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K-shell fluorescence yields of barium and lanthanum
Radiation Physics and Chemistry 80 (2011) 626–628
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
K-shell fluorescence yields of barium and lanthanum L.D. Horakeri a, S.G. Bubbly b, S.B. Gudennavar b,n a b
Department of Physics, S.K. Arts College and H.S. Kotambri Science Institute, Vidyanagar, Hubli 580 031, Karnataka, India Department of Physics, Christ University, Bangalore 560 029, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 October 2009 Accepted 17 January 2011 Available online 25 January 2011
K-shell fluorescence yields for barium and lanthanum have been measured adopting simple 2p geometrical configuration and employing a weak 57Co radioactive source. A scintillation spectrometer with an NaI(Tl) detector of dimensions 44.5 mm diameter 50 mm thickness was employed for the detection and measurement of radiation. The results obtained are in good agreement with the bestfitted values of Hubbell et al. (1994) and also with the other experimental values, indicating that our simple method can be extended to determine fluorescence parameters of high Z materials. & 2011 Elsevier Ltd. All rights reserved.
Keywords: K-shell fluorescence X-ray fluorescence yield 2p geometrical configuration
1. Introduction Accurate values of K-shell fluorescence yield of all elements are of great necessity as X-ray fluorescence phenomena find applications in various fields such as industry, health physics, forensic science, material science, archeology, etc. Since experimental values of fluorescence yield are not available for all elements, the best-fitted values generated by Hubbell et al. (1994) have been employed. The existing experimental methods are quite involved and complicated. The two crucial factors on which the X-ray fluorescence parameters depend are, the total intensity of the photons incident on the target and the total intensity of fluorescent X-rays emitted from the target. Over the years several workers have struggled hard to measure these intensities accurately. Because of their experimental arrangements, many correction factors have to be introduced to estimate these intensities. In order to overcome this difficulty, we have previously suggested a simple but accurate method of measuring X-ray fluorescence parameters (Horakeri et al., 1997, 1998; Gudennavar et al., 2003a, 2003b). The method involves a 2p geometrical configuration in the sense that the target is sandwiched between the source and the detector subtending a solid angle of almost 2p sr. The same thing is true for the measurement of incident intensity where the source is kept on the face of the detector itself. This configuration had been termed ‘‘2p geometrical configuration’’. Moreover this configuration requires a weak radioactive source of the order of 104 Bq, which is of great advantage both from the point of view of avoiding various corrections for the estimation of intensity and safety of the personnel. In this method the thickness of the target is crucial
n
Corresponding author. Tel.: +91 80 40129340; fax: + 91 80 40129000. E-mail address: [email protected] (S.B. Gudennavar).
0969-806X/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2011.01.006
for the accurate determination of fluorescent X-ray intensity. Bambynek et al. (1972) have suggested that in order to obtain the accurate values of X-ray fluorescence parameters, the target thickness should be optimized in such a way that the production of X-rays must be predominant when compared to their attenuation in the target itself (the self-attenuation). Following this suggestion we have found a thickness criterion, 0.75 r b r0.95 for a 2p geometrical configuration, where b is the self-attenuation factor and is given by
b¼
1expððmi þ me ÞtÞ ðmi þ me Þt
where mi and me are the mass attenuation coefficients of the incident and emitted fluorescent X-ray photons, respectively, and t is the thickness of the target. Previously the method has yielded accurate values of X-ray fluorescence parameters for low and medium Z elements. The details of the method and measurements have been given in our earlier papers (Horakeri et al., 1997, 1998; Gudennavar et al., 2003a, 2003b). The present investigations are made for barium and lanthanum to check the applicability of the method for high Z materials.
