Optical remote diagnostics of atmospheric propagating beams of ionizing radiation

#This invention relates to beams of ionizing radiation and, more particularly, to noninterfering diagnostics for determining the performance characteristics of beams of ionizing radiation.

#It is necessary to measure various characteristics of ionizing radiation beams. e.g., charged particle beam, neutral particles beam, or gamma ray beam, in order to determine overall beam performance, to determine the effects of accelerator beam line modifications (tuning) on beam performance, or the effects of changed operating parameters on beam propagation performance. etc. In one available technique, direct current or energy observations can be made with either a Faraday cup or a thermopile to measure the primary beam in the last stage of the vacuum transport and the net beam current after the beam exists the vacuum through a foil window. However, the detectors directly interact and can consume the particle beam, but provide no information on the downrange propagation through the atmosphere.

#In another technique, electron voltage and voltage spread can be determined through independent magnetic sector experiments. Charged particles will be deflected at various angles by a magnetic field where the angle is a function of the particle energy and the angular spread is a measure of the energy spread. Again, the particle beam is consumed in the experiment. Propagation and dispersion properties can also be observed with open shutter photography and gated intensified photography of the beam in air. However, the photographic techniques can pick up beam instabilities and the film can introduce non-linearities in the observed characteristics.

#The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

#FIG. 1 is a schematic illustration of apparatus for carrying out the method according to the present invention.

#FIG. 2 graphically illustrates a single optical power-time curve output by the apparatus of FIG. 1.

#In accordance with the present invention, the interaction of a beam of ionizing radiation in air is detected to provide data which is effective to determine a substantial number of beam characteristics, such as beam current, pulse length, charge losses, electron transport efficiency, total energy deposited in air, and/or electron voltage from both the election range in air and total beam charge. The term beam as used herein means a beam of ionizing radiation such as a neutral particle beam, gamma ray beam, and charged particle beam of electrons or protons. The selection of beam characteristics to be determined is functionally related to the specific beam type.

#The atmosphere provides a natural energy filter for ionizing radiation, such as relativistic electrons. Detectors, such as photomultiplier tubes (PMT'S). measure the air fluorescence generated by beam losses with the atmosphere as a function of time. The detection system is calibrated for absolute detector sensitivity. The range, atmospheric transmission, and the fluorescence efficiency data are displayed as propagating charge versus range, and can be further interpreted to generate a plurality of the above beam characteristics.

#The transport of a high energy beam of ionizing radiation in the atmosphere is accompanied by a loss of energy to the atmosphere, propagating particles have collisional losses where the energy loss rate is dependent on atmospheric density. However, at a given atmospheric density, the collisional energy loss rate is nearly a constant value for particle energies greater than one MeV. For example, for relativistic electrons, the energy loss rate is about 2.5 keV/cm at one atmosphere pressure. Tabulated values for the energy loss rate of electrons are provide in M. J. Berger, et al. "Stopping power and Ranges of Electrons and Positrons." NBSIR-82-2550A, December 1982.