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A high-power liquid-lithium target for production of keV-energy neutrons Research workshop on Nuclear Structure and Astrophysics with Radioactive Beams June 4-6, 2006, Weizmann Institute of Science , Rehovot, Israel The LiLiT (Liquid-Lithium Target) project at the SARAF accelerator: A high-power liquid-lithium target for production of keV-energy neutrons G. Feinberg, S. Halfon, M. Paul, Hebrew U., Jerusalem D. Berkovits, I. Silverman, C. Tzur, Soreq NRC, Yavne Y. Momozaki, J. Nolen, C. Reed, Argonne Nat. Lab., Argonne SARAF Accelerator basic characteristics ref. A. Nagler (Soreq NRC) talk A RF Superconducting Linear Accelerator Parameter Value Comment Ion Species protons/deuterons m/q ≤ 2 Energy Range 5 – 40 MeV Current Range 0.04 – 2 mA Phase I : Emax= 5 MeV Upgradable to 4 mA Operation mode CW and pulsed CW: 176 MHz (pulse width<1ns) PW: 0.1-1 mS; rep.rate: 1-10 Hz Operation 6000 hours/year Radiopharmac. appl. 50%, research 30%, indust. appl. 20% Reliability 90% Maintenance Hands-On Very low beam loss Phase-I Saraf Phase I experimental station • Short-range : p(1.9 – 2.5 MeV, 2-4 mA) + liq. Li target (Phase I) stellar-energy neutrons for astrophysics The case for p + Li to produce stellar-energy neutrons : • with a negative Q-value (Q = -1.644 MeV, Ethr(p)= 1.881 MeV) produces keV-energy forward-collimated neutrons near threshold. No need to moderate MeV neutrons. 7Li(p,n) • liquid-lithium target technology provides a solution to the high dissipation power and power density needed with high intensity beams. 7Li(p,n)7Be : Used extensively at Karlsruhe for (n,γ) cross section measurements on stable targets (mainly). Astrophysics require also measurements on unstable targets with necessarily much smaller mass. Requires higher neutron flux, presently unavailable FZK (Karlsruhe) setup see e.g. W. Ratynski and F. Kaeppeler, PR C 37, 595 (1988) <σAu>T= 586 + 8 mb W. Ratynski and F. Kaeppeler, PR C 37, 595 (1988) Ip ~ 100 μA, Ep = 1.912 MeV, Nn ~ 109 n/s p-only 86 87 80 s-only 76 70 64 82 FZ Karlsruhe: activation of 135Cs (t1/2=2 x 106 yr) + γ-decay measurement of 136Cs (13 d) 70 mm sample activation : 400 ng 135Cs ( 20 Bq) γ measurement : Patronis et al, PRL 2004 FZK n-TOF (CERN) K. Wisshak et al., Phys. Rev. C 73, 015802 (2006) Liquid Li as a high-power target Technology under development at Argonne (J. Nolen, C. Reed, Y. Momozaki) Plans for : high-power fragmentation target stripper target for high-power heavy-ion beams Liquid Li physical properties (T = 220 oC) melting temp. : 181 oC density: ρ = 0.510 g/cm3 specific heat: Cp= 4350 J/kg K thermal conductivity: Kth= 43.9 W/m K thermal diffusivity: κ= Kth/ρ Cp= 2.84 x 10-5 m2/s surface tension : 0.326 N/m dynamic viscosity : η= 5.40 x 10-4 Pa.s kinematic viscosity : ν= η/ρ= 1.06 x 10-6 m2/s electrical resistivity : ρ= 2.5 x 10-7 Ω m Prandtl number: ν/κ= 0.037 vapor pressure: 5 x 10-9 Torr range (Ep= 1.91 MeV)= 9.2 mg/cm2 = 180 μm Water(20oC) 1.0 4183 0.6 1.5 x 10-7 0.075 8.9 x 10-4 8.9 x 10-7 2.5 x 105 6.0 Safety considerations : 1. Violent reaction with: water, water vapor, organics, fluorocarbons Li + H20 -> LiO + H2 attacks Cu, Ni, Ag, Au stable with Fe, SST, Ta 2. Li fire : T > 400 oC in dry air 3. Alkali-metal safety standard procedures 1 MeV electron beam spot J. Nolen et al., Rev. Sci. Inst. 76, 073501 (2005) Power : 20 kW, peak power density : 2.1 MW/cm3 Li flow : 3.6 m/s J. Nolen et al., Rev. Sci. Inst. 76, 073501 (2005) liquid Li 4-5 mm PROTON beam 4 mA 8 kW ~6 MW/cm3 PROTON adapted from : P. Grand and A.N. Goland, NIM 145 (1977) 49 Ip = 4 mA Ep = 1.91 MeV liquid Li ΔS = 0.2 cm2 450 W liquid Li Li VACUUM CONTAINMENT neutron emission cone PROTON ACTIVATION TARGET Li layer ~ 0.2 mm thickness Neutron flux estimate : σn(Li) ~ 120 mb (Ep= 1.89 – 1.91 MeV) Δx(Li) ~ 0.150 mg/cm2 n/p = 1.6 x 10-6 Newson et al., Phys. Rev. 108, 1294 (1957) Ip = 4 mA dn/dt = 4 x 1010 n/s 50 μCi 90Sr “target” ~ 2.4 x 1015 at φ = 1 x 1010 cm-2 s-1 t = 24 h σ ~ 100 mb N(91Sr, t1/2= 9.5 h) = 1.7 x 105 ~ 3.4 Bq @ 1% γ efficiency ~ 1500 cts in 24 h Summary LiLiT : - merging of an established experimental technique and an emerging technology - adapted to the capabilities of SARAF - expected larger flux in the stellar energy regime (neutron-induced astrophysical reactions off the valley of stability) - other applications for keV-neutrons and radioactiveion production are considered.