NIUMI B

Nuclear Instruments and Methods in Physics Research B 114 (1996) 217-220

Gamma-ray attenuation coefficients in some heavy metal glasses at 662 keV

Atul Khanna a, * , S.S. Bhatti a, K.J. Singh a, K.S. Thind b

a Department of Applied Physics, Guru Nanak Deu Universiry, Amritsar 143005, India b Department of Physics, Guru Nanak Dev Uniuersity, Amritsar 143005, India

Received 24 October 1995; revised form received 2 February 1996

Beam Interactions with Materials&Atoms

oxide borate

Abstract The linear attenuation coefficient (p) and mass attenuation coefficients (p/p) of glasses in three systems: xPbO(1 -

x)B,O,, 0.25PbO . xCdO(0.75 - x)B,O, and xBi,O,( 1 - x)B,O, were measured at 662 keV. Appreciable variations were noted in the attenuation coefficients due to changes in the chemical composition of glasses. In addition to this, absorption cross-sections per atom were also calculated. A comparison of shielding properties of these glasses with standard shielding materials like lead, lead glass and concrete has proven that these glasses have a potential application as transparent radiation

shielding.

1. Introduction

The photon attenuation coefficient is an important pa- rameter for characterizing the penetration and diffusion of X-rays and gamma-rays in multielement materials. Photon attenuation coefficients are required in a variety of nuclear science, technology and medical applications. The fact that radiation could be harmful has lead to the development of wide variety of shields to protect against it. As the technol- ogy advances there is a need to develop materials which can be used under most harsh conditions such as nuclear radiation exposure [l]. Several special glasses have been claimed for nuclear engineering applications [2]. Glasses have been developed which accomplish the double task of allowing visibility while absorbing radiation like gamma- rays and neutrons, thus protecting the observer [3]. Glasses rich in boron and cadmium are used to absorb slow neutrons [4]. Transparent radiation shields such as glasses on exposure to high doses of radiation show effects like discolouration, gas evolution and fracture [5,6]. Thus glasses gradually loose transparency on prolonged expo- sure to radiation. A good shielding glass should have high absorption cross-section for radiation and at the same time irradiation effects on its mechanical and optical properties should be small. In this paper we report the gamma-ray attenuation coefficient measurements in borate glasses con- taining oxides of Pb, Cd and Bi.

* Corresponding author. Tel. 258802-9/215.

2. Sample preparation

Cylindrical samples of three glass systems; xPbO(1 - x)B,O,, 0.25PbO. xCdO(0.75 - x)B,O, and xBi,O,(l - x)B,O, (x is the mole fraction of a component) were prepared by melt-quenching technique. The composition of all samples is shown in Table 1. All chemicals used were of analytical reagent grade. Appropriate amounts of metal oxides were mixed with boric acid (H,BO,) and put in a porcelain crucible. The crucible was then put in an electric

Table 1 Chemical composition of glasses

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Sample Composition (mole fraction) Sample no. PbO Cd0 Bi,O, B,O, thickness

t (cm)

1 0.25 - - 0.75 1.116 2 0.30 - _ 0.70 1.855 3 0.36 - - 0.64 2.166 4 0.45 - _ 0.55 1 x09 5 0.50 - - 0.50 2.351 6 0.57 - - 0.43 1.783 7 0.25 0.10 - 0.65 1.294 8 0.25 0.20 - 0.55 1.347 9 0.25 0.30 - 0.45 1.637

10 0.25 0.35 - 0.40 1.203 11 0.25 0.40 - 0.35 1.221 12 - - 0.20 0.80 1.374 13 _ 0.30 0.70 1.230 14 - _ 0.40 0.60 1.633 15 - _ 0.50 0.50 1.222

218 A. Khanna et al./Nucl. Instr. and Meth. in Phys. Res. B I14 (1996) 217-220

Table 2

Measured and theoretical values of attenuation coefficients and absorption cross-section values for glass samples at 662 keV along with their

maximum possible errors

Sample

no.

