Proposal for recoil separators at the NSF by the Velocity Filter Working Party of the NSF Users Committee

This report details how velocity dispersing devices would assist the experimental programme proposed for the Daresbury Nuclear Structure Facility. The general appeal of the devices as spectroscopic tools in an extending experimental programme is revealed in the sections describing how the devices can be used and by indications of some fields where interesting physics could be studied. Two main areas of application have been identified within the programme. The first is the search for superheavy nuclei where a high transmission velocity filter consisting of two cancelling dispersive devices selects reactions products from beam particles, this filter is followed by a gas filled magnet to determine the reaction product masses. This combination of components is referred to as the Recoil Separator for Superheavies (RSS). The RSS is the minimum equipment required for the superheavy search. The second area is in the identification of nuclear mass A and charge Z of compound nucleus residues associated with some specific decay mode. The Recoil Separator (RS) system proposed for this relies on a magnet refocusing the residues after velocity dispersion on to a slit which will pass nuclei with a given A/q (q being the charge state of the ion). The RS can be assembled from the same components as the RSS although only one velocity dispersing device is essential. The RS will assist in investigations of states near the boundaries of stability. Excited states of a specific nucleus can be identified by the association of a signal in the RS with the detection of either a prompt decay (< 1 ns) near the target or a delayed decay (> 1 μs) at the position where the recoils are stopped. The Working Party is of the opinion that both the RS and the RSS should be available at the NSF and recommends the construction and commissioning of all the necessary components. (author)