Total neutron cross section for ¹⁸¹Ta

The neutron time of flight facility nELBE, produces fast neutrons in the energy range from 0.1 MeV to 10 MeV by impinging a pulsed relativistic electron beam on a liquid lead circuit. The short beam pulses (∼10 ps) and a small radiator volume give an energy resolution better than 1% at 1 MeV using a short flight path of about 6 m, for neutron TOF measurements. The present neutron source provides 2 ⋅ 10⁴  n/cm²s at the target position using an electron charge of 77 pC and 100 kHz pulse repetition rate. This neutron intensity enables to measure neutron total cross section with a 2%–5% statistical uncertainty within a few days. In February 2008, neutron radiator, plastic detector and data acquisition system were tested by measurements of the neutron total cross section for ¹⁸¹Ta and ²⁷Al. Measurement of ¹⁸¹Ta was chosen because lack of high quality data in an energy region below 700 keV. The total neutron cross – section for ²⁷Al was measured as a control target, since there exists data for ²⁷Al with high resolution and low statistical error.