Measurement of the⁶Li(n,α) neutron standard cross-section at the GELINA facility

Abstract

Abstract. The 6 Li(n,α) reaction cross-section is commonly used as a reference cross section. However, it is only considered a neutron standard up to 1 MeV. For higher energies, there are discrepancies of several per cents between recent measurements and evaluated data files. In order to extend and establish 6 Li(n,α) as a neutron standard above 1 MeV these discrepancies must be resolved. Our measurement at the GELINA facility at JRC-IRMM in Geel, Belgium is ongoing. We are using a double twin Frisch-grid setup to detect both α-particles from two 6 Li targets and fission products from two 235 U reference targets. Our targets have thick backings but are employed in pairs, one forward facing and one backward facing. In this way we still cover, in principle, a solid angle of 4π. We present some preliminary results showing that the existing cross-section data is well reproduced around the resonance at 240 keV. The final data taking will start in the beginning of 2016, when the GELINA facility goes online again after a few months of shut down.

Measurement of the 6Li(n,α)t neutron standard cross-section at the GELINA facility

“…Solutions proposed in Ref. [6] have now been implemented resulting in a modified setup moved to a new flight path station of 30 m.…”

“…Previously, only one chamber was used allowing both measurements to share the same gas flow. P-10 is still used as counting gas, but now separate chambers are employed to render a higher pressure in the 6 Li(n,α)t chamber. The chamber detecting fission products (FPs) had a 100 kPa pressure, while 200 kPa was used to stop the reaction products of 6 Li(n,α)t. We paired our four targets in back-to-back positions in order to form two double sided targets that also formed the cathodes in their respective chambers.…”

“…One of the uranium targets previously used [6] was replaced. The uranium targets now in use have areal densities of 216.0 and 221.5 µg/cm 2 , respectively.…”

“…The 6 Li(n,α)t reaction cross-section is an established standard up to 1 MeV. One reason for that is its relatively high cross section, while another reason is its high Q-value, of almost 5 MeV.…”

“…In order to extend and establish 6 Li(n,α)t as a neutron standard above 1 MeV some issues must be resolved.…”