Accelerators Cockcroft-Walton

Figure 14.4 Schematic diagram of a Cockcroft-Walton accelerator system on the left and the electronic circuit used to provide the high voltage. (From Segre, 1977.)...

A Cockcroft-Walton accelerator produces 400-keV protons. What is the maximum energy of the neutrons that can be produced with this accelerator using the d+T reaction ... 

Several industrial irradiation facilities can now provide both X-ray and electron beam processing for a variety of applications. There are three such facilities in Japan. One of these is equipped with a 5.0 MeV, 150 kW Cockcroft Walton accelerator [14], Another one has a 5.0 MeV, 200 kW Dynamitron accelerator [15], and the third facility has a Rhodotron... 

The earliest of such devices were the linear Cockcroft-Walton accelerator (1929), the circular cyclotron (1930), and the Van de Graaff generator (1931). Modern synchrotrons are large machines that have both tinear and curved sections. The most powerful synchrotron is the Tevatron proton accelerator at the Fermilab located near Batavia, Illinois (just outside of Chicago) it ties inside an underground circular tunnel ttiat measures almost... 

Cockcroft-Walton accelerators are still used for obtaining "low" kinetic energies, up to 4 MeV for protons. Presently, such accelerators are used in many installations as the first stage of acceleration, injector, in a more complex machine designed to produce high energy beams (see Figures 13.8 and 13.9). 

Accelerators provide a variety of nuclear reactions for production of neutrons. Cockcroft-Walton accelerators can generate 14.8 MeV neutrons by accelerating deuterons ( H) onto a tritium target to produce 10 -10 neutrons s Cyclotrons and linear accelerators can produce high-energy neutrons with a broad spectrum of energies in spallation reactions that result from the bombardment of heavy elements by charged particles. 

To study the moisture distribution in the canister, we made 14-McV neutron radiographs with a Cockcroft-Walton accelerator Using the Berger transfer method, neutrons transmitted through the assembly activated a copper sheet through the Cufn. nl Cu reaction. The reaction has a threshold of 11. MeV, so most of the scattered neutrons will not contribute to the activity. After a 30-min irradiation ( Cu has a half4ife of 9.9 min), the copper plate was loaded into a film holder for a 30-min exposure of a sheet of Kodak-type XR-5 high-speed x-ray film. 

A Cockcroft-Walton accelerator was used for the electron irradiation under vacuum (P < 7.9x10 Pa) with accelerating potential of 200-500 kV. After the dose of 20 MGy, the decrease of elongation at break was comparable to that of proton irradiation. 

There are seven types of electron accelerator available for industrial uses [41] (1) Van de Graaff generator (2) Cockcroft-Walton generator (3) insulated core transformer (4) parallel coupling, cascading rectifier accelerator (5) resonant beam transformer (6) Rhodetron (7) linear accelerator (LINAC). 

Fig. 3. Principle of linear accelerator (linac). Partially accelerated electrons from a source, such as a Cockcroft-Walton generator, arc further accelerated by stages as rhe electrons pass through radio-frequency cavities, powered by if oscillators. Each paiticle receives a small push as it passes from one cavity to the next until the final desired accelerated beam is produced Tile machine must be carefully synchronized CSG = Cockcroft-Walton generator, RFO = radio-frequency oscillator RFC = radio-frequency cavity...

Fig. 5. An early fixed-target accelerator comprised of a laige main-ring synchrotron with four stages of acceleration (MRA) a booster synchrotron a linear accelerator (linac), and a Cockcroft-Walton generator. Pistons aie accelerated to 0, 5 MeV in the Cockcroft-Walton generator to 300 MeV in the linac to 8 GeV in the booster synchrotron, and to 400-500 GeV in the mam-ring synchrotron. Experiments are not limited to accelerated protons, but also can be conducted with beams of secondary particles (mesons and neutrinos) which are knocked out of the target by impacting protons...

The most common sources are based on the 3H(d, n) reaction. Deuterons are accelerated to 150 keV with currents 2.5 mA and strike a tritium target. They produce 2 x 1011 of 14-MeV neutrons/s under these conditions. The neutrons produced are widely used in fast neutron activation analysis for the determination of light elements. The tritium targets are typically metals such as Ti, which have been loaded with titanium tritide. The accelerators are usually small Cockcroft-Walton machines or small sealed-tube devices where the ion source and accelerator structure are combined to produce a less expensive device with neutron yields 108/s. 

Activation analysis is based on the production of radioactive nuclides by means of induced nuclear reactions on naturally occurring isotopes of the element to be determined in the sample. Although irradiations with charged particles and photons have been used in special cases, irradiation with reactor thermal neutrons or 14 MeV neutrons produced by Cockcroft-Walton type accelerators are most commonly used because of their availability and their high probability of nuclear reaction (cross section). The fundamental equation of activation analysis is given below ... 

In a single-stage accelerator, such as a Cockcroft-Walton type, the total potential produced from a high voltage generator is imposed across the accelerator, i.e. between the ion source and the target. The kinetic energy, of the projectile is ... 

In recent years small and relatively inexpensive accelerators have come into use based on the Cockcroft-Walton principle. These are known as tranrformer-rectifier accelerators and are primarily used for acceleration of electrons or acceleration of deuterons for production of neutrons through the reaction ... 

British physicist, who Joined Rutherford at the Cavendish Laboratory in Cambridge, where with Ernest Walton (1903-95) he built a linear accelerator (see Cockcroft-Walton generator), in 1932, using the apparatus to bombard lithium nuclei with protons, they produced the first artificial nuclear transformation. For this work they were awarded the 1951 Nobel Prize. 

Cockcroft-Walton ganarator The first proton accelerator a simple linear accelerator producing a potential difference of some 800 kV (d.c.) from a circuit of rectifiers and capacitors fed by a lower (a.c.) voltage. The experimenters. Sir John Cockcroft and E. T. S. Walton (1903-95), used this device in 1932 to achieve the first artificially induced nuclear reaction by bombarding lithium with protons to produce helium ... 

Table 8.2 shows major accelerators used for creating charged particle beams. In MeV energies. Van de Graaff, Cockcroft Walton and cyclotron accelerators are commonly used. Figure 8.3 shows the DuET at Kyoto University in Japan as an example ion irradiation facility and irradiation... 

Bevatron A six or more billion electron vol-taccelerator of protons and other atomic particles. Energies of 5-6 MeV will produce X-rays equivalent in energy to gamma radiation of 12-20 g of radium. Makes use of a Cockcroft-Walton transformer cascade accelerator and a linear (q.v.) as well as an electromagnetic field in the build-up. 

Cockroft-Walton accelerator (John Douglas Cockcroft and Ernest Thomas Sinton Walton) The Gockcroft-Walton accelerator is used to fling charged particles at atomic nuclei in order to investigate their properties. 

Discovery of the neutron (Chadwick) and positron (Dirac, Anderson). First nuclear reaction induced in an accelerator (7Li(/ , a) Cockcroft and Walton). Baade and Zwicky suggest a neutron star may be created as residue of a supernova explosion. 

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