TECHNICAL ACTIVITIES 1998 - NISTIR 6268

FUTURE DIRECTIONS

• Brachytherapy Dosimetry. An estimated 60,000 brachytherapy procedures are currently performed annually in the U.S., with a significant growth seen for low-energy photon brachytherapy (¹²⁵I and ¹⁰³Pd) in prostate cancer treatment. Moreover, there is the potential for brachytherapy to increase to some 500,000 procedures per year with the advent of intravascular brachytherapy in the treatment of heart disease. Critical to the assurance of absorbed dose in such procedures is traceability to national standards. Early leadership in the dosimetry of beta-emitting brachytherapy sources should be extended toward development of a coherent program for the measurement of absorbed dose in water or tissue for all such sources, including photon-emitting radionuclides.

• Industrial High-Energy Computed Tomography. The MIRF electron linear accelerator should provide an adequate source as a test bed for high-energy CT applications. With past and current experience applications in low- and high-energy CT, the establishment of capabilities at MIRF would provide a valuable resource to pursue collaborations in innovative areas such as studies of the solidification front in metal castings, a subject for which we have been approached. The construction of a high-energy x-ray camera system will help position us to contribute in such studies.

• Industrial and Therapy Electron-Beam Dosimetry Calibrations with EPR. Radiation processing by electron beams with energies from about 0.1 MeV to 25 MeV is carried out in an estimated 700-1000 facilities, with such use on an increasing path. For therapy applications, NIST maintains a measurement quality assurance program for electron beams with energies from about 6 MeV to 20 MeV, based on Fricke dosimetry. With the MIRF electron accelerator capable of beam energies of 7 MeV to 32 MeV and the electron Van de Graaff with energies from 1 to 4 MeV, NIST has the resources to address the need for the direct electron-beam calibrations and traceable reference measurement services for much of the range involved in industrial processing and in therapy. Initial work with graphite calorimetry in MIRF electron beams shows promise for the development of absolute dosimetry measurements for high-energy electron beams, and their transfer to alanine/EPR dosimetry systems. Early field tests indicate the suitability of alanine/EPR dosimetry as a replacement for Fricke dosimetry in our therapy electron-beam measurements. Continued development should promote further maturity in the use of alanine/EPR systems as transfer dosimeters, including such important electron-beam applications.

• Magnetically Trapped Ultra Cold Neutrons. In collaboration with physicists at Harvard University an Ultra Cold Neutron (UCN) experiment is planned, based on "superthermal" cooling of neutrons with wavelength 0.89 nm to the ultra cold neutron energy range by exchange of a single phonon (per neutron) in a superfluid bath of liquid helium. The initial application of this UCN source will be a neutron lifetime experiment with potential improvement in accuracy of better than a factor of 10 compared to the present best value.

• Neutron Tomography. Recent improvements in CCD imaging systems and the widespread availability of computed tomography (CT) and 3D image reconstruction software have made it possible to set up a neutron CT imaging system with only modest resources. Neutron CT imaging can complement x-ray CT scans, by providing higher sensitivity to hydrogen, boron, lithium and certain other elements and isotopes in many important industrial applications.

• Laser Polarization of Neutrons. Commercial developments in the production of inexpensive diode lasers may make laser polarization of neutrons by spin exchange the method of choice for both materials science and neutron physics experiments. However, research in non-perturbing compression of low density polarized ³He from direct optical pumping of metastable ³He may lead to an even less expensive method. Both possibilities are being pursued. The application of laser-polarized inert gases to medical magnetic resonance imaging is also being investigated through collaborations with the University of Pennsylvania, the University of Nottingham, and the University of Virginia.

• Development and Calibration of Very Low-Level Measurement Techniques. (i) A fast, inexpensive method for atom counting based on Resonance Ionization Mass Spectrometry will continue to be developed. Although much progress in this program has been made, the sensitivity must be improved by increasing the duty cycle. A Ti(Saph) laser is being adapted for this application. (ii) The Nuclear Regulatory Commission is moving toward increasing sensitivity requirements for in situ measurements of radioactivity by a factor of 10 from that which can be attained by the present Ge-based systems. NIST will investigate and develop imaging plate technology for the measurement of very low level activities in site remediation, in breakdown in microchips by alpha particle contaminants and other areas.

• Development of New Standards for Nuclear Medicine. National laboratories, universities, and radiopharmaceutical companies report that they are investigating about three dozen potential radiopharmaceuticals. In many cases, the decay scheme and calibration data are suspect. In order to facilitate licensing of these materials, NIST must provide the necessary calibration data and accompanying measurements prior to Food and Drug Administration approval. The Radioactivity Group will continue to collaborate with researchers in the early phases of radiopharmaceutical development to hopefully decrease the amount of time necessary to complete the approval process.

• National and International Intercomparisons in Radioactivity Measurements. Foreign and domestic National laboratories, in order to maintain the highest possible accuracy of radioactive measurements, must periodically intercompare methods and data related to radioactivity measurements. The Radioactivity Group will continue to participate in a number of national and international intercomparisons in environmental radioactivity metrology and nuclear medicine metrology. In environmental metrology we are working on measurements of ⁴⁰K, ⁹⁰Sr, ¹³⁷Cs, ²²⁶Ra, ²²⁸Ra, ²²⁸Th, ²³⁰Th, ²³²Th, ²³⁸Pu, and ^239-240Pu with 20 laboratories worldwide and, through our Radiochemistry Intercomparison Program, NRIP, we are working with eight domestic laboratories to meet the demand for traceability. In nuclear medicine metrology we are working on international intercomparisons of ¹³³Xe; recalibration of ³H for international intercomparisons; and submission of standards to the BIPM/SIR program. We continue with our efforts to assist other agencies and private industry to fulfill consensus standards which call for traceability testing programs linking the quality of operational measurements to the national standards.

• Low-level Radiochemistry Metrology. Many tens of thousands of low-level radiochemical measurements are made annually to support environmental remediation and occupational health programs. To provide infrastructure support for these programs, NIST will focus its efforts into three areas: 1) natural matrix standard reference materials; 2) radionuclide speciation in soils and sediments; and 3) measurement traceability testing. The natural matrix SRM project has certified actinides, and fission and activation radionuclides in soils, fresh-water lake and river sediments, human tissues, and ocean sediment, and is working on additional unique matrices: ashed bone, ocean shellfish, and Rocky Flats Soil-II. A standard protocol for the determination of radionuclide partitioning among geophysical/chemical soil and sediment phases for environmental remediation studies is being developed for future characterization of a new family of radionuclide SRMs. The NIST Radiochemistry Intercomparison Program (NRIP) has recently been initiated to provide traceability testing of laboratories engaged in low-level radiobioassay and environmental radionuclide monitoring and remediation.

Mission  |  Organization  |  Current Directions  |  Technical Highlights  |  Future Directions

TECHNICAL ACTIVITIES 1998 - Contents

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Online: April 1999