Internal beam

Fig. 9. Diagram of the experimental set-up to isolate short-lived, volatile Rf compounds at the internal beam of the U-300 cyclotron in Dubna [104].

A point of consideration for the positive ion cyclotron is that the internal beam of positrons of variable energy can be utilized for radionuclide production by placing a probe with the target at different radial positions. The negative ion cyclotron does not have this provision. 

The maximum energies available in conventional cyclotrons of the constant frequaicy type are about 25 MeV for protons and deuterons, and 50 MeV for a-particles. The shape of the electrostatic field at the gap between the dees as well as the design of the magnetic held to produce a slight non-uniformity at the outer edges of the dees produce a focusing effect on the beam particles. The ion currents are usually 0.5 mA for the internal beam, and about a factor 10 less for an external beam. 

A water-cooled copper foil (0.1 mm thick) is irradiated by the internal beam of a sector focused cyclotron with 1.2 mA H ions of 24 MeV for 90 min. The reaction Cu(p,pn) u occurs with a probability of 0.086 b. Copper consists to 69% of Cu. The proton beam has a cross-section of only 15 mm. (a) How many u atoms have been formed (b) What fraction of the projectiles have reacted to form Cu (c) What cooling effect is required (kW) at the target ... 

The bombarding particle beam is accelerated and transported in the high vacuum system of the accelerator. The X-ray detector unit is encapsulated in a separate clean vacuum system. The irradiation of the sample may be performed in vacuum or under atmospheric conditions, depending on the size, physical state, and other parameters of the sample. To define the physical conditions mentioned above, special PIXE chambers of internal beam and external beam configurations are used for in vacuo and atmospheric irradiations, respectively. 

Internal beam and external beam PIXE chambers (a and b, respectively). See text for details... 

Most of the irradiations for medical radioisotope production at cyclotrons are done using extracted beams. There is more versatility in working with the extracted beam than with the internal beam. Through controlled defocusing and wobbling, it is possible to decrease the... 

Shortly after publication of the Berkeley results, the Dubna research team repeated their original experiments using an external beam of Ne ions rather than an internal beam. They detected a spontaneous-fission activity with a half-life three times shorter than originally reported in 1964 or about 0.1 s [70]. The Dubna researchers attributed this discrepancy to a high background in their track... 

Some sampling accessories [e.g., infrared microscopes (see Chapter 14) and gas chromatography interfaces (see Chapter 23)] are too big to fit in even the largest sample compartment. In these cases, the accessories are mounted outside the instrument and the modulated beam is directed to them by means of a switch-able mirror (often known as di flip mirror). It is very rare that the beam is returned to the detector mounted inside the instrument, so a second detector is usually a component of accessories that are mounted outside the spectrometer in the external beam. Several contemporary instruments are also equipped with flip mirrors to direct the beam to different possible internal beam paths, in one or more of which a different accessory may be mounted permanently. In this way, the user can switch rapidly from one type of measurement to another, making optimal use of a single spectrometer. 

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