(p,n) experiments in inverse kinematics

Properties of stable nuclei can be studied through their response to a variety of probes. Unstable nuclei usually cannot be collected in a target, so the reaction must be performed in inverse kinematics: a beam of unstable nuclei are projected on a target containing the probe.

Charge-exchange reactions are difficult to perform in inverse kinematics, since the recoiling probe typically has very low velocity and loses most or all of its energy in the target material itself. Moreover, the residual (what the beam has turned into) is strongly forward boosted, making it hard to extract kinematical information of sufficient quality.

Compared to other types of charge-exchange reactions in inverse kinematics, the (p,n) reaction has an important advantage: The recoiling neutron can easily escape from the target material, since it is not charged and therefore does not suffer from energy losses or straggling. This has the following consequences:

1. relatively thick target material can be used, increasing the reaction yield.
2. both the tracks of the neutron and the heavy reaction residual can be detected, making it easier to reconstruct the kinematics of the reaction with sufficient resolution
3. if the energy and angle of the neutron can be used to reconstruct the event, the energy resolution is not affected significantly by target thickness

Schematic layout of the Low-Energy Neutron Detector Array LENDA at the S800 spectrometer.

In preparation for (p,n) experiments, the charge-exchange group at the NSCL is constructing a Low-Energy Neutron Detector Array (LENDA) which will be used in conjunction with the S800 spectrometer. The S800 will be used to analyze the residual and the neutron array will be used to detect the recoil neutron, giving both energy and angle information.