Kα X-ray intensity ratios in 3d elements

Radiation Physics and Chemistry 64 (2002) 343–348

Chemical-effect variation of Kb=Ka X-ray intensity ratios in 3d elements b Omer Soguta,*, Erdo&gan Buy . ukkasap . , Hasan Erdo&ganc a

’ Sut, University, Faculty of Arts and Sciences, Department of Physics, 46100 Kahramanmara,s, Turkey . cu. Imam b Ataturk . University, K.K. Education Faculty, Department of Physics Education, 25240 Erzurum, Turkey c Pamukkale University, Technics Education Faculty, Denizli, Turkey Received 20 April 2001; accepted 22 October 2001

Abstract Chemical effects on Kb=Ka X-ray intensity ratios for some Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn compounds are studied experimentally. The X-ray spectra were measured by using a Si (Li) solid state detector with high resolution. The vacancies were produced by heavily filtered 241Am gamma rays. It is found that the Kb=Ka X-ray intensity ratios measured with compounds deviated up to 43% from the corresponding values of the pure elements. The values for pure elements are compared with the other experimental and with theoretical values. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: X-ray intensity ratios; Chemical effect

1. Introduction It is well known experimentally and theoretically that Kb=Ka X-ray intensity ratios in 3d elements depend on the chemical environment (Rao et al., 1986a; Tamaki et al., 1979; Taniguchi et al., 1987; Hallmeier et al., 1987; Kiss et al., 1980; Raghavaiah et al., 1992; Chang et al., 1994; Suguira et al., 1996; Raj et al., 2000; Mukoyama, 2000; Mukoyama et al., 2000; Konishi et al., 1999; . Rebohle et al., 1996; Ku. c-uk . onder et al., 1993a) and the excitation mode (Arndt et al., 1982; Tamaki et al., 1975; Yoshihara et al., 1981). It has been shown that Kb=Ka X-ray intensity ratios increase with increasing oxidation . number (Ku. c-uk . onder et al., 1993a). However, the oxidation number is not a good measure and can be used only for qualitative discussion because it is defined as an integer and Zn good measure, and can be used only for qualitative discussion because it is defined as an integer and different Kb=Ka ratios are observed for compounds with the same oxidation number. Such *Corresponding author. E-mail address: omer [email protected] (O. Sogut).

chemical effects can be caused either by a varying 3d electron population or by the admixture of 3p states from the ligand atoms to the 3d states of the metal or both. In fact, anything which alters the 3d wave function can alter the ratio, such as a change in the 3d electron population and the number of ligand atoms. The change of 3d electron population of the transition metal in the chemical compound modifies 3p orbitals of the atom stronger than 2p orbitals, which must be followed by a change of the Kb=Ka X-ray intensity ratios of the metal atoms in the compound. The influence of 3d electrons on the Kb=Ka ratio was discussed by Brunner et al. (1982) for compounds of Cr, Mn, Fe and Cu. They point out that the chemical influence on the Kb=Ka ratio is caused by the change in the screening of 3p electrons due to delocalization of the 3d electrons and they derived a simple equation to predict the Kb=Ka ratio as a function of the 3d share of the valence–charge difference. There are studies in the literature which suggest that there are chemical effects on L X-rays. For example, Iihara et al. (1993) measured chemical effects on L X-ray intensity ratios for some Nb and Mo compounds. When the measured Lg1 =Lb1

0969-806X/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 6 4 4 - 2

O. Sogut et al. / Radiation Physics and Chemistry 64 (2002) 343–348

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ratios were plotted as a function of the effective number of 4d electrons, they found that the experimental data are almost in a straight line. In addition, in our previous studies, chemical effects on the L . gut X-ray intensity ratios (So& . et al., 1997), L shell . gut fluorescence yields (So& . et al., 1999) and fluorescence cross-sections (Bayda,s et al., 1999) and alloying effect on . gut the Kb=Ka X-ray intensity ratios (So& . et al., 1995) were measured. In this study, the variation of Kb=Ka X-ray intensity ratios in 3d elements is investigated at 59.5 keV. 2. Experimental Various compounds of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn in different oxidation states were obtained in powder form. Powder samples were sieved for 400 mesh and prepared by supporting on Mylar film at 2– 15
102 g cm2 mass thickness. A Si (Li) solid state detector with a resolution 155 eV at 5.9 keV and a system 100 card with pulse height analyser were used to count the characteristic K X-rays emitted from the samples. The experimental setup and the K X-ray spectra of Cu are shown in Figs. 1 and 2, respectively. As shown in Fig. 1, placement of the upper lead shield avoided direct exposure of the detector to radiation from the source. The iron lining on its inner side was used to avoid the Pb L X-rays and the aluminium lining was used to suppress K X-rays from iron, and collimate the K X-rays from the sample (at top).

