Radio age research, manufacturing, communications, broadcasting, television (1941)

MEASURES LIGHT OF FAINTEST STAR Method Uses Photo-Multiplier Tube and Electronic Counter THE amount of light reaching the earth from the faintest stars can now be accurately meas- ured with a new form of photom- eter which incorporates two units developed by the Radio Corporation of America, the photo-multiplier tube and the Electronic Time In- terval Counter. Details of the photometer, which was designed and constructed by William Blitzstein and I. M. Levitt of the Flower Observatory and the Franklin Institute Laboratories, were revealed recently to the As- tronomical Society in Evanston, Illinois. above: with an accuracy of onh millionth second, rca electronic interval counters on table meas- ure electron pulses generated by the faintest starlight. left: a photo-multiplier tube is placed on the telescope where it receives the focused image of the star being observed. In the Levitt-Blitzstein photom- eter, the image of the star is focused through a telescope onto a photosensitive element of the mul- tiplier tube. The light striking this element gives off pulses of electrons which are then directed onto the first of a series of surfaces called dynodes which generate secondary electrons. For every electron strik- ing the first surface, two to five additional electrons are released. By repeating these steps through the nine elements of the photomul- tiplier tube, the final product is a million or more electrons for each electron which left the first sensi- tive surface. Previous methods used by as- tronomers for this purpose utilized a device called a galvanometer but the instrument is inherently un- stable and reacts slowly to changes in the intensity of light pulses. A.stronomers have long realized that if the bursts of electron pulses could be counted, the light from the faintest stars could be measured with great accuracy. In the RCA Electronic Counter, developed re- cently by the RCA Engineering Products Department, scientists found the solution to this problem. The Counter makes the computa- tion completely automatic. After setting a predetermined time inter- val on the device, the astronomer merely pushes a button, which ex- poses the counter to the output of the photomultiplier for the desired time, say 10 to 100 seconds, with an accuracy of 1 millionth of a sec- ond. The number indicated on the counter at the end of this period is proportional to the light intensity of the star under observation. Dr. Zworykin Addresses Foreign Science Groups Carrying credentials naming him official representative of two of the outstanding science societies of the United States, Dr. V. K. Zworykin, Vice President and Technical Consultant of RCA Laboratories, Princeton, N.J., left New York on August 16 to attend important en- gineering conferences in Belgium, France and Italy, and to visit tech- nical laboratories in England, Hol- land and Switzerland. Recognized internationally as an authority on television and electron microscopy. Dr. Zworykin was in- vited to deliver three papers during his European trip. He represented the National Academy of Sciences at the Liege (Belgium) Congress, September 8, on the occasion of the centennial of the Association of Engineering Graduates of the University of Liege. He talked on "Applications of Electron Micros- copy and Electron Diffraction to Metallurgy", a paper prepared in cooperation with Dr. E. G. Ram- berg. Later Dr. Zworykin addressed a conference of the French Society of Electrical Engineers at the Sor- bonne, Paris, France, on the subject of "Progress in Television." As representative of the National Academy of Sciences, the Institute of Physics, and Radio Corporation of America, Dr. Zworykin attended an international conference of radio engineers at Rome, Italy, organized by the Italian National Council of Research to commemorate the fif- tieth anniversary of the invention of radio by Marconi. His address there also dealt with television, covering its latest advances. [RADIO AG E 25]