SMITHSONIAN MISCELLANEOUS COLLECTIONSVOLUME 87, NUMBER 8
IRoeblino jfunbf^ may i? 193^
GRAPHIC CORRELATION OF RADIATIONAND BIOLOGICAL DATA
BYF. S. BRAGKETTChief, Division of Radiation and Organisms,Smittisonian Institution
'SL T W
(Publication 3170)
CITY OF WASHINGTONPUBLISHED BY THE SMITHSONIAN INSTITUTIONMAY 17, 1932

SMITHSONIAN MISCELLANEOUS COLLECTIONSVOLUME 87, NUMBER 8
IRoeblino fxmb
GRAPHIC CORRELATION OF RADIATIONAND BIOLOGICAL DATA
BYF. S. BRAGKETTChief, Division of Radiation and Organisms,Smithsonian Institution
(Publication 3170)
CITY OF WASHINGTONPUBLISHED BY THE SMITHSONIAN INSTITUTIONMAY 17, 1932
Zi>& JSor5 ^akimove (preeeBALTIMORE, MD., U. 8. A.
IRocblino dfun&GRAPHIC CORRELATION OF RADIATION ANDBIOLOGICAL DATABy F. S. BRACKETTChief, Division of Radiation and Organisms, Smithsonian InstitutionIn discussions of the relation of radiation to biological phenomenaone frequently wishes to correlate transmission curves and the char-acteristics of common sources of light with the response curves of thebiological phenomena. Although the facts involved are for the mostpart well known, they are scattered through the literature in such away that it is difficult to form a clear picture of their interrelationwithout gathering this material together graphically. In order to meetthis need the composite graph shown in Figure i has been developed.The accompanying explanation indicates the significance of eachcurve, and the bibliography at the end of the paper will enable anyonewho wishes more detailed data to go immediately to the originalsources.As water is the chief constituent of most living matter, its trans-mission characteristics set definite limits for other than surface efifectsof radiation. It is perhaps significant that radiation therapy has foundits effective wave-length regions in those ranges where transition takesplace from negligible transmission to relatively great transmission.Such a region exists in X rays from lA to shorter wave lengths, andagain in the ultra-violet for wave lengths immediately longer than
.18/A. Another region which has as yet been little studied occurs inthe near infra-red for wave lengths shorter than 1.4/i. The trans-mission characteristics of water may perhaps most readily be indi-cated by plotting the absorption coefficients, that is k in the expressionI— 1^0-^-^, as a function of wave length or frequency over the regionsof interest. The full line curve a iji the upper section indicates thesevalues for the range from io/a to .i/t in wave length as indicated atthe bottom of the graph, or .1 to 10, X 10* wave number (waves percm, i. e., proportional to frequency) as indicated at the top. The valuesof the absorption coefficients are shown at the left outside the frame.Another convenient method is to indicate for each wave length orfrequency the thickness of water which will reduce the light to one-halfSmithsonian Miscellaneous Collections, Vol. 87, No. 8.
SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87
EXPLANATION OF FIGURE 1Upper Section : ABSORPTION.a Water, ultra-violet, visible, and infra-red.Ordinates : Absorption coefficients k in I =1 hc'^'^ (outside left).Thickness transmitting half intensity in cm (inside left)Transmission of i-cm thickness (right).Abscissae: Wave lengths in microns pl (bottom).Wave numbers, waves per cm (top).b Water, X ray (same ordinates).Wave lengths in Angstroms (instead of /i as indicatedat bottom).c ._._._._ Ozone, (same coordinates as in a; gas at standard conditions).Atmospheric transmission is equivalent to about 3 mm and can befound by shifting scale (right) up by approximately half adivision.Middle Section: RADIATION.Relative emission from body at 1,000° K. (dull-red therapeutic lamp).Relative emission from body at 3,000° K. (high-temperature Tungstenlamp).Relative emission from sun.Relative emission from mercury arc in (|uartz.Lower Section: BIOLOGICAL PHENOMENA.a, transmission of flesh (1/2 cm thick) in per cent.b, relative visibility.c, relative phototropism.d, Vitamin A.Absorption and vitamin value disappears when radiated.e, Ergosterol.Absorption disappears under radiation, which produces activationyielding therapeutic value of vitamin D./. Relative erythema effectiveness, zero degree (very light). For extremeerythema, fourth or fifth degree, the relative intensities of thethe two maxima are reversed.
