Radiation detector, 'Scintillation Meter type 5.40', metal / plastic, made by Mini Instruments Inc, Burnham on Crouch, Essex, England, 1963-2005
The detector is encased in a grey metal casing. The front of the unit is grey and shows a 'counts per second' meter in a window and also rotary 3 position switch (off, battery check, on) (the knob is missing). On the top of the unit is mounted a rod shaped grey probe attached with a curly electrical cord.
The mini monitor is well established in teaching, research, hospital and industrial laboratories as a reliable, convenient, and inexpensive contamination meter. The machine has a large logarithmically scaled meter with an open scale at the lower end to show background levels of radiation while displaying high levels without switching. There is also speaker to give an audible estimation of radiation intensity. There is an alarm which can be set to trip at any level on the scale. The unit can be battery or mains operated.
A scintillation counter measures ionizing radiation. The sensor, called a scintillator, consists of a transparent crystal, usually phosphor, plastic (usually containing anthracene), or organic liquid that fluoresces when struck by ionizing radiation. A sensitive photomultiplier tube (PMT) measures the light from the crystal. The PMT is attached to an electronic amplifier and other electronic equipment to count and possibly quantify the amplitude of the signals produced by the photomultiplier.
These detectors are available with different probes, each capable of being used at a specific energy range.