Eric Charles Schreiber

The TUNL-FELL inverse Compton γ-ray source as a nuclear physics facility

Abstract A new technique for producing an intense beam of polarized γ-rays is presented. This High-Intensity Gamma-ray Source (HIGS) will utilize the facilities of the new Duke Free Electron Laser Laboratory. This system includes the LINAC injector, the 1.3 GeV electron storage ring, and the OK-4 undulator.It will be shown that it is possible to tune the electron beam in a manner which allows the FEL photons to backscatter from an electron bunch, all within the ring. This leads to an intense beam of almost 100% linearly polarized γ-rays whose energy can be readily tuned from about 5 to greater than 200 MeV. Furthermore, beam energy spreads of less than 1% can be obtained by pure geometrical collimation. Details of the beam properties and background sources will be presented. It will be shown that this is an ideal beam for nuclear physics and nuclear astrophysics studies. One example of this which takes advantage of the flux, energy resolution and polarization of the beam, is the study of Δ 33 excitations in finite nuclei. These intense polarized beams will also make it possible to perform precision measurements of the nucleon polarizabilities. And we will see that studies in the vicinity of the photo-pion production threshold can provide crucial tests of many of the recent predictions (Low Energy Theorems) of Chiral Perturbation Theory. Our final example will show how the very intense beams available at low energies can be used to determine astrophysically important capture cross sections by measurements of the inverse reactions.

Inverse Compton γ-ray source for nuclear physics and related applications

Abstract The development of intense, short-wavelength FEL light sources has opened opportunities for new applications of high-energy Compton-backscattered photons. These applications range from medical imaging with X-rays to high energy physics with photon colliders. In this paper we discuss the practical aspects applications using polarized Compton backscattered γ-rays in the 5–150 MeV range from the Duke storage-ring-driven FEL. Such applications include: nuclear physics, cancer therapy, radiographic imaging, radiation effects testing, and positron production for material science studies.

High-intensity γ-ray source

A mono-energetic tunable source of 100% linearly polarized γ rays has been developed at the Duke Free-Electron Laser Laboratory in conjunction with Triangle Universities Nuclear Laboratory. The OK-4 FEL is coupled to a 1-GeV electron storage ring and generates intense beams of visible or UV photons. In γ-ray production mode, the OK-4 photons Compton scatter from high-energy electrons inside the optical cavity leading to backscattered γ rays. The strong correlation between scattering angle and γ-ray energy permits a selection of the energy spread of the γ-ray beam that depends on a simple geometrical aperture located along the optical axis. Results obtained/(design parameters) indicate γ-ray beams with energies of 2.2-58/(2.0-175) MeV, ΔE/E<1.0% and total fluxes greater than 107/(1010)γ rays/s.

Radiographic tomography using near-monochromatic gamma rays

We describe a new radiographic technique using quasi- monochromatic (gamma) -rays. Conventional radiography of dense or thick objects is severely limited by the broad energy spread of bremsstrahlung (gamma) -rays. The development of intense, tunable, near-monochromatic (gamma) - rays sources in the 4-30 MeV range affords the opportunity to develop a new type of radiographic tomography. Such (gamma) -rays will shortly be available from inverse Compton free-electron laser sources. The expected narrow energy spread and energy tunability will allow not only the structure and distribution of material in an object to be determined but also the specific elemental composition of the material. This is because each element has a slightly different absorption cross section minimum. Furthermore, the quasi-monochromatic nature of the incident (gamma) -ray beam will allow discrimination between scattered and unscattered photons exiting the test object, and result in reliable composition and density data. In this paper, we present an overview of the radiographic process and some early computer simulation results.