Applied Radiation and Isotopes 82 (2013) 67–71

Contents lists available at ScienceDirect

Applied Radiation and Isotopes

0969-80http://d

n Corrof Scien

E-m

journal homepage: www.elsevier.com/locate/apradiso

Elemental analysis of natural quartz from Um Higlig, Red Sea Aea,Egypt by instrumental neutron activation analysis

A. El-Taher a,b,n, Abdulaziz Alharbi c

a Physics Department, Faculty of Science, Qassim University Buraydah 51452, Saudi Arabiab Physics Department, Faculty of Science, Al-Azhar University, Assuit 71452, Egyptc Qassim university, Agricultural College, P.O. Box 6622, Buraydah 51452, Saudi Arabia

H I G H L I G H T S

� The instrumental neutron activation analysis technique was used for qualitative and quantitative analysis of natural quartz.

� The samples irradiated with thermal neutrons in the TRIGA Mainz research reactor.� The following elements have been determined: As, Ba, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, K, La, Lu, Mg, Mn, Na, Nd, Rb, Sc, Sm, Th, U, Yb, Zn and Zr.

a r t i c l e i n f o

Article history:Received 19 December 2012Received in revised form27 June 2013Accepted 1 July 2013Available online 15 July 2013

Keywords:Elemental analysisQuartzINAATRIGA Mainz

43/$ - see front matter & 2013 Elsevier Ltd. Ax.doi.org/10.1016/j.apradiso.2013.07.002

esponding author at: Qassim University, Physce, Buraydah 51452, Saudi Arabia.ail address: Atef_Eltaher@hotmail.com (A. El-T

a b s t r a c t

A scheme for INAA of 25 elements: As, Ba, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, K, La, Lu, Mg, Mn, Na, Nd, Rb, Sc,Sm, Th, U, Yb, Zn and Zr in quartz collected from the eastern desert along the Egyptian Red Sea coast isproposed. The samples were prepared together with standard reference material and irradiated in aneutron flux of 7�1011 n/cm2 s in the TRIGA Mainz research reactor facilities. The gamma spectra werecollected by a HPGe detector and the analysis was done by a computerized multichannel analyzer.Theaccuracy of the procedure is evaluated by the analysis of two geo-standard reference materials (DoleriteWSE and Microgabro PMS). The choice of the nuclear reaction, irradiation and decay times and of theproper gamma radiation in counting are presented and discussed. The data presented here are ourcontribution to understanding the elemental composition of the quartz rock. Because there are noexisting databases for the elemental analysis of quartz, our results are a start to establishing a databasefor the Egyptian quartz. It is hoped that the data presented here will be useful to those dealing withgeochemistry, quartz chemistry and related fields.

& 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Quartz is widely used in industry and in scientific investiga-tions. In many cases, however, its applicability depends on theimpurity content, which, depends on of production method and onthe purity of the raw materials. Nuclear analytical methods havebeen successfully applied to the determination of a great variety ofelements in environmental, biological and geological samples.Neutron activation analysis techniques have been improved andhave become an excellent tool for such purposes (Hassan et al.,1983; Zaghloul et al., 1993; El-Taher, 2010a; Brunfelt, and Steinnes,1966; Gibson and Jagam, 1980; Gordan et al., 1968; Gurna et al.,1988). Different techniques could be used for estimating the trace,

ll rights reserved.

ics Department, Faculty

aher).

minor and major elements of these environmental samples whichare considered as complex samples. The major advantage of NAAare (a) the relative freedom from matrix interferences, (b) highaccuracy and (c) very low zero blank contributions. Becausenuclear reactions and decay processes are virtually unaffected bychemical and physical structure of the material during and afterirradiation, the composition of the matrix has little influence onthe induced activityand makes INAA a preferred technique(Brodsky, 1986; Zaghloul, and El-Abbady, 1988; Gordus, 1995; Senaet al., 1995; Descantes et al., 2001; Scheid et al., 2009; El-Taher,2010b; Potts and Rogers 1991; Duffey et al., (1970); El-Taher et al.,(2003); El-Taher et al., (2004); Gurna et al., (1990); MonteroCabrera et al., (2000); Senftle et al., (1971); Vereijke, (1992). Inspite of the large number of papers devoted to INAA, those dealingwith quartz are relatively small in number. In the present paper ascheme for INAA of quartz is proposed. Since the concentration ofelements in quartz is poorly known, it is important to measure theconcentrations of major, minor and trace elements in natural

