A NEW APPROACH TO DOORWAY MONITORS

A doorway monitor is described which was designed to detect the passage of 235u, 233JJ, or 239pu through personnel portals without impeding the traffic flow through the portal. The sensitivity of the monitor is equal to or better than required by the specifications for doorway monitors detailed in USAEC Regulatory Guide No. 5.7. An alarm is provided for appropriate action\" by security forces. Several measures are taken by the programmable digital control processor to minimize the possibility of deception, and at the same time provide maximum sensitivity consistent with the ambient background level. The background and its statistical fluctuations are measured continuously, except when the portal is occupied; signals which occur when the portal is occupied cause alarms when they exceed the background with a predetermined statistical confidence. Additional fail-safe features result in alarms for most types of system malfunctions or attempts at tampering with the system.