Sectoring

Before ehding this presentation on mass spectrometry, we should cite the existence of spectrometers for which the method of sorting ions coming from the source is different from the magnetic sector. These are mainly quadripolar analyzers and, to a lesser degree, analyzers measuring the ion s time of flight. 

The quadripolar spectrometers whose resolution is limited to about 2000 are of simpler design than the magnetic sectors and are less costly. They are often used in conjunction with gas chromatography (see section 3.3) for purposes of identification. 

Utilization of LPG as motor fuel represents only a tiny fraction of the market, on the order of 30,000 t/an in France out of a total 3,000,000 t that is, about 1%. Globally, the fraction of LPG used in the transportation industry is on the order of 5% the other applications are essentially petrochemicals (25%) and the heating fuel sectors (70%). However noticeable openings in the LPG-fuel markets in some countries such as Japan (1.8 Mt), the United States (1.3 Mt), the Netherlands (0.9 Mt), Italy (0.8 Mt) and in certain regions (Latin America, Africa, and the Far East) have been observed for specialized vehicles such as taxis. 

In the industrial combustion sector, for a total French market of 6 Mt in 1993, the distribution between the four product types was as follows f/o ... 

For convenience, the probability axis may be split into three equal sectors in order to be able to represent the curve by just three points. Each point represents the average value of reserves within the sector. Again for convenience, the three values correspond to chosen cumulative probabilities (85%, 50%, and 15%), and are denoted by the values ... 

Introduction and commercial application Investment opportunities in the exploration and production (E P) sector of oil and gas business are abundant. Despite areas such as the North Sea, Gulf of Mexico and the North Slope in Alaska being mature areas, there are still many new fields under development in those regions, and new areas of business interest are opening up in South America, Africa and South East Asia. Some fields which have a production history of decades are being redeveloped, such as the Pedernales Field in Venezuela. 

The case of thin-skin regime appears in various industrial sectors such as aerospace (with aluminium parts) and also nuclear in tubes (with ferromagnetic parts or mild steel components). The detection of deeper defects depends of course on the choice of the frequency and the dimension of the probe. Modelling can evaluate different solutions for a type of testing in order to help to choose the best NDT system. 

However, in various industrial sectors the application of the radioscopic inspection technique is aggravated by a lack of the respective standards, contrary to radiography. This leads to complicated approval bureaucracy by the respective supervisory or certificatiomn authorities. 

Fig. 6. Test with one segment of 6 sector transducer in pulse-echo mode on aluminium plate, (a) no defect (b) defect simulated with mercury droplet (c) defect position.

In practice, only a limited number of views are available the scanned sector is typically 180 or 360°, and the angular increment 2°. Moreover the frequency band-width of the employed pulses is very limited, typically one octave. The resolving power of the system is then limited. A typical numerical signal is composed of 1024 samples at a sampling period of 50 nsec. 

In wide sectors of industry there is a growing need of inspection methods which go without liquid coupling media. The excitation of bulk and surface waves by means of air-coupled ultrasonic probes is therefore an attractive tool for NDE. This is tme e.g. for the rapid scanning of large composite structures in the aerospace industry [1]. In other cases, the use of liquid couplants is prohibitive like the thickness measurement of powder layers. 

To support them, therefore, immense activities are prompted both in pubh c private sectors with increasing importance on NDT. The particular application of radiography using Ir-192 isotopes for industrial production, construction maintenance of industries, power plants, oil and gas pipelines plants, railway, aviation systems, naval structures and vessels, etc is currently in the fore front for its reliabih ly, ease of application record keeping advantages. 

The principles referred to so far are common to all New Approach directives. The individual directives obviously need to be specific on topics such as the scope, the essential requirements, the classification of the products and on the use of modules for conformity assessment. The pressure equipment directive includes some additional sector specific dispositions which relate to recognised third party organisations , the European approval for materials , a committee for pressure equipment and the user inspectorates . 

