Main beam

Primary structure Mainframe of a product is the primary structure, Examples include aircraft main supports, building main beams, and automobile frames. If the primary structure fails, it would be damaging or catastrophic to the product and/or people. See Secondary structure. 

A mass-energy filter may be included to remove contaminant ions, and multiply charged and clustered ions of the main beam species. Ions of the required mass and energy pass through the filter, while unwanted species are deflected out of the beam. Prior to final focussing, the beam is deflected through a few degrees, and any neutral particles will be undeviated and are therefore separated out. 

Before any slit operation check, write down, or save the old motor positions Operation of slits can be useful to change the beam intensity (instead of operating absorbers). Imperfect thermal stabilization of mirrors and monochromators can be compensated by proper slit operation. Before such operation is undertaken, it should be made sure that the instrument is close to thermal equilibrium. In particular after opening the main beam shutter for the first time, it may be indicated to wait for several hours. Otherwise the operator will have to follow the thermal expansion continuously. This bears the risk to destroy the adjustment or even the detector. 

The mainbeam of the radar generates a footprint on the ground whose size will depend upon the actual range R. Let Pel represent the main-beam width of the antenna pattern in the elevation plane. Further, let Rt and Rh denote the ranges of the toe and heel of the mainbeam footprint whose center is at range R, as shown in Fig. 7. Further, let ipT... 

For a nuclide of mass M, abundance sensitivity is the ratio between the signal at mass M+ arising from the same species to the signal at mass M. Off-peak ions are present because of collisions behind the magnetic filter, of reflections on the tube wall, or of space-charge effects. As a result of the collisions, the energy of these ions is different from the energy of the main beam. They alter the apparent peak baseline in a continuous way. Abundance sensitivity decreases with the mean free path of ions, i.e., when pressure near the collector assembly... 

Note It has turned out that medium transmission is optimal for structure elucidation. Too strong reduction of the main beam favors ion losses due to scattering, charge exchange (M -i- N M + IST") or charge stripping processes (M -I- N -> + N" ) instead of delivering additional structural information. 

Fig. 2.27. Total collision probability and fractions of single, double, triple and quadruple collisions versus collision gas pressure. The transmission of the main beam /(is given on the right ordinate. Values are for an ion of collision cross section 5 x 10 cm and 1 cm collision path 10 Torr= 1.33 Pa. Reproduced from Ref. [9] with permission. John Wiley Sons, 1985.

One important aspect of the electron diffractometer, is that any ED pattern can be captured before scanning by a CCD camera that is placed off-axis in relation with the ED pattern (can be any commercial CCD, even a webcam see fig.l). A dedicated software corrects for any type of optical distortions that may be produced due to the position of viewing angle of the CCD in relation with the ED pattern. This has the big advantage that the user that may observe and define interactively the reflections or the area of the ED pattern that will be scanned, allowing at the same time the main beam to be blanked, in order to avoid radiation damage. 

For valence band studies, for instance, energy dependent UPS in the 30-300 eV excitation range is certainly of interest, and would be available in synchrotron radiation sources. This experiment, however, is difficult to realize, since it would involve the construction of safely enclosed systems, in which to handle dangerous a, p (and sometimes y or neutron) emitters in considerable quantities. This systems must be well separated from the main beam lines. And all of this must be done in the laboratories of a storage ring, which are usually not adapted for radioactive hazards. 

For cells with a small thickness, the interference pattern method is used. This method consists of measuring the transmittance of the empty cell between two wavenumbers v and v2. It can be seen in Fig. 10.23 that beam S2 has gone through a double reflection on the internal wall of the cell. Thus, if the angle of incidence is normal to the cell wall and if 2d = kX, the addition of both intensities is observed (the two beams Si and S2 are in phase). A modulation of the main beam Si will be observed as a function of wavelength. This modulation is in the order of a few percent. 

An analogous expression holds for electron scattering, except that in such an experiment we usually desire to measure that proportion of the incident beam (of impact energy E0) that has lost energy E. In general, the intensity of such an inelastically scattered beam will depend on the polar angles 8s,s (with respect to the main beam) at which it is measured. If the incident electron beam has an intensity I0, the inelastically scattered beam will have an intensity... 

Figure 2. Spectra of the daughter ions produced by collisionally activating the (M-H) ions of unlabeled palmitic acid (A) and 16,16,16-d-palmitic acid (B). Note the spectra differ only in the mass 3of the main beam.

Feasibility studies have shown that a He-jet activity transport line, with a target chamber placed in the LAMPF main beam line, will provide access to short-lived isotopes of a number of elements that cannot be extracted efficiently for study at any other type of on-line facility. The He-jet technique requires targets thin enough to allow a large fraction of the reaction products to recoil out of the target foils hence, a very intense incident beam current, such as that uniquely available at LAMPF, is needed to produce yields of individual radioisotopes sufficient for detailed nuclear studies. We present the results of feasibility experiments on He-jet transport efficiency and timing. We also present estimates on availability of nuclei far from stability from both fission and spallation processes. Areas of interest for study of nuclear properties far from stability will be outlined. 

A He-jet coupled on-line mass separator, used in conjunction with a target chamber placed in the LAMPF main beam, offers an especially attractive approach for the study of nuclei far from stability. Such a facility would provide access to isotopes of a number of elements that cannot be efficiently extracted for study at any other type of on-line separator system, and the use of a long capillary transport line would allow the separator ion source to be located outside the accelerator beam-line shielding, greatly reducing the installation cost. The He-jet technique requires thin targets in order for the reaction products to escape, and to produce a sufficient yield of radioisotopes far from stability for detailed nuclear studies, a beam intensity comparable to that available at LAMPF is needed. 

Figure 9.6. The point spread function of a circular aperture for 4 different values of the edge taper with Gaussian illumination. The four curves are for uniform illumination or 0 db taper, 9, 18 and 27 db taper. The sidelobe level decreases with increasing taper, while the width of the main beam increases slightly.

---