A. El-Taher, A. Alharbi / Applied Radiation and Isotopes 82 (2013) 67–7168

quartz in addition to rare earth elements and the natural radio-nuclides uranium and thorium. These will be available for sub-sequent evaluations of the possible future environmentalcontamination due to human activity. This research is our contribu-tion to the understanding of the elemental composition of the quartzrock and also to establishing a database.

2. Experimental technique

2.1. Sampling and sample preparation

A total of three natural quartz rock samples collected from(Umm Heglig) in the Eastern Desert along the Egyptian Red Seacoast were collected for investigation by instrumental neutronactivation analysis. Each of the three samples was obtained fromthe same bed and each sample was about a meters from the otherones. Fig. 1 shows the location map for the study area. The studyarea Umm Heglig confined space between the longitudes 33155′ to33159′ and latitudes 25101′ to 25102′. The estimated reserves of

Fig. 1. Location map of the study area (Umm Heglig) in the Eastern Desert alongthe Egyptian Red Sea coast.

Table 1Irradiation cycles, cooling and counting times and elements determined (Kernchemie R

Irradiation time Cooling time Measuring tim

1 min 5 min 4 min5 min 1 h 15 min6 h 2 d 1 h6 h 14 d 8 h

about 13.4 million tons. The rest of the sites that are exploitedquartz which are less important and mostly in feldspar sites andextracted from raw on a small scale. The samples, each about 1 kgin weight, were dried in an oven at about 105 1C to ensure thatmoisture is completely removed. For elemental analysis by instru-mental neutron activation analysis, the powdered samples weresieved using a standard set of sieves to a diameter range of lessthan 125 μm and greater than 63 μm. Each powdered sample washomogenized using an electric shaker (El-Taher, 2007).

3. Irradiations and instrumentation

Polyethylene capsules filled with 100 mg of the powder sam-ples and then irradiated with a standard reference material withthermal neutrons at the university of Mainz Triga research reactor(100 kWth) with a flux of 7�1011 n/cm2s. We have performed fourirradiation cycles for every sample of the collected three samplesindependently, as noted in Table 1, this gives twelve irradiatedsamples. Table 1 illustrates the conditions of irradiation cycles forall samples and the detected elements in the samples afterirradiation processing. INAA achieves a qualitative and quantita-tive analysis of the unknown samples by irradiating them withneutrons through the (n, γ) reaction and detecting the emitted γrays from the resulting radioactive nuclides after irradiation.Qualitative analysis can be achieved by analysis of γ lines in theγ spectrum detected and registered by aHPGe detector and itsassociated electronic circuit (El-Taher, 2010a). The elemental con-tent of our samples were quantitatively determined by comparisonwith the activities of Dolerite WSE and Microgabro PMS referencematerials (El-Taher, 2010b; El-Taher, 2010c). The data were col-lected for various measurements after appropriate cooling times(Kernchemie Report, 1989).

The gamma-ray spectrometer used consists of a HPGe detectorwith its electronic circuit. The detector has the following specifica-tions: energy resolution (FWHM) at 1.33 MeV Co-60 is 1.70 keV,Peak to Compton ratio Co-60 is 65.2, relative efficiency at 1.33 MeVCo-60 is 29.2%, energy resolution (FWHM) at 0.122 MeV Co-57 is686 eV, and bias voltage is +2000 dc. The detector is connected tothe following components: preamplifier, amplifier, ADC converterand MCA. The measurements were performed and analyzed usingthe Intergamma Software produced by Intertechnique Deutsch-land GmbH, Mainz, Germany. The electronic dead time in allmeasurements was less than 10% and was automatically correctedby the Intergamma software.

