Instrumental neutron activation analysis applied to the determination of the chemical composition of metallic materials with study of interferences

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1 Journl of Rdionlyticl nd Nucler Chemistry, Vol. 264, No. 1 (2005) Instrumentl neutron ctivtion nlysis pplied to the determintion of the chemicl composition of metllic mterils with study of interferences E. G. Moreir, M. B. A. Vsconcellos, M. Siki Lortório de Análise por Ativção Neutrônic, Centro do Retor de Pesquiss (LAN-CRPq) - IPEN/CNEN-SP, Cix Postl 11049, , São Pulo - SP, Brsil (Received April 6, 2004) Instrumentl neutron ctivtion nlysis ws pplied to evlute the chemicl composition of metllic mterils, nmely iron, steel, silicon nd ferrosilicon certified reference mterils. As, Co, Cr, Mn, Mo, Ni, V nd W concentrtions were nlyzed in the iron nd steel smples wheres 21 elements were determined in silicon nd ferrosilicon smples. Accurcy nd precision results of out 10% were chieved for most elements, indicting tht the technique is suitle for the nlysis of metllic mterils. Interferences of Cr nd Mn in V; Fe nd Co in Mn; Co in Fe nd Cr in Ti were quntified nd only the lst one ws criticl to the nlysis of the mterils employed in this work. Introduction Vrious nlyticl techniques hve een used in the chrcteriztion of the chemicl composition of metllic mterils. 1 However, nucler techniques including instrumentl neutron ctivtion nlysis (INAA) hve een scrcely used in the nlysis of such mterils. This fct cn e explined y the difficulty of ccess to nucler fcilities nd the gret development, in the lst few yers, of less expensive techniques like ICP-MS, AAS nd XRF. 2 INAA ws used in the chrcteriztion of metllic ores, 3 metls, nd other mterils of interest in the metllurgicl nd semiconductor industries. 4,5 The technique ws successfully used for high purity mterils, like high purity nickel 6 nd iron. 7 Metllic silicon mtrices re very fvorle to INAA s the 31 Si formed during irrdition hs short hlf-life. This llows the nlysis of lrge numer of elements fter its decy nd longer irrdition periods which provide etter sensitivities nd detection limits. This feture mkes INAA technique of choice for the microelectronic industry. 8 However, consistent nlyticl prolems due to the high mounts of interfering elements present in some metllic mtrices cn rise. 9 The following potentilly significnt interferences were selected in the nlysis of steel, iron nd silicon mtrices mong the vrious possile interferences present in INAA Gmm-ry spectrl interference In this kind of interference two rdionuclides hve gmm-ry peks of the sme energy, nd hence, one my interfere in the detection of the other. In this work, the 51 Cr interference in Ti determintion vi 51 Ti rdionuclide, using 320 kev pek (common to oth rdionuclides) ws investigted. Primry interference rections The indictor rdionuclide is produced y other rection thn the nlyticl rection. The following cses were investigted: Cr nd Mn in V determintion: Min rection: 51 V (n, γ) 52 V. Interference rections: 52 Cr (n, p) 52 V nd 55 Mn (n, α) 52 V Fe nd Co in Mn determintion: Min rection: 55 Mn (n, γ) 56 Mn Interference rections: 56 Fe (n, p) 56 Mn nd 59 Co (n, α) 56 Mn Fe in Cr determintion: Min rection: 50 Cr (n, γ) 51 Cr Interference rection: 54 Fe (n, α) 51 Cr Co in Fe determintion: Min rection: 58 Fe (n, γ) 59 Fe Interference rection: 59 Co (n, p) 59 Fe Second order interference rections Rre sitution in which nucler rection or some element in the mtrix produces mesurle mount of the nlyte rdionuclide. The following possiilities were studied: Cr in Mn determintion: Min rection: 55 Mn (n, γ) 56 Mn Interference rection: 54 Cr (n, γ) 55 β Cr 55 Mn (n, γ) 56 Mn Fe in Co determintion: Min rection: 59 Co (n, γ) 60 Co Interference rection: 58 Fe (n, γ) 59 β Fe 59 Co (n, γ) 60 Co * E-mil: emoreir@curingo.ipen.r /USD Akdémii Kidó, Budpest 2005 Akdémii Kidó, Budpest Springer, Dordrecht

