Abstracts of Accelerator Session Presentations and Posters
For those readers who were not able to attend the 49th Annual Meeting of the Health Physics Society in Washington, DC, in July, we've provided several abstracts of the presentations. We'll present additional abstracts in the next issue of this newsletter.
"The Role of Approximations and Empiricism in Predicting Parameters of Radiological Importance at Accelerator Facilities: G. William Morgan Lecture"
Modern computer technology has enabled the creation of programs that simulate the transport of radiation of a nearly infinite number of particle types in a nearly infinite number of geometrical configurations, thus enabling one to predict (sometimes with a nearly infinite degree of accuracy) the doses to operators, users, and maintenance personnel; to components; and to the environment, where these doses are due to the operation of particle accelerators. However these programs require significant knowledge, experience, investment of time, and dedication on the part of the user, even if the hardware required to run these programs is available in the office of most health physicists. In many situations, predictions of sufficient accuracy can be obtained by using simple approximations or empirical formulae to describe the real physical situation.
"A Nondestructive, Highly Penetrating Gamma Activation Assay of Uranics and Transuranics"
V. Makarashvili, D. P. Wells, F. A. Selim, T. White, and T. Roney
A nondestructive and highly penetrating, accelerator-based gamma-ray approach has been developed to identify uranics and transuranics in large-volume samples. Such kinds of samples are an important part of the waste streams of U.S. Department of Energy sites, as well as other industries. Our experimental methods are based on using accelerator-produced Bremsstrahlung gamma-ray beams in the energy range of 6-20 MeV. By using Bremsstrahlung beams from electron linacs, we populate short-lived excited states of nuclei that emit characteristic gamma rays, which are unique to each nuclear species. Subsequently, detection of these characteristic gamma rays from photo-fission (gamma, f) reaction products allows one to identify environmentally important elements in mixed waste samples.
A new synchrotron light source has been proposed for Brookhaven National Laboratory as a replacement for the current facility—the National Synchrotron Light Source (NSLS). The NSLS was designed in the late 1970s and continues to operate successfully more than 20 years after initial start-up. However, improved capability to match the current and future needs of the scientific community is required. The NSLS-II has been proposed to provide ultra-low emittance and high brightness beams, as well as improved experimental facilities. This paper reviews important design concepts for the proposed facility and the associated radiological implication. The current concept for the facility design includes top-off injection from a 3-GeV linac. An important radiological issue created by the short lifetimes of the stored beam and the need for frequent top-off injection is discussed. The radiological implications of operation of the linac and ring in an energy recovery mode are assessed, and shielding design criteria and beam loss assumptions are presented.
S. H. Rokni, J. C. Liu, H. Y. Khater, A. A. Prinz, and A. Fasso
The SPEAR3 storage ring at the Stanford Synchrotron Radiation Laboratory (SSRL) is an upgrade of the existing 234-m-circumference SPEAR2 ring to a third-generation storage ring. The SPEAR3 characteristics are 3 GeV electron beam energy, 18 nm radian emittance, up to 500 mA of circulating current, and a dipole critical energy of 7.8 keV.
Bremsstrahlung doses were calculated for two modes of accelerator operation: 200-MeV injection and 1.3-GeV stored beam for the Center for Advanced Microstructures and Devices (CAMD) electron synchrotron facility. Calculations were evaluated with and without shielding elements (including the shield wall) in place for estimation of the radiation dose at the site boundary of the CAMD facility. The inclusion of shielding in the model serves as a positive control in the calculations and can be used to assess theoretical calculations. A Fortran program derived from published Bremsstrahlung dose equations was used for all the estimations. Since the CAMD facility has no roof, upper and lower limits were given as the vertical height of the shield in relation to the plane of the ring (1.2 m). The line source length was delimited as the distance between the source in question (normally the exit of a magnet) and the next element capable of acting as a shield to the line source being projected. Distances were measured to the back side of the shielding and are cumulative lengths. Source terms were calculated for bending magnets in the transport line (linac) as well as from bending magnets, long straight sections, and insertion devices in the storage ring. Each of the transport line and ring elements was assessed, including the upper and lower limits of the element and its potential to act as a shield. All sources were considered as distributed losses. Results are promulgated for the site boundary and 100 meters from the source. Line-of-sight comparisons with thermoluminescent dosimeter (TLD) results, projected to the site boundary, were also evaluated. Under these conditions, all sources modeled by the program met the current Department of Energy (DOE) site boundary limits of 0.1 mSv per annum. When compared with distributed losses, point sources met the facility site boundary design criteria of 0.5 mSv per annum, but did not all meet the current DOE limit.