4. Results and discussion

As a result of preliminary investigations, the conditions given inTable 1 were chosen as most appropriate for irradiation, coolingand measurement. The radioactive isotopes and the nuclear datafor the elements determined are shown in Table 2. All theelements, under investigation in the present work, were calculatedby means of activities induced by (n,γ) reactions, since some of theradionuclides measured exhibit more than one prominent gamma

eport, 1989).

e Elements detected

Mg, CaNa, Mn, KAs, La, Sm, USc, Cr, Fe, Co, Zr, Zn, Nd, Rb, Ba, Cs, Ce, Eu, Yb, Lu, Hf, Th

Table 2Nuclear data for the elements determined in natural quartz.

Element Activationproduct

Energy keV T1/2 Intensity(%)

Detection Limitppm

Na% 24Na 1369 15 h 100 34Mg% 27Mg 1014 9.5 m 11.01 1.7Ca% 49Ca 3984 8.7 m 75 200Mn% 56Mn 846 2.6 h 99 3Fe% 59Fe 1099 44.5

d56 126

K% 42K 1524.7 12.4 h 18 460Sc 46Sc 889 38.8 d 100 0.012Cr 51Cr 320 27.7 d 16 4.2Co 60Co 1332 5.3 y 100 0.18Zn 65Zn 115 244 d 50 2.6As 76As 559 26.3 h 45 1.6Rb 86Rb 1076 18.6 d 9 5.6Zr 95Zr 756,7 64 d 17.38 19Ba 131Ba 496 11.8 d 41 3.2Cs 134Cs 604.7 2.06 y 89 0.114La 140La 1596 40.3 h 96 5.6Ce 141Ce 145 32.5 d 40 0.72Nd 147Nd 91.1 11.1 d 28 0.18Eu 152Eu 1408 13.3 y 24 0.8Sm 153Sm 103 46.3 h 34 0.16Yb 169Yb 198 32 d 6 0.18Lu 177Lu 208.4 161 d 11 0.014Hf 181Hf 428 42.4 d 83 0.06Th 233Pa 312 27d 38 0.12U 239NP 106 2.4d 21 0.16

Table 3Chemical composition of Dolerite WSE and microgabro PMS standard referencematerials.

Element WSE (%) PMS (%) Element WSE ppm PMS ppm

Si O2 51 47 Ho 1 0.5Al2O3 14 17 La 30 3Fe2O3 13 10 Lu 0.4 0.2Mn O 0.2 0.15 Mo 4 2Mg O 5.5 9.5 Nb 20 2Ca O 9 12.5 Nd 3.5 6Na2O 2.5 2 Ni 55 110K2O 1 0.1 Pb 15 3Ti2O 2.5 1 Pr 8 1P2O5 0.3 o0.1 Rb 30 o2

Sb o0.5 o0.5ppm ppm Sc 30 35

As 1 1 Sm 9 2Ba 350 150 Sn 20 5Be 1 1 Sr 420 300Ce 60 7 Ta 1.2 0.2Co 45 50 Tb 1 0.3Cr 100 350 Th 3 0.3Cs o1 o1 Tm 0.5 0.2Cu 65 60 U 1 0.1Dy 6 2 V 350 190Er 3 1 W 1 1Eu 2 1 Y 30 15Ga 20 15 Yb 3 1Gd 4 2 Zn 120 60Hf 6 1 Zr 200 40

Table 4The average elemental concentrations of natural quartz determined by INAA.