2 The im of this work ws to pply INAA in the study of the chemicl composition of metllic mterils. For this purpose, the technique ws pplied to certified reference mterils (CRMs) of iron, steel, silicon nd ferrosilicon. Possile INAA interferences in the nlyses of these mterils re lso investigted. Smple preprtion Experimentl The following CRMs were used in this study: Stinless Steel 316 (IPT 24), Stinless Steel (NIST SRM 442), Cu-Ni-Cr-Mo Molten Gry Iron (IPT 75), Pure Iron (IPT 73), Ferrosilicon-75% Si (IPT 56), Ferrosilicon-45% Si (IPT 70), Ferrosilicon-73% Si (NIST SRM 58), Ferrosilicon (NIST SRM 59) nd Refined Silicon (NIST SRM 57). Aout g of CRM fillings/powder were weighed in properly clened polyethylene vils nd irrdited with elementl stndrds. Stndrds were prepred y pipetting element solutions of known concentrtion onto Whtmn pper filters, which, fter drying, were kept in polyethylene vils with the sme geometry of the smples. When suitle, multielement stndrds were prepred for silicon nd ferrosilicon CRMs. Most of the smples were prepred in four replictes. Irrdition nd element determintion Two series of irrdition were used, ccording to the hlf-lives of the rdionuclides to e nlyzed. 13 For Mn nd V determintion, smples nd stndrds were irrdited for 30 seconds t the Pneumtic Sttion of IEA-R1 Nucler Reserch Rector t IPEN with n. cm 2. s 1 therml neutron flux. 52 V ws mesured for 5-minute period, immeditely fter irrdition nd 56 Mn ws mesured for 20-minute period, 30 minutes fter irrdition. For determintion of the other elements, 30-minute (iron nd steel mtrices) or 8-hour (silicon nd ferrosilicon mtrices) irrdition t n. cm 2. s 1 therml neutron flux ws used. Intermedite lived rdionuclides were mesured for 1 hour, fter 2-dy decy while long lived ones were mesured lso for 1 hour, fter month decy period. Smples nd stndrds were mesured using Cnerr GX 2020 HPGe detector (coupled to Cnerr multichnnel system nd electronics) with 1.70 kev resolution for 1332 kev gmm-ry pek of 60 Co. Anlysis of gmm-ry spectr ws crried out using the softwre developed y Dr. D. PICCOT (Scly, Frnce). 14 Element concentrtion ws clculted pplying in-house softwre. Interference evlution For INAA interference evlution, incresing msses of pure element or oxides of interest or stndrds (prepred from element solutions) were irrdited nd mesured in the sme conditions tht of the CRM smples. Counting rtes were corrected to initil decy time nd the results were used to determine the specific ctivities of ech rdionuclide. The specific ctivities were pplied in the evlution of possile interferences in the CRMs used in this work. Due to the high counting rtes otined in the irrdition of Mn nd Co, it is not possile to mesure the induced rdioctivity from rdionuclides generted in the interference rections. To void this prolem, epitherml neutrons were used in the irrdition of smples of these elements. This llows the mesurement of the induced rdition from rdionuclides generted in rections other thn the therml neutron flux induced rections. Interferences in INAA Results nd discussion By mens of irrdition of different msses of the vrious elements under investigtion, it ws possile to plot grphs for specific sensitivity of the elements otined in the irrdition nd mesurement conditions used in this work. As n exmple, Fig. 1 shows the grphs otined for the counting rtes of the two peks of 56 Mn otined from the irrdition of different msses of Mn, Fe nd Co. The grphs presented good correltion coefficient, most of them out It ws possile to detect ll the interference rections ut it ws impossile to quntify the specific sensitivity for the second pek in the Co stndrd due to the high counting sttistics uncertinty otined for this element t this energy 1811 kev. From the sensitivity grphs, pprent nlyte msses were clculted for ech interference, s presented in Tle 1. These results my e used in our lortory, independent of the mtrix under investigtion, once the sme irrdition nd mesurement conditions re employed. Although detected, the interferences of Fe in Cr, Cr in Mn nd Fe in Co were not quntified due to very low vlues nd were not tken into ccount in this study. 46

