A N A L Y T I C A L CHEMISTRY
1580 Discussion. The application of the anthrone reaction to the heptuloses is another illustration of the nonspecificity of this reagent within the carbohydrates. It is possible that conditions can be established for the determination of all five-, six-, and seven-carbon sugars. Hydrolysis and dehydration by the sulfuric acid solvent in the reagent are primary factors in the application of this method to a wide range of compounds. Because the over-all accuracy of a colorimetric method depends in part on the susceptibility of the color to fading, the transient blue-green color produced by pentoses has been used in only two recorded cases ( 2 , 4 ) . Rapid loss of color was retarded by rigorous temperature control. Anthrone reagent prepared in 66% sulfuric acid provides a blue-green color with pentoses that is comparable in stability to that of the hexoses. The maximum absorption a t 625 my obtained in the reaction of hexoses with anthrone also represents an unstable intermediate, as longer heating causes a large decrease in this absorption. K i t h glucose (15),it has been shown that this absorption loss is superseded by the appearance of an absorption maximum at 425 my. I n the present work the variation of absorption a t this wave length, with sugar concentration, was found to be linear; however, because of the additional heating time required and the background color produced by nitrate ion, this method has not been used.
presented in this paper. Thanks are also extended to A. A. Benson, who supplied the sample of mannoheptulose.
ACKNOWLEDGMENT
RECEIVED for review February 4, 1966. Accepted June 22, 1956. Work performed under Contract W-7406-eng-26 for the U. S. Atomic Energy Commission. Preliminary report glven a t meeting of Federation of American Societies for Experimental Biology, April 16 to 20, 1956 (abstract, 18).
The author wishes to acknowledge the valuable assistance of D. A. Mondon during various phases of the experimental work
Cellophane-Dye Dosimeter for ERNEST J. HENLEY
and
LITERATURE CITED
(1)
hfERICAN
1956. (2) Bridges, R. R., ANAL.CHEW24, 2004-5 (1952). (3) Dreywood, R., IND. ENG.CHEY., AXAL.ED. 18, 499 (1946). (4) Gary, S . D., Klausmeier, R. E., ANAL.CHEM.26, 1958-60 (1954). (5) Holler, A. C., Huch, R. V.,I b i d . , 21, 1385-9 (1949). (6) Khym, J. X., Zill, L. P., J . Am. Chem. SOC.74, 2090-4 (1952). (7) Koalov, V. V., Kudelina, K. I., J . Gen. Chem. U.S.S.R. 17, 302-8 (1947). (8) Lewis, G. K., Calvin, RI., Chem. Rem. 25, 273-328 (1939). (9) 1Iorris. D. L.. Science 107. 254-5 (1948). (IO) Xordal, A, Klevstrand, R:, Anal. Chim’. Acta 4, 411-21 (1950). (11) Roe, J. H., J . Biol. Chem. 212, 335-43 (1955). J . Am. Chem. SOC.72, 3814 (1950). (12) Sattler, L., Zerban, F. W,, (13) Battler, L., Zerban, F. W.,Science 108, 207 (1948). (14) Schutz, F.,Papier-Fabr. 36 (Tech. Tl.), 55-6 (1938). (15) Scott, T. A., Jr., Rlelvin, E. H., ASAL. CHEM. 25, 1656-61 (1953). (16) Whetsel, K. B., I b i d . , 25, 1334-7 (1953). (17) I b i d . , 26, 1974-7 (1954). (18) Zill, L. P., Federation Proc. 15, 391 (1956). (19) Zill, L. P., Khym, J. X., Cheniae, G. XI., J. Am. Chem. SOC.75, 1339-42 (1953). (20) Zill, L. P., Tolbert, K.E., Ibid., 76,2929-33 (1954).
IO’ to IO’ Roentgen Range
DAVID RICHMAN’
Department o f Chemical Engineering, Columbia University, N e w York 27,
Experimental work in radiation chemistry and biology necessitates careful measurement of the radiation dose used. This paper describes a recording integrating chemical dosimeter, capable of measuring gamma and beta doses from 200,000 to 10,000,000 roentgens. Calibration curves are presented for 0.8-, 2-, and 3-m.e.v. beta radiation, and for a cobalt-60 gamma source over a dose rate range of 106 to 107 roentgens per hour. The dosimeter is fabricated from commercially available cellophane, and is convenient, inexpensive, and stable.