2. Experimental details The experimental arrangement is as shown in Fig. 1. A 57Co radioactive source of strength of the order of 104 Bq obtained from Board of Radiation and Isotope Technology (BRIT), Mumbai, India, is used as the excitation source. 57Co decays by pure electron capture to an excited state of 57Fe, emitting characteristic Fe X-rays of energy 6.47 keV and gamma rays of energies 122 keV (85%), 136 keV (11%) and 14.39 keV (8.5%). A NaI(Tl) scintillation detector (44.5 mm diameter 50 mm thickness) connected to a high voltage unit, an amplifier and a PC-based multi-channel
L.D. Horakeri et al. / Radiation Physics and Chemistry 80 (2011) 626–628
Source
627
3. Results and discussion
Target NaI (Tl) Detector
PMT
Fig. 1. Schematic diagram of the experimental arrangement.
Table 1 Calculated values of self-attenuation factor, b, for selected target thickness at a mean excitation energy 123.6 keV. Sl. no.
Compound
1.
Lanthanum chloride Barium nitrate Barium chloride Barium hydroxide
2. 3. 4.
Atomic number of element, Z
mi
me
(cm2/g)
(cm2/g)
t (g/cm2)
57
0.601
3.300
0.03856 0.906
56 56
0.742 0.918
4.313 4.959
0.03491 0.917 0.03750 0.897
56
0.647
3.567
0.03106 0.936
b
analyzer has been employed for the detection and measurement of radiation. The spectrometer is calibrated using several gamma and X-ray sources. Its linearity and stability were checked before it was put to use. Due to the unavailability of very thin elemental foils at our laboratory, we have selected water-soluble compounds of barium (Z¼56) and lanthanum (Z¼ 57). Barium being a material used in X-ray diagnosis and lanthanum being a rare earth element we feel it is worth measuring the fluorescence parameters of these materials. The details of these targets are presented in Table 1. Compound targets were prepared by depositing a solution of known concentration on grade 1 Whatman filter paper. The required thickness of target has been achieved by varying the concentration of solution. Out of several targets prepared, only those which have a uniform thickness in the range 0.75 r b r0.95 have been selected. The details of the preparation of targets have been given in our earlier papers (Horakeri et al., 1997, 1998; Gudennavar et al., 2003a, 2003b). The energy resolution of the NaI(Tl) scintillation spectrometer employed in the present investigation is poor and so it cannot resolve the 122 and 136 keV gamma rays. As a result, we see only one peak instead of two in the source spectrum. Therefore in the calculations, we have used the photon energy 123.6 keV, the weighted average of 122 and 136 keV. Since 122 keV gamma rays are predominant (85% of the total disintegration) and 136 keV gamma rays are only 11%, we can safely take the weighted average value of these two energies, which comes out to be 123.6 keV. The incident photon intensity has been measured by keeping the source directly on the face of the detector, while the fluorescent X-ray intensity has been measured by sandwiching the target between the source and the detector as shown in Fig. 1.
For each target of lanthanum chloride, the K X-ray fluorescence yield, oK, has been determined in several trials to check the reproducibility and reliability of our method and the weighted average of oK values calculated. In Table 2, we give the oK values along with their associated errors obtained in several trials for lanthanum chloride compound and compare them with the fitted value of Hubbell et al. (1994). From Table 2, it is clear that our oK values are not only in agreement amongst themselves but also in agreement with the weighted average value and the fitted value (within 2%), indicating the credibility of our method. To check the effect of chemical environment around the target atom, we determined oK values for different compounds of barium. In Table 3, we give the results along with the fitted values of Hubbell et al. (1994). From this table, it is clear that the presence of low Z atoms around a high Z atom in the compound do not affect the oK value of the high Z element. This is because the target is so thin that there is no significant attenuation from the constituent elements of the compound. Thus oK values for high Z elements can be obtained even if the target is in compound form, provided that it consists of low Z elements only. However, it may be interesting and worthwhile to check the applicability of the method for target materials consisting of more than one kind of high Z atoms in a compound. This is because for high Z elements photoelectric absorption becomes important whereas for low Z elements it is the scattering that becomes important. However we could not proceed in this direction as we do not have such targets at present in our laboratory. In Table 4, we compare our experimental values with other experimental values measured by adopting different geometries and methods. The errors involved in our experimental values are about only 1%. The errors quoted in others values are also about 1%. The agreement with the others value in the case of lanthanum is + 3.4% and –3.2% and in the case of barium it is + 2% and 4.3%. However, our values agree within 2% with the fitted values of Hubbell et al. (1994). This indicates that our simple method also yields oK values on par with those measured using elaborate arrangements such as single and double reflection methods. Also oK values are independent of incident photon energies but
Table 2 Measured values of fluorescence yield, oK, for lanthanum chloride at a mean excitation energy 123.6 keV in six trials. Trial no.
