First nuclear astrophysics experiments with high-intensity neutrons from the liquid-lithium target LiLiT

Abstract

A high-intensity neutron source based on a Liquid-Lithium Target (LiLiT) and the 7 Li(p,n) reaction was developed at SARAF (Soreq Applied Research Accelerator Facility, Israel). The setup is used for nuclear-astrophysics experiments owing to the quasi-Maxwellian shape of the neutron energy distribution at stellar thermal energies (kT ~ 30 keV). The LiLiT device consists of a forced-flown (> 2 m/s) film of liquid lithium (~200 o C) whose free surface is bombarded by a proton beam. The lithium film acts both as the neutron-producing target and as a power beam dump. The setup was commissioned with a 1.2 mA proton beam at 1.91 MeV, producing a neutron yield (peaked at ~28 keV) of ~ 3 ×10 10 n/s, more than one order of magnitude larger than conventional 7 Li(p,n)-based neutron sources. The target dissipates a peak power areal density of 2.5 kW/cm 2 and a peak power volume density of 500 kW/cm 3 with no significant temperature or vacuum pressure elevation in the target chamber. We present preliminary results of first activation measurements on Zr and Ce stable isotopes performed with the SARAF-LiLiT setup, using Au as neutron monitor and of the determination of their Maxwellian-averaged neutron capture cross section.

StellarAr36,38(n,γ)ArTessler1, Paul2, Halfon3 et al. 2018Phys. Rev. Lett.Self Cite172110View full textAdd to dashboardCite

“…A proton beam energy spread of ∼15 keV, estimated from beam dynamics calculations, was verified experimentally [24]. Autoradiographic scans [25] of the Au foils were conducted to determine proton beam centering.…”

The activation method for cross section measurements in nuclear astrophysics

“…The element indium has two stable isotopes 113 119 Sb isotope is far the longest, therefore, by measuring long enough the yield of the emitted Xrays, the radiative α-capture cross section of 115 In could be derived. Figure 15 shows the yield of the time-dependent characteristic X-rays together with the fitted exponential functions.…”

“…It is worth noting that the signal-to-background ratio is similar in the activity measurements carried out at LNGS and Atomki. Decay curve: X-ray yield 115 In + E Lab = 11.5 MeV Fig. 15.…”

“…For comparison, the highest fluxes reached at the most intense TOF facilities LAN-SCE [113] and n TOF-EAR2 at CERN [114] are about 5×10 5 s −1 . A further increase by more than an order of magnitude in beam power and, correspondingly in neutron flux, has been gained in activation measurements at the SARAF facility [115].…”

“…However, after sufficient waiting its activity decreases to a level low enough and the contribution to the total X-ray yield of the longer half-life isotope becomes dominant. As an example, in the following the cross section measurement of the 115 In(α,γ) 119 Sb and 115 In(α,n) 118 Sb m reactions is discussed in some detail.…”