The method of conc entration determination of l ead nitrate
solutions in the concentration range up to 20 grams per 100 ml by
g amma rays absorption measurements was described. GOCo and 1s1 cs
were used as gamma r ay sources. The gamma ray intensities were
measured using a sc intillation co unter.
Using a simple equation for the absorption of gamma rays , the
equation which contains the directly measured values only, was
developed. Using that equation the absorption for all used concentrations
was calcula ted . The agreem ent between measured and
calculate d values is fairly well. The possible reason of obtained
dis ag reement is discussed

S. Žilić

Z. Kolar

English

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CROATICA CHEMICA ACTA 34 (1962) 103 CCA-249 539.166.75 :546.817'17'21 The Comparison Between Measured and Calculated Values of Gamma Ray Absorption on Lead Nitrate Solutions Z. Kolar and S. Zilic D epartment of Radiochemistry, Institute Ruder Boskovic« and D epartment of Radiochemistry, Faculty of Technology, University of Zagreb, Zagreb, Croatia, Yugoslavia Receive<! March 9, 1962 The method of concentration determination of lead nitrate solutions in the concentration range up to 20 grams per 100 ml by gamma rays absorption measurements was described. GOCo and 1s1cs were used as gamma ray sources. The gamma ray intensities were measured using a scintillation counter. Using a simple equation for the absorption of gamma rays, the equation which contains the directly measured values only, was developed. Using that equation the absorption for all used concen-trations was calculated. The agreement between measured and calculated values is fairly well. The possible reason of obtained disagreement is discussed. INTRODUCTION The interaction of gamma rays with matter can occur in two general ways: scattering and absorption. Because b oth gamma ray scattering and absorption intensities are dependent upon the atomic number of the material, they can be applied to the quantitative analysis of two-component systems. In a number of published papers the use of gamma ray absorptiometry in analysis of heavy metal salts and especially uranium salts have been described1- 3• Some published articles describe the application of the method for chemical processes4 • Miller and Conally described the gamma ray absorptio-meter for in-line determination of plutonium and uraniums. As gamma ray sources in these experiments americium-241 and thulium-170 were used in most cases. It can be said in general that low energy gamma ray sources are more convenient than those of higher energy, because .of the greater difference between the mass absorption coefficients of water or solvent and dissolved heavy metal salt. The judicious application of these facts can confer a higher sensitivity to the method. In most cases an ionization chamber was used for the measurement of gamma ray intensities. Thurnau used a scintillation detector instead of the ionization chamber and the signals were recorded on a ratio recorder1• The concentration determination by absorption is fast, simple and non-destrucive. EXPERIMENTAL A schematic diagram of the apparatus used in the gamma ray absorption measurements is shown in Fig. 1. 104 Z. KOLAR AND S . 2ILIC As gamma ray sources 0.5 mC of cobalt-60 and 3 mC of caesium-137 were used. In order to prevent the contamination of the equipment used, the sources were sealed in aluminium capsules having walls 0.2 mm in thickness. The sources were placed in the lead container and a collimated gamma ray beam was allowed to pass through the test tube filled with the test solution. The lower energy 662 keV gamma rays are more readily absorbed by the lead test solution than the 1.33 and the 1.17 MeV gamma rays emitted from a cobalt-60 source. The measurement of the absorption with caesium-137 and cobalt-60 emitting gamma rays was easily done because of the very long half-life of both isotopes. The gamma ray sources used in this work were obtained from Harwell. - TO COUNTER LEAD SHIELD BLACK PAPER - -=.._,.. LEAD COLLIMATOR - ~ (HOLE .IMmm) MULTIPLIER PHOTOTUBE NaJCTLl 1 V2x 1'" CRYSTAL ~ GLASS ·- - SAMPLE TUBE LEAD COLLIMATOR - ::(HOLE.0'·8mm) , - . . - LEAD CONT:INER.,, SOURCE Co or Cs ;...