Fig. 2. A typical spectra of Cu.

The Kb=Ka intensity ratios values have been calcu. gut lated using the relation (So& . et al., 1995): IðKbÞ NðKbÞ eðKaÞ bðKaÞ ¼ ; IðKaÞ NðKaÞ eðKbÞ bðKbÞ

ð1Þ

where NðKaÞ and NðKbÞ are counts observed under the peaks corresponding to Ka and Kb X-rays, respectively, and eðKaÞ and eðKbÞ are the efficiencies of the detector for the Ka and Kb series of X-rays, respectively. bðKaÞ and bðKbÞ are the target self-absorption correction factors for both the incident and the emitted radiations. I0 is the intensity of the incident radiation and G is a geometrical factor. In the present experimental setup, the I0 Ge values were determined in a separate experiment. Targets of pure elements, having areas of physical cross-section similar to those used in the main experiment, with atomic numbers 22pZp58 and emitting fluorescence X-rays in the energy range 4.5–41 keV were irradiated in the same experimental geometry, and fluorescence X-rays were counted. The I0 Ge values for the present set up were determined by the relationship . gut (So& . et al., 1997): I0 Ge ¼

NKi ; sKi bKi t

ð2Þ

where NKi is the number of Ka or Kb X-rays recorded at the Ka or Kb peaks, and sKi is the sKa or sKb fluorescence cross-section. The self-absorption correction factor has been calculated by using an expression . gut (So& . et al., 1999) obtained by assuming that the incidence angle of the fluorescence X-rays subtended at the detector was approximately 901    minc 1  exp ð1Þ þ memt t cos f   bemt ¼ ; ð3Þ minc þ memt t cos f

Fig. 1. Experimental set up.

where minc (cm2 g1) and memt (cm2 g1) are the mass attenuation coefficients (Hubbell and Seltzer, 1995) at the incident photon energy and at the fluorescence X-ray

Table 1 Kb/Ka X-ray intensity ratios of 3d elements Element and compounds

Present work

0 4 0 2 3 4 5 0 3 3 3 6 3 2 3 6 6 3 3 3 0 2 2 2 2 2 3 2 7 4 4 0 3 3 2 2 2 3 3

0.1395 0.1549 0.1456 F 0.1529 F 0.1474 0.1469 0.1447 F F F F F F F 0.1544 F F F 0.1471 0.1478 0.1495 F F 0.1436 F F 0.1490 F F 0.1362 0.1413 F F F 0.1478 F F

0.1137

0.1350

0.1161

0.1370

0.1153

0.1350

Oh

Td Oh Oh Td Td

0.1195

0.1290

Oh Oh Oh Oh

Td Td 0.1208 Oh

Oh

0.1270

0.180 F 0.1280 F F F F 0.1320 F F F F F F F F F F F F 0.1280 F F F F F F F F F F 0.1330 F F F F F F F

0.1034 0.1161 F F 0.1114 0.1190 0.1198 0.1124 0.1204 F F 0.1317 F 0.1159 0.1191 F 0.1264 F F F 0.1151 F 0.1277 F 0.1203 F F F F 0.1242 F 0.1160 0.1216 F 0.1232 0.1160 0.1189 F 0.1255

Raj et al. (2000) and Mukoyama et al. (1986)

Ertu&grul et al. (2001), Exp. 0.121

0.1314 (Raj et al., 2000) 0.128 0.1168 (Mukoyama et al., 1986)

0.1146 (Mukoyama et al., 1986)

0.1252 (Mukoyama et al., 1986)

0.1344 (Raj et al., 2000) 0.131 0.1171 (Mukoyama et al., 1986) 0.1191 (Mukoyama et al., 1986)

0.1240 (Mukoyama et al., 1986)

0.133

345

. Rebohle Ku. c-uk . onder et al. et al. (1993a, b, c), (1996), Exp. Exp.