F
OR process control, equipment design, and safety it is necessary to measure the effects of atomic radiation quantitatively. Most well-developed systems now in common use are biological monitors, operating a t levels up to 50 roentgens. I n the higher ranges (loj to 107 roentgens) there are several chemical systems in use, most of which require analytical chemical techniques before dose exposure can be ascertained. Many have been suggested and actually calibrated Yith some degree of care; these include: ( a ) oxidation-reduction dyes in agar ( 2 , 13); ( b ) benzene or sodium benzoate in water ( 3 ) ; 1
Preaent address, Brookhaven National Laboratory, Upton, Long Island,
ti.Y.
CHEMICAL SOCIETY, “Reagent Chemicals,” p. 400,
N. Y.
(c) degree of polymerization of various monomers ( I d ) ;
( d ) reduction of methylene blue dyes in water (4,1 7 ) ; (e) phosphate and cobalt glasses (8, 16); (f) depigmentation of rats (11); ( 9 ) poly(viny1 chloride) films, in which a redox dye is incorporated (6); ( h ) ferrous-ferric oxidation in 0.8N sulfuric acid (10, 19); (i) ceric-cerous reduction in 0.8Nsulfuric acid ( 7 , 19). For monitoring applications in radiation sterilization or radiation chemistry, cost, convenience, and reliability are the chief criteria. Of the nine dosimeters described only the poly(viny1 chloride) films and phosphate and cobalt glasses approach these specifications. Unfortunately, both have severe limitations. The phosphate glass is subject to fading, is expensive, and has a poor radiation response above 1,000,000 roentgens. The poly(vinyl chloride) films are expensive and not generally available. I n view of the shortcomings of the present dosimeters, an investigation of some commercially available polymeric systems which could be adapted for this use was initiated. Of the many tested, a Du Pont moisture-proof, heat-sealable cellophane, containing a dimethoxydiphenylbisazobis-8-amino-l-naphthol-5,7disulfonic acid dye (14) proved to be most suitable. One of the advantages of this system is the stability of the dye. It is relatively insensitive to pH, light, and heat. Films stored in the dark for periods of 2 years do not change optically. They fade only on exposure to temperatures over 60’ C. for long periods of time-e.g., 10 hours gives a readable change.
V O L U M E 2 8 , NO. 10, O C T O B E R 1 9 5 6
1581
The irradiation irreversibly decolorizes the dye. The cellophane does not regain color, nor is there a dark reaction for strips stored for over 1 month. Dye solutions irradiated to almost clarity do not recover color on addition of acid or base or after contact with oxygen.
1
"
"
'
"
"
'
"
not vary haphazardly from film t o film. A plot of the initial transmittance for a number of films follows a typical random distribution curve. This is due to nonuniformity of film thickness. DISCUSSION
The initial calibrations were carried out a t Columbia with a cobalt-60 gamma source ( 5 ) . This had previously been calibrated with the ferrous-ferric system, ion chambers, and other techniques. All irradiations were carried out with the cellophane films in separate envelopes, sandwiched bet\%-een polyethylene sheets l/8 inch thick. Figure 1 shows the per cent transmittance as a function of radiation dose for gamma radiation. A continuous straightline relationship is obtained; this is also the case for the electron radiation. When the transmittance change is more than about 20%, the decomposed dye molecules begin t o compete for the radiation, and the kinetics no longer hold. At this point i t becomes more convenient to plot the log of the absorbance us. dose. This plot gives a straight line over a very wide range, illustrating that the destruction follon-s a target or direct hit theory. Figure 2 is a presentation of another series of calibrations and includes data from the University of Michigan's cobalt source. The 95% confidence limits are a function of the total radiation dose. For a single determination they vary from 60% a t 200,000 roentgens to 6% a t 3 X loeroentgens.
