216 COMMUNICATIONS [AnaZyst, Vol. 91 Communications Material for publication as a Communication must be on an urgent matter and be of obvious scientific importance. Manuscripts must not exceed 300 words; rapidity of publication precludes the use of diagrams, but tables or formulae may be included if the length of text is reduced appropriately. Communications should not be simple claims for priority. This facility for rapid publication is intended for brief descriptions of work that has made some progress and is likely to be valuable to workers faced with similar problems. A fuller original paper may be offered subsequently, if justified by later work. Manuscripts are not subjected to the usual examination by referees. In- clusion of a Communication is at the Editor’s discretion; a manuscript not accepted as a Communication may, if the author wishes, be submitted to the Editorial Committee as a possible Short Paper and subjected to the usual scrutiny by referees.THE DETERMINATION OF FLUORINE BY NEUTRON ACTIVATION WHEN rapid, repetitive analyses are required, physical methods are usually adopted, as these are readily available for a large number of elements, including most of the metals and many of the non-metals in the periodic table of elements. One notable exception is fluorine. For this we now suggest neutron activation as a means of easily and rapidly examining large numbers of mill products containing fluorite. TABLE I NEUTRON-INDUCED REACTIONS OF FLUORINE Product P Reaction Half-life Ey, MeV lgF (n,y) 20F 10 seconds 1-63 18F (n,2n) l*F* 112 minutes (0.51) l9F (n,p) lgO 29.4 seconds 0.2 and 1.37 18F (n,a) lSN 7.2 seconds 5 to 7 * Positron emitter.Four separate neutron-induced reactions (Table I) can be used to determine fluorine. The (n,y) reaction occurs with neutrons of thermal energies, for which ready access to a nuclear reactor is a t present required. The (n,2n) reaction produces fluorine-18, a positron emitter which, although it has been used to determine fluorine, may be subject to interference from other positron emitters. The long half-life is also a disadvantage. The (n,p) reaction, giving oxygen-19, is clearly a better choice where a fast-neutron generator is available. An expensive high-resolution multi-channel y-spectrometer is required to isolate the 0.2 or 1-37 MeV activity.The (n,a) reaction gives nitrogen-16, which can conveniently be measured with a single- channel spectrometer. Oxygen interferes by giving nitrogen-16 in a (n,p) reaction when a 14-MeV neutron generator is used for the irradiation. However, the threshold value of neutron energy for this latter reaction to occur is about 10 MeV, whilst that for the laF (n,a) 16N reaction is only about 2 MeV. The interference from oxygen can therefore be avoided by using neutrons of intermediate energy. To demonstrate this we have used an available thorium - beryllium radio- isotope source of 1.5 curies, giving approximately 2.8 x lo7 neutrons (of 3 to 5 MeV) per second. Other isotope sources, such as americium - beryllium, of even higher neutron output, would be preferred.Samples (75 g) of fluorite ores and concentrates were weighed into specially designed polythene containers, irradiated for 35 seconds and counted for 30 seconds. The analysing system comprised a thallium-activated sodium iodide crystal, photomultiplier and single-channel y-spectrometer set with a discriminator bias to count only the high-energy activity from nitrogen-16. The fluorine contents were calculated by using a sample of pure crystalline fluorite, ground to pass through This is not practical for industrial use.March, 19661 BOOK REVIEWS 217 a 70-mesh sieve, as the reference material. The results are shown in Table I1 in comparison with results obtained with a pyrohydrolysis technique. TABLE I1 SOME FLUORINE RESULTS Fluorine found Sample material by neutron activation, by pyrohydrolysis; O/ 0) i 0 Fluorite concentrate 1 . . . . 44-5 Fluorite concentrate 2 . . .. 46.2 Fluorite head ore . . .. 19.5 Fluorite flotation product 1 . . 15.8 Fluorite flotation product 2 . . 10.0 Fluorite tailing . . . . . . 5.2 /O 44.7 44.3 19.6 15.7 10.0 5-2 Further work on this system will include the examination of products from a commercial fluorite mill and a short field trial in a fluorite-producing area. Warren Spring Laboratory, Gunnel’s Wood Road, Stevenage, Herts. J. M. BAKES P. G. JEFFERY Received February 2nd, 1966