Determination of fission barrier height of 210Fr and 210Ra via neutron measurement

Fission barrier heights of short-lived nuclei away from line of beta stability are not known reliably. Low-energy fission of 210Fr and 210Ra, produced by (d, p) and (d, n) transfer reaction on the re-accelerated unstable beam 209Fr was investigated at HIE-ISOLDE. Four Timepix3 pixel detectors were installed on the body of the ACTAR TPC demonstrator chamber. Polyethylene converters were used for the detection of fast neutrons. Since no significant background was observed, it was possible to measure the spatial distribution of emitted neutrons reflecting the fission excitation function. Subsequent simulations employing the results of the TALYS code and available data on fission fragment distributions allowed to estimate directly the value of the fission barrier height for the neutron-deficient nucleus 210Fr. This first direct measurement confirmed the reduction of the fission barrier compared to available theoretical calculations by 15-30%.