oK
1. 2. 3. 4. 5. 6. Weighted average value Hubbell et al. (1994)’s value
0.902 70.026 0.914 70.024 0.911 70.025 0.915 70.025 0.909 70.025 0.914 70.023 0.911 70.010 0.9049
Table 3 Comparison of fluorescence yield, oK, values at incident photon energy 123.6 keV with standard fitted values of Hubbell et al. (1994) for various targets. Sl. no.
Compound
Z
Present experimental values
Standard fitted values
1. 2. 3. 4.
Lanthanum chloride Barium nitrate Barium chloride Barium hydroxide
57 56 56 56
0.911 7 0.010 0.885 7 0.005 0.888 7 0.008 0.881 7 0.009
0.9049 0.8997 0.8997 0.8997
628
L.D. Horakeri et al. / Radiation Physics and Chemistry 80 (2011) 626–628
Table 4 Comparison of measured values of fluorescence yield, oK, with other experimental values. Element
Z
oK Present experimental values
Other experimental values
References
0.880 7 0.010 0.940 0.870 7 0.007 0.850
Kettele et al. (1956) Gray (1956) Broyles et al. (1953) Gray (1956)
Lanthanum
57
0.911 7 0.010
Barium
56
0.888 7 0.008
Acknowledgement The authors are grateful to Professor S.R. Thontadarya, formerly professor of Physics, Department of Physics, Karnatak University, Dharwad, for his encouragement and help in this work. References
depend only on Z value of the material. However the incident energy should be such that the photoelectric interaction is predominant in the material.
4. Conclusions The present investigations demonstrated that our method of measuring fluorescence parameters can be extended to high Z elements. Taking into consideration our earlier measurements for materials of various Z, we conclude that our experimental method can be adopted to measure fluorescence parameters of any Z with suitable detector systems.
Bambynek, W., Crasemann, B., Fink, R.W., Freund, H.U., Mark, H., Swift, C.D., Price, R.E., Venugopala Rao, P., 1972. X-ray fluorescence yields, Auger, and Coster– Kronig transition probabilities. Rev. Mod. Phys. 44 (4), 716–813. Broyles, C.D., Thomas, D.A., Haynes, S.K., 1953. The measurement and interpretation of the K Auger Intensities of Sn113, Cs137, and Au198. Phys. Rev. 89, 715–724. Gray, P.R., 1956. Auger effect in the heaviest elements. Phys. Rev. 101, 1306–1314. Gudennavar, S.B., Badiger, N.M., Thontadarya, S.R., Hanumaiah, B., 2003a. K-shell fluorescence parameters of medium-Z elements. Radiat. Phys. Chem. 68, 721–726. Gudennavar, S.B., Badiger, N.M., Thontadarya, S.R., Hanumaiah, B., 2003b. A method for measuring K-shell fluorescence parameters in a 2p geometrical configuration. Radiat. Phys. Chem. 68, 745–750. Horakeri, L.D., Hanumaiah, B., Thontadarya, S.R., 1997. Method for the determination of K-shell fluorescence yields. X-Ray Spectrom. 26, 69–74. Horakeri, L.D., Hanumaiah, B., Thontadarya, S.R., 1998. K-shell fluorescence yields of medium and heavy elements using a simple method. X-Ray Spectrom. 27, 344–348. Hubbell, J.H., Trehan, P.N., Singh, N., Chand, B., Mehta, D., Garg, M.L., Singh, S., Puri., S., 1994. A review, bibliography and tabulation of K, L, and higher atomic shell X-ray fluorescence yields. J. Phys. Chem. Ref. Data 23 (2), 339–364. Kettele, B.H., Thomas, H., Brosi, A.R., 1956. Decay of the cerium-139 isomers. Phys. Rev. 103, 190–195.
