A Technical Review of Penning Trap based Investigations in Neutron Decay
  This review is concerned with a detailed analysis of some of the technical problems which arise in the application of the Penning trap method to the experimental study of neutron $\beta $ -decay,a technique which was first successfully tested on the low-flux swimming-pool reactor LIDO (capture flux =3$\cdot 10^6$cm$^(-2)$s$^(-1)$) at AERE Harwell in the 1970's. It does not discuss the scientific merits or demerits of these studies. Of particular importance are the trapping and release of neutron decay protons, and the influence of magnetic mirror effects and radial drifting on the trapped particles. Since these have energies < 1 keV they must be accelerated to energies of order 20-30 keV following release, at which point they are recorded in a silicon surface barrier detector. However serious difficulties were encountered in the post-release acceleration process with vacuum breakdown in the presence of crossed electric and magnetic fields. 
J. Byrne
nucl-ex physics.ins-det