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The Cadmium Sulfide X‐Ray Detector
1.R. H. Herz, Fortschr. Gebiete Röntgenstrahlen 54, 6 (1936). It is interesting to note that in his first papers Röntgen tried to determine the distribution in space of the x‐rays around the tube by photometrie of barium platino cyanide screens. Now the expensive and unstable barium platino cyanide screens have generally been replaced by crystal phosphors.
2.R. H. Morgan, Am. J. Roent. Rad. Ther. 47, 777 (1942).
3.H. M. Smith, Gen. Elec. Rev. 48, 13–17 (1945).
3.Marshall, Coltman, and Hunter, Rev. Sci. Inst. 18, 504 (1947).
3.J. W. Coltman, Proc. I.R.E. 37, 671 (1949).
4.R. Frerichs, Naturwiss. 33, 281 (1946).
4.R. Frerichs, Phys. Rev. 72, 594 (1947).
5.Natural amplification phenomena will play a more important role as the number of electronic devices applied in complicated mechanism (electronic calculators, electronic brains) reaches values which make it necessary to reduce the size and the labor involved in the individual device. An example is the recently developed transistor, which can replace complicated electron tubes. See furthermore: V. K. Zworykin and E. G. Ramberg, Photoelectricity, p. 469.
6.R. Frerichs, Phys. Rev. 76, 1869 (1949).
7.The author is greatly indebted to Dr. J. C. M. Brentano, who made the equipment of his x‐ray laboratory available to him.
8.This is to be expected from the theory outlined in reference 6. High luminescence proves that sufficient activating impurities are present which furnish the positive stationary space charges necessary for the compensation of the transported negative charges.
8.(a) S. Laubert, Ann. d. Physik 40, 553–578 (1941).
8.H. H. Biermann, Ann. d. Physik 26, 740 (1936).
9.Nail, Perlman, and Urbach, “Preparation and characteristics of solid luminescent materials,” Cornell University, Symposium (1946), p. 190.
10.O. Glasser, Medical Physics (Chicago 1944), p. 1293. Figure 1, Patterson Type B screens show an increase of brightness which is less than proportional to the impinging radiation at high intensities (3–4 r per min.) especially at lower x‐ray tube potentials.
11.W. de Groot, Physica 6, 393 (1939).
12.F. H. Day and L. S. Taylor, J. Research Nat. Bur. Stand. 40, 393 (1948).
13.The author is much indebted to Mr. Jacobs for the facility of using these values in the present investigation.
14.It might be useful to determine this dependency, for instance, with the powerful filter method developed by H. Kustner, Zeits. f. Physik 70, 324 (1931). According to his measurements monochromatic radiations with intensities from to can be produced in the wave‐length region 0.128 to 2.50A.
15.For a comparison of the effects produced by x‐rays of different wave‐lengths at ionization in air, at fluorescent screens and at the photographic plate see: G. L. Clark, Applied X‐Rays (New York, 1940), p. 68, Fig. 48.
16.The intensity of the afterglow of the phosphor is proportional to the number of recombination processes The photo‐current is proportional to the number n of electrons in the conduction band. Hence the optical decay is faster than the decay of the photo‐current. Verified by L. Gildart and A. W. Ewald in a paper given at the Oak Ridge meeting of the Physical Society (March, 1950).
16.(a) T. Broser and R. Warminsky, Zeits. f. Naturforschung 5A, 63 (1950).
17.W. B. Nottingham, Rev. Sci. Inst. 11, 2 (1940).
17.R. J. Cashman, reference 10, p. 918, Fig. 20.
18.S. G. Zizzo and J. B. Platt, Phys. Rev. 76, 704 (1949) studied the pulses due to x‐ray quanta as well as the continuous photo‐current in CdS crystals obtained from the author.
18.Note added in proof: Measurements of the efficiency of the photocurrents produced in CdS crystals by irradiation with x‐rays have been recently published by Y. Fassbender and O. Hachenberg, Ann. d. Physik (6) 6, 229 (1949). They confirm our results regarding the amplification factor in CdS.
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