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Ionizing Radiation |
Division Contact: Lisa Karam To enhance quality-control methods used in industrial radiation processing of foods and in the production and use of medical devices, electronic components, and polymers, NIST researchers are developing standardization and measurement assurance methods for industrial high-dose applications of ionizing radiation. As part of this program, they are investigating radiation, chemical mechanisms, and kinetic studies applied to chemical dosimetry systems in the condensed phase, including liquids, gels, thin films, and solid-state detectors. They also plan to examine sensor materials such as doped plastics, solid-state matrices, fiber optics, organic dye solutions, semiconductors, scintillators, amino acids, metallo-porphyrins, and organic or inorganic radiochromic and luminescent aqueous solutions and gels. A number of analytical methods will be used, including transmission and fluorescence spectrophotometry and electron spin resonance spectrometry as well as optical waveguide analysis and pulse radiolysis. Various X-ray and gamma-ray sources and electron accelerators with energies in the 0.1 to 10-megaelectronvolt range are used in this work. Conventional ultraviolet, visible, and infrared spectrophotometers; high-intensity gamma-ray sources; pulsed and continuous beam electron accelerators; and organic-chemical analytical equipment also are available. Contact: Marc F. Desrosiers Credibility of ionizing radiation measurements has been a critical issue for the U.S. radiation, medical diagnostics and therapy, occupational safety, industrial, energy, defense, and environmental communities. To this end, NIST scientists disseminate the standards and technology required for reliable measurement of ionizing radiation to federal, state, and local radiation control programs as well as to the medical, industrial, and defense communities. In addition, NIST researchers monitor and evaluate radiation measurements needs; participate in radiation research, metrology development, and quality control activities; and develop methods for improving the accuracy of field measurements through a national system of secondary standards laboratories. NIST has a strong influence on the design and implementation of measurement quality assurance programs that are accredited under the National Voluntary Laboratory Accreditation Program (secondary calibration laboratories for ionizing radiation and personnel dosimetry programs), the Conference of Radiation Control Program Directors (diagnostic X-ray radiation), Health Physics Society (private-sector calibration laboratories), and American Association of Physicists in Medicine (therapeutic radiation). Programs currently being developed will address measurement quality assurance needs in sectors that include industrial processing, radio-bioassay, and radioanalyses for environmental remediation and waste management. In support of the accreditation programs, NIST provides technical expertise for laboratory technical document review and evaluation, traceability to the national physical standards through performance evaluation testing, and on-site assessments. The major research thrust is the development of a wide variety of appropriate transfer standard instruments and materials. Contact: Lisa Karam NIST researchers are exploring three major areas of fundamental neutron physics: neutron interferometry, laser polarization of neutron beams, and various coupling coefficients of the weak interaction. The Neutron Interferometer and Optics Facility (NIOF) in the cold neutron guide hall has achieved unprecedented levels of phase contrast and stability. Work is under way at this new facility on the development of phase contrast imaging, on a measurement of the neutron-electron scattering length, and on neutron tomography. The NIOF also will operate part-time as a user facility for university and industrial scientists. At another location in the guide hall, development is in progress on neutron spin filters, based on laser polarization of 3He. These neutron polarizers offer advantages over conventional methods in experiments on parity-violating aspects of neutron beta decay and in studies of magnetic materials. This project also is providing assistance to medical researchers who employ polarized 3He for improved magnetic resonance imaging of the lung. Another major research and user facility is the Fundamental Physics Station. At this station three experiments have been carried out in collaboration with major universities: a beam measurement of the free neutron lifetime, a measurement of parity non-conserving neutron spin rotation in liquid 4He, and a search for time-reversal asymmetry in neutron beta decay. At present, a potentially much more accurate measurement of the neutron lifetime employing trapped ultracold neutrons is being carried out in collaboration with Harvard University, Los Alamos National Laboratory, and Berlin's Hahn Meitner Institute. Contact: David Gilliam NIST physicists develop and maintain standards for neutron dosimetry, both at the very high fluence levels appropriate to materials damage studies for nuclear reactors and at the much lower levels appropriate to standardization of radiation protection instruments. Standard neutron fields at NIST and at the University of Michigan have been characterized to provide test irradiation fields for the neutron dosimetry employed in assurance of materials integrity at nuclear power reactors in the United States. NIST scientists also collaborate with engineers and scientists from industry and the Nuclear Regulatory Commission in drafting regulatory guides for accurate measurements in neutron dosimetry at these reactors. Another set of standard neutron fields at much lower fluence rate levels is maintained at NIST for calibration of radiation protection instruments and personnel dosimeters. Efforts are under way to establish and maintain accreditation of other laboratories so that routine calibrations of neutron radiation protection instruments can be taken over by the private sector and by central military laboratories. Contact: David
Gilliam
Date
created:November
6, 2001 |