Resonance Neutron Radiography Measures Isotope Concentrations
Monitoring Toxic Substances ACS Symposium Series No. 94 Dennis Schuetzle, Editor Ford Motor Company Based on a symposium sponsored by the Division of Industrial and En gineering Chemistry of the Amer ican Chemical Society. The recently legislated Toxic Sub stances Control Act (January 1, 1977) has emphasized the need for evaluating the effect of chemicals on the environment. This relevant and timely volume de scribes the most widely recognized state-of-the-art techniques for the rapid biological screening of chem ical substances for potential mutagenicity and carcinogenicity, and surveys present instrumental analytical techniques for monitoring toxic substances.
tope distribution. Total amounts of different isotopes in the sample can also be determined. The fact that spatial isotope distri butions can be obtained is a big ad vantage of RNR. In one established technique, for example, nuclear fuel rods are dissolved in a tank of highly concentrated nitric acid. The resulting solution is then analyzed to determine the composition of the rods. The pro cedure obviously gives no spatial in formation about the distribution of isotopes in the rods, as RNR would do, and the RNR technique also would preserve the physical integrity of the sample. RNR is even capable of deter mining radial isotope distributions— the amount of each isotope at differ ent radial distances from the center axis of a cylindrical fuel rod. Fuel rods represent an RNR application of great importance, but the technique will, of course, be applicable to many other types of sample. The NBS research team wants to prove that expensive high-energy ac celerators are not requisite to the use of the RNR technique. If they can show that low-energy accelerators, in the 15 MeV range, are up to the task, then the cost of the instrumentation needed for a complete set-up would be in the same range as the price of a good mass spectrometer. Stuart A. Borman
Although a number of methods for the determination of isotopes in nucle ar power fuel rods are presently avail able, a new technique under develop ment at the National Bureau of Stan dards (NBS) may prove to be easier and more versatile. And even though use of the technique is now restricted to laboratories that happen to have a high-energy linear accelerator on hand, research is planned that may prove less expensive, low-energy accel erators to be perfectly adequate for the task. NBS researchers Roald A. Schrack, James W. Behrens, and Charles D. Bowman reported on the new tech nique, called resonance neutron radi ography (RNR), in the May/June 1980 issue of Dimensions, an NBS maga zine. The technique is based on the se lective absorption and scattering of neutrons by nuclei of different iso topes—each isotope has a different ability to either capture or deflect neutrons. In RNR, neutrons generated by a linear accelerator are collimated down to a thin fan-shaped beam. The sample to be measured is moved through this beam on a precision drive tray while the neutrons that pass through the sample are determined with a position-sensitive neutron de tector. Information from the detector is collected by a computer, which then produces a picture of the sample's iso
CONTENTS Environmental Carcinogens/Mutagens · Human Lymphoblasts · Multimedia Discharges · Volatile Organic Compounds · Industrial Wastewater Toxins · Adsor bent Accumulation of Pollutants for Bioassays · Trace Metal Monitoring by Atomic Absorption Spectrometry · Determination by Inductively Coupled Plasma-Atomic Emission Spectroscopy · Surface Microanalytical Techniques · Fourier Transform Infrared Analysis · Opto-Acoustic Spectroscopy · Mass Spectrometric Analysis of Air Pollutants · Semivolatile Brominated Organics · Ion Chromatographic Analysis · W-Nitroso Compounds · Use of the NIH-EPA Chemical Informa tion System
Pulsed-Neutron Source
Neutron Collimator
Pb y -Flash Shield and Cd Overflap Filter
L
Boron Loaded Polyethylene Shield
Neutron ^ Collimator
289 pages (1979) Clothbound $26.50 LC 78-27490 ISBN 0-8412-0480-2
Precision Drive Tray
SIS/American Chemical Society 1155 16th St., N.W./Wash., D.C. 20036 Please send _ Toxic Substances
Linear PSPC
_ copies of S S 94 Monitoring (ACI 0480-2) at $26.50 per copy.
G Check enclosed for $ Π Bill me. Postpaid in U.S. and Canada plus 75? elsewhere. California residents please add 6% state use tax. Name
Imaging System
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ZiD
Data Acquisition System and Data Processor
(TOF)
Schematic diagram of a resonance neutron radiography system. Neutrons are generated in a source, and are then collimated into a fan-shaped beam. The sample is passed through the beam to produce an image in a computer-controlled system. PSPC = position-sensitive proportional counter
282 A · ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
