Activation by charged particles

In contrast to neutrons, the penetration depth of charged particles is relatively small, with the result that only the surface layers of thicker samples are activated. Furthermore, the energy of charged particles decreases drastically with the penetration depth, and consequently the cross section varies with the penetration depth. On the other hand, these properties of charged particles offer the possibility of surface analysis. 

In all cases, the determination of oxygen is limited by the range of the charged particles. For determination by reaction (17.10), a Li compound is mixed with the sample. 

The elements Be, B, C, which are not activated by irradiation with thermal neutrons, can also be determined by charged particle activation. Limits of quantitative determination down to the order of about 1g/g can be achieved. The same holds for F which gives a nuclide of short half-life ( °F, fj/2 = 11 s). 

Heavy ions such as Li, °B or others may also be used for charged particle activation, provided that a suitable heavy-ion accelerator is available. Examples of activation analysis by charged particles are given in Table 17.4. 

Element determined Main component of the sample Nuclear reaction Projectile energy [MeV] Detection limit 

---

It has been stated that the bulk of the published work on activation analysis has been concerned with the more general technique of neutron activation. A low probability of neutron activation or an overlong or overshort half-life of the activated species produced can, however, result in poor sensitivity for the method. This is the case with a number of the lighter elements such as beryllium, aluminum, carbon, nitrogen, and oiQTgen. In a number of these cases a satisfactory alternative may be found in activation by charged-particle bombardment (65). 

The simultaneous occurrence of several different nuclear reactions which lead to a variety of products is a feature of activation by charged particles. This may be exemplified by the following reactions which may occur in deuteron bombardment ... 

Debrun, J. L., J. N. Barrandon, and P. Albert Contribution to Activation Analysis by Charged Particles Determination of Carbon and Oxygen in Pure Metals, Possibilities of Sulphur Determination. The 1968 International Con-... 

A Study of Coal Oxidation by Charged-Particle Activation Analysis... 

The effect of the solvent on the reactions involving ions has been treated by a number of different authors without great quantitative success. The major factor is undoubtedly the lack of either theoretical or experimental information concerning the behavior of polar molecules in the presence of the enormous fields in the immediate neighborhood of an ion. The problem is to ascertain how the activities of charged particles change with a change in dielectric constant. 

Choice of other projectiles for activation, for instance activation by 14MeV neutrons, by charged particles or by y-ray photons. 

De Neve K, Strijckmans K, and Dams R (2000) Feasibility study on the characterisation of thin layers by charged particle-activation analysis. Analytical Chemistry 72 2814-2820. 

Activation analysis is another technique that has found some applications. In these methods, the desired stable isotope is made to undergo a suitable nuclear reaction. The parent isotope is determined by measurement of the resulting nuclide. As an example, the 0 content of water samples as small as 1.S jul has been determined by charged particle activation [142]. 

K. De Neve. K. Strijckmans, R. Dams "Fea.sibility Study on the Characterization of Thin Layers by Charged-Particle Activation Analysis." Anal. Chem. 72 (2(X)0) 2814 - 2820. 

IS satisfactory. The precision obtained by the N(p,a) C reaction (ca 3 %) is however significantly better. The latter procedure (49) is therefore recommended for the determination of nitrogen in zirconium and zircaloy by charged particle activation analysis. 

Analysis methods for nitrogen in nickel have been examined within BCR on cast metal (36). Although the nitrogen content in the sample was low (about 1 >g/g) an acceptable agreement was found between photon activation analysis, charged particle activation analysis, the Kjeldahl method and reducing fusion (Table VI-14). With the latter method some discrepancies were however noted low results (a) could be explained by too low extraction temperatures. A study carried out using photon activation showed that a temperature of 2000"C or more is recommended (see 3.3.1.1). 

The determination of oxygen in non-ferrous metals by charged particle activation was reviewed by Engelmann (209). 

Numerous papers (228 to 233) deal with the determination of oxygen in aluminium by charged particle activation analysis using protons, helium-3 and helium-4 as activating particles. Vialatte (230) showed that of these methods only He activation allows the determination of low (< 0.2 Mg/g) oxygen concentrations. 

The oxygen concentration in titanium, zirconium and their alloys is usually fairly high (several hundred to several thousand Mg/g). Activation analysis with 14 MeV neutrons can thus be used for an accurate determination of oxygen in those metals. Less attention has therefore been given to the determination of oxygen by charged particle activation analysis. 

From round robins organized by EURISOTOP in the early seventies, it appeared that the determination of oxygen at concentrations of 20 to 30 nq/g by reducing fusion, 14 MeV neutron activation analysis, charged particle and... 

He activation, the activated mass corresponds to about 150 mg, so that the standard must at least be homogeneous at that level. Five 150 mg samples of the mixture were irradiated in a nuclear reactor. The Na activity from the sodium in the disodium hydrogenphosphate was measured and showed a standard deviation of 2.7 %. Furthermore, 5 standards were analysed by charged particle activation. The induced activity, cor-... 

---