Energy deposition processes

At low and medium doses, it is well established that the nutritional value of proteins, carbohydrates, and fats as macronutrients are not significantly impaired by irradiation, and neither the mineral bioavailability is impacted. Like all other energy depositing process, the application of ionizing radiation treatment can reduce the levels of certain sensitive vitamins. Nutrient loss can be minimized by irradiating food in a cold or frozen state and under reduced levels of oxygen. Thiamin and ascorbic acid are the most radiation sensitive, water-soluble vitamins, whereas the most sensitive, fat-soluble vitamin is vitamin E. In chilled pork cuts at the 3 kGy maximum at 0-10°C, one may expect about 35 0% loss of thiamin in frozen, uncooked pork meat irradiated at a 7 kGy maximum at —20°C approx., 35 % loss of it can be expected [122]. 

Second, the velocity distribution function (VDF) of hot electrons was directly measured to clarify the energy deposition process using X-ray line polarization spectroscopy. When the plasma has electromagnetic field anisotropy, polarized X-rays corresponding to the magnetic quantum number are emitted. In the case of polarization spectroscopy in an electron beam ion trap (EBIT) [21], the polarization degree P is generally defined by... 

Indeed, these methods were largely developed for such systems and then applied to CID processes. One key advantage of bimolecular reactions is the absence of a third body, such that the energy available to the reaction intermediate, ABC+, is the entire kinetic energy of the collision. In such a case, the parameter n no longer describes the energy deposition process, but rather the efficiency of the reaction, such that Eq. (3) is still an appropriate means to determine the threshold for such reactions. 

Consider that the final effect of these collisionally induced internal energy deposition processes are the production of molecular species with a wide internal energy distribution, as shown in Fig. 3.14. Area A corresponds to the molecular species that have experienced a low internal energy uptake, while areas B and C correspond to molecular species experiencing internal energy deposition, so as to promote decomposition processes. In the case of C, the decomposition will take place inside the source prior to acceleration (and the decomposition products will be consequently detected in the usual MALDI spectrum),... 

On exposure to high-energy radiation, the energy deposition process engenders ionized, e.g., RH " , and excited, e.g., RH, species [Klots, 1968 Willard, 1968 Burton and Magee, 1969-1976 Mozumder, 1972 Freeman, 1987 Sauer et al., 1991] ... 

If radiolysis is to be used as a precise source of reactive species then it is essential to ensure that the fundamental energy deposition processes do not... 

There are several possibilities for the formation of adjacent radical pairs. They may be produced in spurs where in the energy deposition processes at least two activated molecules are populated in each other s vicinity. A radical pair may form if the detached H atom abstracts hydrogen firom a neighboring polymer chain, or if a radical center migrates along the polymer chain until it encounters a radical on a neighboring chain. Ion-molecule reactions of the type shown here may also yield neighboring radical pairs (O Fig. 23.11) ... 

Directed-energy-deposition processes are used primarily to add features... 

The defects generated in ion—soHd interactions influence the kinetic processes that occur both inside and outside the cascade volume. At times long after the cascade lifetime (t > 10 s), the remaining vacancy—interstitial pairs can contribute to atomic diffusion processes. This process, commonly called radiation enhanced diffusion (RED), can be described by rate equations and an analytical approach (27). Within the cascade itself, under conditions of high defect densities, local energy depositions exceed 1 eV/atom and local kinetic processes can be described on the basis of ahquid-like diffusion formalism (28,29). 

The MD simulations provided the necessary thermodynamic information to obtain the equilibrium configurations of the films. Often the deposition process will produce films which are not in the equilibrium configuration, and then the problem is to determine the stablity of these films against changes in morphology. Here simulations can also be helpful, since data on the surface energies and chemical potentials of strained films can be used to calculate the probability of cluster nucleation, using classical nucleation theory. 

In order to study the influence of ions on the deposition process, a reliable quantification of the ion flux and energy is imperative. This flux cannot be determined directly from the detected number of ions in an lED as measured by means of QMS, for three reasons [332]. First, the orifice size decreases during subsequent measurements due to deposition of a-Si H on the edges of the orifice. Second, due to the limited acceptance angle of the mass spectrometer system, only a fraction of the ions that arrive at the substrate is actually detected. This fraction depends on the type and number of interactions that an ion experiences while traversing... 

Characterizing the radiation dose to persons as a result of exposure to radiation is a complex issue. It is difficult to (1) measure internally the amount of energy actually transferred to an organic material and to correlate any observed effects with this energy deposition and (2) account for and predict secondary processes, such as collision effects or biologically triggered effects, that are an indirect consequence of the primary interaction event. 

---