3 Fig. 1. Counting rte for 56 Mn otined y INAA using Mn, Fe nd Co stndrds The pprent mss results otined re in good greement with the nucler chrcteristics of the investigted rdionuclides s cross sections nd isotope undnces. In Ti nlysis, 50 Cr hs therml neutron cross section much higher thn 50 Ti, thus, even for very short irrdition periods, Cr my interfere in Ti determintion. The smll cross sections for the (n,p) nd (n,α) rections, descried in the Introduction of this pper, ccount for the very smll contriution of these rections for the primry interferences oserved. The exception goes to the interference of Co in Fe, which rdinuclide cross sections re 1.42 nd 1.31 rns, respectively. 12 In ddition, isotope undnce for the Co rdionuclide is much higher thn for the Fe rdionuclide. The quntifiction of the second order interferences ws unfesile, not only y virtue of unfvorle cross sections of the (n,γ) rections, ut lso ecuse connected β-decys re necessry for the second order interference to occur. In Tle 2 re presented the errors in element determintion in the vrious CRMs due to INAA interferences under the conditions used in this work. At higher interferent/nlyte rtio, higher interference occurs. It cn e noticed tht with the exception of the spectrl interference of Cr in Ti, for high Cr/Ti rtio, the other interferences my e neglected in the nlysis of the CRMs used in this work. In the cses of the interferences of Cr in V nd Fe in Mn, ccording to the type of smples nd/or high interferent/nlyte rtio, corrections should e considered. For the interference of Co in Fe, even though the pprent mss of Fe due to Co interference is significnt, the rtio of these two elements is very smll in the CRMs used in this work nd, hence, the interference my e ignored. Since 56 Mn hs very high ctivities in these smples nd longer hlflife thn 51 Ti, it ws not possile to determine Ti in the nlyzed smples due to the high 56 Mn ctivities. Nevertheless, in cses when it is possile to determine Ti, it is mndtory to consider the correction due to the Cr interference. Tle 1. Anlyte pprent mss formed y INAA interference in the irrdition nd mesurement conditions of this work Interference type Interferent Anlyte Apprent mss, g Spectrl Cr Ti Primry Cr V Primry Mn V Primry Fe Mn Primry Co Mn Primry Fe Cr ND Primry Co Fe nd order Cr Mn ND 2 nd order Fe Co ND Mss of nlyte formed during irrdition, considering one grm of interferent. Not detected. 47

4 Tle 2. Element determintion error due to INAA interferences for g of CRM Interferent Anlyte CRM R i/ Error, % Cr Ti NIST SRM IPT IPT IPT NIST SRM NIST SRM Cr V NIST SRM IPT Mn V NIST SRM IPT Fe Mn NIST SRM IPT IPT IPT IPT NIST SRM NIST SRM NIST SRM Co Mn NIST SRM IPT Co Fe NIST SRM IPT Mss rtio etween interferent nd nlyte in the CRM. Positive error in the concentrtion otined y INAA due to interference. Element determintion The results otined y INAA of elements in iron nd steel, nd in silicon nd ferrosilicon CRMs re given in Tles 3 nd 4, respectively. All results re presented t 95% confidence intervl. Using INAA, it ws possile to otin results for non certified elements such s As, V nd W in the iron nd steel CRM nd mny other elements in the silicon nd ferrosilicon CRM. For most of the elements determined in the iron nd steel smples, the results were otined with reltive stndrd devitions nd reltive errors lower thn 10%. Although it ws not possile to determine the concentrtion of some elements of interest y INAA such s Al, C, Cu or Ti in silicon nd ferrosilicon CRMs, the concentrtion of elements which re hrdly determinle y other techniques, such s U, Th nd rre erths, could e determined. In the nlysis of these CRMs, most of the results were otined with reltive stndrd devition lower thn 15% with reltive error of out 12% in respect to the certified vlues. In Figs 2 nd 3 re shown the grphicl representtions of the results s normlized concentrtion in respect to the certified vlues for some CRMs studied in this work. The ccurcy is mesured y devition from unit wheres precision is mesured y