In compliance with the requirements stated in the System of accreditation to the practical experience and qualification the technical manager in NDT must have at least level 2 on each of NDT methods used in the laboratory seeking accreditation, where not more than 3 NDT methods are in practice, and level 3 on the basic method used in the laboratory where there are more than 3 methods. Moreover all specialists must be certified in relevant NDT method and industrial sector. 

Metrological attestation as the procedure that ensures reproducibility and comparability of the results of measurements is specified in GOST 8.010-90 State System of Measurements. Procedures of Measurements Implementation didn t find wide use in NDT. In airspace industry, railway and naval transport the requirements of approval of test procedures is in force more than 20 years. In chemical and oil-chemical sectors the similar requirements were less explicit. In some industries, for example in building GOST 8.010-90 was not put into account. 

Cullen reviewed this philosophy and the way in which it was applied, endorsing the approach and recommending that it should be applied to the offshore sector... 

This equation may be solved by the same methods as used with the nonreactive coupled-channel equations (discussed later in section A3.11.4.2). Flowever, because F(p, p) changes rapidly with p, it is desirable to periodically change the expansion basis set ip. To do this we divide the range of p to be integrated into sectors and within each sector choose a (usually the midpoint) to define local eigenfimctions. The coiipled-chaimel equations just given then apply withm each sector, but at sector boundaries we change basis sets. Let y and 2 be the associated with adjacent sectors. Then, at the sector boundary p we require... 

Figure Bl.6.3 Electron energy analysers that use magnetic fields (a) the trochoidal analyser employing an electromagnet, (b) the Wien filter and (c) the sector magnet analyser. Trajectories for electrons of different energies are shown.

The chapter is divided into sections, one for each general class of mass spectrometer magnetic sector, quadnipole, time-of-flight and ion cyclotron resonance. The experiments perfonned by each are quite often unique and so have been discussed separately under each heading. 

Figure Bl.7.4. Schematic diagram of a reverse geometry (BE) magnetic sector mass spectrometer ion source (1) focusing lens (2) magnetic sector (3) field-free region (4) beam resolving slits (5) electrostatic sector (6) electron multiplier detector (7). Second field-free region components collision cells (8) and beam deflection electrodes (9).

Most instruments are configured with a fixed value for the radius of curvature, r, so changing the value of B selectively passes ions of particular values of momentum, mv, tlirough tlie magnetic sector. Thus, it is really the momentum that is selected by a magnetic sector, not mass. We can convert this expression to one involving the accelerating potential. 

Magnetic sector instruments typically operate with ion sources held at a potential of between 6 and 10 kV. This results in ions with keV translational kinetic energies. The ion kinetic energy can be written as zt V = Ifur and thus the ion velocity is given by the relationship... 

In odier words, ions with a particular mass-to-charge ratio, m/z, can be selectively passed tlirough the magnetic sector by appropriate choice of a value of V and B (though nonnally V is held constant and only B is varied). 

Magnetic sectors can be used on their own, or in conjunction with energy analysers to fomi a tandem mass spectrometer. The unique features of the reverse geometry instrument are presented from this point. 

The electrostatic sector consists of two curved parallel plates between which is applied a potential difference producing an electric field of strengtir E. Transmission of an ion tlirough the sector is governed by the following relationship... 

A single magnetic sector can be used as a mass filter for other apparatus. However, much more infonnation of the simple mass spectrum of a species can be obtained using the tandem mass spectrometer. 

Ions accelerated out of the ion source with keV translational kinetic energies (and m/z selected with the magnetic sector) will arrive in the FFR of the instrument in several microseconds. Ions dissociating on this... 

In the FFR of the sector mass spectrometer, the unimolecular decomposition fragments, and B, of tire mass selected metastable ion AB will, by the conservation of energy and momentum, have lower translational kinetic energy, T, than their precursor ... 

Figure Bl.7.5. (a) MIKE spectrum of the iinimoleciilar decomposition of 1-butene ions (m/z 56). This spectrum was obtained in the second field-free region of a reverse geometry magnetic sector mass...

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