MICROSCOPY 



95 



impinging x-rays 

 80 kvp 



1.32 



1.35 



+ + 



Co 20 



5.0 



0.99 

 Four targets or absorbers 



1.54 



transmitted 

 x- rays 



photographic plates 



Figure 4- 10a. Absorption of X Rays by Atoms. Energy of the incoming wave is trans- 

 ferred to the electron cloud. Absorption is proportional to electron density, electrons 

 per cubic A (bold numbers inside). Number of electrons (i.e., atomic number - valence) 

 and atomic weight are given, as is atomic radius (at 7 o'clock). Note shift of both ampli- 

 tude (number of photons per sec) and frequency (energy per photon). 



unit is defined later — only relative numbers are of interest now), although 

 electronic intensification of the image now permits one to reduce this dose by 

 a factor of ten. Although immediately measurable damage appears only if 

 the dose is hundreds of times higher, more subtle effects, such as malignant 

 growths, may show up years or even generations later if the greatest caution 

 is not exercised. The effects of absorbed radiation dose can be cumulative. 



These questions are considered in more detail under "Therapy" in Chap- 

 ter 9. 



MICROSCOPY 



A microscope is a device which throws a large image of a small object on 

 the retina of the eye. It does this by passing definitive light through a sys- 

 tem of lenses. A few useful notes are now given on the two most common 

 types. All the necessary details are set out in a very useful, practical manner 

 in the little book by Martin and Johnson entitled: "Practical Microscopy," 8 

 and in literature happily supplied by the optical companies. 