O. Sogut et al. / Radiation Physics and Chemistry 64 (2002) 343–348

Ti 0.136470.0134 0.143370.0131 TiO2 V 0.131670.0111 VO 0.141770.0141 0.141970.0140 V2O3 0.128970.0130 V2O4 0.122570.0120 V2O5 Cr 0.134170.0130 0.112570.0110 Cr2O3 0.113070.0120 Cr(NO3)3 0.151670.0121 Cr(NO3)3  9H2O 0.152370.0120 Cr2O7(NH4)2 0.160670.0128 Cr3(OH)2 (CH3COO)7 0.181770.0128 CrCl2 0.191870.0128 CrCl3  6H2O 0.140970.0140 Na2Cr2O7 0.139370.0130 K2Cr2O7 Cr2(SO4)3 K2SO4  24H2O 0.130670.0130 0.148670.0130 Cr2(SO4)3H2O 0.111470.0088 [Cr(H2O)4Cl3]  2H2O Mn 0.123570.0104 MnO F 0.137370.0120 MnO2 0.178570.0141 MnCl2  2H2O F MnBr2 0.145570.0125 MnSO4 0.126770.0112 Mn(CH3COO)3 0.140970.0124 MnCO3 0.150770.0130 KMnO4 0.154970.0135 MnCl4 0.125770.0103 MnCl4  4H2O Fe 0.128770.0110 0.130070.0110 Fe2O3 0.132270.0119 FeCl32(NH4Cl)  H2O 0.134670.0120 FeCl2  6H2O FeS 0.139370.01120 0.142770.0130 FeSO4 0.137670.0124 FeNH4(SO4)2  6H2O 0.135670.0126 Fe(NO3)3  9H2O

Oxidation Symmetry Scofield Khan and Rao et al. state (1974), Karimi (1986b), Theo. (1980), Exp. Exp.

346

Table 1 (continued) Present work

Oxidation Symmetry Scofield Khan and Rao et al. state (1974), Karimi (1986b), Theo. (1980), Exp. Exp.

FePO4 FeF3 Co CoO Co2O3 Co(SCN)2 CoSO4 CoF2 CoF3 CoSO4  7H2O CoCl2 CoCl2  6H2O Co(ClO4)2  6H2O Co(CH3COO)2 Co(SCN)2 Co(NO3)2  6H2O Ni NiO NiCl2 NiSO4 Cu CuO Cu2O CuCl CuCl2 CuCl2  2H2O CuC2O4 Cu(CN)2 CuBr CuBr2 Cu(CH3COO)  H2O CuCO3 Zn ZnO ZnS ZnSO4 Zn(CH3COO)2  2H2O ZnCl2 ZnSO4  7H2O

0.143570.0132 0.135870.0123 0.138770.0140 0.111470.0105 0.137670.0124 F 0.152870.0125 0.110370.0089 0.119770.0110 0.151470.0128 0.141470.0119 0.149170.0130 0.144670.0128 0.158470.0132 0.125670.0102 0.168670.0140 0.146670.0124 F 0.119970.0108 0.139470.0116 0.137470.0113 0.160970.0132 0.145570.0121 0.136570.0113 0.124970.0104 0.134770.0107 0.142470.0121 0.145470.0130 0.154870.0137 0.119570.0103 0.127370.0115 0.144770.0132 0.125470.0102 F 0.111470.0098 0.128470.0114 0.136070.0124 0.145970.0132 0.140970.0129

4 3 0 2 3 2 2 2 3 2 2 2 2 2 2 2 0 2 2 2 0 2 1 1 2 2 6 2 1 2 2 2 0 2 2 2 2 2 2

0.1218

0.1380

0.1227

0.1460

0.1216

0.1370

0.1241

0.1320

Oh

Oh

Oh Oh

Th

Oh Oh

Th

Th Th

F F 0.1350 F F F F F F F F F F F F F 0.1360 F F F 0.1360 F F F F F F F F F F F 0.1380 F F F F F F

. Rebohle Ku. c-uk . onder et al. et al. (1993a, b, c), (1996), Exp. Exp. F F 0.1400 0.1450 F F F F F F 0.1445 F F F F F 0.1403 0.1450 F F 0.1412 0.1459 0.1436 F F F F F F F F F 0.1528 0.1487 F F F F F

F 0.1244 0.1194 0.1242 F 0.1241 F 0.1236 0.1274 F F F F F F 0.1262 F F F F 0.1211 0.1257 0.1259 F F 0.1305 F F F F F F F F F F F F F

Raj et al. (2000) and Mukoyama et al. (1986)

Ertu&grul et al. (2001), Exp.