Element Activation product Average Statistical error (%)

Na% 24Na 0.4 2.5Mg% 27Mg 0.3 5.5Ca% 49Ca 2.9 7.2Mn% 56Mn 0.1 4.8Fe% 59Fe 0.8 5.5K% 42K 1 2.5Sc 46Sc 35 2.1Cr 51Cr 41 2.9Co 60Co 0.20 10.9Zn 65Zn 45 7.8As 76As 1.7 2.8Rb 86Rb 5.0 1.5Zr 95Zr 380 3.5Ba 131Ba 159 19.9Cs 134Cs 1.2 12.4La 140La 1.71 22.2Ce 141Ce 1.2 6.3Nd 147Nd 14 5.2Eu 152Eu 0.05 15.2Sm 153Sm 7.2 6.2Yb 169Yb 0.40 7.9Lu 177Lu 0.7 10.2Hf 181Hf 32.2 6.4Th 233Pa 0.40 9.9U 239NP 1.9 5.7

A. El-Taher, A. Alharbi / Applied Radiation and Isotopes 82 (2013) 67–71 69

line. In all other cases the elements were determined by their mostprominent peaks, free of interference and with lower statisticalerrors. The accuracy were evaluated by the irradiation of replicates ofthe WSE and PMS geostandard reference materials produced by theopen University Milton Keynes, U.K and counted under the sameconditions as the samples. Table 3 shows chemical composition ofDolerite WSE and Microgabro PMS standard reference materials.Twenty five elements were identified. It should be noted that thethree samples have been homogenized each separately, see above.

Consequently, The concentration values of the detected elementsdetermined from each irradiation cycles have been averaged andpresented in Table 4. The average concentration values are expressedin μg/g for all elements except for Na, K, Mn, Mg, Fe, and Ca which aregiven in units of percentage.

Quantitative analysis was carried out for each isotope by compar-ing the activities from the most favorable peaks in the gamma spectraof samples with those of the standard reference material. In thisanalysis the highest-energy peaks were usually used, as in the case of59Fe, 140La, 60Co and 46Sc, since these peaks normally had lessinterference than lower-energy peaks due to the Compton effect.In some cases, the use of low-energy gamma lines permitted thedetermination of some elements, since these radionuclides have nohigh energy peak, as in case of 141Ce and 153Sm. Another reason to usea low-energy peakis because of interferences associated with the high-energy peaks due to the complex spectra of irradiated quartz as in caseof 181Hf, where its high-energy line of 482 keV is interfered with bythe 487 keV gamma line of 140La. Scandium is the most favorableelement to be determined by INAA, due to the 100% abundance of itssingle stable nuclide, and its 100% branching ratio of the measuredgamma lines at 889.4 keV and 1120.5 keV and its convenient half-lifeof 83.8 days.

In neutron activation analysis (NAA), the following three typesof interfering nuclear reactions should be taken into account,(1) Nuclides produced by (n, p) and (n, α) reactions on other heavierelements which often produce the same nuclide as the nuclideproduced by the (n, γ) reactions. (2) Daughter nuclides which succeedthe (n, γ) reactions of different target elements and become the sameas radionuclides of interest (Miyamoto et al., 1999). The isotopes 140La,141Ce and147Nd commonly used in the activation analysis of thecorresponding elements are also produced by fission of 235U. For eachof these radioisotopes an interference factor, defined as the activityproduced by irradiating 1 μg of pure natural uranium divided by theactivity produced by irradiating 1 μg of the chosen element, wasdetermined. The fission product correction factor has been deter-mined experimentally by analysis of natural uranium standards usingthe same conditions as those of granite rock samples. There is also apossibility of interference of the 320 keV 51Cr line with the 319.4 keV147Nd line, but neodymium has been identified via the 531 keV line.

Table 5Comparison between some elements determined in natural quartz from Umm Heglig in the Eastern Desert along the Egyptian Red Sea coast in mg/kg and percent and withthe Turekian models.

