If you've been wondering whether to attend the 2008 Midyear Topical Meeting of the Health Physics Society (HPS), here's a sneak preview just to whet your appetite. The following abstracts from the upcoming meeting were chosen at random from the more than 120 abstracts received to date. They represent just a small portion of the many fascinating talks on a broad range of radiation-generating device topics that you will hear at the midyear meeting. Hope this sampling convinces you that the midyear meeting in Oakland in January 2008 will be well worth your time!
Mary Jo Ridenour, Marcia Maria Campos Torres, Tatiana Burtseva, Michael Billone (Argonne National Lab)
This work involves radiological characterization of irradiated zirconium cladding (alloy) samples (100-mm long or less). The samples were irradiated in a nuclear reactor in Sweden and sent to Argonne National Laboratory for structural and chemical analysis. A series of measurements were made using thermoluminescent dosimeter (TLD) chips and an ion chamber to estimate the exposure to the extremities of a worker. Gamma and beta-gamma exposure rate measurements were performed which recorded rates over 300 R/hr on contact with the samples. A number of lead and tungsten gloves were tested in search of the best material to minimize the worker’s extremity exposure. Included in this experiment is the installation of the sample into the cutting machine inside a glovebox. Measurements were made by inserting the chips and ion chamber into the gloves of the glovebox with the reactor sample present. Then a series of dry runs were performed by the workers to optimize the tasks and remove unnecessary steps in the process. Based on the radiological characterization of the samples, workers were authorized to perform the cuts and exposures were kept as low as reasonably achievable (ALARA). Overall, this experience could benefit other facilities that perform work with extremely "hot" samples where exposures to extremities can be more than 300R/h beta-gamma at contact.
Chris Morris (Los Alamos National Lab)
Over 120 million vehicles enter the U.S each year. Many are capable of transporting hidden nuclear weapons or nuclear material. Currently deployed x-ray radiography systems are limited because they cannot be used on occupied vehicles and the energy and dose are too low to penetrate many cargos. We present a new technique that overcomes these limitations by obtaining tomographic images using the multiple scattering of cosmic radiation as it transits each vehicle. When coupled with passive radiation detection, muon interrogation can provide safe and robust border protection against nuclear devices or material in occupied vehicles and containers.
Ronald Ruth (Lyncean Technologies, Inc.)
Past research at Stanford Linear Accelerator Center introduced a new x-ray source concept, a miniature synchrotron light source (1). This early research led later to the formation of a corporation, Lyncean Technologies, Inc., which has recently completed development of the Compact Light Source (CLS) (2). The CLS is a near-monochromatic, tunable, home-lab-size x-ray source with up to three beamlines that can be used like the x-ray beamlines at the synchrotrons--but it is about 200 times smaller than a synchrotron light source. The compact size is achieved using a laser undulator and a miniature electron-beam storage ring; in other words, inverse Compton scattering from an electron beam in a miniature storage ring. The CLS is designed to produce a photon flux on the sample that is comparable to the flux of highly productive synchrotron beamlines. This presentation will first introduce the basic principles of the CLS and show how the quality, tunability, and flux of a synchrotron beam line can be brought to an x-ray scientist’s local laboratory. The construction of the production-prototype CLS, funded by the National Institute of General Medical Sciences (NIGMS) Protein Structure Initiative, is now complete, and the commissioning and testing phase of the CLS prototype is well advanced. The second CLS is under construction as part of the second round of the Protein Structure Initiative (3) The presentation will show details of the storage ring, laser system, and x-ray optics and will conclude with initial results of using the prototype CLS to test new imaging techniques.
References
(1) Z. Huang and R. D. Ruth, "Laser-Electron Storage Ring,” Phys. Rev. Lett., 80:976-979, 1998.
(2) Supported by the National Institute of General Medical Sciences, National Institutes of Health, R44 GM66511 and R44 GM074437.
(3) The Accelerated Technology Center for Gene to 3D Structure (ATCG3D), supported by PSI II, the National Institute of General Medical Sciences, and the National Center for Research Resources, NIH, 5U54 GM074961.
Frederic Stichelbaut (IBA)
The IBA Company is actively involved in the design of new industrial irradiation systems based on high-energy x-rays. These systems make use of 5 MeV to 7 MeV electron accelerators able to deliver beam currents as high as 100 mA. The x-rays are produced by sending the electron beams on a tantalum target. To optimize these x-ray irradiation systems, use is made of Monte Carlo simulation codes such as GEANT3 and MCNPX. These simulation tools are invaluable to designing the best irradiation methods as a function of product size and product density and to determining their performance figures. The Monte Carlo predictions have been verified by irradiating homogeneous products with densities ranging from 0.035 to 0.25 g/cm3 at an industrial x-ray facility located in Germany. The various configurations will be presented, together with the results of the experimental tests.
Fred Mettler (University Of New Mexico)
Medical radiation exposure of the U.S. population has not been systematically evaluated for almost 25 years. In 1982, the per capita dose was estimated to be 0.54 mSv and the collective dose 124,000 person-Sv. The preliminary estimates of the National Council on Radiation Protection and Measurements (NCRP) Scientific Committee 6-2 medical subgroup are that in 2006 the per capita dose from medical exposure (not including radiotherapy) had increased almost 600 percent to about 3.2 mSv and the collective dose had increased over 750 percent to about 970,000 person-Sv. The largest contributions and increases have come primarily from computed tomography (CT) scanning and nuclear medicine. The 67 million CT scans accounted for 12 percent of the total procedures and about almost half of the collective dose. Nuclear medicine accounted for about 3 percent of all procedures but 23 percent of the total collective dose. Medical exposure has equaled or exceeded natural background and is now the largest source of radiation exposure to the U.S. population.
Tom Mclean (Los Alamos National Lab)
CHELSI is a portable neutron dose equivalent meter designed at Los Alamos National Lab for use in leakage fields around high-energy particle accelerators. The instrument uses a digital signal processor to distinguish, in real time, neutron-induced spallation products from external gammas based on the pulse-shape discrimination properties of CsI(Tl). In field use, pulse shape information in conjunction with signal pulse height, is used to assign a count-to-dose conversion factor to calculate neutron dose equivalent. The appropriate conversion factors were calculated using the G-value or spectrum-weighted method. A personal digital assistant (PDA) is used to display integrated neutron dose and dose rate to the user. In addition, an estimation of gamma dose rate is also displayed. The shape and energy data can be logged and analyzed off-line using deconvolution routines for a determination of neutron fluence and a more accurate calculation of dose. A description of CHELSI and an outline of the data analysis techniques are followed by a presentation of data obtained in the field including an intercomparison with survey instruments in current use at the Los Alamos Neutron Science Center (LANSCE). The talk concludes with an assessment of CHELSI performance to date and the outlook for the future.