Single Session

[Schedule Grid]

MAM-A - Accelerator Health Physics

Woodrow Wilson A   09:45 - 12:15

Chair(s): Robert May and Adam Stavola
MAM-A.1   09:45  Enhanced radiation attenuation and shielding ability of materials by changing their crystal structure and electron density M Maqbool*, The University of Alabama at Birmingham ; B Wright, The University of Alabama at Birmingham

Abstract: The linear attenuation coefficient of materials plays an important role in shielding and protection from radiation. It has been observed that the higher the density of a material, the higher its linear attenuation coefficient. Thus, to make a material more suitable for shielding from hazards of radiation, o its linear attenuation coefficient should be increased through an increase in the density of the material. The atomic packing factor within the unit cells of a crystal structure determines the density of the material. This work reports that the density and linear attenuation coefficient of a material can be increased if its crystalline structure is changed from a simple cubical structure to a body-centered cube (BCC) and a faced-centered cube (FCC). Our results show that by changing the crystal structure of a material, its atomic packing factor also increases which is responsible for the increase in density and linear attenuation coefficient. Our results also show that the linear attenuation coefficient increased by 30 % when a crystal structure is changed from simple cubical to BCC. An increase of 41% is found when a simple cubical structure transforms into an FCC structure. The increase in the linear attenuation coefficient with changing the crystal structure of a material enhances the ability of the material to be used for radiation shielding and protection.

MAM-A.2   10:00  Analysis of Misalignment Fault Conditions for the Accelerator Test Facility Plasma Shutter A Rosenstrom*, Georgia Institute of Technology ; S Dewji, Georgia Institute of Technology; S Rokni, SLAC National Accelerator Laboratory; M Santana, SLAC National Accelerator Laboratory; J Liu, SLAC National Accelerator Laboratory; M Palmer, Brookhaven National Laboratory

Abstract: The Accelerator Test Facility at Brookhaven National Laboratory investigates advanced electron acceleration techniques using interactions with laser generated plasmas. The CO2 (9300 nm) laser used in the experiments is being upgraded to increase the pulse energy, from 5 to 15 Joules, and decrease the pulse length, from 2.3 ps to 2 ps. The proposed upgrades significantly increase the focused laser intensity from 5.4*10^16 W/(cm^2 ) to 1.86*10^17 W/(cm^2 ) leading to an increase in the amount of radiation produced from the focused laser plasma interaction. The laser is focused in two locations, the experimental location inside of a shielded vault and when passing through a plasma shutter inside of an occupied controlled area. To assess the hazard posed to workers by a misalignment fault at the plasma shutter updated methods coupling a particle in cell code, EPOCH, and Monte Carlo radiation transport code, FLUKA, were used to directly simulate the radiation produced from the laser plasma interaction. The modified methods were shown to correlate well with experiments and can be used to assess the empirical methods originally used in the design of the plasma shutter shielding. In addition, the use of FLUKA allows for the complex geometry of the plasma shutter to be accurately captured allowing for a high-fidelity assessment of the weak points with regard to the radiation shielding and the proposal of mitigations so that the laser can be upgraded while still being able to operate safely.

MAM-A.3   10:15  Comparison of Analyzed Soil Activation Results to FLUKA Analysis Model CC Papas*, Jlab ; M Schake, JLab

Abstract: The Thomas Jefferson National Accelerator Facility (TJNAF) performed detailed analyses of excavated soil from the area adjacent to the Hall B end station beam dump. Soil samples were taken at standardized 2’ intervals between 20’ and 46’ adjacent to the beamline. A liquid aliquot was prepared for analysis by means of distillation using a RADDEC Pyrolyzer ™. The distilled sample was analyzed for tritium and gamma-emitting radionuclides. The remaining soil samples were dried to verify water content prior to gamma analysis. A liquid scintillation counter and a Reverse-Electrode High Purity Germanium detector were utilized for the analysis of tritium and gamma-emitting radionuclides, respectively. The analytical results were compared to FLUKA modeling estimates to evaluate the accuracy of the model and the impact of the underlying, conservative assumptions. This presentation focuses on the sampling methods, analytical processes, and a summary of the overall results. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177

MAM-A.4   10:30  Medical Radioisotope Production Using Novel Electron Accelerators SW Kelley*, Northstar Medical Radioisotopes

Abstract: NorthStar Medical Radioisotopes started with the promise of producing Molybdenum 99 without uranium (HEU or LEU) and the associated high levels of long-lived fission product and actinide waste, as well as creating a domestic supply of this vital medical radioisotope to prevent to recurring shortages due to overseas production in aging reactors. NorthStar received FDA approval for Mo-99 produced via neutron capture of Mo-98 at the University of Missouri Research Reactor (MURR) in 2018, achieving the first part of that initial goal. In 2023 NorthStar will begin producing Mo-99 without the need for a nuclear reactor via “neutron knockout” (γ,n) of Mo-100, as well as producing Cu-67 from Zn-68 (γ,p). The high energy photons required for these reactions come from bremsstrahlung radiation created by high-powered, high-energy electron beams from the first on their kind IBA TT300HE electron accelerators installed at NorthStar. This presentation will discuss the theory, design and key radiation safety aspects of these accelerators and associated isotope productions equipment.