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
K-shell fluorescence yields of barium and lanthanum L.D. Horakeri a, S.G. Bubbly b, S.B. Gudennavar b,n a b
Department of Physics, S.K. Arts College and H.S. Kotambri Science Institute, Vidyanagar, Hubli 580 031, Karnataka, India Department of Physics, Christ University, Bangalore 560 029, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 October 2009 Accepted 17 January 2011 Available online 25 January 2011
K-shell fluorescence yields for barium and lanthanum have been measured adopting simple 2p geometrical configuration and employing a weak 57Co radioactive source. A scintillation spectrometer with an NaI(Tl) detector of dimensions 44.5 mm diameter 50 mm thickness was employed for the detection and measurement of radiation. The results obtained are in good agreement with the bestfitted values of Hubbell et al. (1994) and also with the other experimental values, indicating that our simple method can be extended to determine fluorescence parameters of high Z materials. & 2011 Elsevier Ltd. All rights reserved.
Keywords: K-shell fluorescence X-ray fluorescence yield 2p geometrical configuration
1. Introduction Accurate values of K-shell fluorescence yield of all elements are of great necessity as X-ray fluorescence phenomena find applications in various fields such as industry, health physics, forensic science, material science, archeology, etc. Since experimental values of fluorescence yield are not available for all elements, the best-fitted values generated by Hubbell et al. (1994) have been employed. The existing experimental methods are quite involved and complicated. The two crucial factors on which the X-ray fluorescence parameters depend are, the total intensity of the photons incident on the target and the total intensity of fluorescent X-rays emitted from the target. Over the years several workers have struggled hard to measure these intensities accurately. Because of their experimental arrangements, many correction factors have to be introduced to estimate these intensities. In order to overcome this difficulty, we have previously suggested a simple but accurate method of measuring X-ray fluorescence parameters (Horakeri et al., 1997, 1998; Gudennavar et al., 2003a, 2003b). The method involves a 2p geometrical configuration in the sense that the target is sandwiched between the source and the detector subtending a solid angle of almost 2p sr. The same thing is true for the measurement of incident intensity where the source is kept on the face of the detector itself. This configuration had been termed ‘‘2p geometrical configuration’’. Moreover this configuration requires a weak radioactive source of the order of 104 Bq, which is of great advantage both from the point of view of avoiding various corrections for the estimation of intensity and safety of the personnel. In this method the thickness of the target is crucial
n
Corresponding author. Tel.: +91 80 40129340; fax: + 91 80 40129000. E-mail address: [email protected] (S.B. Gudennavar).
0969-806X/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2011.01.006
for the accurate determination of fluorescent X-ray intensity. Bambynek et al. (1972) have suggested that in order to obtain the accurate values of X-ray fluorescence parameters, the target thickness should be optimized in such a way that the production of X-rays must be predominant when compared to their attenuation in the target itself (the self-attenuation). Following this suggestion we have found a thickness criterion, 0.75 r b r0.95 for a 2p geometrical configuration, where b is the self-attenuation factor and is given by
b¼
1expððmi þ me ÞtÞ ðmi þ me Þt
where mi and me are the mass attenuation coefficients of the incident and emitted fluorescent X-ray photons, respectively, and t is the thickness of the target. Previously the method has yielded accurate values of X-ray fluorescence parameters for low and medium Z elements. The details of the method and measurements have been given in our earlier papers (Horakeri et al., 1997, 1998; Gudennavar et al., 2003a, 2003b). The present investigations are made for barium and lanthanum to check the applicability of the method for high Z materials.
2. Experimental details The experimental arrangement is as shown in Fig. 1. A 57Co radioactive source of strength of the order of 104 Bq obtained from Board of Radiation and Isotope Technology (BRIT), Mumbai, India, is used as the excitation source. 57Co decays by pure electron capture to an excited state of 57Fe, emitting characteristic Fe X-rays of energy 6.47 keV and gamma rays of energies 122 keV (85%), 136 keV (11%) and 14.39 keV (8.5%). A NaI(Tl) scintillation detector (44.5 mm diameter 50 mm thickness) connected to a high voltage unit, an amplifier and a PC-based multi-channel
L.D. Horakeri et al. / Radiation Physics and Chemistry 80 (2011) 626–628
Source
627
3. Results and discussion
Target NaI (Tl) Detector
PMT
Fig. 1. Schematic diagram of the experimental arrangement.