Element Activation product Energy Eγ,keV

T1/2 Detection Limits,ppm

Concentration Statistical Error,(%)

Rock Turekianmodel 1

Rock Turekianmodel 2

Na Na-24 1369 15 h 1.2 0.4% 2.5 3.19 2.32Mg Mg-27 1014 9.8 min 1.7 0.3% 5.5 2.30 2.77K K-42 1524 12.4 h 90 1% 2.5 2.95 1.68Fe Fe-59 1099 44.5 d 65 0.8% 5.5 34.3 58Sc Sc-46 889 83.8 d 0.007 35 ppm 2.1 14Cr Cr-51 320 27.7 d 0.45 41 ppm 2.9 48 96Co Co-60 1332 5.3 y 0.16 0.20 ppm 10.9 12 28Zn Zn-65 1115 244 d 1.1 45 ppm 7.8 63 82Ba Ba-131 496 11.8 d 16.4 159 ppm 19.9 610 380Ce Ce-141 145 32.5 d 0.3 1.2 ppm 6.3 74 83Eu Eu-152 1408 13.3 y 0.09 0.05 ppm 15.2 1.6 2.2Hf Hf-181 482 42.4 d 0.1 32.2 ppm 6.4 4 4Th Pa-233 312 27 d 0.2 0.40 ppm 9.9 12 5.8U NP-239 106 2.4 d 0.3 1.9 ppm 5.7 2.9 1.6

A. El-Taher, A. Alharbi / Applied Radiation and Isotopes 82 (2013) 67–7170

The cobalt determination was based on the 1332 keV line. Rubidiumwas determined from the clear 1077.2 keV line. The 602.6 keV line of124Sb (T1/2¼60d) could interfere with the 604.6 keV134Cs line, in someof the examined samples. Europium was determined from the1406 keV line of 152Eu and the 1273 keV line of 154Eu. Uranium andthorium contents were measured via 106 keV and 312 keV gammalines from 239Np and 233Pa respectively. In the following a briefdiscussion of several elements is given. Seven rare earth elementswere determined in all quartz samples. The elements determined areLa, Ce, Nd, Sm, Eu, Yb and Lu. The selection of photopeaks for theanalysis is briefly discussed below for each element. For lanthanum,the high abundance photopeak of 140 La at 1596 keV was used, whichis free of interference. The other peak at 487 keV cannot be used dueto interferences from 47Ca 489 keV and 192Ir 488 keV. For cerium, thephotopeak of 141Ce at 145 keV was used. For neodymium, thephotopeak of 147Nd at 531 keV which is free of interference wasused. Other peaks surround the high abundance peak at 91 keV,which cannot be resolved from the peak of 177mLu 113 keV. Forsamarium, the isotope 153Sm is used. As far as europium is concerned,152Eu has a number of photopeaks where the high abundance peaksat 1408 and 799 keV are free from interference. Both peaks were usedfor the determination of this element. Another peak at 122 keVcannot be resolved from the 124 keV line of 154Eu. However, thecombined peaks can be used as these are obtained from two isotopesof the same element and have similar half-lives. Ytterbium can bedetermined using the 198 keV peak of 169Yb. The 396 keV peakcannot be resolved from nearby peaks of 152Eu 383 keV and 233Pa381 keV. For lutetium, the high abundance peak at 208 keV of 177mLuwas used. In uranium containing samples, this peak cannot be fullyresolved from the 210 keV peak of 239Np. For uranium we use of themost intensive 106 keV peak of 239Np. The degree of interferencestrongly depends on the detector resolution and on the way ofactivation (El-Taher, 2010d; El-Taher, 2010e; Borovička et al., 2011;Zhao et al., 2008; Suzuki et al., 2010).

Table 5 summarizes the nuclear data and the average concentra-tions of fifteen elements determined in natural quartz samples inmg/kg or percent compared with Turekian models of geochemicaldistribution of elements in the earth crust (Turekian, 1971; Turekianand Wedepohl 1961). Our quartz results for most element are slightlylower than Turekian results except for the results of Sc and Hf areslightly higher, however, the elements: K, Cr and u are in agreementwith Turekian results. This means that our results agree with theconcentration of these elements in the earth crust.

The concentration of uranium via 238U and thorium via 232Thwere measured in granite samples by neutron capture andsuccessive β-decay, the activation converts 238U and 232Th into239Np and 233Pa, respectively, according the following equations:

238U (n, γ) 239U�!β−

239Np Eγ=106 keV

232Th (n, γ) 233Th�!β−

233Pa Eγ=312 keV.