Density p

(g cme3)

Linear

attenuation

Mass attenuation coeffccient

(P/P) (g- ’ cm*) Absorption

cross- coefficient

P (cm-‘) exp. theor. section

per atom

o (barn/atom)

1 3.487 I 0.008 0.291

2 3.870 * 0.005 0.341

3 4.280 + 0.004 0.387

4 4.468 + 0.006 0.408

5 4.658 + 0.005 0.43 1

6 4.860 f 0.007 0.467

7 4.026 + 0.009 0.361

8 4.412 + 0.008 0.388

9 4.635 + 0.007 0.402

10 4.882 k 0.010 0.428

11 4.949 f 0.010 0.437

12 3.948 + 0.008 0.383

13 4.554 + 0.010 0.442

14 4.958 i 0.008 0.495

15 5.306 f. 0.012 0.529

0.0836 i. 0.0030 0.0921 3.526

0.0880 + 0.0025 0.0941 4.128

0.0904 + 0.0023 0.0960 4.709

0.0903 + 0.0019 0.0988 5.767

0.0921 rt 0.0016 0.100 6.401

0.0961 + 0.0016 0.101 7.42

0.0890 i 0.0029 0.0915 4.272

0.0870 + 0.0025 0.0905 4.746

0.0860 i_ 0.0023 0.0899 5.346

0.0870 f 0.0026 0.0895 5.250

0.0880 + 0.0025 0.0892 6.318

0.0970 + 0.0034 0.0963 4.742

0.0971 + 0.0036 0.1002 6.100

0.0997 f 0.0028 0.102 7.553

0.0996 + 0.0033 0.104 8.861

furnace and heated to 800°C at the rate of 200°C per hour. Boric acid decomposes to B,O, on heating. The melt was kept at 800°C for 12 h and occasionally stirred with a quartz tube to ensure its homogeneity and to remove bubbles. The temperature was then raised to 900°C for 2 h and the melt poured into a cylindrical graphite mould kept at room temperature. The samples were then transferred to an annealing furnace kept at 270°C. All the samples were

annealed at 270°C for 12 h and then cooled very slowly at the rate of 35”C/h to room temperature.

The samples were ground and polished with different grades of Sic emery powder on a soft leather piece fixed on a flat platform. The grinding and polishing was contin- ued until the sample length measured, at the four comers and the centre coincided, within 5 pm. The sample length was measured with a micrometer which could measure

Table 3 Attenuation coefficients for some standard shielding materials at 662 keV

Material

Lead

Lead glass

(Coming

8362) Lead glass

(Coming

8363)

Concrete

Composition

(wt%o>

100 lead metal

30 lead

76 lead

hydrogen = 0.56 oxygen = 49.8 sodium = 1.70 magnesium = 0.24

aluminum = 4.50

silicon = 31.8

sulfur = 0.12

potassium = 1.92

calcium = 8.26

iron = 1.22

Density p P./P (g cm-‘> (cm’ g- ‘>

11.3 1.20 0.106

3.27 0.28 a 0.0856

6.22 0.65 = 0.104

2.22 0.170 b 0.0774

(0.0738)

a Ref. 131; b Ref. [lo], the value given in brackets for concrete is the theoretical value calculated using XCOM, Ref. [91.

A. Khanna et al./Nucl. Instr. and Meth. in Phys. Res. B 114 (1996) 217-220 219

down to 1 pm. The final length at the centre was taken as the sample length. It was in the range of 1 to 2 cm.

3. Experimental setup

The experimental setup of narrow beam collimated geometry, as outlined in Ref. [7], was used in the present work. A 1.5” X 1.5” NaI(Tl) crystal having energy resolu- tion of 12.5% at 662 keV gamma-rays from the decay of ‘37Cs was used for the measurement of total mass attenua- tion coefficients. The detector and source were both pro- vided with adequate lead shielding. The radioactive source 13%s used in the present work was obtained from Bhabha Atomic Research Centre, Bombay, India. The sample-de- tector solid angle was < 0.5 X 10m4 Sr.

The incident and transmitted intensities were deter- mined for a fixed preset time in each experiment by choosing a narrow region symmetrical with respect to the

centroid of the photopeak. A sufficient number of counts was always collected under the photopeak to limit the statistical error to less than 1%. The criterion (k/p) < t, given by Gopal and Sanjeevaiah [8], where t is the sample thickness was adhered to and thus, the influence of multi- ple scattering on the measurements of attenuation coeffi- cients was reduced. The photopeaks were analyzed by using PC/AT based plug-in-card Multichannel analyzer (MCA).

