A high-brightness, electron-based source of polarized photons and neutrons
- Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States)
A compact and comparatively inexpensive system that is practical for universities is described based on a low-energy, electron storage ring with at least one undulator based oscillator to store photons. If the oscillator cavity length is relativistically corrected to be an harmonic of the ring circumference (L{sub C}={beta}L{sub R}n/n{sub B} with n{sub B} the number of bunches), higher-energy, secondary photons from Compton backscattering may become significant. Then, besides synchrotron radiation from the ring dipoles and damping wigglers as well as undulator photons, there are frequency upshifted Compton photons and photoneutrons from low Q-value targets such as Beryllium (Q{sub n}={minus}1.66) or Deuterium (Q{sub n}={minus}2.22&hthinsp;MeV). For 100 MeV electron bunches, an adjustable-phase, planar, helical undulator can be made to produce circularly polarized UV photons having a fundamental {epsilon}{sub {gamma}1}=11.1&hthinsp;eV. If these photons are stored in a multimode, hole-coupled resonator they produce a Compton endpoint energy up to {epsilon}{sub {gamma}2}=1.7&hthinsp;MeV. When incident on a Be conversion target these secondary photons make unmoderated, epithermal neutrons having mean energy {epsilon}{sub n}=24.8{plus_minus}6.8&hthinsp;keV from the two-body reaction Be{sup 9}+{gamma}{r_arrow}n+Be{sup 8}({r_arrow}2{alpha})with negligible, residual radioactivity. The system is shown in Fig. 1. When the target is unpolarized, one expects neutron rates of 10{sup 11} epithermal n/s for 10{sup 15} Comptons/s and a circulating current of 1 A with polarizations P{sub RHC}({rvec n})={minus}0.5, P{sub LHC}({rvec n})=0.5, both with reduced flux, and P{sub Lin}({rvec n})=0. With a 1 cm thick cylindrical tungsten sheath surrounding the Be to attenuate scattered photons exiting at 90{degree} to the incident photons, there is a peak neutron flux of {approx}10{sup 9} epithermal n/s/cm{sup 2} cylindrically symmetric around the surface. No attempt was made to optimize this because there is still no accepted treatment protocol (dose rates or preferred neutron energy distribution). Although these factors depend on the individual case, several thousand BNCT treatments per year appear feasible. A potential clinical advantage of this system is that it also provides the photon beams required for analogs of NCT such as photon activation therapy PAT. Other medical applications, depending on electron energy, include real-time production of radioactive nuclides (both proton and neutron rich) e.g. tracers for PET scans useful for measuring boron uptake rate and distribution prior to treatment. While the primary electron energy depends on the application, higher energies are more versatile and technically simpler. Certain innovations that make such a system feasible are discussed. {copyright} {ital 1999 American Institute of Physics.}
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 700997
- Report Number(s):
- CONF-981122-; ISSN 0094-243X; TRN: 9919M0048
- Journal Information:
- AIP Conference Proceedings, Vol. 475, Issue 1; Conference: 15. international conference on the application of accelerators in research and industry, Denton, TX (United States), 4-7 Nov 1998; Other Information: PBD: Jun 1999
- Country of Publication:
- United States
- Language:
- English
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