Sources Bremsstrahlung

As early as the 1930s X-ray absorption experiments were being carried out using a continuum source of X-rays (the bremsstrahlung mentioned in Section 8.1.1.1), a dispersive... 

A typical x-ray photoelectron spectmm consists of a plot of the iatensity of photoelectrons as a function of electron E or Ej A sample is shown ia Figure 8 for Ag (21). In this spectmm, discrete photoelectron responses from the cote and valence electron energy levels of the Ag atoms ate observed. These electrons ate superimposed on a significant background from the Bremsstrahlung radiation inherent ia n onm on ochrom a tic x-ray sources (see below) which produces an increa sing number of photoelectrons as decreases. Also observed ia the spectmm ate lines due to x-ray excited Auger electrons. 

The sources used in Ni Mossbauer work mainly contain Co as the parent nuclide of Ni in a few cases, Cu sources have also been used. Although the half-life of Co is relatively short (99 m), this nuclide is much superior to Cu because it decays via P emission directly to the 67.4 keV Mossbauer level (Fig. 7.2) whereas Cu ti/2 = 3.32 h) decays in a complex way with only about 2.4% populating the 67.4 keV level. There are a number of nuclear reactions leading to Co [4] the most popular ones are Ni(y, p) Co with the bremsstrahlung (about 100 MeV) from an electron accelerator, or Ni(p, a) Co via proton irradiation of Ni in a cyclotron. 

Nuclear science in particular obtains from laser-driven electron sources a brand new input to perform interesting measurements in the context of many laboratories equipped with ultrashort powerful lasers. The ultrashort duration of these particle bunches represent a further attractive feature for these kinds of studies. In the following, we will focus on nuclear reaction induced by gamma radiation produced by bremsstrahlung of laser-produced electrons in suitable radiator targets. This way is usually mentioned as photo-activation and is particularly efficient for photons of energy close to the Giant Dipole Resonance of many nuclei. 

Figure 5.6 Interaction of a beam of primary electrons with a thin solid sample, showing the various processes which can take place (Pollard and Heron 1996 51). Various types of electron can be scattered or ejected back towards the source, or transmitted through the sample. Characteristic X-rays and bremsstrahlung can be produced, and also cathodoluminescence. These products form the basis of analytical and imaging electron microscopy, and of a range of other techniques. (After Woldseth 1973 Fig. 4.1 - reproduced by permission of the Royal Society of Chemistry.)...

For the measurement of thickness and coverage (coatings) of very thin materials, the absorption of alpha radiation may be used as a measure of weight/unit area. For moderately thick materials, the beta radiation emitted by °Sr (strontium-90),35Kr (kryplon-85), or 14C (carbon-14) is used. For greater thicknesses, bremsstrahlung or gamma sources are used. 

Activation by photons (PAA) usually takes place via the (y, n) reaction, although other reactions such as (y, p), (y, a), and the like are possible. Of special interest is the determination of lead by PAA with a detection limit of 0.5 p,g. [Lead is very hard to detect using NAA (Fig. 13.2).] Photon sources are usually electron accelerators, which produce high-energy photons through the bremsstrahlung process when the electrons strike a heavy-metal target. 

When using an electron accelerator, fast positrons are produced by pair production from bremsstrahlung gamma-rays generated as the high energy electrons from the accelerator slow down in matter, whereas with cyclotrons and reactors, very intense primary positron sources are produced directly. Slow positron beams are then produced and transported using similar techniques to those described previously in this section. 

Whether the radiation source is a machine-generated e-beam, isotopic gamma rays, or machine-generated x-rays (bremsstrahlung), a continuum of x-rays and electrons is produced as the initial event dissipates its energy in the irradiated medium. This chapter will focus on an e-beam source, as this is the most likely source to be used in a waste-treatment application. It should be noted that most of the comments made here are equally applicable to other sources of radiation. 

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