GB732893A - Portable ray meters - Google Patents

Abstract

732,893. Luminescent screen. PRINGLE, R. W., ROULSTON, K. I., and BROWNELL, G. M. Nov. 10, 1950 [Nov. 10, 1949; Jan. 12, 1950], No. 27528/50. Class 39 (1). [Also in Group XL (b)] intensity of gamma and neutron radiation is determined by detecting photo-electrically the scintillations of a single crystal receiving the radiation. Crystal and mounting.-Examples of crystals which scintillate when bombarded with gamma rays are napthaleno, anthracene, stilbene, chrysene, calcium or cadmium tungstate, or potassium or sodium iodide activated with thallium. As shown in Fig. 2, the crystal 1 is secured by a transparent cement upon the roughened end of a photo-multiplier tube 2. The crystal is in the form of a truncated cone and is covered bv a shield 11 of foil adhesively secured to the crystal this shield serving both to exclude moisture from the crystal and to reflect the scintillations into the tube. In a modification (Fig. 4, not shown), the crystal is situated near the cathode of an image dissector, the cathode emitting in response to the scintillations and the electrons being accelerated by a grid and allowed to impinge on a fluorescent screen the scintillations of which are detected by a conventional photo-cell. Circuit (Fig. 1).-The scintillations received at the cathode of the multiplier 2 or the image dissector referred to above produce current pulses in an inductance in the anode circuit of the multiplier. A damped oscillatory voltage of longer duration than the scintillations is developed across the inductance 221, this voltage being fed through a screened lead 19 to a cathode follower 15 and a pair of resistance capacity coupled valves 17, 17<SP>1</SP>. If the amplification of the multiplier is adequate these valves may be omitted. The output of the second valve is rectified by a germanium diode 5 and used to trigger a conventional flip-flop circuit comprising valves 23 and 24 the magnitude of the pulse which triggers the circuit being preset by varying the bias on the valve 23. A microammeter 26 is connected in the anode circuit of valve 23<SP>1</SP> and is shunted by a condenser C10 to smooth out statistical fluctuations. Resistance R19 in series with the meter permits variations of the averaging period of the instrument. In modifications a pulse dividing circuit with earphones might be used.