Ionization by radiation

The triangular planar (D3h symmetry) CO/ molecular ion with 24 electrons (AB324-type) in CaC03 is easily ionized by radiation to electron and hole centres self-trapped in the lattice or an oxygen vacancy type C02 molecular ion at the anon site. Molecular orbital schemes based on the general scheme of AB3 molecules with 25,24 and 23 electrons for atoms A (B, C, Si, N, P, As and S) and B (O) characterize their specific -factor. Hence, the anisotropic -factor of these radicals estimated from the powder spectrum has been to identify the radical species.1... 

Scheme 3. A single guanine, once ionized by radiation, becomes a sink for three or more other holes, here presiuned to be dG". Holes on other bases or sugars will serve equally well for the reactions shown. The reduction potentials for the three subsequent oxidations are highly favorable. ...

OSL could also be used for container verification. Luminescent phosphor additives, ionized by radiation, are mixed with paints or clear coats and are applied to the surface of a container (Miller et al. 2009). The OSL phosphors luminesce in proportion to the ionization radiation dose and the intensity of excitation light. The OSL coatings/additives will be invisible to the naked eye, but could be seen using an InGaAs infrared detector. The OSL additives would tag the container and reveal an attempt to tamper with the container and therefore increase the confidence that its integrity had not been compromised. 

Figure 9.1 PrincipLeofionizationspectroscopy,frompar-tidesin a gas mixture, after absorption oftuneabLe Laser Light Ipump(r i) and subsequent ionization by radiation from a second Laser Iprobe(r 2)- The charged particLes (eLectrons or ions) are extracted from the i nteraction voLum e a n d detected by a charge-sensitive detector...

A counter contains argon gas, which is ionized by radiation, making possible the measurement of radioactive decay rates. 

The existence of isotope shifts and of tunable lasers with narrow Hnewidth leads to the possibHity of separating isotopes with laser radiation (113,114). This can be of importance, because isotopicaHy selected materials are used for many purposes in research, medicine, and industry. In order to separate isotopes, one needs a molecule that contains the desired element and has an isotope shift in its absorption spectmm, plus a laser that can be tuned to the absorption of one of the isotopic constituents. Several means for separating isotopes are avaHable. The selected species may be ionized by absorption of several photons and removed by appHcation of an electric field, or photodissociated and removed by chemical means. 

Mass spectrometry is not based on absorption of electromagnetic radiation, but monitors what happens when a substance is ionized by collision with a high-energy electron. 

Radioisotopes have important commercial applications. For example, americium-241 is used in smoke detectors. Its role is to ionize any smoke particles, which then allow a current to flow and set off the alarm. Exposure to radiation is also used to sterilize food and inhibit the sprouting of potatoes. Radioisotopes that give off a lot of energy as heat are also used to provide power in remote locations, where refueling of generators is not possible. Unmanned spacecraft, such as Voyager 2, are powered by radiation from plutonium. 

The radicals are produced by various processes, although little is known for certain. A major question exists as to whether the radicals are produced by the initial bond rupture - , by recoil impact , by Auger ionization , by gamma radiation damage or by normal exchange . ... 

Total Ionization—The total electric charge of one sign on the ions produced by radiation in the process of losing its kinetic energy. For a given gas, the total ionization is closely proportional to the initial ionization and is nearly independent of the nature of the ionizing radiation. It is frequently used as a measure of absorption of radiation energy. 

REMPI provides high detection sensitivity for free radicals similar to that of LIF.4 In the REMPI method, one or more photons typically from a focused laser radiation initially excite the free radicals to an intermediate excited electronic state. The radicals are further excited and ionized by another photon in the same laser pulse (one-color REMPI) or by a photon of different wavelength from another laser beam overlapping in space and time... 

Sankaranarayanan, K. 1991b. Ionizing radiation and genetic risks III. Nature of spontaneous and radiation-induced mutations in mammalian in vitro systems and mechanisms of induction of mutations by radiation. Mutat. Res. 258 75-97. 

In gas clouds containing one or more hot stars (7 cn > 30 000 K), hydrogen atoms are ionized by the stellar UV radiation in the Lyman continuum and recombine to excited levels their decay gives rise to observable emission lines such as the Balmer series (see, for example, Fig. 3.22). Examples are planetary nebulae (PN), which are envelopes of evolved intermediate-mass stars in process of ejection and... 

Lastly, we mention one more excitation mechanism that has been observed in molecules. It is well-established that following strong field ionization in atoms and molecules, under certain conditions, the ionized electron can be driven back to the ion core where it can recombine to produce high-harmonic radiation, induce further ionization, or experience inelastic scattering. However, there is also the possibility of collisional excitation. Such excitation was observed in [43] in N2 and O2. In both molecules, one electron is tunnel ionized by the strong laser field. When the electron rescatters with the ion core, it can collisionally ionize and excite the molecular ion, creating either N + or Ol+ in an excited state. When the double ion dissociates, its initial state can... 

As mentioned above, one type of mechanism proposed for photoactivation is that the drug is ionized by the radiation and the electron is taken up by the target compound (e.g. a nudeobase), with subsequent rearrangements, fragmentations, dimerizations,... 

Figure 4. Outline of the cellular respose to ionizing radiation. 1.Early changes induced by radiation. 2. Adaptive response. 3. Initiation of apoptosis. 4. Execution of apoptosis. S. Late phases of apoptosis. The point of no return from death is the transition hum 3 to 4.

Borazine, substituted borazines and some boron hydrides are ionized by absorption of 121.5 mn radiation (H-a line). Types of ion sources used in these studies are illustrated in Fig. 16. The absorption process results in loss of an electron to form a cation without fragmentation ... 

Increased initial damage Agents that act to increase the initial DNA damage caused by ionizing radiation would be expected to augment the cytotoxicity caused by radiation... 

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