INSTRUMENTATION by Ralph H.
Radioisotope techniques for chemistry students and use of x-ray in analytical chemistry described in recently published books
UCLEAR-CHICAGO
CORP.
has
an-
N nounced the availability of a new
184-page manual, "Radioisotope Experiments for the Chemistry Curriculum." The manual, prepared under contract for the Atomic Energy Commission's Office of Isotope Development, is designed to introduce the chemistry student to radioisotope techniques and to demonstrate their potential contribution to his future work. The manual reflects the growing routine use of radioisotopes as valuable tools in chemistry and biological laboratories, hospitals, industrial laboratories, and scientific research centers. Faculty members of Northwestern University, Illinois Institute of Technology, and Pennsylvania State University participated in developing the experiments. Testing was carried out under actual teaching conditions at Pennsylvania State University, Emory University, Loyola Unwersity, St. Procopius College, Monmouth College, and Illinois Wesleyan University. Each of the 23 chemistry experiments is designed to be easily worked into established courses in introductory chemistry, qualitative analysis, quantitative analysis, organic chemistry, physical chemistry, biochemistry, or instrumental analysis. All experiments may be done without special AEC license, with an inexpensive package of 13 radioactive compounds. Only basic nuclear detection equipment—a scaler, timer, Geiger tube, and mount—is required to conduct the experiments. A sample copy of the manual, together with a set of instructor notes, is available to college and university teachers at no charge upon request to Nuclear-Chicago Corp. 359 East Howard Ave., Des Plaines, 111. Multiple copies for student use may be purchased through Nuclear-Chicago or through the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C , at $2.00 per copy for the experimental manual and $1.00 per copy for the instructor notes. Ten general introductory experiments acquaint the student with the principles and techniques of radioactivity: the characteristics of GeigerMuller counters, statistics of counting, determination of half lives, specific ionization of alpha particles in air, ab-
sorption of beta particles, absorption of γ-rays, ion exchange separation of cobalt and nickel, analysis of complex radioactive decay curve, backscattering of beta particles, and calibration of an end-window Geiger-Miiller counter. Of the remaining 23 chemistry ex periments, at least seven are of direct interest to the analytical chemist : the determination of atomic weights, de termination of a solubility product, separation of ions by liquid-liquid ex traction, coprecipitation of calcium and permanganate with barium sulfate, de termination of phosphate in a phos phate rock by an isotopic yield method, determination of the formation con stant of a complex ion, and the deter mination of calcium. This manual is very well written and contains an extraordinary amount of up-to-date information in its 184 pages. We object to the statement that ''satu ration backscattering (betas) factors increase monotonically with increasing atomic number of the scattering ma terial," when two references are given which show that we proved that this is not so. These well chosen experiments would seem to be absolutely essential in the training of a modern chemist and we hope they will receive the attention which they deserve. Nuclear-Chicago is to be congratulated for its selection of experts to devise and test these ex periments. The venture is but one of several hundred which Dr. Paul Aebersold, Director of the Office of Isotope Development, has launched to en courage the more widespread scientific and technical uses of radioisotopes. X-Ray Use in Analytical Chemistry
We have read with great interest and profit "X-Ray Absorption and Emission in Analytical Chemistrv" bv H. A. Liebhafsky, H. G. Pfeiffer/E. H. Winslow, and P. D. Zemany, General Electric Research Laboratory (John Wiley and Sons, New York-London, 1960). In the first lines of the preface we read, Like it or not, the chemistry is going out of analytical chemistry. For a long time indeed, Chaucer with his
Müller
The lyf so short, the craft so long to lerne, Th assay so hard, so sharp the conquering The Parlement of Foules proved a better prophet than he knew. But, nowadays, physics and electronics are in part being fused with analytical chemistry to make the assay easier and the conquering less painful. These are not the words of an ex uberant physicist, ignorant of the com plexities of analytical chemistry, but of the senior author, a well known ana lytical chemist. For many years he and his associates have prepared the biennial reviews in ANALYTICAL C H E M
ISTRY on x-ray absorption and emission. Although there are many branches of x-ray science and technology, the authors have written this book for the analytical chemist who wants to use x-ray methods and to understand them. It is fortunate that the entire sub ject, from the analytical point of view, has been put in systematic and logical order in this monograph. Ten princi pal chapters deal with (1) origin and properties of x-rays, (2) the measure ment of x-ray intensity, x-ray detectors, (3) absorptiometry with polychromatic beams, (4) x-ray spectra and x-ray optics, (5) absorptiometry with mono chromatic beams, (6) the determina tion of film thickness, (7) x-ray emis sion spectrography, (8) x-ray emission spectrography, general, (9) notes on equipment, representative spectro graphs, and (10) reliability of x-ray emission spectrography. Chapter 11, special topics, discusses absorption and emission of 7-rays, point sources of xrays, the x-ray microscope, histochemical analysis, and mineral elements in biological tissue sections. There are seven sections in the appendix with ex tensive tables of absorption edges, line intensities, wave length of Κ lines, and 2 β values for the eight crystals ordi narily used in spectrometers. The authors have explained that references later than August 1957 could not be included. Considerable atten tion is devoted to 7-ray absorptiom etry and to absorptiometry with the Mn x-ray emitted by the radioisotope Fe 55 as a result of Κ capture. This VOL. 33, NO. 1, JANUARY 1961 ·
93 A
Cary®
ΝO.2
INSTRUMENTATION Evaluating Spectrophotometer Performance
DATA S E R I E S
WAVELENGTH
accuracy and reproducibility:
The precision with which the indicated wavelength corresponds to the true wavelength of dispersed radiation (accuracy) and repeats this indication (reproducibility).
