Download A high-power liquid-lithium target for production of keV

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