By means of thin-target differential-range experiments, we have measured the average ranges and range straggling of 72-min Sm 142 recoils from a number of nuclear reactions induced by heavy ions. Beams of Li 6 , Li 7 , B 10 , C 12 , and N 14 with kinetic energies up to 10.5 MeV per nucleon were used in conjunction with targets of Cs 133 , Ba 136 , Ba 137 , Ba 138 , La 139 , and Pr 141 . A range-energy curve was obtained for Sm 142 in Al, covering the region 2-10-MeV recoil energy. Strong evidence for a pure compound nucleus reaction mechanism is provided by (a) the uniqueness of the range-energy curve for all the reactions, (b) Gaussian-range distributions, and (c) direct comparison of the experimental ranges with stopping theory. The reaction Nd 142 (a,4w)Sm 142 was studied by integral range methods, and the average ranges in Nd were found to be consistent with theoretical expectations when projected ranges were corrected to true ranges. The experimental straggling parameters are compared with theoretical predictions of straggling inherent in the stopping process. For Li 6 and Li 7 experiments, where the recoil velocities are smaller than the Bohr velocity (2.2X10 8 cm/sec), an attempt is made to extract the range straggling due to the nuclear reaction. From this analysis, qualitative information is obtained about the average total energy removed by neutrons and photons.
We report on single electron capture in slow collisions of doubly charged nitrogen molecules with the rare gases He, Ne and Ar. The vertical double ionization energy of N, as well as vertical excitation energies of N F have been calculated by means of the multiconhguratian coupled electron pair approximation ( MC-CEPA) method. Furthermore, experiments have been carried out applying the technique o f translational energy spectroscopy. T h e energy gain spectra of the resulling N : molecules have been analysed, showing the single electron capture to be dominated by N:+(X 'Xl) projectile ions, as well as by N r i o n s i n the low-lyingmetastable C'X: state. Thepasitionaftheexperimentally observed reaction window is discussed in terms of Franck-Condon transitions and is compared with predictions of classical descriptions.
The radicals formed in the flash photolysis of 2-methylbut-1-ene and then subsequent reactions have been investigated by kinetic spectroscopy and gas-liquid chromatography. Less than 10 % of products are formed by a molecular mode of fission of the excited olefin, and of the radical modes the relative probabilities of bond fission, B(C-H) : /3(C-H): a(C-C) are 13 : 1.37 : 1. The extinction coefficient of the B methallyl radical measured for the strongest band (238 nm) was E = 1.32+ 0.11 x lo4 1. mol-' cm-I. The decay of the methyl and / 3 methallyl radicals was second order. The rate constant for methyl combination was in agreement with the literature value and that for / 3 methallyl combination measured for the first time was 2.6 k 0.3 x 10' O moI-' I. s-' at 295 -t-2 K.
The repartition of nuclear charge in fission has a narrower dispersion than almost any other property connected with the fission process. T o a crude approximation, the distribution of nuclear charge between light and heavy partners L and H leads to the most probable charges (ZP)L and (Zp)= displaced from the respective charges ZA of 8-stability by the same amount for the two fragments (Glendenin rule of equal charge displacement ECD, 1946). The existence of shell offsets in the Z,i vs. A function for different neutron-and proton-shell regions must be considered. All available data for thermal fission U235 (nt~,,F) are examined critically. The data show sudden offset-like drifts (fine structure) that may well be associated with shell properties of the products before the "neck" has dissolved. It is shown that these data eliminate naive equal charge displacement ECD, also an older competitive prescription of constant charge ratio CCR for the products, and an empirical Russian prescription (Apalin et al., 1960). The data are also examined in the light of the postulate that fission gives minimum nuclear plus coulombic potential energy (Present 1947, Fong 1955, Swiatecki-Blann 1960, and it is shown that the present mass formulas give too much uncertainty three to four &decays from stability t o give a useful test, but that shell effects in masses must be retained. Data from charged-particle fission with energy deposit up to 40-50 Mev are in reasonable accord with the low-energy data on correcting for composition and neutron boil-off. It is concluded from experiment that Zp is a single-valued function of A, known to about f 0.15 unit for low-energy fission and f 0.25 unit for medium-energy fission, and that the fine structure very probably present is a n indication of intrinsic nuclear chemistry.The early thinking on the wartime Manhattan Project about nuclear charge distribution in low-energy fission, before any yield data were available, was based on the concept (1, 2) of constant charge ratio CCR. Professor Wheeler had suggested (4) a search for positron enlitters t o see how wide the charge dispersion might be: the results of crude searches in the products of U235 (n,h,F) were, of course, negative (5). Way and Wigner (7) postulated t h a t the charge would distribute t o give a minimum nuclear potential energy, and Present (8) postulated a minimum for the sun1 of nuclear potential energy plus coulombic energy (equal to final kinetic energy). Present took considerable pains to handle the coulombic term for polarizable spheres with non-uniform proton density.The identification of shielded nuclides4 36-hour BrS2, 19-day Rbs6, and 13-day Cs136 among the fission products gave the first experimental leverage on charge distribution. The first detailed treatment of the problem (5) established the classical rule, or prescription (3, 6) of equal charge displacement E C D ; namely that the nuclear charge distribution between light and heavy partners L and H leads to most probable charges Zp displaced from stability...
The reactions of photochemically generated deuterium atoms of selected translational energies with neopentane have been investigated. The variation with energy of the relative probability of reaction or energy loss on collision with neopentane was followed, and the phenomenological threshold energy measured as 45 k 5 kJ mol-l. The threshold values for molecules containing only primary or secondary C-H bonds and molecules with both bond types are discussed. The probabilities of reaction per bond for different bond types are compared and a simple model for reaction probability assessed.
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