NO. 8 RADIATION AND BIOLOGICAL DATA—BRACKETT
I I I—I—I—
r
to^ i 7 t> S '^ JINFRA-RED ULTRA-VIOLETFigure i.
4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/
its incident intensity value. These may be found from the same curveby reference to the ordinates at the left within the frame.Thus at the limit of the visible in the red we find that some 30-cmwater path is required to reduce the intensity of light to one-half itsoriginal value, whereas at i^ix only .03 cm or .3 mm will produce thesame result. As water cells are frequently used of i-cm thickness it isconvenient to indicate the wave-length range over which such a cellwill yield appreciable transmission. The values of transmission forI -cm path are indicated at the right of the upper section. Theseenable one to immediately estimate the wave-length range for thecut-ofT from such a cell.In order to compare the absorption characteristics which are fa-miliar to radiologists in the X-ray range with those exhibited in thevisible range the X-ray values have been indicated by the dotted curveb, the wave lengths being found by reading Angstroms instead of /x atthe bottom of the graph. It is interesting to note the relatively smoothtransition from low to high transmission in the X-ray region com-pared with the highly selective characteristics exhibited in the infra-red, visible, and near ultra-violet.As the presence of ozone in the atmosphere plays an important rolein limiting the light which reaches the earth, the transmission char-acteristics of ozone gas under standard conditions have been indicatedby curve c. The transmission values at the right now apply to a cellof I -cm thickness of ozone gas under standard conditions. Since,however, the whole absorption in the atmosphere is equivalent to about3 mm, in order to estimate the absorption of atmospheric ozone it isnecessary to shift the transmission scale bodily upward by one-halfof one of the large spaces indicated. We thus find the transition from90 per cent to i per cent occurring in a very narrow region from3,200 A to 2,950 A respectively.With these curves in mind we may now profitably turn to the matterof sources of radiation with which one has commonly to deal. For thesake of comparison we have assumed that lamps will be chosen of sucha size and used at such a distance that a comparable amount of maxi-mum energy is received. The curve at the left shows the relativeemission per unit wave length of radiation at each wave length for asoHd body at the absolute temperature of 1,000° K. Here we findmost of the energy occurring for wave lengths longer than 1.4.(1, or, inother words, in a region where practically all the energy will be ab-sorbed in an extremely thin layer of water. The customary dull redtherapeutic lamp has characteristics not greatly different from this
NO. 8 RADIATION AND BIOLOGICAL DATA BRACKETT 5
curve. For that reason it must be regarded for the most part simplyas a surface heater.The next curve indicates the emission of a soHd body at an absolutetemperature of 3,000° K, where it is now seen that its maximumenergy lies in a region which would be relatively well transmitted bywater. Such a radiation might well be expected to penetrate some-what into the living matter. It does, however, contain a considerableproportion of energy which will be absorbed in a thin layer, that is forwave lengths longer than 1.4/*. If one wishes radiation that is asnearly free as possible of this surface-absorbed energy, a light of thistemperature should be used with a water filter. A modified curve isindicated terminating at approximately i.4fx, which shows the type ofradiation which one would receive from an ordinary high-temperaturelamp such as the customary Tungsten light when equipped with awater cell of i-cm thickness. Again, on approximately the same scalethe relative distribution of solar energy is shown as it would be with-out atmospheric absorption. Owing to atmospheric ozone no ap-preciable ultra-violet reaches us from the sun beyond 2,950 A. As theamount of ozone fluctuates this limit varies considerably. Further-more, large amounts of energy are absorbed in the infra-red by at-mospheric molecules, particularly water vapor. This, again, is subjectto extreme variations, depending upon the location, time of day, andamount of humidity. In the solar curve we see that the chief energylies in the visible region, whereas our high-temperature lamp, evenwith a water filter, has the larger proportion of its energy in the nearinfra-red. Since for therapeutic purposes the mercury arc is verywidely used, its energy distribution has also been shown. As its lightis radiated chiefly in a large number of restricted regions of prac-tically monochromatic light, it can best be shown simply by verticallines. The height of these lines is proportional to the intensity. Since,however, they difter