dispersion of the otined vlues. The z score of the results lso shows tht most figures re within the expected ±3z score in INAA. 15 Tle 3. Element concentrtions in steel nd iron CRMs otined in this work y INAA t 95% confidence intervl Element, µg. g 1 IPT 24 NIST SRM 442 IPT 75 IPT 73 As 83 ± 5 76 ± ± 2 29 ± 2 Co 417 ± 14 (450 ± 30) c 1256 ± 36 (1300) 46 ± 2 29 ± 2 (40 ± 10) Cr 18 ± 1 (17.81 ± 0.05) 15 ± 1 (16.1) 0.47 ± 0.03 (0.487 ± 0.006) ± (0.030 ± 0.003) Cu 346 ± 283 (390 ± 20) 1022 ± 235 (1100) 0.46 ± 0.06 (0.433 ± 0.004) 783 ± 94 (760 ± 30) Mn 1.34 ± 0.04 (1.50 ± 0.02) 2.6 ± 0.1 (2.88) 0.75 ± 0.04 (0.722 ± 0.005) ± (0.044 ± 0.003) Mo 2.6 ± 0.2 (2.54 ± 0.03) 1176 ± 148 (1200) 0.42 ± 0.05 (0.439 ± 0.005) 47 ± 4 (49 ± 4) Ni 10 ± ± ± 0.05 NO (9.93 ± 0.05) (9.9) (0.425 ± 0.004) V 310 ± ± ± 39 NO (320) (300 ± 20) W 6.4 ± ± 50 (800) 12.2 ± ± 0.2 Concentrtion in mss percentge. NO: Not otined. c Certified vlues in prenthesis. 48

5 Tle 4. Elements concentrtion in silicon nd ferrosilicon CRMs otined in this work y INAA, t 95% confidence intervl Element, µg. g 1 IPT 56 IPT 70 NIST SRM 58 NIST SRM 59 NIST SRM 57 As 1.2 ± ± ± ± ± 0.2 Br 0.15 ± 0.4 NO 0.48 ± ± ± 0.1 Co 4.6 ± ± ± 2 40 ± ± 0.6 Cr 112 ± 25 (110 ± 20) 415 ± 34 (460 ± 40) 182 ± 19 (200 ± 10) 785 ± 59 (800 ± 30) 241 ± 24 (250 ± 10) K NO NO NO 27 ± 2 78 ± 12 Eu 0.15 ± ± ± 0.1 NO 0.8 ± 0.1 Fe 24 ± 1 (24.1 ± 0.3) 48 ± 2 (54.1 ± 0.2) 27 ± 1 (25.23 ± 0.03) 48 ± 2 (50.05 ± 0.04) 0.63 ± 0.03 (0.65 ± 0.02) L 5.3 ± ± ± ± ± 0.7 Mn 276 ± 28 (290 ± 20) 2572 ± 239 (2830 ± 50) 1558 ± 92 (1600 ± 100) 7646 ± 400 (7500 ± 100) 332 ± 39 (360 ± 40) Mo 6 ± 3 28 ± ± ± ± 13 N 14 ± 2 16 ± ± 3 21 ± 7 38 ± 11 Nd 5 ± 3 18 ± 3 NO NO 27 ± 3 S 0.3 ± ± ± ± ± 0.03 Sc 0.9 ± ± ± ± ± 0.03 Sm 0.9 ± ± ± ± ± 0.6 T NO NO NO NO 0.4 ± 0.1 Th 0.8 ± ± 1.3 NO 1.2 ± ± 0.8 U 0.9 ± ± ± ± ± 0.2 V 19.2 ± ± ± 5 25 ± 4 23 ± 3 W 0.35 ± ± ± ± 4 NO Y 0.2 ± 0.1 NO 2.2 ± 0.2 NO 1.2 ± 0.1 Concentrtion in mss percentge. NO: Not otined. c Certified vlues in prenthesis. Fig. 2. Normlized concentrtion s function of certified vlue nd z score for iron CRMs 49

6 Fig. 3. Normlized concentrtion s function of certified vlue nd z score for ferrosilicon CRMs Conclusions The results showed tht INAA my e used successfully in the determintion of vrious elements in iron nd steel nd 21 elements in silicon nd ferrosilicon. Precision nd ccurcy of out 10% indicte tht INAA is suitle lterntive technique for element determintion in metllic smples. From the interference study, it ws possile to quntify Cr interference in Ti nd V, Mn interference in V nd Fe nd Co interferences in Mn. Only the Cr interference in Ti could impose corrections for the smples nlyzed. * The uthors re indeted to Instituto de Pesquiss Tecnológics do Estdo de São Pulo (IPT) for provision of some of the CRMs used in this work. References 1. T. R. DULSKI, Anl.Chem., 36 (1995) 21R. 2. IAEA, Use of Reserch Rectors for Neutron Activtion Anlysis, TECDOC 1215, Vienn, M. A. RAOOF, A. NAEEM, R. ZAGHLOUL, A. F. ABDUL-FATTAH, M. A. OBEID, J. Rdionl. Nucl. Chem., 60 (1980) R. E. JERVIS, M. M. C. KO, T. JUNLIANG, L. PULING, J. Rdionl. Nucl. Chem., 169 (1993) I. POPESCU, T. BADICA, A. OLARIU, C. BESLIU, A. ENE, A. IVANESCU, J. Rdionl. Nucl. Chem., 213 (1996) J. H. ZAIDI, S. WAHEED, S. AHMED, J. Rdionl. Nucl. Chem., 242 (1999) K. TOMURA, H. TOMURO, J. Rdionl. Nucl. Chem., 242 (1999) S. C. MCGUIRE, T. Z. HOSSAIN, C. GOLKOWSKI, N. D. KERNESS, J. P. SOLCER, J. Rdionl. Nucl. Chem., 192 (1995) W. H. EL-ABBADY, Z. H. EL-TANAHY, A. A. EL-HAGG, Czech. J. Phys., 49 (1999) W. D. EHMANN, D. E. VANCE, Rdiochemistry nd Nucler Methods of Anlysis, John Wiley & Sons, New York, Y. MIYAMOTO, H. HABA, A. KAJIKAWA, K. MASUMOTO, T. NAKANISHI, K. SAKAMOTO, J. Rdionl. Nucl. Chem., 239 (1999) A. TRAVESI, Anlysis por Activción Neutrónic Teorí, Práctic y Aplicciones, Servicio de Pulicciones de l J. E. N., Mdrid, IAEA, Prcticl Aspects of Operting Neutron Activtion Anlysis Lortory, TECDOC 564, Vienn, D. PICCOT, personl communiction. 15. P. BODE, P. DIJK, J. Rdionl. Nucl. Chem., 215 (1997)