As to the distribution of the elements determined in the quartzsamples studied with regard to their parent sediments andlocation, it is quite clear that the elemental composition of quartzsamples varies according to rock type and consequently accordingto the nature of parent sediments fromwhich these rock are derived.It is noteworthy that the presence of any element in higher or lowerlevels in a certain quartz rock samples is strictly contingent on theoccurrence of its bearing minerals, nature of parent sediments anddepositional environments of these sediments.

5. Conclusion

Analysis of rock specimens by neutron activation analysis assistsgeochemists in research on the processes involved in the formation ofdifferent rocks through the analysis major and trace elements.A scheme for the instrumental neutron activation determination of25 elements in natural quartz collected from the eastern desert alongthe Egyptian Red Sea coast is proposed. The sensitivity and accuracy ofthe method permit the determination of major, minor and traceelements in quartz samples. The elements determined include majorand trace elements in addition to seven rare earth elements and thenatural radionuclides uranium and thorium. The scheme may be usedfor routine analysis. The data obtained here are reference values to beused as a data baseline for drawing an environmental map of easterndesert along the Egyptian Red Sea region. It is hoped that the datapresented here will be useful to those dealing with geochemistry ofnatural quartz and related fields.

Acknowledgment

The authors wishes to thank Prof Dr. K.L.Kratz, Dr. N. Trautmann,Dr. K, Eberhardt and the staff of the TRIGA Mainz research reactor forassistance during the progress of the work.

References

Borovička, J., Kubrová, J., Rohovec, J., Randa, Z., Dunn, C.E., 2011. Uranium, thoriumand rare earth elements in macrofungi: what are the genuine concentrations.Biometals 24 (5), 837–845.

Brunfelt, A.O., Steinnes, E., 1966. Instrumental neutron activation analysis ofstandard rocks. Geochemet Cosmochim. Acta V30, 921–928.

Duffey, D., El-Kady, A., Senftle, F.E., 1970. Analytical sensitivities and energies ofthermal neutron capture gamma-ray–I. Nucl. Instrum. Methods 80, 149.

A. El-Taher, A. Alharbi / Applied Radiation and Isotopes 82 (2013) 67–71 71

El-Taher, A., Kratz, K.L., Nossair, A., Azzam, A.H., 2003. Determination of gold in twoEgyptian gold ores using instrumental neutron activation analysis. J Radiat.Phys. Chem. 68, 751–755.

El-Taher, A., Nossair, A., Azzam, A.H., Kratz, K.-L., Abdel-Halim, A.S., 2004. Determi-nation of traces of uranium ad thorium in some egyptian environmentalmatrices by instrumental neutron activation analysis. J. Environ. Prot. Eng. 29(1–2), 19–30.

El-Taher, A., 2007. Rare earth elements in Egyptian granite by instrumental neutronactivation analysis. J. Appl. Radiat. Isot 65, 458–464.

El-Taher, A., 2010a. Elemental analysis of two Egyptian phosphate rock mines byinstrumental neutron activation analysis and atomic absorption spectrometry.J. Appl. Radiat. Isot. 68, 511–515.

El-Taher, A., 2010b. Rare earth elements content in geological samples fromgabalgattar eastern desert-Egypt determined by INAA. Appl. Radiat. Isot. 68,1859–1863.

El-Taher, A., 2010c. Determination of chromium and trace elements in El-Rubshichromite from eastern desert Egypt by neutron activation analysis. Appl. Radiat.Isot. 68, 1864–1868.

El-Taher, A., 2010d. INAA and DNAA for uranium determination in geologicalsamples from Egyptl. App. Radiat. Isot. 68, 1189–1192.

El-Taher, A., 2010e. Elemental content of feldspar from eastern desert, Egypt,determined by INAA and XRF. Appl. Radiat. Isot. 68, 1185–1188.

Gibson, I.X., Jagam, P., 1980. Instrumental neutron activation analysis of rocks andminerals. In: Muecke, G.K. (Ed.), Short course in neutron activation analysis inthe geosciences, 5. Mineral Assoc Can short course Handbook, pp. 109–131.

