79

THE DETERMINATION OF FLUORINE BY PROTON INDUCED GAMMA RAY EMISSION SPECTROMETRY (PIGE) IN EIGHTEEN CHINESE STANDARD REFERENCE SAMPLES OF STREAM SEDIMENTS, SOILS AND ROCKS: GSD 9-12, GSS 1-8 AND GSR 1-6

Iwan ROELANDTS (l), Guy ROBAYE (2), Panagiotis ALOUPOGIANNIS (2,3), Georges WEBER (2*) and Jeanne-Marie DELBROUCK-HABARU (2)

(1) Geology, Petrology and Geochemistry, University of Libge, B 4OOO Sart Tilman, Libge, Belgium (2) Experimental Nuclear Physics, University of Libge, B 4000 Sart Tilman, Likge, Belgium (3) Laboratoire de Physico-Chimie de 1'Atmosphbre. UniversitC de Paris 7, F 75005 Paris, France

Eighteen new Chinese standard reference samples (including stream sediments, soils and rocks) have been analysed by an automated proton induced gamma ray emission (PIGE) method for fluorine. Results of determinations are reported and are generally in good agreement with the "usable values" previously published.

The Geochemical Standard Reference Group in China, led by the Institute of Geophysical and Geochemical Exploration (IGGE) and the Institute of Rock and Mineral Analysis, has prepared four new stream sediment samples (GSD 9-12), eight soil samples (GSS 1-8) and six rock samples (GSR 1-6). A brief description of these samples and "usable values" (derived mainly from data by Chinese laboratories) may be found in this Journal (1).

Recently we reported the feasibility and the advantages of using proton induced gamma-ray emission (PIGE) spectrometry for the non destructive measurement of fluorine in a great variety of geological materials (2-3). This rapid instrumental method was based on the 19F (p, ay) 160 reaction and was free from any spectral interference. It is now routinely applied at the Department of Experimental Nuclear Physics (University of Likge) to geological samples with fluorine content as low as 25 ppm and up to several percent of fluorine.

In this paper we present the results of PIGE measurements on fluorine in eighteen Chinese standard reference samples.

EXPERIMENTAL

Sample preparation. Samples were prepared as

described in detail previously (2-3). They consist of a homogenized mixture made from 180 mg of powdered sample and 20 mg of graphite, compressed into pellets of 13 mm diameter and about lmm thick. Duplicate pellets were prepared for each refcrence material analysed here.

PIGE analysis. The PIGE experimental set-up used in this study was described elsewhere (4). The samples, mounted on a ladder with sixteen positions, were bombarded in vacuum with a 1.5 MeV proton beam of 5 mm in diameter from the Experimental Nuclear Physics Van de Graaff accelerator. Beam currents of 500 nA were used. Gamma-rays were detected with a 3" x 3" NaI (TI) detector placed at 20 cm from the target at a direction of 100' relative to the incident proton beam, shielded with lead and connected to a multichannel analyser. The accumulated charge for each sample was 1 mC. Spectra were recorded on ffoppy disks for off-line processing.

RESULTS AND DISCUSSION

Fluorine analyses were performed on two separate pellets of each reference material taken from the same sample bottle. Individual PIGE results and mean values on each of the eighteen standard reference samples are listed in Table 1. "Usable values" given by Xie Xuejing et al. (1) from a variety of techniques have also been included in the Table for comparison.

Precision and Accuracy. An indication of the precision of our PIGE procedure can be obtained from the figures presented in Table 1. The precision is similar to that found in our earlier publications (2-3) i.e. 5-10% depending on the concentration level.

* Research Associate of the National Fund for Scientific Research (Belgium).

In general, satisfactory agreement between our data and "usable values" can be observed. The absence of any

Geostandards Newsletter, Vol. 11, N"1, AvriI 1 9 8 7 , ~ . 79 d 80

80

systematic errors indicates that our PIGE method is free from interferences and accurate for the various types of samples analysed here (sediments, soils and rocks). Figure 1 shows the comparison between the "usable values" and those obtained in this work, the diagonal representing

Table 1. Fluorine in eighteen Chinese standard reference samples (in ppm)

Samples This work

Individual Mean Usable Analvses Values ( 1 )

River sediment GSD-9

Stream sediment GSO-10

Stream sediment CSD-11

Stream sediment GSD-12

Sail GSS-1

so11 GSS-2 S o i l GSS-3

Soil GSS-4

Sail GSS-5

Soil GSS-6

Laterite GSS-7

Loess GSS-8

Granite GSR-1

Andes lte GSR-2

Basalt GSR-3

Sandstone GSR-4

Shale GSR-5

Carbonate GSR-6

515

93

1691

1119

512

2482

185

602

654

1050

314

594

2373

288

817

162

1250

463

573

116

1655

1191

535

2379

198

616

704

1001

343

540

2470

325

891

143

1429

457

544

105

1673

1155

524

2431

192

609

679

1026

344

567

2422

307

869

153

1340

460

490

155

1650

1250

500

2230

245

540

610

91 5

320

570

2380

275

700

183

1300

400

1000 2000 jooo Usoblo valuos (ppm)

Figure 1. Comparison of "usable values" for fluorine in Chinese standard reference samples to those determined in this study

theoretical agreement. On the whole, we observe that the deviations are small.

Furthermore, different pellets of the USGS granodiorite reference sample GSP-1 were irradiated in each run. The mean value of our GSP-1 analyses was 3477 k 192 ppm (n = 36).

These results confirm the usefulness of *the proposed PIGE method for the determination of fluorine.

ACKNOWLEDGEMENTS

Professor Xie Xuejing, Institute of Geophysical and Geochemical Exploration, People's Republic of China, is thanked for providing the reference samples analysed in the present paper. We are indebted to the "Institut Znteruniversitaire des Sciences NuclCaires" for financial support.

RESUME

Dix-huit nouveaux echantillons geochimiques de reference (sediments alluvionnaires, sols e t roches) provenant de Chine ont ete analyses par une methode de spectrometric d'kmission gamma induite par protons (PIGE) automatisee pour leur teneur en fluor. Les rksultats obtenus sont en gCneral en accord avec les "valeurs utilisables" ("usable values") publiees.

REFERENCES

(1) Xie Xuejing, Yan Mingcai, Li Lianzhong and Shen Huijun (1985) Usable values for Chinese standard reference samples of stream sediments, soils and rocks: GSD 9-12, GSS 1-8 and GSR 1-6, Geostandards Newsletter, 9 277-280.

(2) I. Roelandts, G. Robaye, G. Weber and J.M. Delbrouck ( 1985) Determination of fluorine in eighty international geochemical reference samples by proton induced gamma ray emission spectrometry (PIGE), Geostandards Newsletter, 9: 191-197.

(3) I. Roelandts, G. Robaye, G. Weber and J.M. Delbrouck (1 986) The application of proton-induced gamma-ray emission (PIGE) analysis to the rapid determination of fluorine in geological materials, Chemical Geology, 54: 35-42.

(4) G. Robaye. J. M Delbrouck-Habaru, I. Roelandts, G. Weber, G. Girard-Reydet, L. Morelli and J.P. Quisefit (1 985) Pige coupled with PIXE for sodium determination in atmospheric aerosol samples. Nuclear Instruments and Methods, B6: 558-56 1.