0.1335 (Raj et al., 2000)

0.133

0.135

0.134

0.136

O. Sogut et al. / Radiation Physics and Chemistry 64 (2002) 343–348

Element and compounds

O. Sogut et al. / Radiation Physics and Chemistry 64 (2002) 343–348

energy of the sample, respectively, and t (g cm2) is the measured mass-thickness of sample. f has been calculated by using the following expression (Zarars"yz et al., 1989): cos f ¼

l ½l þ 0:25ðR0 þ R1 Þ2 1=2

;

ð4Þ

where l is the distance from source to the sample and R0 and R1 internal and external diameters of radioisotope source, respectively. f was found to be 191. In addition to this, we have also checked the angle from the shift in energy of the incoherent peak from the coherent peak using the Compton scattering formula.

3. Results and discussion The measured values for the Kb=Ka intensity ratios in Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and previous experimental values of Kb=Ka intensity ratios for pure elements and their compounds are listed in Table 1. The errors in the experimental Kb=Ka intensity ratios are estimated to be 4–10%. This error arises from uncertainties in the various parameters used to calculate the Kb=Ka intensity ratios, including errors due to peak area evaluation 3%, I0 Ge factor (2%), target thickness measurements (E3%) and self-absorption factors (E2%). As seen in Table 1, we observed chemical effects in the Kb=Ka intensity ratios. Chemical bonding type (ionic, metallic, covalent) affects the Kb=Ka intensity ratios. The individual characteristics of the structure of molecules, complexes and crystals (polarity, valency and electronegativity of atoms, co-ordination number, ionicities of covalent bond etc.) also affect the Kb=Ka intensity ratios. A change in chemical bond leads to a change in its valence electron density. The effect of the electronegativity, the nature of the ligands and the distribution of ligands around the central emitting atoms are some of the factors which may cause this variation (Sawhney et al., 2000). The electron density decreases or increases depending on the type of bonding with adjacent atoms in the molecule or crystal. The chemical bonding is more covalent in the Td symmetry than in the Oh symmetry and the bond length in the former is shorter than that in the latter. Both effects increase the interaction between the central metal atom and ligands in the Td symmetry as mentioned by Mukoyama et al. (1986). In general, the Kb=Ka ratios for Td symmetry compounds are larger than those for Od symmetry compounds. The effect of the chemical environment in coordination compounds of some 3d elements and the oxidation state on Kb=Ka X-ray . intensity ratios were investigated by Ku. c-uk . onder et al. (1993c). Mukoyama et al. (2000) calculated variations of Kb=Ka X-ray intensity ratios in 3d elements and the

347

results are explained according to the number of 3d electrons, Oh and Td symmetry. They concluded that for the compounds with Td symmetry, the intensities of the Kb’’ and Kb2;5 satellite lines increase the Kb=Ka ratios considerably and the change in the Oh symmetry is ascribed to changes in the screening constant of the metal 3p electrons by valence electrons as well as the satellite intensities (1986). Raj et al. (2000) investigated the influence of the chemical effect on the Kb=Ka X-ray intensity ratios of Cr, Mn and Co in CrSe, MnSe, MnS, CoS and the results are explained as a hybridisation effect between 3d and 4s states. Their work demonstrates that the Kb=Ka ratio in 3d elements is a function of the effective number of 3d electrons. Recently, a correlation between the widths of the Ka1 and Ka2 emission lines for Cr compounds and the number of 3d electrons has been shown by Mukoyama (2000). In general, for pure elements our results are in good agreement with experimental values of Khan and Karimi (1980). There are some differences between the results of this study and that of our previous one (Ertu&grul et al., 2001) because the measurements for these studies were carried out in different laboratories and in different systems. Although for both studies Si (Li) solid state detector was used, the detector’s resolution used in this study is better than the previous one. Compared to pure elements (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn), the Kb=Ka X-ray intensity ratios of compounds are found to deviate by 5, 2–8, 3–43, 2–43, 10–21, 1–22, 5–18, 1–17 and 2–16%, respectively. Rebohle et al. (1996) found deviations of only 1–5% for the same ratio in the case of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn for some compounds. For Ti and V, no significant dependence of chemical state on the Kb/Ka intensity ratio was observed, but the absolute Ka and Kb X-ray yields show a strong dependence on the chemical state of Ti and V. It was reported that Kb=Ka X-ray intensity ratios increase with increasing formal oxidation number of the elements for Cr, Mn, Co and . Cu compounds (Ku. c-uk . onder et al., 1993a b c) but we did not find any systematic relation between the Kb=Ka X-ray intensity ratio and the formal oxidation number of the element in the compound. The present experimental results indicate that the Kb=Ka X-ray intensity ratios for compounds with tetrahedral symmetry are, in general, larger than those with octahedral symmetry, but this is different for distinctive compounds of elements. These results also indicate that K X-ray spectroscopy for 3d elements is very useful for studying the electronic structures of chemical compounds.

