NEWS
Analytical Applications of Radioisotopes Reported at Copenhagen C O P E N H A G E N , DENMARK.
E a r l y last
September the D a n e s played host, in t h e grand m a n n e r , t o a Conference on the Use of Radioisotopes in the Physical Sciences a n d I n d u s t r y sponsored b y t h e International Atomic E n e r g y Agency in cooperation with t h e United Nations Educational, Scientific a n d Cultural Organization ( U N E S C O ) . W e present our readers with some of t h e analytical developments which were reported, m a n y of which promise entirely new a p proaches t o t h e problems confronting t h e analyst. A full d a y was devoted t o radioisotopes in analytical chemistry, a n d another day to applications having indirect use in analysis. Kuykendall, Wainerdi, and associates, of A & M College of Texas, reported on an investigation of a u t o m a t e d activation analysis in which a reactor neutron source, an anticoincidence g a m m a spectrometer, a n d a n I B M 704 computer are being used as an integrated activation analysis system. T h e computer considers t h e characteristic half lives of the various isotopes in addition t o t h e conventional consideration of characteristic gamma spectra in activation analysis. This enables t h e computer to identify more component isotopes in a given sample with reduced prior chemical separations, all of which further enhances the speed and accuracy of analysis. As an example, d a t a from a sample containing four component elements is processed in a few minutes. Albert a n d Gaittet of t h e Centre d ' E t u d e s de Chimie Métallurgique, V i t r y / S e i n e , explained t h e systematic determination of impurities in metals of very high p u r i t y . Since t h e zone melting method provides metals with i m p u r i t y concentrations of 10~ e to 1CH*, very sensitive tests a r e required: B y neutron irradiation in fluxes of approximately 10 1 2 n e u t r o n s / s q . c m . / s e c . in the E L 2 reactor a t Saclay, t h e sensitivity of i m p u r i t y detection was a t least 0.1 p.p.m. (ΙΟ- 7 ) a n d frequently 0.001 p.p.m. (10~ 9 ). Some 45 elements can be determined in this way. W i t h some variations in technique, including d e u teron b o m b a r d m e n t a n d special chemi-
This article was prepared for ANALYTI CAL CHEMISTRY by Ralph Millier, contri buting editor on Instrumentation, based on a recent trip to Europe. 46 A
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ANALYTICAL CHEMISTRY
Members of royalty visited the Research Establishment of the Danish Atomic Energy Commission at Riso on the Roskilde Fjord, near Copenhagen. Shown left to right are the Queen of Thailand, Prof. Niels Bohr, Queen Ingrid and King Frederick IX of Denmark cal separations, some 60 elements arc accessible. Aitken, Emeleus, a n d Hall of t h e R e search L a b o r a t o r y for Archeology and the History of A r t a t Oxford e m p h a sized t h e peaceful a n d cultural a d v a n tages of nuclear techniques b y drawing convincing a n d interesting evidence of t r a d i n g connections and deliberate de basement of coinage b y t h e examina tion of some 500 Greek silver coins of the fifth century B.C. T h e gold and copper content was determined by measuring t h e intensity of t h e 0.411m.e.v. γ - r a y from A n 1 9 8 (2.69 d a y s ) , the 0.511-m.e.v. positron annihilation radiation from Cu ( i 4 (12.8 h o u r s ) , and the silver 0.884-m.e.v. γ - r a y from Agi 10m (253 d a y s ) , all after neutron ir radiation. Decay measurements were used as a check of identity. I t was em phasized t h a t t h e technique of using total gamma-activity decay curves b y themselves is insufficiently sensitive and t h a t for accurate work it is important to use a p p r o x i m a t e facsimile standards. Gibbons a n d Simpson of Harwell have determined sulfur in chromium and arsenic b y utilizing fast neutron activation analysis. Fast neutrons produce radiophosphorus b y a n (n.p) reaction in sulfur a n d their use makes it possible t o determine sulfur in m a terials of high t h e r m a l neutron absorp tion cross section. This is so because the absorption cross sections for fast
neutrons a r e , in general, much lower than those for slow neutrons, so t h a t self-shielding errors a r e considerably reduced. Interference due to t h e slow neutron (η,γ) reaction on natural phos phorus is eliminated b y a double ir radiation technique involving irradia tion in regions of differing slow/fast flux ratios. B. J . C a r r of Colorado Springs d e scribed small neutron sources operating on a pulsed basis a n d utilizing t h e T(r/,/i)He 4 reaction to produce 14m.e.v neutrons. I n these new sources, both t h e ion source a n d t h e accelerator are pulsed simultaneously to produce high source currents. A further a d v a n tage is that t h e small accelerators re quire no v a c u u m equipment for proper operation. These small neutron sources have been applied to numerous radio chemical problems, among them t h e routine determination of oxygen in beryllium oxide. B y counting between high intensity pulses t h e flux require ments for a fixed percentage accuracy are greatly reduced. T h e technique simplifies t h e analysis of short-half-life elements. Applications of t h e accelera tors to oil well logging were also dis cussed. W a y n e W . Meinke of t h e University of Michigan is well known to readers of ANALYTICAL C H E M I S T R Y
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odic reviews of nucleonics, which a r e so carefully documented a n d of inesti-
