Radiation Damage in Ice at Low Temperatures Studied by Proton Channelling

Abstract

ABSTRACT. 100 keV protons with flux es between 3 X 10 15 and 3 X 10 16 m -2 S-I and in doses up to 4 X 10 20 m -2 have been used in ice between -19 1°C a nd -B7°C to create damage and to analyse it. T h e Rutherford backsca ttering minimum yield a long the c-axis (about 0.05 in good monocrystals) increases up to uni ty with the dose, according to a function w h ich ca n be scaled by a critical dose d epending mainly on temperature (Arrhenius law with activation enthalpy ofo.17 ± 0.04eV a bove -IB5°C ) . Higher flu x prod u ces more damage above -IBo°C, but less below. A beam in a random d irection is more effici ent below -IBo°C, but less at higher temperature than a n a ligned bea m. Beam-induced reord ering is observed at d efinite temperat ures and doses. T h e damage is sh own to be due to energy loss by electron ic excitations, whi ch d ecay and produce disordered molecule clusters, m a inly by incoherent aggregation of vacancies and interstitia ls. 100 kcV Protonc n mit Fli.issen zwisehe n 3 X 10 15 un d 3 X 10 16 m -2 S-I und D ose n bis 4 X 10 20 m -2 wurden in E is zw ischen -191°C und -B7°C be nutz t, um St ra hlungssehiiden zu er zeugen und zu a nal ys ie re n. Das minima le Ruthe rfordsehe Ru ckstre uungsvermogen entla n g del' c-Achse (e twa 0,05 in gute n E inkrista ll en ) nimmt m it der Dose zu (bis 1,0 ) , gemiiss einer Funktion, d ie a ls Pa rameter e in e kritische Dose enthiilt , welche ha uptsiiehli ch von der Temperatur abhangt (A rrhen ius Gesctz mit 0 , 17 ± 0,04 eV Aktivierungse ntha lpi e oberhalb -IB5°C). Ein hbherer Fluss erzeugt mehr Schaden o b crhalb -IBo°C , abcr weniger un terha lb dieser Temperatur. E in Strahl mit Zufa llsri ch tung ist unter -IBo°C w irksamer a ls e in g erichteter Strahl, aber we niger bei hoheren Temperaturen. E ine vom Stra hl induzie rte Unordnung wird bei wohl bes timmten Dosen und Temperaturen beobachtct. Die Schiiden ruhren von dem durch e le ktronische Anregungen verursachtcn En ergie-Ve rlust her. Sie besteh e n aus ungeordnete n Bezirken, w elch e hauptsiichlich durch Agregat ion von Lee rs tell e n unci Zwisch engittermoleku len e ntsteh en. I. I NTRODUCTIONFor several d ecades considerable interest has b een devoted to the radiation d a mage produced by energe tic particles in solids, not only from the point of view of technological a pplications (e.g. nuclear power) but also in ord er to assess the effect of nuclear technology or of outer-space conditions o n a nimate and inanimate matter. A lthough the d a mage mechanisms are complex, sign ificant a nalogies can be found in quite different materials.W e have been prompted to stud y the damaging which lOO keY protons cause in ice in the course of an investigation into the ch annelling of the surface stru cture of ice monocrystals (Huber andothers, 1972, 1973;Huber, unpublished). For details of the method the reader is referred to a comprehensive review of Cem mell ( 1974), Briefly, one measures the backscattering yield X of a well-collimated proton b eam incident on the crystal. The yield is norma...