The Tandem Accelerator

I.2. The Tandem Accelerator. As indicated in the diagram of Figure 4.13, a tandem accelerator uses a positive terminal located in the centre of the device. Negatively charged He- particles are injected into the accelerator and attracted to the terminal, where a stripper element removes two or more electrons from each... 

It is necessary to calibrate the 14C time scale for greater dating accuracy. However, the second-order variations are at least as important as the first-order constancy of atmospheric 14C. For example, they provide a record of prehistoric solar variations, changes in the Earth s dipole moment and an insight into the fate of C02 from fossil fuel combustion. Improved techniques are needed that will enable the precise measurement of small cellulose samples from single tree rings. The tandem accelerator mass spectrometer (TAMS) may fill this need. 

Simulation of the neutron-induced damages using triple ion beams is schematically shown in Fig. 7. A proton and a helium ion are provided by the ion implanter and the single-ended accelerator, respectively. Heavy ions, such as iron or silicon, accelerated by the tandem accelerator, are injected into the target simultaneously. For example, the SiC/SiC composite was tested under triple ion beam irradiation consisting of a 380-keV proton, a 1.2-MeV helium ion, and a 7.8-MeV Si " ion. The triple irradiation system is equipped with an energy degrader and a beam scanner for uniform three-dimensional (3-D) irradiation. 

The Tandem Accelerator Superconducting Cyclotron facility at Chalk River, which is nearing completion of phase 1, will be capable of accelerating all ions to at least 10 HeV/u. Together with the on-line isotope separator it will provide a powerful means of studying exotic nuclei ... 

During phase 1 of construction of the Tandem Accelerator Superconducting Cyclotron (TASCC) facility at Chalk River, the existing tandem accelerator was reversed, a superconducting cyclotron built and some 60 metres of beam-transport line installed to connect the two and to deliver beams to an interim target line" The result, which required an appreciable building extension, is shown in figure 1 ... 

The Chalk River isotope separator has been operating on-line with the tandem accelerator since April 1979, When the tandem shut down in 1982, the separator was completely dismantled and reassembled with some improved components at its present location, where it will be on-line with TASCC (see figure 1), It is now working again and, although recommissioning is not yet complete, it has already achieved some of the excellent performance characteristics met before the move, A picture of the relocated instrument appears as figure 3. 

The ratio A/A0 is measured either by P" counting or with the tandem accelerator mass spectrometer (TAMS) in which direct atom counting is used. 

The fine structure interval AEqi is obtained from the laser wavenumber and the ion beam velocity using the relativistic Doppler formula. To caUbrate the 90° analysing magnet we tuned a beam from the tandem accelerator,... 

The tandem accelerator (in which the ion beam experiences two acceleration stages one before stripping and one after stripping) is the most often used accelerator in the AMS facilities. Negative ions are injected in the tandem accelerator. Stripping of electrons at the center of tandem converts the negative ion to a positive ion, which is then accelerated and transmitted as positive ion from the accelerator. 

As the ions collide with the gas molecules in the central stripper canal , the molecular ions (such as CH2 and CH) are broken up. The carbon atoms are stripped of three or four electrons making them into C + or C + ions, while the C ions are stripped of four electrons making them into C + ions. These are then accelerated down the second half of the tandem accelerator reaching energies of about 8 MeV. The second magnet selects ions with the momentum expected of C ions and a Wien filter checks that their velocity is also correct. 

Accelerator Mass Spectrometry is a special tool for quantitative measurements of very long-lived radionuclides. This technique consists of counting the nuclides themselves instead of waiting for their decay. As for as the tandem accelerator is concerned, no molecular background exists because of the stripping process. Any isobaric background is also drastically suppressed due to the nuclear techniques involved in the measurements. There occurs an extremely wide area of applications in different fields because of the capability of the AMS technique to determine the radioisotopes at the faintest level (the isotopic concentrations down to the range of 10 in some cases). 

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