The implantation behavior of S b in silicon has been investigated by studying the orientation dependence of the baclcscattering yield of a 1.0-MeV helium bearn. This orientation dependence ("clianneling") provides quantitative information on the location of iinplanted atoms in the lattice and also on the ainount of lattice disorder accompanying the implantation. The general principles of the channeling technique and the advantages of using a beam of I-Ie+ rather than I-I+ are discussed. Results for 25 "C and 450 "C irnplantations are presented and compared. The hot implant introduces very little lattice disorder, and a large fraction (up t o 95%) of the S b atoms is found on substitutional sites. I11 the 25 "C implants, however, a heavily damaged region is formed around the traclc of each iinplanted Sb. At doses greater than -10" ions/cm2, these damaged regions overlap to produce an essentially a m o r p h o~~s layer, which then requires an annealing temperature of -650 "C t o reorder the lattice and to achieve a high level of substitutional Sb. "I-Iot implant" studies have also been made for several other dopants-Ga, As, In, and -Ye; however, unlilce Sb, the substit~~tional level in all these cases never exceeded 60%. This unique behavior of Sb implants in silicon has also been found in a corresponding study of the electrical characteristics (Paper 11). A preliminary investigation of boron-doped silicon, sing the orientation dependence of 610-1ceV protons, indicates that substitutional boron atoms are removed from lattice sites by relatively small doses of energetic protons. This enhanced sensitivity t o radiation does not occur for the Sb-doped samples.

The 'mixture law' states that, if the radiolysis of nlaterial A gives a product 31 with ),ield G>r, then, in a mixture where the mole fraction of A is SA, the yield of M is G\rX;L.In the radiolysis of dilute mixtures of cyclohexane-dl? or of n~ethylcyclohexane-dl., with other aliphatic hydrocarbons D? IS formed in a process which is first order with respect to the deiitero compound. As a conseqLlence these inixt~~res provide a sensitive method of detecting deviations from the mixture law.Experilllentally the yield of D, and the yield of H D vary nridely from one solvent to another anlongst the Ca to CIO hydrocarbons selected. The yields of Dz and H D are, approximately, linearly related. The solvents have si~nilar quantitative erfects on the yields for both deuterated hydrocarbons. These deviations from the mixture law cannot be explained in ternls of lci~~etic effects (variations in rate constants caused by differing bond strengths), because the D? yield measures a process without free radical inter~nediates. Mcchanisn~s involving excitation transfer, ionmolecule reactions. and subexcitation electrons are discussed.

Wide-angle Rutherford scattering has been used to investigate experimentally the channeling behavior of several projectiles ('H, 'He,~C, "0, and~Cl) in tungsten crystals in the energy region 2 to 30 MeV; the study has also been extended to silicon crystals, using a 3.0-MeV H beam The observed critical angles and minimum scattering yields are compared with theoretical predictions. In general, the agreement is excellent. In both W and Si, precise energy analysis of the scattered beam has also provided detailed information on the depth and temperature dependence of channeling; a marked difference is observed between the planar and axial channeling processes. Some preliminary measurements in Au and UO& crystals are included.

A physical interaction occurs in the radiolysis of liquid alkane hydrocarbon mixtures which may lead to a much larger amount of decomposition of one component than is to be expected from its mole fraction. This is shown by measurements of the isotopic composition of hydrogen evolved from mixtures of cyclohexane-dl2 with other alkane hydrocarbons. The additives carbon tetrachloride, cyclohexene, p-benzoquinone and benzene change the extent of decomposition of the cyclohexane-dl2 in a similar fashion ; we conclude that they reduce the total hydrogen yield from alkanes by the same physical mechanism and not by hydrogen-atom scavenging. This physical interaction is absent in the vapour phase showing that there are major differences in mechanism between liquid-and vapour-phase radiolysis of hydrocarbons.* Physical interactions include all processes such as energy transfer and charge transfer which can change product yields and which do not involve the making or breaking of chemical bonds.

The radiolytic yields of olefins and dilners have been measured in mixtures of cyclohexane and cyclope~lta~le. While the di~neric products ((C6H11)2, CsH11.CjHs) 'show a bias towards C j groups, the olefins show a bias towards Cs groups; the yield of cyclohexene a t low concentrations of cyclohexane is more than twice the maximum predicted by the "mixture law". These results confirm earlier isotopic work which showed a higher reactivity of cyclohexane-dlz in cq-clohexane-dIz -cyclopentane mixtures relative to that in cyclohexane-dlz -cyclohexane. The results also confirm the preferential change of identity of cyclohexyl radicals to cyclopentyl radicals, which leads to a predominance of Cg groups in the ditner.