Table 1 Calculated values of self-attenuation factor, b, for selected target thickness at a mean excitation energy 123.6 keV. Sl. no.
Compound
1.
Lanthanum chloride Barium nitrate Barium chloride Barium hydroxide
2. 3. 4.
Atomic number of element, Z
mi
me
(cm2/g)
(cm2/g)
t (g/cm2)
57
0.601
3.300
0.03856 0.906
56 56
0.742 0.918
4.313 4.959
0.03491 0.917 0.03750 0.897
56
0.647
3.567
0.03106 0.936
b
analyzer has been employed for the detection and measurement of radiation. The spectrometer is calibrated using several gamma and X-ray sources. Its linearity and stability were checked before it was put to use. Due to the unavailability of very thin elemental foils at our laboratory, we have selected water-soluble compounds of barium (Z¼56) and lanthanum (Z¼ 57). Barium being a material used in X-ray diagnosis and lanthanum being a rare earth element we feel it is worth measuring the fluorescence parameters of these materials. The details of these targets are presented in Table 1. Compound targets were prepared by depositing a solution of known concentration on grade 1 Whatman filter paper. The required thickness of target has been achieved by varying the concentration of solution. Out of several targets prepared, only those which have a uniform thickness in the range 0.75 r b r0.95 have been selected. The details of the preparation of targets have been given in our earlier papers (Horakeri et al., 1997, 1998; Gudennavar et al., 2003a, 2003b). The energy resolution of the NaI(Tl) scintillation spectrometer employed in the present investigation is poor and so it cannot resolve the 122 and 136 keV gamma rays. As a result, we see only one peak instead of two in the source spectrum. Therefore in the calculations, we have used the photon energy 123.6 keV, the weighted average of 122 and 136 keV. Since 122 keV gamma rays are predominant (85% of the total disintegration) and 136 keV gamma rays are only 11%, we can safely take the weighted average value of these two energies, which comes out to be 123.6 keV. The incident photon intensity has been measured by keeping the source directly on the face of the detector, while the fluorescent X-ray intensity has been measured by sandwiching the target between the source and the detector as shown in Fig. 1.
For each target of lanthanum chloride, the K X-ray fluorescence yield, oK, has been determined in several trials to check the reproducibility and reliability of our method and the weighted average of oK values calculated. In Table 2, we give the oK values along with their associated errors obtained in several trials for lanthanum chloride compound and compare them with the fitted value of Hubbell et al. (1994). From Table 2, it is clear that our oK values are not only in agreement amongst themselves but also in agreement with the weighted average value and the fitted value (within 2%), indicating the credibility of our method. To check the effect of chemical environment around the target atom, we determined oK values for different compounds of barium. In Table 3, we give the results along with the fitted values of Hubbell et al. (1994). From this table, it is clear that the presence of low Z atoms around a high Z atom in the compound do not affect the oK value of the high Z element. This is because the target is so thin that there is no significant attenuation from the constituent elements of the compound. Thus oK values for high Z elements can be obtained even if the target is in compound form, provided that it consists of low Z elements only. However, it may be interesting and worthwhile to check the applicability of the method for target materials consisting of more than one kind of high Z atoms in a compound. This is because for high Z elements photoelectric absorption becomes important whereas for low Z elements it is the scattering that becomes important. However we could not proceed in this direction as we do not have such targets at present in our laboratory. In Table 4, we compare our experimental values with other experimental values measured by adopting different geometries and methods. The errors involved in our experimental values are about only 1%. The errors quoted in others values are also about 1%. The agreement with the others value in the case of lanthanum is + 3.4% and –3.2% and in the case of barium it is + 2% and 4.3%. However, our values agree within 2% with the fitted values of Hubbell et al. (1994). This indicates that our simple method also yields oK values on par with those measured using elaborate arrangements such as single and double reflection methods. Also oK values are independent of incident photon energies but
Table 2 Measured values of fluorescence yield, oK, for lanthanum chloride at a mean excitation energy 123.6 keV in six trials. Trial no.
