Radiation damage produced with synchrotron radiation

Radiat. Phys. Chem. 1977, V o l . 10. pp. 315-317.

Pergamon

Press.

P r i n t e d in G r e a t B r i t a i n

RADIATION DAMAGE SYNCHROTRON

PRODUCED RADIATION

WITH

ROBERT J. BOOTH* and MARTYN C. R. SYMONS Department of Chemistry, The University, Leicester. LEI 7RH and KENNETH R. LEA Daresbury Laboratory, Daresbury. Warrington. WA4 4AD (Received 4 April 1977; in revised form 6 ~,fay 1977)

Abstract--The wide spectral range of the N I N A synchrotron has been used to study the effect of wavelength change on radiation damage, using E.S.IL spectroscopy to detect trapped damage centres. 1. INTRODUCTION RESEARCH on radiation damage has for the most part been carried out using conventional "line'" sources in the vuv, X-ray and v-ray regions"'. The continuous spectrum of electromagnetic radiation emitted by electron synchrotrons, such as the 5 GeV NINA machine at the Science Research Council's Daresbury Laboratory, extends smoothly through the vuv and X-ray region, before falling off in intensity below about 1 A. It is attractive to use the wide spectral coverage of synchrotron radiation to examine wavelengthdependent features of the radiation damage mechanism. This note reports our first efforts to do

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2. METHOD At the Daresbury Laboratory Synchrotron Radiation Facility, several vacuum monochromators are available to disperse the primary beam of radiation. The wavelength and bandwidth of the monochromatized radiation can be selected as required. Chemical samples were held in the path of the beam, using a specially designed liquid nitrogen cryostat to maintain them at low temperature (Fig. 1). This is described in depth elsewhere Cz~and is shown schematically in the Figure. Up to eighteen samples, in the form of 3 mm diameter pellets of compressed, powdered chemical, were carried in the cryos-tat, and sequentially exposed to radiation for various lengths of time. Low temperature handling procedures were worked out for unloading the samples from the cryostat and transferring them to an electron spin *Present address: Department of Chemistry, University of Windsor, Windsor, Ontario, Canada.

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FIG. 1. Sectional drawing of the liquid nitrogen cryostat. (a) Gear wheel; (b) Thrust bearing; (c) Double O-ring seal; (d) Nitrogen port (a total of three); (e) Outer reservoir; (f) Inner Reservoir: (g) (arrow) to P.M. Tube; (h) Shroud; (i) Copper support; (j) Port for synchrotron radiation; (k) Axis of incident light beam; (1) Sample holder (shaded). 315

R. J. BOOTH et aL

316

resonance (E.S.R.) spectrometer. E v i d e n c e for radiation damage centres was sought in the E.S.R. spectra. To identify and exclude possible impurity signals, the spectra were re-taken after the samples had been w a r m e d to r o o m temperature and cooled d o w n again. Differences b e t w e e n pre- and post-annealing spectra characterize radicalproducts that are unstable at r o o m temperature.

3.

OBSERVATIONS

AND

INTERPRETATIONS

E x p e r i m e n t s began using light from a normal incidence m o n o c h r o m a t o r , with wavelengths from about 300 ,~ upwards. No radiation damage signals were seen in all the chemicals tried. Thereafter, a grazing incidence m o n o c h r o m a t o r ~3~ was used, which provided light in the range 50--400A. Damage signals were o b s e r v e d in a number of cases, but were weak, despite long ( - 4 h) periods of irradiation. To enhance the damage signals, some samples were exposed to " z e r o - o r d e r " light from the monochromator. The zero-order light contained a wide spread of photon energies extending up to the reflectivity limit of the diffraction grating. The E.S.R. spectra obtained with samples so irradiated were of assistance in searching for

the w e a k e r spectra arising from the same chemicals after exposure to m o n o c h r o m a t i c light. Table i lists the results of this investigation, noting the occurrence, or absence, of detectable radiation damage in selected chemicals. Three types of irradiation are distinguished, as follows: T y p e A: Zero-order light from the normal incidence monochromator, extending up in w a v e l e n g t h from approx. 300 A (photon energies ~<41 eV). T y p e B: Zero-order light f r o m the grazing incidence m o n o c h r o m a t o r , extending upwards from approx. 50 ,~ (photon energies ~<248 eV). T y p e C: First-order diffracted light from the grazing incidence monochromator, with w a v e l e n g t h s of approx. 75, 130, 200,and 300 ,~, and bandwidths of 8, 8, 16 and 1 6 A respectively (photon energies within the bands 165 ± 9 eV, 95 ± 3 eV, 62 ± 2.5 eV and 41 -+ 1 eV respectively). The light flux on the sample was not measured quantitatively. H o w e v e r , estimates based on previous m e a s u r e m e n t s of the grazing incidence m o n o c h r o m a t o r p e r f o r m a n c e suggest it can provide 8 x 10 ~° photons s -~ at the exit slit in the bandwidths e m p l o y e d in type C irradiations, when the synchrotron is running at 5 GeV and 2 0 m A

TABLE 1. Results of searches for radiation damage Irradiation Chemical KCI K2CrO4 Dimethyl Glyoxime NaOOCCH3 NaOOCCH2CI NaOOCCF3 KNO3 MgCO3 Na3PO( Na:HPO4 NaH2PO4 Polythene Polythene Oxide Polyvinylpyrrolidone Polyvinylamide Polyvinylnitrile

Type A

Type B

~41 eV

~248 eV

No No No No No -No No No No No No No No No No

No . No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

Type C 165 eV

95 eV

No .

