Systematics of (n,.gamma.)-activated hot iodine-128 reactions in gaseous methane and halomethanes. Energy Degradation factor

Abstract

It was found in a systematic study of 128I reactions activated by radiative neutron capture in various gaseous halomethanes that the formation of 128I-labeled organic products proceeds entirely by hot (requiring excess kinetic energy to occur) reactions. This is unlike the reactions of 128I with CH4 where the organic product CH8128I was formed not only by hot 128I atoms but by thermal ion-molecule reactions involving 1+ in the 'D2, 8P0, 8Pi, and 3P2 states. In the various halomethane systems only two 128I-labeled organic products were found, those resulting from halogen and hydrogen substitution. The limiting 128I organic yields in gaseous CH3F, CHgCl, CHjBr, and CH3I were 11.2, 4.2, 0.67, and 0.20%, respectively. The kinetic energy spectra for (n, 7)-activated 128I atoms or ions were calculated and the results showed that an appreciable fraction of the 128I species are bom with low kinetic energies, in or near the reactive zone. The only physical or chemical parameter that explained the trend in organic yields was the energy degradation factor of the halomethane system, correlating well with the kinetic energy spectrum of 128I.

REACTIONS OF 130I ACTIVATED BY RADIATIVE NEUTRON CAPTURE AND ISOMERIC TRANSITION IN GASEOUS CH4 AND CD4

“…Unlike the condensed-state studies [3,4] which showed that the total (n, 7)-activated yields were lower than the total (I. T.)-activated yields, our results from gas phase studies (see Table 2) showed consistently that the hot yields of 130 I + 130m I activated by radiative neutron capture were consistently higher than hot (I. T.) activated 130 I yields. This is consistent with the fact that (η, γ), activated 130 I species are formed with larger kinetic energies [12] than l30 I activated by (I. T.). Thus the (η, γ)-activated 130 I + 130m i has available the full reaction energy range in which to undergo reactive collision.…”

Computer Simulation Evaluating Kinetic Theory Parameters in Hot Atom Chemistry

“…The model appears insensitive to variation in the initial energy sampling (Energy Gaussian). It is interesting to note that this appears in agreement with kinetic theory [7][8][9] even though the iodine-128 activation is in violation of Assumption la of the theory [38]. However, it has been previously demonstrated [20] that kinetic theory relationships may be obtained in systems known to be in violation of some kinetic theory requirements.…”

“…The cell size and location of the acetylenes were variable and adjusted to vary the effect of a collapsing molecular environment on the system. The locations and spacings of the acetylene were chosen [38] to mimic actual physical conditions. For simplicity, the acetylene molecules were "fixed" since their thermal motions were much smaller than the translational motions of the iodine.…”

“…This model also chose to ignore differences between molecular and caged-complex reactions since both must proceed through a common intermediate and no investigation of energy distributions within the reaction intermediate was attempted. Each event was initiated by locating the iodine at the origin of a coordinate system based on the cell and the generation of a random energy vector sampled from the 128 1 kinetic energy spectrum [38] (Fig. 1).…”

Production of ¹²⁸I Atoms through ¹²⁷I (n,γ) ¹²⁸I Reactions in some Solid Iodocompounds using an (²⁴¹Am-Be) Neutron Source

“…Moreover, the characteristics of 128 I compound nucleus and its subsequent de-excitation through photon emission or electron conversion and the associated recoil spectra [6] have made the subject interesting. The spin and parity i.e.1 + [7] of the ground state of 128 I is different from the spin and parity of 127 I i.e.…”