Patent GB-1289811-A (GB)
IPC: G01J5/34
Filed: 1970-01-05
Abstract: 1289811 Radiation detectors CARBORUNDUM CO 5 Jan 1970 [8 Jan 1969] 411/70 Heading G1A [Also in Division H1] Electromagnetic radiation is measured by applying the radiation to at least one ferro-electric crystalline sensing element, thereby raising its temperature in accordance with the applied radiation, and comparing a temperature dependent property e.g. the capacitance, of the element, with that of at least one ferro-electric crystalline reference element of the same basic composition as the sensing element and which is shielded from the applied radiation, the temperatures of the elements being maintained within about 0À1‹ C. of the crystallographic transition temperatures of the elements. Ferro-electric materials which may be used are triglycine sulphate (T.G.S.), triglicine fluoberylate, barium niobate, strontium niobate, mixtures of the former and latter pairs of materials, and potassium tartrate tetrahydrate. The crystals may be modified by inclusions of e. g. deuterium oxide to provide crystals having different transition temperatures as used in the apparatus of Figs. 6-9 (not shown). Construction, Fig.1. In the arrangement shown, a single crystal 11 provides both the sensing and reference elements 12, 13 and has its ferro-electric axis 14 oriented as shown. Gold electrodes 17, 18 19 are evaporated using masking techniques in grooves 15, 16 cut into the body 11 e.g. by a hot wire or a wet string. The sizes of the electrodes are adjusted so that, in the absence of incident radiation, substantially equal capacitances between pairs 17, 18 and 17, 19 (the sensing and reference elements respectively) are obtained. End surface electrodes may alternatively be provided. The sensing element 12 may be coated with a carbon black (wide band spectrum) or a petroleum jelly (ultra violet) layer 23 depending on the wavelengths to be detected. The reference element 13 is shielded from applied radiation by a brass foil 40 blackened by an arsenic cyanide wash. The temperature stabilizing element is constituted by a second ferro-electric crystal 31 whose axis 32 is at right angles to that of body 11. The element 31 is electrically insulated from, but thermally connected by means of a sheet 34 of polyethylene terephthalate, to the crystal 11. This sheet is coated with a thin layer of gold to form electrically conductive layer 35 by stretching over an aluminium ring and then evaporating the gold into it. The element 31 has gold electrodes 36, 37 evaporated thereon before attachment to the layer 35 on sheet 34. Attachment of both crystals to sheet 34 is by electrically and thermally conductive cement containing suspended colloidal silver. Silver leads are attached to electrodes 17, 18, 19, 37 and to gold layer 35. The apparatus is mounted in an evacuated enclosure. Operation, Fig.1. The sensing and reference elements are connected as shown in Fig. 5 and before application of the radiation to be evaluated, tap 46 is adjusted to yield zero voltage between it and lead 20. The temperature of the device is at this time stabilized by element 31, to the leads 38, 39 of which is applied an A. C. voltage of suitable frequency and voltage, such that it operates as a TANDEL. When the radiation is applied to sensing element 12 its temperature increases and its capacitance changes and the resulting A. C. voltage on leads 20, 46 is a measure of the radiation intensity. Alternative arrangement, Figs. 6-9 (not shown), uses a plurality of sensing and reference elements and is more sensitive than that of Figs.1, 5 and 2-4 (not shown). The sensing elements comprise two ferro-electric crystals which have been grown with varying amounts of D 2 O inclusion and are chosen such that one crystal has its crystalline transition temperature slightly above and the other, slightly below, the temperature of intended temperature stabilization. Two pairs of electrodes are provided on each crystal so as to provide four capacitative sensing elements which are connected in an A. C. bridge Fig.8 (not shown). The bridge is balanced at the stabilization temperature but the incidence of radiation causes it to unbalance in accordance with the intensity thereof. The bridge voltage is compared with that from a similar bridge of reference elements so as to provide a true measure of the intensity Fig. 9 (not shown). Constructional details and materials are otherwise similar to those of the Fig.1 apparatus.