Ionization by X-rays

We mentioned above that, at the dawn of the 20 century, the nature of X-rays was already well known. Evidence of gas ionization by X-rays quickly led to the creation of devices designed to quantitatively measure the intensity of X-ray beams. This enabled researchers at the beginning of the last century to study in detail the interaction between X-rays and solid matter, leading, naturally, to the observation and quantitative analysis of scattering, and then diffraction, of X-rays. 

Hard X-rays (A < 1 nm) also penetrate into the D-region. The production of ionization by X-rays is somewhat complex, since it involves the absorption of an X-ray photon by a neutral particle, leading to the production of photoelectrons which are sufficiently energetic to ionize other particles. It thus becomes necessary to distinguish between primary and secondary ionization. The mean number of secondary ion pairs produced depends on the energy of the incident photon. For example, this number has been estimated at about 45 for A = 0.6 nm, 75 for A = 0.4 nm, and 165 for A = 0.2 nm (Nicolet and Aikin, 1960). 

Figure 8.21 Schematic diagram of a gas-filled X-ray detector mbe. He filler gas is ionized by X-ray photons to produce He+ ions and electrons, e . The electrons move to the positively charged center wire and are detected. (Modified from Parsons, used with permission.)...

In Auger electron spectroscopy an atom is ionized by X-ray, electron or ion bombardment. This ionic state has a certain probability to decay in a radiationless transition whereby an additional electron is emitted (the so-called Auger electron). Thus the atom is finally left in a double ionized state. The energy distribution of the Auger electrons is recorded. 

AES dilfers from XPS in that the surface is ionized by a finely focused electron beam of 5 30 kV (Fig. 1). The secondary electrons have no specific information content in AES, but the Auger electrons, which are emitted shortly after the secondary electrons, and which involve transitions between different orbitals, are recorded as a function of their kinetic energy. Such Auger electrons are also emitted after ionization by x-rays in XPS and consequently the same Auger transitions lines are also observed in XPS. In XPS, this aspect of the technique is sometimes referred to as XAES (Table 1). Because of a very high background, AES spectra are conveniently represented as differentiated spectra. The peak-to-peak heights (more accurately, peak areas in the nondifferentiated spectrum) are proportional to the number of atoms in the probed sample volume. 

The air in the vicinity of the droplet was ionized by X-rays. As Millikan observed a single drop, he found sudden changes Aw in the velocity which he attributed to the picking up of a single unit of charge e from the ionized air. By... 

An unambiguous observation of hole transport was reported for liquid xenon (Hilt and Schmidt, 1994a). Electrons and holes were produced via ionization by X-rays and the mobility of the holes was measured by a time-of-flight method (see Section 2.5). The current signal due to holes followed the electron signal (see Figure 17). 

The flexible large area screen with photostimulable phosphor called the imaging plate, which temporarily stores the image induced by the ionizing radiation, e g. by X-rays, electrons or other charged particles ... 

Ionization chamber pulses, 51, 59, 60 Ionization chambers, 49-52, 93 Ion pairs, 48-50 Ion tubes, characteristics, 3, 4 Ion yield in counter tubfes, 50, 51 Iridium, determination by x-ray emission spectrography, 328 Iron, determination by x-ray emission spectrography, 222, 328 in cements, 260, 261 in domestic ores, 200, 202, 203 in hi h-temperature alloys, 179-183 in solution, 185, 255... 

The new arylphospholes were examined by means of photoelectron spectroscopy and, in three cases, by X-ray crystallography [36, 39,40], The ionization energy of 7.5 eV obtained for the 2,4,6-tri-icrt-butylphenylphosphole (17d) is the smallest value that has ever been recorded for phospholes [41],... 

Inner electrons are usually excited by X-rays. Atoms give characteristic X-ray absorption and emission spectra, due to a variety of ionization and possible inter-shell transitions. Two relevant refined X-ray absorption techniques, that use synchrotron radiation, are the so-called Absorption Edge Fine Structure (AEFS) and Extended X-ray Absorption Fine Structure (EXAFS). These techniques are very useful in the investigation of local structures in solids. On the other hand, X-Ray Fluorescence (XRF) is an important analytical technique. 

Highly crosslinked UHMWPE can be produced by irradiation of a blank UHMWPE with ionizing radiation, in particular by X-rays, y-rays or electron beams, in order to produce radicals. The subsequent treatment of the irradiated material consists in exciting free radicals, which have not recombined, by means of microwave radiation or ultrasound. The process is claimed to ensure a substantially complete recombination of the free radicals. In addition, the crosslinking of the UHMWPE is also further optimized (30). 

The white crystalline solids are readily soluble in organic solvents (even alkanes) but are insoluble in water and the lower alcohols. They are inert to water but are hydrolyzed by dilute acid. In solution they are monomeric and non-ionized. An X-ray crystallographic study of Be40(0Ac)6 shows the O to be centrally coordinated to four Be atoms in a tetrahedral geometry each of the Be atoms is tetrahedrally surrounded by four O donors from bridging acetates and the central oxygen (62).322... 

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