GB837172A - Improvements in or relating to x-ray apparatus - Google Patents

Abstract

837,172. X-ray responsive electroluminescent screens. WESTINGHOUSE ELECTRIC CORPORATION. March 5, 1958 [March 13, 1957], No. 7051/58. Class 39(1). The contrast in the luminous response to an X-ray signal of a phosphor screen displaying an enhanced electroluminescent output when irradiated by X-rays and simultaneously excited by an alternating electric field is varied by the following steps:-passing X-rays of selected intensity through a stationary object having varying X-ray permeability to generate a first X-ray signal which is applied to the screen together wtih an alternating electric field to effect a phosphor-screen presentisization varying in degree according to the quantity of X-rays applied thereto, removing the applied X-ray signal and the applied field, repassing X-rays of preselected intensity through the object to generate a second signal, and applying this signal to the screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of the second X-ray signal and with the degree of screen presensitization previously effected whereby the contrast between individual portions of the transient object image formed on the screen is varied. The applied first X-ray signal may be removed before or simultaneously with the applied electric field. In the example recited the brightness of a portion of the screen receiving through the object first X-ray irradiation of 160 ÁA per minute and an applied electric field is shown as O-T-U, Fig. 5 and, for the screen portions adjacent the more X-ray opaque portion of the object with an irradiation of 80ÁA per minute the brightness is shown as O T<SP>1</SP> U<SP>1</SP>. The first X-ray signal and the applied field are removed and after a quiescent time of about one minute, the second X-ray irradiation is applied to the presensitized screen. The brightness curves of the " high " and " low " spots after this irradiation are hsown as OXY and OX<SP>1</SP>Y<SP>1</SP>, the contract ratio to the peaks X, X<SP>1</SP> being greater than that in the presensitization image. The contrast ratio may be lowered by using lower X-ray strengths in the second irradiation. The phosphor screen construction is of the kind described in Specification 772,572. The electroluminescent material may be mixtures of zinc and cadmium sulphide wherein the ratio of Zn to Cd is from 9 : 1 to 3 : 7 activated by from 0À01 x 10-<SP>2</SP> to 6À0 x 10-<SP>2</SP> mole of manganese. Silver may also be present from a mere trace up to 1À0 x 10<SP>-2</SP> mole Ag per mole Mn. Specification 837,171 also is referred to.