Announcinq the New S&SEA System for ELECTROPHORESIS
£4-4 Power Control Supply Designed especially for electropho resis. Continuously variable voltage Ο to 500 V. Stable: Supplies constant volt age. (Ripple less than ± 0 . 1 % . Unit regulates to ± 0.1%.) Also can supply constant current over entire range. No v a r i a n c e in mA w i t h c h a n g e in load ± 90%. Double scale meter shows V and mA. Exclusive built-in timer with automatic shut-off. Four chambers — simultaneous operation (7 tests per c h a m b e r ) . Constant c u r r e n t control over entire electrophoretic range.
£4-7 Electrophoresis Chamber High impact polystyrene; water cooling jacket. Domed see-through lid. Safety interlock. Platinum electrodes run en tire chamber length. Polarity reversing switch. Simple, accurate method of attaching sample strip with flexible holders in integral part of chamber unit. This system offers features and advan tages never before found in electro phoresis equipment. The design is su perb—and the system was precision built by scientists expressly for scien tists. Our free brochure will give you a full description complete with addi tional pictures.
FREE BROCHURE MAIL COUPON TODAY! Carl Schleicher & Schuell Co. Keene, New Hampshire—Dept. AC-672 Please send free brochure on new S&S/EA System for Electrophoresis
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ANALYTICAL CHEMISTRY
REPORT FOR ANALYTICAL CHEMISTS An additional factor associated with 14 MeV activation for the analysis of samples of completely unknown composition (such as on the moon's surface) is the possibil ity of interferences from nuclides other t h a n those expected. The last column of Table I I includes several possible interferences which must be taken into account. I t has been found t h a t in practice interference from reaction (a) is negligible. This is also the case for reaction (b) if small samples are used; the possible interference with larger samples will be considered later. I n the case of the other interfering reactions, it is only possible to con sider the extent of the interference which would be present if the lunar concentrations of these elements were comparable to those estimated to be present in the earth's crust or in the chondritic meteorites, for which data are readily available. An estimation of the elemental con centration in the earth's crust and a knowledge of the relative specific activities of the isotopes produced from these elements by 14 MeV neutron activation (10) (given in Table I) indicates t h a t for fluorine, cobalt, and phosphorous the inter ference will be less t h a n 1%. In the case of manganese an interfer ence of approximately 5 % would be expected if the [Mn] : [Fe] ratio is comparable to t h a t on earth, and approximately 3 % if the ratio is comparable to t h a t in chondritic meteorites. An additional advantage of the 14 MeV neutron activation analysis technique, however, is t h a t should an element be present on the lunar surface in quantities greater t h a n those anticipated on the basis of its concentration on earth, there is the possibility t h a t it m a y be de termined using 14 MeV neutron activation. Several catalogues of the gamma ray spectra and yields
obtained by the 14 MeV neutron irradiation of a wide range of ele ments are available (10, 11, 14) to further substantiate this position. Although this study deals pri marily with the products of 14 MeV neutron activation it is also neces sary to consider effects resulting from thermal neutron activation. A number of possible thermal neu tron reactions are given in Table III. It has been found that with small (encapsulated) samples these reactions do not interfere to any great extent. In the case of mas sive rock samples, however, partic ularly if light elements such as hydrogen are present, the thermalizing effect may be quite significant and the possibility of thermal reac tion interference should be consid ered. In addition to producing interferences, thermal neutron acti vation also introduces the possibil ity of determining sodium and po tassium using a 14 MeV neutron generator surrounded with a suita ble neutron moderator since these elements possess high thermal neu tron cross sections. This would in crease from five to seven the num ber of geologically important ele ments which could be determined using a 14 MeV neutron source. Preliminary Investigations A series of preliminary experi ments was carried out to determine the feasibility of instrumentally analyzing small samples of rocks of known composition. The samples used for these analyses were gran ites and basalt. The elemental composition of these varied suffi ciently to demonstrate the utility of the neutron activation analysis technique. Approximately one gram of pul verized samples, contained in poly ethylene vials, were activated at the Texas A&M Activation Analy-
Table III. Nuclear Reactions With Thermal Neutrons Element Magnesium Sodium Potassium Aluminum Oxygen Silicon Iron
Nuclear Reactions 26
2
Mg(n, T ) 'Mg Na(n, T ) M Na «Κ(η, Ύ )«Κ 27 ΑΙ(η,Ύ)28ΑΙ 18 0(η, Ύ ) 1 9 0 30 Si(n,->031Si 58 Fe(n,-y)59Fe 23
Half Life
Decay G a m m a Energy (MeV)
9.5 m i n 15.0 hr 12.8 hr 2.3 m i n 29 sec 2.62 hr 45 days
0.84,1.01 1.37,2.75 1.52 1.78 0.20,1.36 1.27 1.10,1.29
