Patent GB-1207838-A (GB)
Title: Monitoring instrument for detecting beta and gamma radiation
Inventor: ROULET ROGER
IPC: G01T7/12
Filed: 1967-09-19
Abstract: 1,207,838. Monitoring # and γ radiation. COMMISSARIAT A L'ENERGIE ATOMIQUE. Sept. 19, 1967, [Oct. 19, 1966], No. 42652/67. Addition to 1, 013, 755. Heading G1A. A detector arrangement for monitoring # and y radiation from the shoes of personnel who have been exposed to radio-activity comprises a detector instrument including a device as defined in claim 1 the parent Specification and a further integrating circuit with an intermediate time constant. The instrument is mounted under a footbridge, and there are also provided means to control the initiation of a measuring cycle, the displaying of orders to the person monitored, the triggering of an alarm if the person does not wait for the full duration of a measuring cycle and the energization of a warning display if the measured activity exceeds a predetermined level. A person to be monitored passes through the light beam provided by source 62. This cuts off the light reaching a photo-resistor 64 which controls the operation of a time-delay circuit 66, detailed in Fig. 3 (not shown), comprising a transistor (90), a differentiator circuit (108, 110, 111) and a monostable multi-vibrator (92) having a delay set by a potentiometer (99). Transistor (90) is cut off causing switching of the multi-vibrator whose output transistor is then cut off. This causes de-energization of a first relay (A) in a control circuit 67, comprising five relays (A-E), Figs. 4-5 (not shown), resulting in the measuring cycle being started, the "STOP" indicator 58 being lit and the flip-flop circuit 44 being actuated. Radiation from the shoes of the person standing on the footbridge 52 is detected by Geiger-Muller counter 54. The detector output is passed through a pre-amplifier 82, main amplifier 84 and a pulse shaper 20 (a multi-vibrator) to the integrating circuits 2, 4 detailed in Fig. 1 (not shown) and operating as defined in claim 1 of the parent Specification and to a further integrating circuit 6 having a time constant intermediate those of the circuits 2, 4. If the background radio-activity in the surrounding area is normal, i.e. that to be expected, then a visual indicator controlled by flipflop 46 indicates this condition and measurement may proceed. If an activity of the person's shoes higher than a predetermined level, is detected, the detector output is operated on by integrators 2, 4 to cause switching of flip-flop 44, causing energization of visual alarm 69 controlling luminous panels 63 and audible alarm 65. At the end of the measurement cycle, determined by the time the multivibrator (92) in delay circuit 66 switches back to its stable state, the "GO" indicator 56 is lit and "STOP" de-energized. The person then passes through a gate which causes relays in the control circuit to operate to extinguish the "GO" indicator. There is provision in the control circuit for the actuation of an alarm when a person leaves the footbridge before the measuring cycle has elapsed. Opening of the above-mentioned gate closes a switch (57S2) to energize a relay (E) in the control circuit thereby causing an alarm bell to sound. A push button (57S1) is provided to switch off this alarm, and is also used to switch off the visual indicator 63. The relay circuit is also arranged so that a person passing through the gate in the opposite direction will not initiate a measuring cycle.