X-RAY MICROSCOPY 



Fig. 15. The utilization of standard light mi- 

 croscope optics for high resolution microphotom- 

 etry. 



less presents a relatively difficult problem in 

 microdensitometry which has been solved in 

 the following manner: A very intense, con- 

 centrated light source is necessary, such as 

 the high pressure mercury arc (AH-6 of Gen- 

 eral Electric for example). A trinocular mi- 

 croscope with a Leitz photomicrographic 

 attachment has been found to be most con- 

 venient for the optical system, as shown in 

 Fig. 15. The light is diverted to the binocular 

 section only when surveying the microradio- 

 gram and centering the object area to be 

 measured. For densitometric measurement 

 the first image, as formed by the objective 

 just below the projector lens in the photo-at- 

 tachment, falls upon a stop with a 0.5 mm 

 hole at its center. Only light from this cen- 

 tral portion of the image proceeds directly to 

 the top of a camera chamber which has been 

 added to the Leitz attachment. Here 2" x 2'' 



lantern slide plates can be exposed for con- 

 venient photomicrography, at 500 X or less. 



A low-power eyepiece is placed here for 

 critical, direct focusing on the enlarged field. 

 Also, at this final image plane, a "light pipe" 

 may be slid into place consisting of a thin 

 piece of glass with a 45° polished end and 

 masked so that light from a 0.25 X 0.5 mm 

 central field area may be internally and to- 

 tally reflected at its tip, and channeled down 

 the long glass section to a 1P21 (RCA) pho- 

 tomultiplier tube. The precise position of the 

 equivalent 0.5 by 1.0 micron object field 

 which is being measured may be simultane- 

 ously viewed by the upper eyepiece. The 

 phototube output is "matched" to a ten 

 millivolt chart recorder by connecting it di- 

 rectly to the 1.5 volt input of a standard 

 vacuum tube voltmeter. The recorder is at- 

 tached to the meter circuit of the VTVM. 

 The sensitivity of the system is set by vary- 

 ing the multiplier tube voltage in the range 

 450-900 volts. 



When a profile rather than point meas- 

 urement is desired, the microradiogram is 

 translated by means of a simple mechanical 

 linkage between the stage screw and a syn- 

 chronous motor. The latter is geared down 

 to effect a 40 micron motion of the stage 

 in about 3 minutes. 



A 95X oil immersion apochromat objec- 

 tive is used. Monochromatic light, effectively 

 the mercury 4360 A blue light, is obtained 

 by a filter — it has been found that the (y/N) 

 ratio for blue light is 30 % higher than that 

 for the green Hght (5461 A) because of the 

 higher scattering efficiency of the Lippmann 

 grains for the shorter wavelengths. The mon- 

 ochromatic light yields a significant improve- 

 ment in image quality also. 



Once the image field to be measured is lo- 

 cated in the central hole at the stop in the 

 projector lens, the prisms for side viewing 

 are thrown out of the beam so that there are 

 a minimimi number of glass svirfaces in- 

 volved, and only the light fonning the cen- 

 tral image area which closely surrounds that 



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