Total neutron cross section for 181 Ta

The neutron time of flight facility nELBE, produces fast neutrons in the en- ergy range from 0.1 MeV to 10 MeV by impinging a pulsed relativistic electron beam on a liquid lead circuit (1). 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 · 10 4 n/cm 2 sa t 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 (2) and data acquisition system were tested by measurements of the neutron total cross section for 181 Ta and 27 Al. Measurement of 181 Ta was chosen because lack of high quality data in an anergy region below 700 keV. The total neutron cross - section for 27 Al was measured as a control target, since there exists data for 27 Al with high resolution and low statistical error (3).