. Radium, X rays and the living cell. Two typical cases are represented. Curve I. illustrates theway in which the rays from a soft bulb (spark gap of about10 cms. between points) are absorbed by interposed screens ofaluminium. Curve II. illustrates the same procedure for veryhard Xrays (spark gap of about 30 cms. between points), all ofthe softer components being cut out by 7 mm. of curve I. be anal^sed in the manner suggested above, thelogarithms of the ionisation will be found not to lie upon a straight line, but the curvemay be arbitrarily dividedinto three sections, D, E andF,
. Radium, X rays and the living cell. Two typical cases are represented. Curve I. illustrates theway in which the rays from a soft bulb (spark gap of about10 cms. between points) are absorbed by interposed screens ofaluminium. Curve II. illustrates the same procedure for veryhard Xrays (spark gap of about 30 cms. between points), all ofthe softer components being cut out by 7 mm. of curve I. be anal^sed in the manner suggested above, thelogarithms of the ionisation will be found not to lie upon a straight line, but the curvemay be arbitrarily dividedinto three sections, D, E andF, over which the radiationis practically of one degreeof hardness, and numericalvalues may be apportionedto them for purposes of com-parison. Although nominallya soft bulb, analysisshows that the radiation isheterogeneous, consisting of soft ra3^s (portion D),medium rays (£), and hardravs (F). When a similar I0-2 ~ anah^sis is made of curve II., the radiation is found to be practically homogeneous character. Numerical values will be. 48 72 Mms of Aluminium Tig. 6. and of a ver}^ hardfound in Table 3. THE COEFFICIENT OF ABSORPTION OF THE RAYS. It is convenient to refer to the penetrating power of a beam ofrays in terms of a coefficient * (X), the numerical value of which * The value of \ is obtained as follows : The intensity of a homogeneousbeam in its passage through matter may be represented by the equation : I=I,/-A</. Where I,, is the initial ionisation produced by the beam and I the ionisationproduced after a thickness of matter d has been traversed. Hence \= i^HIiiiliLziSSiidl. d X RAYS THROUGH MATTER 23 is inversely proportional to the penetrating power of thebeam. A large value of A corresponds to an easily absorbedbeam, and a small value to a very penetrating one. Thevalue of A also varies according to the nature of the absorbingmaterial. If after traversing i cm. of matter the ionisation in the electro-scope is reduced to one-half its initial value, A =.69 cm
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