The density of each sample was measured by Archimedes principle using benzene as the immersion fluid. The maximum errors in the measurement of mass attenuation coefficients were calculated from errors in intensities 1, (without sample), I (with sample) and densi- ties using the following relation:

*!I! 2!5+~+!q?, (1 1 P Pt IO P ( ,I (1)

where t is the sample thickness in centimeter, A I,, A I and Ap are the errors in the intensities IO, I and density p, respectively.

4. Results and discussion

The linear attenuation coefficient, p+ mass attenuation coefficient (p/p) for the glass samples are presented in Table 2. The (b/p) values were also calculated theoreti- cally using the XCOM computer program and database [9], and are also shown in Table 2. These values were used for calculating the effective atomic cross-section in barns per atom for all the 15 glass samples by using the following expression:

o= (P/P)/KCWi/Ai, (2) I

where wi and Ai are fractional abundances by weight and mass numbers of the constituents and NA is the Avogadro

A .50

45 -

-T .40- E

.Y 1 .35-

.30 -

.25 I I I I I I .45 .50 ,585 .60 .65 .70 .75

Weight froctmn of Pb

.ea

a35 1 0 0.1 0.2 03

Weight traction Of Cd

C 60,

- .50- T

E ” 2 .45-

-40-

351 I I I I ! I .50 .55 .60 55 .70 .75 40 .a

Weight fraction of Bi

Fig. 1. (A) Linear attenuation coefficients, ~(cn- ’ ) in lead borate

glasses against Pb concentration (weight fraction); (B) linear attenuation coefficient, p(cm- ‘) in iead cadmium borate glasses against Cd concentration (weight fraction); (Cl linear attenuation coefficient, F(cm- ’ ) in bismuth borate glasses against Bi concen-

tration (weight fraction).

number. It is seen from Table 2 that the bismuth borate glasses show the highest attenuation coefficients and ab- sorption cross-section values. In order to study the varia-

220 A. Khanna et al./Nucl. Insn. and Meth. in Phys. Res. B 114 (1996) 217-220

tion in linear attenuation coefficient with change in con- centration (fraction by weight) of Pb, Cd and Bi, these attenuation coefficients were plotted against the metal concentration in case of each glass series as shown in Figs. IA-1C. It is seen from the graphs that variation in linear attenuation coefficients with metal concentration is maxi- mum for Bi and the least for Cd. This is because of the fact that atomic number of Bi is more than that of Pb and Cd. We see in Fig. 1B that the experimental points show large scatter about the linear best fit curve. This is ex- plained by the fact that the curve is for a ternary glass system containing both Cd0 and PbO, such that the mole fraction of PbO is kept constant at x = 0.25. Thus increas- ing Cd0 content leads to increase in Cd weight fraction but at the same time decreases the weight fraction of Pb, which is also expected to have a significant influence on p. Hence we do not expect a truly linear relationship between total attenuation coefficient, p and Cd weight fraction. The attenuation coefficient values of some stan- dard shielding materials like lead, lead glass, and concrete are given in Table 3. It is concluded that these glasses have

shielding properties comparable to those of concrete with an added advantage of being transparent to visible light.

References

[ll

I21

[31

[41

El 61 [71

@I [91

1101

J.F. Krocher and R.E. Bowman, eds., in: Effects of Radiation on Materials and components (Reinhold, New York, 1984). M.J. Kreidl and J.R. Hensler, in: Modem Materials, Vol. 1, ed. H.H. Hower (Academic Press, New York, 1958) p. 217. W.S Rothwell, Radiation Shielding Window Glasses, Bull. PE-50 (Coming Glass Works, Coming, New York, 1958). L.M. Melnick, H.W. Safford, K.H. Sun and A. Silverman, J. Am. Ceram. Sot. 34 (1951) 82. V.O. Altemose, J. Am. Ceram. Sot. 49 (1960) 440. H.A. Batal and F.M. Ezz-Eldin, Nucl. Sci. J. 30 (1993) 179. R. Cesareo, J.T. De Assis and J. Crestana, Appl. Radiat. Isot. 4.5 (1994) 613. S. Gopal and R. Sanjeevaiah, Phys. Rev. A 7 (1973) 1912. M.J. Berger and J.M. Hubbell, NBSIR 87 (1987) 3597. G.S. Bhandal, Study of absorption and scattering of radia- tions in some multielement materials and compound materi- als, PhD thesis (Guru Nanak Dev University, Amritsar, India, 19941, unpublished.