Beam-tube

A number of pool, also called swimming pool, reactors have been built at educational institutions and research laboratories. The core in these reactors is located at the bottom of a large pool of water, 6 m deep, suspended from a bridge. The water serves as moderator, coolant, and shield. An example is the Lord nuclear reactor at the University of Michigan, started in 1957. The core is composed of fuel elements, each having 18 aluminum-clad plates of 20% enriched uranium. It operates at 2 MW, giving a thermal flux of 3 x 10 (cm -s). The reactor operates almost continuously, using a variety of beam tubes, for research purposes. 

At 40 MW operation, the core damage frequency is 3.7E-04/y. The proportion of accident classes is LOCA, 50% beam tube rupture, 27% ATWS, 17% LOOP, 4% and other transients, 2 7. Three minutes of forced flow are not required and large LOCAs with break size smaller than 2.8 inches can be mitigated. 

Schiene,/. rail skid slat, strip, bar beam tube support rim, tire (of a wheel) (Med.) splint. 

Relatively recent developments are electron generators that are essentially sealed vacuum tubes with a 2.5 pm thick silica ceramic window or a 6 pm titanium window as the beam exit. Such electron beam tubes or bulbs are capable of operating at 50 to 150 g d can be connected into mod-... 

Research reactors are widely used for scientific investigations and various applications. Neutrons produced by research reactors provide a powerful tool for studying matter on nuclear, atomic, and molecular levels. Neutrons, often are used as probes by nuclear and solid state physicists, chemists, and biologists. Neutron experiments can also be performed outside the biological shield by means of installed beam tubes. Additionally, specimens can be positioned in or near research reactor cores for neutron irradiation, e.g. to produce radioactive isotopes for medical or research use. 

Neutrons are neutral and little can be done to influence their trajectories, beam-tubes serve only to remove the moderator from the neutron s path. Indeed, neutrons hit monochromators, or samples, held in... 

Typically, incident beam-tubes are evacuated to avoid the 0.2% m attenuation from air scattering. On spallation sources this technique is often applied to all instrumental flight-paths but on reactors the secondary flight-paths of many instruments are in air, helium (low absorption, some scattering), or argon (low scattering, some absorption). 

Table 3.1 Potential gain in flux (relative to a simple beam-tube) as a function of energy by the use of an m = 4 supermirror guide on TOSCA.

Fig. 3.16 The FDS at LANSCE (a) schematic and (b) cut-away view. Key filter, detectors, shielding, closed cycle refrigerator to cool filter, shielding, sample (usually annular or cylindrical), cryostat for sample, incident beam tube. Reproduced from [20] with permission from Elsevier.

The structure just described generates a large, uniform potential gradient across the length of the beam tube. Electrons or ions emitted from a cathode or ion source placed at the high-potential end of the tube are accelerated to the full potential of the machine (typically 2-5 MeV) when they reach the ground terminal. The electrons or ions are then directed to a target for radiolysis experiments. 

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