"
I
19.
o
IP 16 ROENTGEN x 10-5
4
0
PO
24
Pa
Figure 1. Cobalt-60 calibration of per cent transmittance us. dosage Ta
=
initial film transmittance
The sheets of cellophane cost 0.042 cent per 1000 square inches, and the optical and physical characteristics are satisfactorily uniform for use as a control device, provided strips are cut in the direction of th.e extrusion. The chemical effects of radiation on cellulose itself can be deduced from experiments conducted by Lawton and coworkers a t General Electric (9). For all changes measured, almost no detectable effects were noted when basswood was irradiated with electrons to a dose below 6 X 106 roentgens. Dosages between 6 X lo6and 1 X 108 roentgens caused the wood t o become hygroscopic and friable, and resulted in large increases in pentoses. reducing sugar, and soluble extract. The basswood became as digestible as hay to rumen bacteria as a result of this treatment. Similar chemical changes ivere observed when pure cellulose was irradiated. 30 chemical tests of the irradiated cellophane were undertaken in this study. Infrared and ultraviolet anal)-sis failed to reveal changes in qamples irradiated to 3 X 106 roentgens. METHOD
The techniques used in handling the dosimeters present no unusual problems. Sheets of the cellophane are cut into strips '/z inch wide and l l / a inches long. They are then inserted into an aluminum holder, and the initial transmittance of the system is read. Thorough scanning of the absorption spectrum of irradiated and unirradiated films showed that the most suitable peak, for purposes of dosimetry, was a t 6500 A,; all subsequent readings m r e made a t 6550 A. on a Beckman Model D U spectrophotometer. The thickness of commercial cellophane is satisfactorily controlled a t 1 mil, so the initial transmittance does
0
Figure 2.
P
4 6 DOSE IN ROENTGEN X 10-
8
10
Gamma ray calibrations a t 100,000 roentgens per hour Cobalt-BO:
0 2 X X
0
105 roentgens per hour
1 X 106 roentgens per hour 5 X 104 roentgens per hour
For radiation chemistry experiments electron sources are proving t o be as important as gamma ray units. For this reason calibration curves for the cellophane films were obtained using a number of electron generators. Initial calibrations xl-ere determined a t Brookhaven National Laboratory using a Van de Graaff generator. An aluminum plate, '/z inch thick and 8 inches in diameter with a centered hole a/8 inch in diameter, was interposed between the cellophane films and the primary dosimeter, a current-collecting solution. This technique circumvented the problem of defocusing the beam or of integrating across the cellophane films. The transmittances of the irradiated portion of the films were determined by using a micro attachment on the Beckman or 2-mm. holes punched into an aluminum screen. Dosages were calculated in two ways: (1) from Trump, Wright, and Clarke's (18)depth dose curves for 2-m.e.v. electrong,
1582
ANALYTICAL CHEMISTRY
by determining the fraction of the total energy absorbed, assuming an entrance dose of three fifths of maximum dose; and (2) using an unpublished experimental result (15),linear energy transfer (LET), dE/dx = 1.73 m.e.v. per gram per sq. cm. The two methods agreed to within 1%. For the 1-m.e.v. irradiations the unpublished figure of 1.8 m.e.v. per gram per sq. cm. was used (15). This correlated the data very well. Figure 3 is a plot of rate of dye destruction us. dose. I n the experiments a t Brookhaven National Laboratory a rate of 3.2% transmittance per 1,000,000 roentgens, independent of dose rate and energy, was found.
P
10
2
c
J
4
. $
3
2
B P Lt
I
0.5
10'
10' 10' 108 DOSE RATE, ROENTGENWHOUR
Figure 4.
H X
A
109
Effect of dose rate
Cobalt hI. 1. T. 2.9 m.e.v. G. E. 0.8 m.e.v. B. N. L. 1.95 m.e.v. B. N. L. 1.0 m.e.v.