. Impurity Yes Yes Yes Yes Impurity Yes No No ? Yes ? No No

62 eV

No .

41 eV Radical Detected

No

--

-Yes Yes Yes ? -Yes* --~ ? ~ ---

-Not Not Not Not -Yes* --Not Not ----

.

-Yes Yes Yes Impurity Impurity Yes Impurity Impurity -Yes ----

CH:CO:-" CH(CI)CO 2- b N O 3 2- :

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"Yes" denotes damage signal detected, " N o " means not detected. A dash (--) means no experiment was performed under the given conditions, tSignifies an experiment tried once only, which should be repeated to confirm results. ?Indicates a possible signal was seen, but the experiment needs to be repeated. *Denotes that the signal obtained was different from that found in other irradiations. "Impurity" indicates a situation in which a signal from an impurity in the chemical made it impossible to detect the presence or absence of a genuine signal. "P. B. AYSCOUGH,Electron Spin Resonance in Chemistry, London, Methuen, 1967. bS. P. MIsHRA, G. W. NE/LSON and M. C. R. SYMONS,J.C.S. Faraday 1"I, 1973, 69, 1425. ¢C. JACCARD,Phys. Rev. 1961, 124, 60; P. W. ATK1NSand M. C. R. SYMONS,J. Chem. Soc. 1962, 4794. ds. S L r a ~ , M. C. R. SYMONSand H. W. W,~,DAL~, J. Chem. Soc. A, 1970, 1239.

317

Radiation damage produced with synchrotron radiation

circulating current. Various factors which reduced the flux actually incident on the sample include the (unavoidable) distance between exit slit and sample, loss of optical efficiency of monochromator (e.g. deterioration of grating with use), and synchrotron energies and currents smaller than 5 GeV and 20 mA, respectively. These factors might have combined to diminish the flux on the sample by IO*. Exposure times ranged up to four hours per sample. Thus for samples exposed to the flux of - 100 eV photons for 4 h, the total incident energy is estimated to be -IO” eV. Table 1 also lists the radicals produced, as identified from the E.S.R. spectra. When seen, the E.S.R. signals were broader than those obtained in y-ray damage. This is interpreted in terms of surface damage; the incident light has a low penetrating power, and in order to have sufficient centres for detection, their surface concentrations are high, hence spin-spin broadening between neighbouring radicals becomes significant. 4. CONCLUSIONS The rate at which radiation damage was produced in these experiments proved slower than originally hoped for, and severely limited the quantity of data that could be obtained during periods of access to synchrotron radiation. The considerably higher flux of radiation, which will be provided by the new electron storage ring under construction at Daresbury Laboratoryr4’, should

speed up these experiments, and permit a more systematic and quantitative investigation of crosssections and threshold energies for radiation damage processes to be made. The present work has shown the feasibility of using synchrotron radiation in this area of research, and has tested the associated experimental techniques. Acknowledgements-The design and construction of the equipment employed in this research benefited greatly from the assistance of D. J. Bradshaw (Daresbury Laboratory), J. A. Brivati (Leicester University). and representatives of the firms of Oxford Instrument Co. Ltd. and Vacuum Generators Ltd. The authors are also grateful for the provision of synchrotron radiation and other facilities at the SRC’s Daresbrury Laboratory. One of US (RJB) wishes to acknowledge a Research Assistantship grant from the Science Research Council.

REFERENCES G. HUGHES, Radiation Chemistry, Clarendon Press. Oxford, 1973; J. H. O’DONNELLand D. F. SANGSTER, Principles of Radiation Chemistry, Arnold, London. 1970. R. J. BOOTH,M. C. R. SYMONS,D. J. BRQSHAW and K. R. LEA, Daresbury Laboratory Technical Memorandum, DLISRN7M9. Copies available from the Librarian, Daresbury Laboratory, Daresbury, Warrington WA4 4AD, U.K. J. B. WEST,K. CODLINGand G. V. M~RR, J. Phys. .E. 1974, 7. 137. Design study for a dedicated source of Synchrotron Radiation, Science Research Council. Daresbury

Laboratory,

1975. Document

reference

DL/SRF/RI.