References Arndt, E., Brunner, G., Hartmann, E., 1982. Kb/Ka X-ray intensities ratios for X-ray production in 3d elements by

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O. Sogut et al. / Radiation Physics and Chemistry 64 (2002) 343–348

photoionisation and electron capture. J. Phys. B: At. Mol. Opt. Phys. 15, L887–L889. . S, ahin, Y., B.uy.ukkasap, E., 1999. Chemical Bayda,s, E., S.o&gut, . O., effect on L X-ray fluorescence cross-sections of Ba, La and Ce Compounds. Radiat. Phys. Chem. 54, 217–221. Brunner, G., Nagel, M., Hartmann, E., Arndt, E., 1982. Chemical sensitivity of Kb/Ka X-ray intensities ratios for 3d elements. J. Phys. B 15, 4517–4522. Chang, C., Chen, C., Yen, C., Wu, Y., Su, C., Chiou, S.K., 1994. The vanadium Kb/Ka intensities ratios of some vanadium compounds. J. Phys. B 27, 5251–5256. . S, im,sek, O., . Buy . gut, Ertu&grul, E., So& . O., . ukkasap, . E., 2001. Measurement of kb/ka intensities ratios for elements in the range 22pzp69 at 59.5 keV. J. Phys. B 34, 909–914. Hallmeier, K.H., Szargan, R., Fritsche, K., Meisel, A., 1987. Soft fluorescent X-ray emission spectra of coordination compounds of Manganese. Physica Scripta 35, 827–830. Hubbell, J.H., Seltzer, S.M., 1995. Tables of X-ray mass attenuation coefficients and mass energy absorption coefficients 1–20 MeV for elements Z=1–92 and 48 additional substances of dosimetric interest. US Department of Commerce, Technology Administration, National Institute of Standards and Physics Laboratory. NISTIR 5692. Iihara, J., Omorr, T., Yoshihara, K., Ishii, K., 1993. Chemical effects in chromium L X-rays. Nucl. Instrum. Methods B 75, 32–34. Khan, M.R., Karimi, M., 1980. Kb/Ka ratios in energy-dispersive X-ray emission analysis. X-ray Spectrom. 9 (1), 33–35. Kiss, K., Palinkas, J., Schlenk, B. 1980. Investigations of the chemical-state dependence of the Kb/Ka intensities ratios following electron impact ionisation. Radiochem. Radioanal. Lett. 45, 213–220. Konishi, T., Kawai, J., Fujiwara, M., Kurisaki, T., Wakita, H., Gohshi, Y., 1999. Chemical shift and lineshape of high resolution Ni Ka X-ray fluorescence spectra. X-ray Spectrometry 28, 470–477. . Ku, . cuk . onder, A., S, ahin, Y., Buy . ukkasap, . E., Kopya, A., 1993a. Chemical effects on the Kb/Ka intensities ratios in coordination compounds of some 3d elements. J. Phys. B 26, 101–105. . Ku, . cuk . onder, A., S, ahin, Y., Buy . ukkasap, . E., 1993b. The effect of the chemical environment on the Kb/Ka intensities ratio. IL Nuovo Cimento 15 (10), 1295–1300. . Ku, . cuk . onder, A., S, ahin, Y., Buy . ukkasap, . E., 1993c. Dependence of the Kb/Ka intensities ratios on the oxidation state. J. Radioanal. Nucl. Chem. 170 (1), 125–132. Mukoyama, T., 2000. Ka1,2 X-ray emission lines of chromium and its compounds. X-ray Spectrometry 29, 413–417. Mukoyama, T., Taniguchi, K., Adachi, H., 1986. Chemical effect on Kb/Ka intensities ratios. Phys. Rev. B. Phys. 34, 3710–3716. Mukoyama, T., Taniguchi, K., Adachi, H., 2000. Variation of Kb/Ka X-ray intensities ratios in 3d elements. X-ray Spectrometry 29, 426–429.