oK
1. 2. 3. 4. 5. 6. Weighted average value Hubbell et al. (1994)’s value
0.902 70.026 0.914 70.024 0.911 70.025 0.915 70.025 0.909 70.025 0.914 70.023 0.911 70.010 0.9049
Table 3 Comparison of fluorescence yield, oK, values at incident photon energy 123.6 keV with standard fitted values of Hubbell et al. (1994) for various targets. Sl. no.
Compound
Z
Present experimental values
Standard fitted values
1. 2. 3. 4.
Lanthanum chloride Barium nitrate Barium chloride Barium hydroxide
57 56 56 56
0.911 7 0.010 0.885 7 0.005 0.888 7 0.008 0.881 7 0.009
0.9049 0.8997 0.8997 0.8997
628
L.D. Horakeri et al. / Radiation Physics and Chemistry 80 (2011) 626–628
Table 4 Comparison of measured values of fluorescence yield, oK, with other experimental values. Element
Z
oK Present experimental values
Other experimental values
References
0.880 7 0.010 0.940 0.870 7 0.007 0.850
Kettele et al. (1956) Gray (1956) Broyles et al. (1953) Gray (1956)
Lanthanum
57
0.911 7 0.010
Barium
56
0.888 7 0.008
Acknowledgement The authors are grateful to Professor S.R. Thontadarya, formerly professor of Physics, Department of Physics, Karnatak University, Dharwad, for his encouragement and help in this work. References
depend only on Z value of the material. However the incident energy should be such that the photoelectric interaction is predominant in the material.
4. Conclusions The present investigations demonstrated that our method of measuring fluorescence parameters can be extended to high Z elements. Taking into consideration our earlier measurements for materials of various Z, we conclude that our experimental method can be adopted to measure fluorescence parameters of any Z with suitable detector systems.
Bambynek, W., Crasemann, B., Fink, R.W., Freund, H.U., Mark, H., Swift, C.D., Price, R.E., Venugopala Rao, P., 1972. X-ray fluorescence yields, Auger, and Coster– Kronig transition probabilities. Rev. Mod. Phys. 44 (4), 716–813. Broyles, C.D., Thomas, D.A., Haynes, S.K., 1953. The measurement and interpretation of the K Auger Intensities of Sn113, Cs137, and Au198. Phys. Rev. 89, 715–724. Gray, P.R., 1956. Auger effect in the heaviest elements. Phys. Rev. 101, 1306–1314. Gudennavar, S.B., Badiger, N.M., Thontadarya, S.R., Hanumaiah, B., 2003a. K-shell fluorescence parameters of medium-Z elements. Radiat. Phys. Chem. 68, 721–726. Gudennavar, S.B., Badiger, N.M., Thontadarya, S.R., Hanumaiah, B., 2003b. A method for measuring K-shell fluorescence parameters in a 2p geometrical configuration. Radiat. Phys. Chem. 68, 745–750. Horakeri, L.D., Hanumaiah, B., Thontadarya, S.R., 1997. Method for the determination of K-shell fluorescence yields. X-Ray Spectrom. 26, 69–74. Horakeri, L.D., Hanumaiah, B., Thontadarya, S.R., 1998. K-shell fluorescence yields of medium and heavy elements using a simple method. X-Ray Spectrom. 27, 344–348. Hubbell, J.H., Trehan, P.N., Singh, N., Chand, B., Mehta, D., Garg, M.L., Singh, S., Puri., S., 1994. A review, bibliography and tabulation of K, L, and higher atomic shell X-ray fluorescence yields. J. Phys. Chem. Ref. Data 23 (2), 339–364. Kettele, B.H., Thomas, H., Brosi, A.R., 1956. Decay of the cerium-139 isomers. Phys. Rev. 103, 190–195.