The utility of these dosimeters is apparent. They are already in routine use in several laboratories. I n radiation chemistry n-ork their small size and flexibility permit dosage measurements to be made inside and outside reactors. For monitoring and control work the price of these films puts them in a class by themselves. ACKNOWLEDGMENT
ov 0
I
I
4
I
I
1 2 3 4 5 DOSE IN ROENTGEN X 10-8
6
Figure 3. Electron calibration of per cent transmittance change us. dosage Symbol
0
20 X
Roentgens/Hour 9 . 6 X 10'
x x x
107 9.2 8 . 4 X 10s 1.0 10' 1.0 106
M.e.v. 1 1.95 1.95 1.95 1.95
Figure 4 shows that the rate for electron radiation is higher by a factor of 2.2 than the rate of destruction of dye by cobalt gamma radiation. The dotted lines give an indication of the precision. All of the approximately 100 films irradiated gave values within & l o % of the mean. Included on this plot for purposes of comparison are some points obtained a t Massachusetts Institute of Technology with a 2.9-m.e.v. Van de Graaff generator, and a t General Electric using an 0.8-m.e.v. resonance generator. It is difficult to reconcile the factor of 2.2 between the effectiveness of cobalt and beta radiation. The dye molecules are only about 10 A. in size, and there is approximately 50 A. between molecules. One, therefore, would not expect any dose rate effects. One possible explanation lies in the L E T difference between cobalt and 2-m.e.v. beta radiation. Using Cormack's and Johns's (1) integration of the secondary spectrum from cobalt-60, and Schuler's value of dE/dx, the factor is found to be 2.2. This is exactly the ratio of destruction rates. Until more data are taken over a greater range of LET'S, this agreement must be considered fortuitous. It would also be desirable to obtain dose rate data in the range from 2 X los to 1 x 106 roentgens per hour in order to confirm the dose rate independence.
It is a pleasure to acknowledge the contributions of A. 0. Allen, Robert Schuler, and particularly of Nathaniel F. Barr, who conducted the Van de Graaff irradiations a t Brookhaven. Thanks are also due to S. A. Goldblith, Sol Davidson, and L. E. Brownell who supplied some of the data which are plotted. The help of B. M. Henley, who prepared many of the samples, was most welcome. A portion of this work was supported by the Atomic Energy Commission Contract AT(30-1)-1186, and by the Quartermaster Corps. LITERATURE CITED
(1) Cormack, D. V., Johns, H. E.. Brit.J . Radiol. 25, 369 (1952). (2) Day, M.J., A'ature 166, 146 (1950). (3) Day, hl. J., Stein, G., Ibid., 164, 671 (1949). (4) Goldblith, S. A., Proctor, B. E., Hammerle, 0. 8 . ,Ind. Eng. Chem. 44,310 (1952). (5) Henley, E. J., Nucleonics 11, No. 10, 41 (1953). (6) Henley, E. J., Miller, A., Ibid., 9, KO.6, 62 (1951). (7) Hochanadel, C. J., Oak Ridge National Laboratory, ORNL-879 (1950). (8) Kreidl, N. J., Blair, G. E., ArucZeonics 14, No. 1, 56 (1956). (9) Lawton. M. P.. - - ~E.~ J.. . Bellamv. W. D.. Humate. - . R. E.., Brvant. Hall, E., i c i e n c e 113; 380 (1951). (10) Miller, N., J. Chem. Phys. 18, 79 (1950). (11) Noshman, J., Upton, A. C., Science 119, 186 (1954). (12) Prevot, A., Compt. rend. 230, 288 (1950). (13) Proctor, B. E., Goldblith, S.A., Nucleonics 7, Xo. 2, 83 (1950). (14) Rowe, F. M., "Colour Index," Society of Dyers and Colourists, Index 518,1924. (15) Schuler, Robert, Brookhaven National Laboratory, personal communication. (16) Schulman, J. H., Nucleonics 13, No. 2, 30 (1955). (17) Shekhtman, Ya. L., Krasnovskii, A. A., Vereshchinskii, I. T., Doklady Akad. X a u k S.S.S.R. 74,767 (1950). (18) Trump, J. G., Wright, K. A., Clarke, A. M., J . A p p l . Phys 21,345 (1950). (19) Weiss, J., h'ucleonics 10, No. 7, 28 (1952). \-,
RECEIVED for reiiew December 2, 1955. Accepted M a y 3, 1956. Division of Polymer Chemistry, Symposium on Effect of Radiation on Polymers 127th meeting, ACS, Cincinnati, Ohio, March-April 1955.