FIGURE 1
FIGURE 2
Rut Roentgen's achievements transcended mere discovery. He studied the properties of the new rays so well that he laid the foundations not only for important methods of x-ray detection (fluorescence of a phosphor darkening of a photographic plate, ionization of a gas) and for radiography, but for the application of x-ray absorption to analytical chemistry as well.
Cary Model 14 records spectra ο
accurate to 4A, reproducible O
u
to 0.5A over its 28,000 A range
High wavelength accuracy assures recording of absorption peaks at their t r u e wavelength. This is essential for differentiation of similar samples or identification of unknowns. It is equally important for quantitative measurements on mixtures where overlapping bands may distort band contours. The high wavelength accuracy of t h e Cary Model 14 is shown in the spectrum of mercury emission lines which appear at 3906.4, 4046.6, and 4077.8 angstroms. As shown in F i g u r e 1, these a r e recorded to within 2A absolute or better. Since sample absorbance is a function of wavelength, high ivavelength reproducibility is essential to insure reliable quantitative results. The excellent reproducibility of the Cary Model 14 is illustrated in both F i g u r e s 1 and 2 which show three superimposed records (with t h e baselines a r b i t r a r i l y shifted after each r e c o r d ) . The two peaks (5790.7 A and 5769.6Â) shown in F i g u r e 2 were recorded on a greatly expanded wavelength scale in order to observe any small error. ( I t is interesting to note t h a t t h e scale expansion used would require a chart over 300 feet long to record the entire wavelength range of the Model 14). The maximum deviation between the three records is only about 0.35A. Wavelength accuracy and reproducibility are just two of several import a n t criteria on which spectrophotometer performance should be based. Others include : Resolution ; photometric accuracy and reproducibility ; s t r a y light. Because the Cary Model 14 excels in each of these performance criteria, it is regarded as t h e finest instrument of its kind. A descriptive brochure is yours for t h e asking. Write for data file A19-11.
Cary®
INSTRUMENTS
source has now replaced conventional x-ray techniques in the precise determination of sulfur in petroleum. For good reason it was not possible therefore to describe extensive work which has been done in the last few years on x-rays excited by beta-emitting radioisotopes. Such cheap sources are eminently suited to absorptiometric analysis. The authors, of course, are well acquainted with these techniques. This excellent book is both scholarly and eminently practical. It is also very readable with interesting and pertinent quotations. There are times when one feels the authors have stopped writing, and started conversing with the reader, making a difficult point clear by apt analogy or comparison. Their case for the analytical uses of x-rays is clearly stated, wherein it excels and saves time and money, or where its answers are tentative and require additional information. Their scholarship is attested by some of the quotations. It has bored us for years to hear people describe how Rôntgen happened to stumble on the disco\'ery of x-rays. Of course it was a happy accident that the barium platinocyanide screen was lying nearby and obligingly lit up. As Liebhafsky and his colleagues put it:
Many years ago we had an unforgettable example before us of scientific integrity, dignity, and honesty. The late Arthur Willis Goodspeed of the University of Pennsylvania was our physics professor in an advanced course. He showed us x-ray pictures of very definite clinical value which he had taken in his laboratory with an old Crookes tube some months before Rôntgen's announcement. Sensing our pride in our professor, he squelched it with the stern remark, "Although these things were of enormous interest to our surgeons, we were bewildered by these strange radiations and were trying to determine their nature. When Rôntgen's paper appeared, the nature of these rays was crystal clear. So thorough were his studies that all the principal properties and characteristics of the phenomenon were established." Smiling wryly, he added, "Of course it would have been amusing if these penetrating radiations had been destined to be called Goodspeed rays."
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