Gordan, G.E., Randle, K., Goles, G.G., Corles, J.B., Beenson, M.H., Oxley, S.S., 1968.Instrumental activation analysis of standard rocks with high resolutiongamma-ray detectors. Geochem.et Cosmochim. Acta V32, 369–396.

Gurna, S.S., Satyanaranaya, N., Pandey, B.K., 1990. Multielement analysis of someProterozoic granitic rocks of India by instrumental neutron activation. In:Proceedings of the Second Indo-Ussr Symposium on Rare Earth MaterialsResearch, Trivandrum, November, 5p.

Gurna, S.S., Satyanarayana, N., Dhanaraju, R, Selvam, A.P and Virnave, S.N., 1988Instrumental neutron activation analysis in the study of rare earth elementsand related trace elemental distribution in the Mahadek sandstones fromPdengshakap, Jaintia Hills district, Meghalaya and its bearing on exploration.Proc. symp on analytical applications in earth sciences, Shillong, Nov, pp 2–7.

Kernchemie Report, 1989. Tables for Neutron Activation Analysis. Triga MainzResearch Reactor.

Miyamoto, Y., Hoba, H., Kajikawa, A., Masumoto, K., Nakanishi, T., Sakamoto, K.,1999. Interferences in neutron and photon activation analysis. J. Radioanal.Nucl. Chem 239 (1), 165–189.

Montero Cabrera, M.E., Herrera Herna, Â. ndez H., Herrera Perazaa, E., Rodrõ ÂguezMartõ Ânez, N., LoÂpez Reyes, M.C., 2000. Instrumental neutron activationanalysis of rocks from Cayajabos petroleum ore. Appl. Radiat. Isot. 52, 143–146.

Potts, P.J., Rogers, N.W., 1991. Determination of trace elements in selectedgeological reference materials by Instrumental neutron activation analysis.Geostand. News Lett. 15, 111–116.

Scheid, Nicole, Becker, Stefan, Ducking, Marc, Hampel, Gabriele, Volker Kratz, Jens,Watzke, Peter, Weis, Peter, Zauner, Stephan, 2009. Forensic investigation ofbrick stones using instrumental neutron activation analysis, laser ablation–inductively coupled plasma–mass spectrometry and X-ray fluorescence analy-sis. Appl. Radiat. Isot. 67, 2128–2132.

Senftle, F., Moore, G.D., Leep, D.B., El-Kady, A., Duffey, D., 1971. Analyticalsensitivities and energies of thermal neutron capture gamma-rays–II. Nucl.lnstrum. Methods 93, 425.

Suzuki, Y., Suzuki, T., Furuta, N., 2010. Determination of rare earth elements (REES)in airborne particulate matter (APM) collected in Tokyo, Japan, and a positiveanomaly of europium and terbium. Anal. Sci. 26 (9), 929–935.

Turekian, K.K., 1971. Geochemical distribution of elements, third ed.4. McGraw-HillEncyclopedia of Science and Technology, pp. 627–630.

Turekian, K.K., Wedepohl, K.H., 1961. Distribution of the elements in some majorunits of the crust. Bull. Geol. Soc. Amer 72, 175–192.

Vereijke, M.L., 1992. Instrumental Neutron Activation Analysis Developed forSilicon Integrated Circuit Technology. TechnischeUniversitüt Eindhoven.(Thesis).

Zaghloul, R., El-Abbady, W.H., 1988. Proceedings of the 4th Conference NuclearScience and Applications, Cairo (Egypt), March 1988. Atomic Energy Authority,p. 606.

Zaghloul, R., Abdel-Haleem, A.S., Mostafa, M., Gantner, E., 1993. An in-beamCompton suppressed Ge spectrometer for nondestructive neutron activationanalysis. (KFK 5181).

Zhao, L., Zhang, F.S., Zhang, J., 2008. Chemical properties of rare earth elements intypical medical waste incinerator ashes in China. J. Hazard Mater 30 (158),465–470.