Delta rays

Delta Ray—Electron removed from an atom during the process of ionization (also called secondary electron). Delta rays cause a track of ionizations along their path. 

Primary Ionization—(1) In collision theory the ionization produced by the primary particles as contrasted to the "total ionization" which includes the "secondary ionization" produced by delta rays. (2) In counter tubes the total ionization produced by incident radiation without gas amplification. 

Radiation, Secondary—A particle or ray that is produced when the primary radiation interacts with a material, and which has sufficient energy to produce its own ionization, such as bremsstrahlung or electrons knocked from atomic orbitals with enough energy to then produce ionization (see Delta Rays). 

The electrons produced during the first and subsequent collisions may be energetic enough to cause further ionisation and excitation (delta rays) until they reach the subionisation and suhexcitation levels characteristic of the material. Finally, they undergo rotational-vibrational interactions until they reach thermal energies. 

The few studies that have been made indicate that the free ion yield for exposure of liquids to alpha particles is quite small. For hydrocarbons, Ga is very small, 0.005 per 100 eV [30,31]. Theoretically, a zero yield is expected for cylindrical geometry and alpha particles create such a track. The low yields in hydrocarbons can be attributed to those electrons on the tail of the distribution that thermalize some distance from the track these are often called delta rays. For liquid rare gases, the yields are higher for example, the zero field yield is 0.16 per 100 eV for Xe [32] because the thermalization ranges are much longer. 

The foil was fixed on the substrate with cyanoacrylate adhesive, and then the wafer on the foil. Finally the gold layer of the detector was covered with a 10ym thick copper, both ends of which were fixed on the sides of the substrate. The copper foil conducts the current from the detector to the ground and, on the other hand, protects the detector from the scattered beam and low energy delta-rays from the target. Five detectors are assembled on an aluninum holder The annular detector is fastened with two screws by the back of the substrate and the four plain others are put upright arround the annular detectors. 

The relatively low overall yields of radicals were attributed to the high recombination rate of closely spaced base ion radicals in the densely ionized track core. The proximity of these radicals coupled with Coulomb attractions facilitates fast core ion radical-ion radical recombination. However, neutral sugar radicals in the core are not affected by Coulomb attractions, thus they do not recombine as readily. Therefore, most of the neutral sugar radicals stabilized at 77 K are presumed to form in the core. On the other hand, most of the base radicals that are stabilized at 77 K are assumed to form in the isolated, low LET-like spurs formed by delta-rays. The similarity in the behavior of the base radicals in argon ion-beam irradiated samples and in y irradiated samples lends support to this picture.In this model C(N3)H is in equilibrium with C and is found to act as an ion-radical. 

Fig. 2. Schematic of track of an Argon ion-beam in DNA. A high-energy density core is generated by deposition of ca. 50% of the energy of the ion in a relatively small volume. At 77 K, neutral sugar radicals are stabilized largely in the core. A much larger region of space formed by delta rays from the core is characterized by low LET-like spurs. Ion base radicals are stabilized in the spurs, with one-electron-reduced cytosine actually existing as a protonated species.

Figure 1 Simulated ionization track due to an alpha ray of a few MeV of energy coming from the left side in the blue water continuum. Each red circle is an ionization event. This local distribution, in the nanometer range, is the beginning ofa complex chemistry. Ionizations occur mainly around the trajectory axis of this incident ion, and this area is named "core track". Some high energy electrons can be ejected and they can form their own track named "delta ray". When delta rays are sufficiently numerous (that depends on the inciden t ion energy and charge) a new area around the core can be named "penumbra". The penumbra has the characteristics structure ofa "low LET area" because the ionizations are produced by high enrgy electrons.

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