Raghavaiah, C.V., Vankataratnam, S., Murty, G.S.K., Rao, M.V.S.C., Reddy, S.B., Sastry, D.L., 1992. Kb/Ka ratios and chemical effects in partially filled 3d-shell elements. X-ray Spectrometry 21, 239–244. Raj, S., Padhi, H.C., Polasik, M., 2000. Influence of chemical effect on the Kb-to-Ka X-ray intensities ratios of Ti, V, Cr and Fe in TiC, VC, CrB, CrB2 and FeB. Nucl. Instrum. Methods B 160, 443–448. Rao, N.V., Reddy, S.B., Satyanarayna, G., Satry, D.L., 1986a. Kb/Ka intensities ratios in elements with 20pZp50. Physica 138C, 215–218. Rao, N.V., Reddy, S.B., Raghavaiah, C.V., Vankataratnam, S., Sastry, D.L., 1986b. A study of chemical effects on Kb/Ka X-ray intensities ratios in 3d elements. Port. Phys. 17, 143–148. Rebohle, L., Lehnert, U., Zschornack, G., 1996. Kb/Ka intensities ratios and chemical effects of some 3d elements. X-ray Spectrometry 25, 295–300. Sawhney, K.J., Lodha, G.S., Kataria, S.K., Kulshreshtha, S.K., 2000. X-ray Spectrometry 29, 173–177. Scofield, J.H., Lawrence Livermore Laboratory, Livermore, 1974. Cal. 94550, Atomic Data and Nuclear Data Tables, Vol. 14, pp. 121–137. . Buy . gut, . So& . O., . ukkasap, . E., Ku, . cuk . onder, A., Ertu&grul, M., . 1995. Alloying effect on Kb/Ka intensity ratios S, im,sek, O., in CrxNi1x and CrxAl1x alloys. Appl. Spectrosc. Rev. 30 (3), 175–180. . Buy . gut, . So& . O., . ukkasap, . E., Ku, . cuk . onder, A., Ertu&grul, M., 1997. Chemical effect on L X-ray intensity ratios of mercury, lead and bismuth. Appl. Spectrosc. Rev. 32 (1– 2), 167–175. . Bayda,s, E., Buy . gut, So& . O., . ukkasap, . E., 1999. Chemical effect on L shell fluorescence yields of Hg, Pb and Bi Compounds. J. Trace Microprobe Techniques 17 (3), 285–291. Suguira, C., Yorikawa, H., Muramatsu, S., 1996. Kb X-ray emission spectra and chemical effects of phosphorus in some selected elements. J. Phys. Soc. Japan 65(9), 2940–2945. Tamaki, Y., Omori, T., Shiokawa, T., 1975. Chemical effect on the Kb/Ka intensities ratios in the 51Cr-labelled chromium. Radiochem. Radioanal. Lett. 20, 255–262. Tamaki, Y., Omori, T., Shiokawa, T., 1979. Chemical effects on the Kb/Ka intensities ratios of the daughter atoms formed by the EC decay of 51Cr and 54Mn. Radiochem. Radioanal. Lett. 37, 39–44. Taniguchi, K., Mukoyama, T., Adachi, H., 1987. Chemical effects on K X-ray spectrum. J. Phys. C 9, 757–765. Yoshihara, H.A., Yamoto, I., Kaji, H., 1981. Chemical effect of Tc Kb X-ray intensity in the decay 99Mo-99mTc-99Tc. Radiochem. Radioanal. Lett. 48 (5), 303–310. Zarars"yz, A., Aygun, . E., 1989. A theoretical and experimental investigation of the sourceFsample detector geometry for an angular type radioisotope excited XRF spectrometer. J. Radioanal. Nucl. Chem. Article 129, 367–375.