Guide To NIST, July 1998
ELECTRON PARAMAGNETIC RESONANCE FACILITY
NIST is leading a national and international effort in electron
paramagnetic resonance (EPR) dosimetry for measuring ionizing radiation.
Paramagnetic centers (molecules or atoms with unpaired electrons) are
produced by the action of radiation on materials. In the EPR
measurement, irradiated materials are placed in a magnetic field and
electron spin transitions are induced by an electromagnetic field of the
appropriate frequency (typically in the GHz range). EPR is used as a
non-destructive probe of the structure and concentration of paramagnetic
centers. The centers created by ionizing radiation are proportional to
the absorbed dose and provide a sensitive and versatile measurement
Capabilities: The EPR dosimetry facility is supported by three
state-of-the-art X-band EPR spectrometers capable of measuring radiation
effects on a wide range of materials from inorganic semiconductors to
biological tissues. The data acquisition system provides full computer
control of all spectrometer functions, including real-time spectral
display and rapid acquisition scan to analyze rapidly decaying signals.
The data acquisition system is interfaced with an advanced data analysis
station for data manipulation and is capable of simulating and
deconvoluting multi-component spectra.
Applications: EPR dosimetry is operable over many orders of magnitude
in absorbed dose (10-2 Gy to 105 Gy) and
impacts many facets of society and industry. Areas of application include:
The EPR facility also serves as a fully functional, materials
research facility for analyzing radiation effects on semiconductors,
optical fibers, functional polymers, and composites.
- Radiation accident dosimetry. Using biological tissues (bone, tooth
enamel) or inanimate materials (clothing), retrospective dose assessment and
mapping can be accomplished.
- Clinical radiology. Ionizing radiation doses administered in cancer therapy
can be measured for external beam therapy using dosimeters of crystalline
alanine (an amino acid) or validated for internally delivered bone-seeking
radiopharmaceuticals using bone biopsies.
- Industrial radiation processing. Routine and transfer dosimetry for
industrial radiation facilities can be performed using alanine dosimeters
(see figure below for a sample of the alinine dosimeters used throughout
the world) as well as post-irradiation monitoring of radiation-processed
meats, shellfish, and fruits using bone, shell, or seed.
|Availability: The EPR facility is available for
collaborative research by researchers from industry, academia, and other
government agencies under the supervision of NIST staff.
| Radiation Interactions and Dosimetry Group
| Ionizing Radiation Division |