Proton beam source

X-radiation can also be induced by high energy (several Me proton beams from ion accelerators. Such particle-induced x-ray emission (PIXE) (284) is useful for thin samples and particulates, having detection Hmits of g. Intense synchrotron x-ray sources have found appHcations in... 

Si(Li) spectroscopy, with the capability of simultaneous quantitative analysis of 72 elements ranging from sodium through to uranium in solid, liquid, thin film and aerosol filter samples. The penetrating power of protons allows sampling of depths of several tens of microns, and the beam itself may be focussed, rastered or varied in energy. The use of a proton beam as an excitation source offers several advantages over other X-ray techniques, for example there is a higher rate of data accumulation across the entire spectrum which allows for faster analysis. 

In the Detroit apparatus, illustrated in Figure 2.4, the (3+ source is created in situ by bombarding a boron target with a 4.75 MeV proton beam emanating from a van der Graaf accelerator. An unstable carbon isotope is then produced via the reaction... 

The Isolde separator started to work on-line to the CERE 600 fceV synchrocyclotron (SC) as long aoo as 1967, when the accelerator was already 10 years old. In those days the SC could produce an extracted proton beam of up to about 50 nA which, combined with the early taroet/ion sources used by... 

ISOLDE at CERN (SC), make it feasible to consider using such secondary ions as projectiles for nuclear reactions. A pressing need for reaction rate data involving radioactive species exists in nuclear astrophysics. This requires having available projectiles (A < 60) in the energy range from about 200 keV/amu to 1.5 MeV/amu. It has been proposed to install an ISOL device at the TRIUMF facility to utilize the available intermediate energy (200-500 MeV), intense (<100 yA) proton beam as the primary production source. The mass analyzed, radioactive beam (RB),... 

The lunar transient events could be excited by protons in the solar wind but experiments with silicate minerals in proton beams show that the process is inefficient, quantum efficiencies from lxl0 4 to 1x10 , and given the concentration of protons in the solar wind the mechanism cannot account for the intensity of the observed luminescence (33). Another possibility is that neutral particles in the background solar wind or associated with disturbances on the sunfs surface provide the excitation source (34). This would be a process very similar if not identical to the candoluminescence and radical recombination luminescence observed in the laboratory. 

Reactor sources are much more common than spallation sources there are around 20 reactors that produce core fluxes >10 cm s. To generate the proton beam needed for a spallation source requires considerable infrastructure and by 2004 there were only five spallation sources world-wide ISIS [8], IPNS (Argonne, USA) [12], LANSCE (Los Alamos, USA) [13], KENS (Tsukuba, Japan) [14] and SINQ (Villigen, Switzerland) [11] with two more under construction, SNS (Oak Ridge, USA) [9] and J-PARC (Tokai, Japan) [10]. Reactor sources are also much more developed, the first neutron experiments were carried out in the 1950s and the ILL opened in 1975. In contrast the first spallation user facility, opened only in 1980, with ISIS in 1985. 

Fig. 3.11 The schematics of a spallation source (L) a proton linear accelerator (linac), (P) pulsed proton beam (800 MeV), (T) heavy-metal target (tantalum, uranium, etc.), (F) fast neutrons, (M) moderator (H20,CH4,), (TH) thermal neutrons, (S) sample location, (D) 90°...

This particular reaction is of interest for several reasons. It was the first nuclear reaction that was produced in a laboratory by means of artificially accelerated particles (Cockcroft and Walton 1932 cf. 13.3). Reaction (b) is still used for the production of y-radiation (17 MeV), while reaction (c) is used as a source of mono-energetic neutrons. The energy of the neutrons from reaction (c) is a function of the proton energy and the angle betwe the neutron and the incident proton beam. A necessary requirement, however, is that the threshold energy (1.64 X (8/7) = 1.88 MeV) must be exceeded, the g-value for reaction (c) being —1.64 MeV. 

The first source is installed in the secondary beam lines (H6) from the Super Proton Synchrotron (SPS). A proton beam is stopped in a copper target, 7 cm in diameter and 50 cm in lei jh. These roof-shields produce almost uniform radiation fields over two areas of 2 x 2 m, each divided into 16 squares of 50x50 cm. Each element of these grids represents a reference exposure location. The intensity of the primary beam is monitored by an air-filled, precision ionisation chamber (PIC) at atmospheric pressure. One PIC-count corresponds to 2.2 x 10 particles (error 10%) impii ng on the target. Typical values of dose equivalent rates are 1-2 nSv per PIC-count on top of die 40 cm iron roof-shield and 0.3 nSv per PIC-count outside the 80 cm concrete shields (roof and side). Behind the 80 cm concrete shield, the neutron spectrum has a second pronounced maximum at about 70 MeV and resembles the high-energy component of the radiation field created by cosmic rays at commercial flight altitude. ... 

With an external proton beam both of these experimental sources of energy spread can be avoided. The type of neutron energy spectrum one obtains are illustrated by the measurements of Cassels et al. at 145 Mev, of Nelson et al. at 220 Mev, of Goodell et aL at 350 Mev and of Nedzel at 410 Mev. 

A mass spectrometer utilizing a meV proton beam from a Van der Graaff accelerator and with which the proton charge exchange problem does not exist has been described by Wexler et This instrument has been used with ion source pressures only up to 1.3 Torr. The high cost of the accelerator precludes continuous use with the mass spectrometer. 

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