File:The American journal of roentgenology, radium therapy and nuclear medicine (1906) (14570922799).jpg

Identifier: americanjournroen08ameruoft (find matches)
Title: The American journal of roentgenology, radium therapy and nuclear medicine
Year: 1906 (1900s)
Authors: American Radium Society American Roentgen Ray Society
Subjects: Radiotherapy X-rays
Publisher: Springfield, Ill. C.C. Thomas
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

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Rutherford. This shows that the hard- * In thinkinsr of the coefficient of absorption in theseterms, care should he exercised to choose a unit o£thickness which will make the amount of radiationabsorbed by a filter of unit thickness a small fractionof the incident radiation. Absorption of Radium Radiation by Tissues 219 ness of the gamma radiation from radiumincreases with the thickness of filter beyond2 cm. of lead. In fact, from the experimentsof Tuomikoski* and others, it appears thatthe penetration of the gamma radiation ofradium increases even after filtration by sev-eral centimeters of lead. Such excessive fil-tration, however, is entirely out of the ques- the aluminum and brass curves becomestraight lines beyond a thickness of a fewmilllimeters indicates that radium radiationfiltered through 6 mm. of aluminum or 2mm. of brass is sufficiently homogeneous tobe absorbed by these metals according tothe exponential law given above, withinthe range of thicknesses shown in Figure 2.
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Figure 2. tion in radium therapy, on account of theweight of the filter and the diminution ofthe quantity of radiation which passesthrough it. Even for 20 mm. of lead theionization produced by the transmitted radia-tion is only 1.5% of the value for the un-filtered beta and gamma radiation, and lessthan 54 the value for radiation through imm. of lead. Fortunately no such filtration is necessaryin therapy. In the first place, the fact that The reason is that for substances of lowatomic weight the coefficients of absorptionas here defined do not vary much with thewave length, for gamma radiation of thequality considered.^ A fortiori this is true ofthe absorption of tissue, the principal con-stituents of which are much lighter thanthese metals. Iji the case of lead, the mechan-ism of absorption is further complicated bythe fact that the element is an isotope ofRadium B.* 220 Absorption of Radium Radiation by Tissues In Figures 3 and 4 are shown the curvesof absorption by tissue of the ra

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