Nonresonant nuclear reaction

Table 1 Selected recently used nonresonant nuclear reactions ...

Minor actinides present in some nuclear waste produce large quantities of helium when they decay. When considering materials for storage of this waste, it is necessary to have some knowledge of helium diffusion in the material matrix. Helium diffusion into possible materials has been simulated by exposing them to a He ion beam (i.e., implantation). The implanted helium has then been profiled using the He(D,p)" He nonresonant nuclear reaction enabling diffusion coefficients to be determined. 

There are a few potential future developments. The possibility of combining the position scanned He microbeam NRA technique and the D-( He,p)" He nonresonant nuclear reaction technique to produce three-dimensional profiles has been discussed in the literature. 

In nonresonant profiling, the silicon surface barrier detectors that detect the products of the nuclear reaction may also detect signals from incident ions that have been backscattered from the sample. Figure 4 shows an a particle spectrum from the reaction (p, a) along with the signal produced by backscattered... 

Figure 4 Spectrum of diffusion in the mineral olivine ((Mg, Fe)2 SiO ) taken using nonresonant profiling technique with the reaction (p, a) Both the a particles resulting from the nuclear reaction and backscattered protons are collected. Inset shows expanded region of the spectrum, where a yield indicates diffusion of into the material.

Figure 12.9 Rate of nonresonant stellar nuclear reactions as a function of temperature. (From S. S. M. Wong, Introductory Nuclear Physics. Copyright 1988 by John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.)...

The modification of the electronic potentials due to the interaction with the electric field of the laser pulse has another important aspect pertaining to molecules as the nuclear motion can be significantly altered in light-induced potentials. Experimental examples for modifying the course of reactions of neutral molecules after an initial excitation via altering the potential surfaces can be found in Refs 56, 57, where the amount of initial excitation on the molecular potential can be set via Rabi-type oscillations [58]. Nonresonant interaction with an excited vibrational wavepacket can in addition change the population of the vibrational states [59]. Note that this nonresonant Stark control acts on the timescale of the intensity envelope of an ultrashort laser pulse [60]. 

Consider first some of the factors affecting the design of such laser schemes. Ground electronic state based laser enhancement schemes [216, 3 366] rely on the induction of nuclear dipole moments to aid in promoting a desii reaction [30, 367], For example, the use of infrared (IR) radiation has been propoS to overcome reaction barriers on the ground electronic state [30, 367]. However proposal requires powers on the order of terawatts per centimeter sipis (TW/cm2). At these powers nonresonant multiphoton absorption, which irtvar leads to ionization and/or dissociation, becomes dominant, drastically reducin, yield of the reaction of interest. 

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