widely for different conditions of excitation, theymust be regarded at best as only a rough basis for estimation.In addition to the blue and ultra-violet lines with which we arechiefly concerned, this arc shows not only strong yellow and greenlines, but in most cases a line at 1.014/^ of an intensity which exceedsany other line. This great line in the near infra-red occurs in a regionwhere it is readily transmitted by water and, as we shall see in amoment, to a great extent by flesh. This wave length of radiation isreadily transmitted by the aqueous humor of the eye and will bechiefly absorbed in the retina. While undoubtedly ultra-violet effectswould be noticed long before any danger would be incurred from thisradiation in the case of a quartz mercury arc, on the other hand in the
6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/
case of ordinary glass mercury arc caution should be used to avoidtoo great exposure as it may produce a lasting injury in the natureof an actual burn on the retina.In order to be able to correlate these physical characteristics whichwe have indicated with the direct observations of biological material,the lower portion has been devoted to characteristics for which datais available. Curve a shows the transmission of flesh, having beencorrected for surface absorption. On the long wave-length side un-doubtedly water is most important in setting the limit. On the shortwave-length side other constituents of the living matter account forthe fact that this transmission drops off rapidly on passing into thevisible range. It will be noticed, therefore, that the region of themaximum transmission of flesh occurs roughly in the range emittedfrom a water-filtered high-temperature light. The near infra-red thusconstitutes a region of relatively penetrating radiation for therapeuticpurposes. Curve b shows relative visibility of light for the human eye.Curve c shows the relative phototropic response of an oat seedling tolight. It will be noticed that it is insensitive to red and a considerableportion of the yellow, the maximum occurring in the blue. Curve (/shows the absorption band that seems to be correlated with vitamin A.Radiation that is damaging to the vitamin value causes a weakening inthis band. Curve e shows the absorption band that seems to be corre-lated with ergosterol and vitamin D. Radiation that seems to produceactivation destroys this absorption. Curve /, the full line curve, showsthe erythema response of the human skin in the case of a very lighterythema (zero degree). Here it will be seen that a minor maximumoccurs at .298/* and a great maximum in the region of .253111. In thecase of extreme erythema, fourth or fifth degree, the relative effective-ness of these two regions is reversed, the great maximum occurringat .300ja and the smaller maximum at the region of .253;^. It is,however, very significant and perhaps important from a therapeuticstandpoint that a minimum of erythema occurs between these tworanges and that this minimum coincides with the chief ergosterolabsorption. It may thus be possible to secure a maximum therapeuticdosage with a reduction in resulting erythema by the use of mono-chromatic light in this range. The magnesium spark lines at .280/x arepromising for this purpose.Another point of interest is that the lethal region for algae occursin this same range as ergosterol absorption, the threshold for thiseffect being indicated by the arrow marked D. The solar energy falls
oft" rapidly at this jKiint.
NO. 8 RADIATION AND BIOLOGICAL DATA BRACKETT 7BIBLIOGRAPHYUpper Section of Figure i
:
0. Becquerel, J., and Rossignol, J., International Critical Tables, vol. 5,p. 269, 1929. Lyman, T., The spectroscopy of the extreme ultra-violet,p. 67, New York and London, Longmans, Green & Co., 1928.b. Siegbahn, M., The spectroscopy of X-rays, p. 248, London, Oxford Uni-versity Press, 1925.c. Fabry, C, Guthrie Lecture, The absorption of radiation in the upperatmosphere. Proc. Phys. Soc, vol. 39, pt. i, pp. 1-14, Dec, 1926.Middle Section:1000° K. Fowle, F. E., International Critical Tables, vol. 5, p. 240, 1929-3000° K. International Critical Tables, vol. 5, p. 241, 1929.Sun. Ann. Astrophys. Obs., vol. 3, p. 200, 1913.Hg. McAlister, E. D., Phys. Rev., vol. 34, no. 8, p. 1142, 1929. Also Rep.Seer. Smithsonian Inst., 1931, p. 133, 1931.Lower Section
:
a. Cartwright's curve corrected for reflection by Forsythe and Christian,Journ. Opt. Soc. Amer., vol. 20, no. 12, p. 696, 1930.b. Ives, H. E., International Critical Tables, vol. 5, p. 436, 1929.c. Unpublished data from Division of Radiation and Organisms, Smith-sonian Institution.d. Morton and Heilbron, Biochem. Journ., vol. 22, p. 987, 1928.e. Pohl, R., Nach. Ges. Wiss. Gottingen. Math.-Phys. Klasse 1926, Heft 2,p. i8s, 1927-/. Adams, Barnes, and Forsythe, Journ Opt. Soc. Amer., vol. 21, no. 4,p. 217, 1931-