A high-power liquid-lithium target for production of keV-energy neutrons

Research workshop onNuclear Structure and Astrophysics with Radioactive Beams

June 4-6, 2006, Weizmann Institute of Science , Rehovot, Israel

The LiLiT (Liquid-Lithium Target) projectat the SARAF accelerator:

A high-power liquid-lithium target for production of keV-energy neutrons

G. Feinberg, S. Halfon, M. Paul, Hebrew U., JerusalemD. Berkovits, I. Silverman, C. Tzur, Soreq NRC, YavneY. Momozaki, J. Nolen, C. Reed, Argonne Nat. Lab., Argonne

SARAF Accelerator basic characteristics ref. A. Nagler (Soreq NRC) talk

A RF Superconducting Linear Accelerator

ParameterParameter ValueValue CommentCommentIon Species protons/deuterons m/q ≤ 2

Energy Range 5 – 40 MeV Phase I : Emax= 5 MeV

Current Range 0.04 – 2 mA 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-ISaraf Phase I

experimentalstation

• 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 :

• 7Li(p,n) with a negative Q-value (Q = -1.644 MeV,Ethr(p)= 1.881 MeV) produces keV-energy forward-collimated neutrons near threshold. No needto moderate MeV neutrons.

• liquid-lithium target technology provides a solution tothe 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 targetswith necessarily much smaller mass.Requires higher neutron flux, presently unavailable

FZK (Karlsruhe) setupsee e.g. W. Ratynski and F. Kaeppeler, PR C 37, 595 (1988)

W. Ratynski and F. Kaeppeler, PR C 37, 595 (1988)

Ip ~ 100 μA, Ep = 1.912 MeV, Nn ~ 109 n/s

<σAu>T= 586 + 8 mb

p-only

s-only

64

76

70

80 82

86 87

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

K. Wisshak et al., Phys. Rev. C 73, 015802 (2006)

FZK

n-TOF(CERN)

Liquid Li as a high-power target

Technology under development at Argonne(J. Nolen, C. Reed, Y. Momozaki)

Plans for : high-power fragmentation targetstripper target for high-power heavy-ion beams

Liquid Li physical properties (T = 220 oC) Water(20oC)melting temp. : 181 oC

density: ρ = 0.510 g/cm3 1.0specific heat: Cp= 4350 J/kg K 4183thermal conductivity: Kth= 43.9 W/m K 0.6thermal diffusivity: κ= Kth/ρ Cp= 2.84 x 10-5 m2/s 1.5 x 10-7

surface tension : 0.326 N/m 0.075dynamic viscosity : η= 5.40 x 10-4 Pa.s 8.9 x 10-4

kinematic viscosity : ν= η/ρ= 1.06 x 10-6 m2/s 8.9 x 10-7

electrical resistivity : ρ= 2.5 x 10-7 Ω m 2.5 x 105

Prandtl number: ν/κ= 0.037 6.0

vapor pressure: 5 x 10-9 Torr

range (Ep= 1.91 MeV)= 9.2 mg/cm2 = 180 μm

Safety considerations :

1. Violent reaction with: water, water vapor, organics,fluorocarbons

Li + H20 -> LiO + H2attacks 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 MeVelectronbeamspot

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)

PROTON

liquid Li

4 mA8 kW~6 MW/cm3

4-5 mm PROTONbeam

adapted from : P. Grand and A.N. Goland, NIM 145 (1977) 49

Ip = 4 mAEp = 1.91 MeV ΔS =

0.2 cm2

450 W

liquid Li

Li VACUUM CONTAINMENT

ACTIVATIONTARGET

Li layer~ 0.2 mm thickness

PROTON

liquidLi

neutronemissioncone

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

Ip = 4 mA dn/dt = 4 x 1010 n/s

Newson et al., Phys. Rev. 108, 1294 (1957)

50 μCi 90Sr “target”~ 2.4 x 1015 atφ = 1 x 1010 cm-2 s-1

t = 24 hσ ~ 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 techniqueand 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 radioactive-ion production are considered.