MAM-A.5   10:45  Activity simulation study in the soil surrounding the Hall-B dump at Jefferson Lab L Zana*, Jefferson Lab

Abstract: Activity has been simulated for the past and future irradiation of the Hall-B dump system at Jefferson Lab. Results from different configurations and times from exposure have been convoluted to get the evolution over time of Isotopes of interest in the soil surrounding the dump. The goal of this simulation is to obtain a spatial activity profile to determine the volume of the desired percentage of total activity produced and the maximum activity density in this volume. The maximum activity density is then used over time to evaluate the radiation impact on water in this soil at Jefferson Lab due to past and future experimental running conditions.

MAM-A.6   11:00  Studies of Residual Doses for the MEC-U Laser Facility P Connolly*, Georgia Institute of Technology, SLAC National Accelerator Laboratory ; J Bauer, SLAC National Accelerator Laboratory; J Liu, SLAC National Accelerator Laboratory; A Rosenstrom, Georgia Institute of Technology, SLAC National Accelerator Laboratory; S Rokni, SLAC National Accelerator Laboratory; S Dewji, Georgia Institute of Technology

Abstract: The Matter in Extreme Conditions Upgrade (MEC-U) is a flagship laser facility for plasma physics and fusion science that will combine high power petawatt (PW), high energy kilojoule (kJ), and high rep rate lasers with the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory. With MEC-U’s high-intensity optical laser systems, laser-target interactions accelerate electrons and protons that will become a source of prompt dose from ionizing radiation. This radiation will also be able to cause activation of the target chamber, experimental systems, and concrete housing, with the potential for residual dose to workers and users. It is necessary to understand the radiological effects of residual radiation from this optical laser operation. These studies will be a guide for a design that will minimize the residual dose and will provide the scope for safety procedures and mechanisms that will need to be designed and implemented to protect personnel and users. This study utilized the Monte Carlo radiation transport code FLUKA to simulate electron and proton source terms that are based on previous particle in cell (PIC) code studies. The FLUKA simulations provide estimates of dose rates from activation during facility operation and after various cooling periods. With these results, we estimate the amount of time users could work in an area of the facility before reaching their yearly radiation dose limit of 1 mSv (100 mrem). Results indicate that radiological controls will need to be implemented to protect workers. Further investigation using these methods will assist in forming the basis for safe operation of the MEC-U facility and in designing the necessary radiological controls. This work was supported by Department of Energy contract DE-AC02-76SF00515.

MAM-A.7   11:15  Radiation Safety Lessons Learned from Re-installation of a Clinical Linear Accelerator F Boateng*, NIST ; J Shupe, NIST; M Mejias, NIST; F Bateman, NIST; L Pidida, NIST

Abstract: Purpose: To share valuable operational radiation safety lessons learned per re-installation of Clinical linear accelerator (CLINAC) in a newly constructed multi-purpose building, and to help ensure that other facilities and stakeholders employ strategies to eliminate avoidable mistakes. A CLINAC was dismantled, removed from its original location, and installed in a newly constructed complex multipurpose building housing a variety of laboratories. Prior to the construction of the new building, shielding calculations were performed by an external design firm in consultation with all stakeholders including NIST Management, building contractor, the laboratory owners and scientists, and the Radiation Safety Division (RSD). RSD ensured that the predicted dose rates in adjacent rooms/labs were well below regulatory limits per the needs of the individual labs. However, in addition to regulatory limits, some labs also required a radiation background lower than 10 µR/h in order to perform the required measurements. This too was part of the initial requirement and shielding calculations. A third-party vendor was hired to perform pre-installation and post-installation radiation safety surveys to validate the expected shielding integrity. RSD performed independent (in-house) radiation surveys to permit acceptance testing and commissioning of the CLINAC, and a thorough post-commissioning radiation survey to ensure the safety of personnel, the public, and the environment. All these surveys confirmed there were no radiological concerns per regulations and for occupancy of adjacent laboratories or rooms. However, it turns out that the dose rates agreed on per the shielding calculations exceed the dose limits needed from a metrological standpoint due to the sensitivity of the applicable instruments. This abstract focuses on the radiation surveys performed, lessons learned, and proposes strategies that other facilities and stakeholders could employ to eliminate avoidable mistakes.

MAM-A.8   11:30  Panel

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