Betatron X-ray

Another unique feature of the betatron X-ray beam is its intensity as a function of the electron density of the plasma. It is found to be sharply peaked at ne = 1.1 x 1019cm-3, as shown in Fig. 11.10. Below this critical density, the X-ray signal rapidly vanishes, mainly because the number of trapped electrons is too low. This was confirmed by experiment no electrons were detected by the spectrometer. At larger densities the X-ray signal drops and a plateau is reached. For these experimental conditions, the resulting amplitude of the plasma wave becomes too weak. The pulse must first be modulated and additional laser energy would be needed. As a result, the temperature of the electron beam decreases and its divergence increases. The PIC... 

Fig. 11.10. Betatron X-ray intensity and spatial distribution in the beam as a function of the electronic density of the gas jet. Efficient X-ray beam generation is observed to occur within a sharp density range centered at 1 x 1019 cm 3...

Because of the large thickness x-rayed by high-current betatron (more than 1500 ram on plastic) the picture of defect situated near the front wall of the sample is too increased what makes difficult to detect in practice real dimensions of the defect. But there is a possibility of stereosurvey due to existence of two radiation beams simultaneously generated by betatron. 

KBC-25 M betatron allows to x-ray steel layer with thickness 280-340mtn in an hour at radiation energy of 25 MeV and F=2 m with the help of PT-5, D4, MX-5 and D7 film types. 

At 45 MeV mode BC-50 betatron allows to x-ray steel barrier with 500mm thickness using PT-1 film type at F=3m in less than seven minutes. During one hour exposure and at the same focal distance betatron allows to x-ray 500mm thickness steel on PT-5 film type. And 700mm thickness steel on PT-1 film type. 

A unique high-energy radiation laboratory is functioning at the Institute, in which studies Can be performed and thick items can be controlled using powerful X-ray units and betatrons. 

A completely different emission process, which can in principle provide table-top ultrashort X-ray sources up to 100 keV has been recently discovered and studied, both from an experimental and a theoretical viewpoint [9]. It can be understood as one consider that the electrons, trapped and accelerated in a plasma wake as described earlier, can also experience, in some cases, a transverse force pulling them toward the beam axis. This force is basically due to the creation of a sort of plasma channel at low electron density, which is a consequence of the ponderomotive force that expels the electrons from the laser beam axis (the ions, due to their larger inertia, being fixed). The trapped electrons thus undergo a sort of wiggler motion, thus producing so-called betatron radiation. 

Historically, the progress in radiation therapy has been linked mainly to technological developments. The physical selectivity of the irradiations was significantly increased when 200-kV x-rays were progressively replaced by cobalt-60, betatrons, and linear accelerators. As a consequence, the clinical results were dramatically improved. 

In addition to the penetrating power of the x-rays there are certain other characteristic phenomena encountered in radiography with the betatron not found with low voltage x-rays, such as a) A relative freedom from scattered radiation. The secondary radiation will tend to retain direction which the primary radiation originally had. Hence, no blocking is necessary around an irregular object or be-... 

The formation of one or more cavities(air spaces or voids) in cast-loaded solid, expl or proplnt c hges is called cavitation (See under Loading of Ammunition). A cavity in a HE chge of a shell may cause premature expln in the gun because of collapse of the chge under the force of acceleration. A cavity in a propint chge may affect its ballistic characteristics(Ref 1). Cavities in loaded ammo may be discovered by x-ray devices such as Betatron(qv)... 

The properties of this X-ray beam are in a good agreement with the synchrotron radiation emitted by the trapped electrons undergoing betatron oscillations in an ion channel, as described by numerical simulations. The... 

Fig. 11.9. Experimental setup used for the betatron experiment. Permanent magnets are used simultaneously to deviate the accelerated electron beam off-axis in order to make sure that the X-ray detection is unperturbed and to provide spectral information on the electron energy distribution. CCD pictures of the X-ray beam and the electron spectrum for a gas jet electronic density of 1019 cm-3 are also shown...

The purpose of radiotherapy is to deliver a large radiation dose to the tumor and a minimal dose to the surrounding normal tissues. Depending upon the location and volume of the tumor, the radiation can be a photon source (e.g., x-ray tubes, cobalt teletherapy unit, linear accelerator, Betatrons) or a source for a high-energy particle (e.g., electrons, protons). 

A typical site investigation may use a portable X-ray system such as the Betatron (Figure 4.28). The system comprises three units with interconnecting cables with a total weight of 190 kg. Although this is bulky compared to the other equipment described in this section this system is compact and portable with a power output comparable with permanent systems (capable of penetrating concrete in excess of 1 m thick in ideal circumstances). Smaller systems are available that have associated reduced penetration and resolution. 

A betatron accelerates electrons to high speeds in a magnetic field such beta ray-like electrons can then be directed onto a target to produce intense beams of high-energy X rays. 

Electrons. The circular electron synchrotrons and betatrons have been used more for the X-rays they produce rather than for studies of the interaction of electrons with nuclei. Experiments with electrons have been more conveniently performed at machines with straight sections (e.g. University of Michigan racetrack) or with linear accelerators. 

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