---:: Fig. 1. Schematic diagram of gamma ray absorptiometer A lead tube, 75 mm long, with a hole 8 mm in diameter was used as a collimator. After passing the glass tube filled with the lead nitrate solution, the beam passed through another collimator. The gamma ray beam thus collimated was allowed to enter the 17\?"X l " Nal(Tl) scintillation crystal connected with a multiplier phototube and the scaler. The counting equipment used in this work was obtained from EKCO Electronics. The known solutions were prepared by weighing the desired amount of lead nitrate and dissolving it in distilled water. The concentration of the investigated solutions varied from O to 200 grams of lead nitrate per liter. The high purity (p.a .) lead nitrate used was obtained from Merck. The sample tube was always f illed with the same volume of solution (50 ccm). As sample a glass test tube 200 mm long and 23±0.5 mm inner diameter was used. Measurements of intensities without the gamma r ay beam p assing the absorption solution and after its passing solutions of various concentrations of lead nitrate were taken. The obtained values were corrected for the background by measuring the activity when the gamma ray source was closed in the lead container by a lead plug. RESULTS The results of a:bsorption measurements obtained with the cobalt-60 source a re shown in Fig. 2, and those obtained with the caesium-137 source in Fig. 3. 0,5 GAMMA RAY ABSORPTION I EXPERIMENTAL POINTS · 1 • CALCULATED LINE FOR ·2· · 3· 0·2,25 0·2,30 0·2,35 s 0,4 .,. 0 1--- ---_-=::---~-:::~~::::::::--- 1, --- ------ --------- I --- i 0·30 s 10 1s 2o CONCENTRATION OF Pb!NO;l, !g/ 100cm' solution) Fig. 2 -log I /Io vs. concentration of lead nitrate. "Co used as a gamma ray souroe. 'f Solution volume 50 ccm. I EXPERIMENTAL POINTS · 1 ·CALCULATED LINE FOR . 2· . 3· D· 225cm D· 2:30cm D· 2.35 cm -----< 0,5 ' ---~~~:=:----==-, --==-- -3------C> 0 -- ------0·40 5 10 CONCENTRATION OF Pb(NO,l, 15 !g/100cm' solution) 20 Fig. 3. -log I /I o vs. concentration of lead nitrate. mcs used as a gamma ray source. Solution volume 5() ccm. 105 Results are plotted in the form of -log I/I0 vs. concentrartion of lead nitrate. I and I0 represent the intensity of gamma rays after passing the test tubes filled or not filled with the solubon investigated. The size of the plotted points show the standaJ'.'d error. The dotted lines represent calculated values for concentra-tions used in the exper.imenta·l work. The diameter of the test tube was 2.30±0.05 cm, so the calculations were done for 2.25, 2.30, and 2.35 cm. DISCUSSION Values of -log I/ I 0 as a function of concentration can be calculated using the formula: -log I/I 0 = X d log e where, X is the mass absorption coefficient in cm2/g d is the thickness in g/cm2• (1) 106 Z. KOLAR AND S. 2ILIC Eq. 1 can be transformed into the following form: -log I/I0 = -- - -+- y X 2 4 V [ c(X1-X.,) ] D?n 100 loge where, D is the diameter of the test tube in cm; V the volume of the solution in the test tube in cm3 ; y the specific gravity of the solution in g/cm3 ; X 1 the mass absorption coefficient of lead nitrate in cm2/g; X" the mass absorption coefficient of water in cm2/g; c the concentration o.f lead nitrate in g/100 cm3 ; n and e are common values. (2) The mass coefficients for lead nitrate were calculated from the data of R. G. Jaeger6• The values used in our calculations are shown in Table I. TABLE I Gamma source D v c [cm] [cm3] [g/100 cm3J I Caesium-137 · 1 2.30 ± 0.05 50 from 0 to 20 Cobalt-60 I 2.30 ± 0.05 50 from Oto 20 The specific gravity was calculated from the formula: y = 0.008191 c + 1 X1 X2 [cm2/g] [cm2/g] ,. 0.093 I 0.085 0.058 0.063 evaluated on the basis of m easured data observed at the temperature of 17.5°C. Calculated values obtained in that way are not far from the experimental points, especially those calculated on the bas is of D = 2.25 cm. There is a small discrepancy between calculated results and experimental points. The probable reason for this is that the calculated values were obtained using the specific gravity at 17.5°C, while the actual temperature was different from 17.5°C. REFERENCES 1. D. H. Thurn au, Anal. Chem. 29 (1957) 1772. 2. R. E. Conn a 11 y, Nucleonics 17 (1959) 98. 3. A. J. Broderick and J. C. Whitmer, Anal. Chem. 33 (1961) 1314. 4. G. J . A 1 k ire, U.S. Atomic Energy Comm., Rept. HW-45664, 1-9 (September 1956). Cit. Nuclear Sci. Abstr. 12 (1958) 9946. · 5. D. G. M i 11 er and R. E. C on n a 11 y, U. S. Atomic Energy Comm., Rept. HW-36788, 1-45 (June 1955). Cit. Nuclear Sci. Abstr. 12 (1958) 721. 6. R. G. Jaeger, Dosimetrie und Strahlenschutz, Georg Thieme Verlag, Stuttgart 1959, p. 157. IZVOD Komparacija mjerenih i izracunatih vrijednosti za apsorpcuu gama zraka u otopinama olovnoga nitrata z. Kolar i s. Zilic Opisana je metoda za odredivanje koncentracije olovnoga nitrata u vodenim otopinama od 0 - 20 g/100 ml, mjerenjem apsorpcije gama zraka. Kao izvori gama GAMMA RAY ABSORPTION 107 zraka upotrebljavani su GOCo i 1a1cs. Mjerenje intenziteta gam a zraka vrseno je scintilacionim brojaeem. Na temelju osnovne jednadzbe za apsorpciju gama zraka izvedena je jednadzba, koja saddi samo direktno mjerljive velicine, i po njoj je izracunata apsorpcija za sve upotreblj ene koncentracije. Slaganje izmedu mjerenih i izracunatih vrijednosti dosta je dobro. Prikazan je i vjerojatni razlog odstupanja. ODJEL RADIOKEMIJE INSTITUT »RUDER BOSKOVIC• I ZA VOD ZA RADIOKEMIJU TEHNOLOS KI FAKULTET ZAGREB Primljeno 9. ozujka 1962. 

The Comparison Between Measured and Calculated Values of Gamma Ray Absorption on Lead Nitrate Solutions

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