Some aspects of the J phenomenon in X-rays

Abstract

Though many of the important facts concerning the J phenomenon are now known, lack of control of the critical conditions for J-absorption and J-transformation leads to complexity in the results obtained in the case of experiments where each of the quantities to be determined involves a number of different measurements. In many cases it becomes extremely difficult not only to interpret the results obtained in the measurement of absorption coefficients, but - as already pointed in connection with the examination of Sn K - radiation - even to assign a value to the absorption coefficient as ordinarily understood.From this complexity we are impelled to return to the simplest possible methods of investigation. For example, to compare the quality of secondary radiation from light substances with that of the primary, the procedure now adopted in this laboratory is to determine the relative intensity of secondary to primary as successive equal thicknesses of absorber are interposed in the path of each beam. This method has now been adopted in the examination of the primary radiation from an X-ray tube in different directions about the cathode stream. It is in this investigation that the writer is at present engaged; and it is hoped that, by combining the results of it with those already known on the effect of the direction of the secondary(relative to the exciting primary radiation' on the appearance of the J absorption phenomenon in the secondary, it may be possible to get a better conception of the processes involved in the J phenomenon, and to determine the critical conditions necessary for the appearance of the phenomenon.Further, concerning the use of the X ray spectrometer in these matters (apart from its aid as a means of providing homogeneous X-rays), it is necessary to insist that it is likely at this stage to be of very little help either in examining the physical processes involved or in elucidating the entirely new facts of the J phenomenon. The spectrometer is an instrument which examines the wave-motion aspect of radiation; the quantum aspect of the interaction between radiation and matter can only properly be examined by the measurement of quantum effects, as such. Finally, it is quite evident that, had spectroscopic methods alone been employed; the remarkable coherence property of X radiation observed in the J phenomenon would either have remained undiscovered or required ultimately for its investigation the very methods which have brought it to light.COPY, without diagrams of Letter to Nature , April 25th 1925, p.604 "SPECTROSCOPIC EVIDENCE OF THE J-TRANSFORMATION OF X-RAYS" by S.R. Khastgir and W.H. Watson. (fig. I of the letter is quoted in section III above)PROCEEDINGS OF THE ROYAL SOCIETY OF EDINBURGH. SESSION 1924 -1925. VOL. XLV -PART I -(No. 7). An Investigation of the Absorption of Superposed X- radiations. By Wm H. Watson