7. Energy loss rate and beam penetration depth (effective target thickness) of various target material. Proof-of-Principle Experiment of Hydrocarbon Liquid Target Operation Condition and Result of Cryogenically-cooled Liquid Target [3] - Target temperature: 150 K - Base pressure: < 1 x 10-3 Pa - Flow rate: 265 Liters/min - Flow speed: > 5.6 m/s - Pressure: 6.7 x 10-2 Pa (Min.) 2.7 x 10-1 Pa (CW) Assumption - Target material: Titanium hydride (TiH1.6) - 100% of D+ ion, 1 mA beam ‼ The pressure inside the neutron generator should be maintained lower than 10-1 ~ 10-3 Pa for stable operation [4]. FIG. 8. (a) Schematic view of liquid target system. (b) Picture of liquid ethanol target fabricated in vacuum Conclusion This study suggests new concept of the D-D neutron generator which can achieve the high neutron yield and energy without tritium. The highly accelerated beam up to 10 MeV will enhance not only the total neutron yield but also the forward yield and the neutron energy. Also, the hydrocarbon liquid target is expected to reduce the required beam current by its low energy loss rate, and treat the high energy beam by the self-cooling and healing function. This study is useful to develop the intensive neutron generator which is applicable for the fusion material irradiation test as well as the neutron activation analysis, neutron radiography, medical application and so on. FIG. 2. Neutron yield of D-D and D-T neutron generator with 1 mA beam. FIG. 3. Normalized neutron energy spectrum of D-D NG according to beam energy. Anisotropy and Forward Flux of Beam-Target Neutron Generator - Anisotropy of flux: differential cross section, beam energy - In practice, the neutron flux distribution biased the forward direction is efficient for the neutron generator, because the neutron field behind the target is mainly utilized. - Forward flux is defined as following: Acknowledgement This research was supported by National R&D Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT & Future Planning (No. 2014M1A7A1A03045374) Reference [1] J. Csikai, CRC Handbook of Fast Neutron Generators, Vol. I, CRC Press, Boca Raton, p. 25, 1987. [2] S. G. Kim, Generation of isomeric cross sections and a study on D-T neutron application for production of therapeutic radioisotopes, Ph. D. Thesis, Seoul national university, 2006 [3] Y. S. Hwang, et al., R&D on Neutron Generator for ITER Neutron Diagnostics, Final report, Seoul National University, Ministry of Science, ICT and Future Planning, Korea, 2014. [4] H. Nakamura, et al., Status of engineering design of liquid lithium target in IFMIF-EVEDA, Fusion Engineering and Design, Vol. 84, p. 252, 2009. Beam Target 15o FIG. 4. Normalized angular flux of D-D NG KNS Spring Meeting, May 11 - 13, 2016, Jeju Korea P07B30