Radioluminescence 421 



alpha particles. The instrument to do so was called a spinthariscope 

 by Crookes. 



In recent years the spinthariscope has been greatly improved and 

 become a scintillation counter/^ capable of detecting a single beta 

 particle (electron) or a gamma ray quantum. Photo-tubes and then 

 photomultiplier tubes have been used for detecting the light flashes. 

 A particularly practical instrument was described by P. J. van 

 Heerden '° in 1945, using AgCl at low temperatures as detecting 

 material. In 1947 H. Kallmann ^^ demonstrated that naphthalene 

 crystals emit flashes of ultraviolet light, which can be recorded by a 

 photomultiplier tube and amplifier system. The light flashes are 

 well above the background " noise " of the instrument. Since then, 

 liquids as well as crystals have been found to emit similar pulses 

 of ultraviolet light. The technical advances in this latest field of 

 luminescence have been extremely rapid and highly interesting. 

 Their importance is the only excuse for mentioning them in a his- 

 tory which is not intended to cover the twentieth century. 



Since the development of high voltage particle accelerators, cyclo- 

 trons, synchrotrons, betatrons, etc., the known phenomena of lumi- 

 nescence have been greatly multiplied. The many types of new 

 particles, positrons, neutrons, protons, deuterons, etc., projected as 

 an intense beam will excite various substances to emit a lig^ht, either 

 directly or as a secondary efi:ect. Such a light can be called a radio- 

 luminescence. Many of the new isotopes and the new elements 

 which decay spontaneously also emit particles or rays which can 

 excite luminescence, and, like radium, some of the radioactive 

 isotopes are self-luminous. 



The discoverers of various phenomena connected with radiolumi- 

 nescence have been amply rewarded. The first Nobel Prize (1901) 

 went to W. Roentgen, the third to A. H. Becquerel and the Curies 

 (1903) , the fifth (1905) to P. Lenard, and the sixth (1906) to J. J. 

 Thomson. In more recent times the discoverers of new particles, 

 which are associated with luminescence effects, have also become 

 Nobel prizemen. It is indeed surprising to note how frequently 

 the award has been connected with men whose concern was in the 

 field of radiation even though their research was not primarily con- 

 nected with luminescence. From 1901 to 1950, forty-four Nobel 

 Prizes in physics have been given to fifty-four men. The principal 



^' See A. T. Krebs, Early history of the scintillation counter, Science 122: 17-18, 1955. 

 2° Van Heerden, The crystal counter. Utrecht dissertation, 1945. 

 21 Luminescent naphthalene crystals and photomultiphers as gamma ray counters, 

 Natur und Technik, July, 1947. 



