MeV neutron activation analysis

Although activation analysis with 14 MeV neutrons can also be used e.g. for the determination of nitrogen in metals (184), using the N(n,2n) N nuclear reaction, this method has been most useful for the determination of oxygen. 

Ep = 11.5, 9.3 E = 2.13, 4.67, 5.85, 6.79, 7.97 MeV) reactions. The interference of boron varies with the irradiation, cooling and counting times, with the effectiveness of the (3-shielding of the detector and with the setting of the single channel analyser. 

A brief description of neutron generators has been given in Chapter II, 

In the installation described by Hoste et al. (185) and Gijbels et al. (187) and in the one used by Beurton and Pi 11 on (188) a sample (standard) is irradiated simultaneously with a flux monitor, the flux monitor being situated behind the sample (standard) along the axis of the beam. The irradiation geometry is shown in Fig. II-2. A pneumatic transfer system allows to transfer the sample (standard) and the flux monitor to the irradiation positions. After the irradiation, the sample (standard) and the flux monitor are conveyed to 2 separate measuring stations (185) or sequentially to the same station (188). 

The installation described by Hoste et al. (185) and used e.g. by Vandecasteele et al. (186) consists of 2 identical measuring set-ups, one for the sample (standard) and one for the flux monitor. Each set-up consists of  

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II. Some Non-Destructive Activation Methods A. 14 MeV Neutron Activation Analysis... 

In 14 MeV neutron activation analysis the four principal nuclear reactions leading to the formation of indicator radionuclides are as follows ... 

It is obvious, therefore, that 14 MeV neutron activation analysis can not compete with thermal neutron activation analysis as a technique for trace element analysis. In simple matrices, however, the rapid and non-destructive nature of the technique recommends its use for routine analysis of large numbers of samples for elemental abundances at the one milligram level, or above. It is unfortunate that the element carbon can not be determined by this technique. The nuclear reaction 12C(n, 2n)1 C which would be of great analytical importance is endoergic to the extent of nearly 19 MeV. This reaction is obviously not energetically possible using the 14.7 MeV neutrons produced by the 2H(3H,w)4He reaction commonly employed in most neutron generators. 

The majority of the applications of 14 MeV neutron activation analysis involve the use of short-lived indicator radionuclides. Therefore, it is essential that the sample be returned quickly to the counting station following irradiation. Pneumatic sample transfer systems employing compressed nitrogen, or a vacuum are most commonly used 34-35>. An inexpensive system may be constructed from ordinary low density polyethylene tubing 18>. Irradiation, delay and counting times are ordinarily controlled by means of preset timing circuits. Completely automated control and transfer systems are available commercially. 

Fig. 5. Use of a 4096-channel analyzer in the multiscaler mode for the determination of oxygen via 14 MeV neutron activation analysis...

Cuypers, M., and /. Cuypers Gamma-Ray Spectra and Sensitivities for 14 MeV Neutron Activation Analysis. Activation Analysis Research Laboratory, Texas A and M University, College Station, Texas (1966). 

Determination of Pellet Weight and of the Copper/Oxygen Ratio for Special Primers (from Ref 6) 14 MeV Neutron Activation Analysis (Weight in Grains)... 

Other major shale constituents such as C, H, N, and S are determined by thermal decomposition and instrumental detection methods. Oxygen is determined by 14 MeV neutron activation analysis. Parr or Leco BTU bomb combustion and subsequent ion chromatographic determination is used for halogens, sulfate and nitrate. Ion chromatography is also suitable for anionic characterization of shale process waters. Two analytical procedures for oil shales should be used with caution. Kjeldahl nitrogen procedure has been found to give reproducible but considerably low results for certain oil... 

MeV neutron activation analysis has been widely employed in the direct determination of oxygen in rocks and of nitrogen in food grains and explosives. Charged-particle activation analysis is useful in the analysis of thin films or coatings on metals. 

B6di AC, Csikai J, Kirschner I (1994) Z Phys B95 181 Body Z, Csikai J (1987) Data for 14 MeV neutron activation analysis. Handbook on Nuclear Activation Data Technical Reports 273, International Atomic Energy Agency, Vienna, p 261... 

The results of the sandwich technique agree very well with those obtained by 14 MeV neutron activation analysis, and are furthermore characterized by a lower standard deviation. 

Systematic errors due to matrix effects in 14 MeV neutron activation analysis have been studied by several authors. These studies were relative to the determination of oxygen in steel (187)(190), in aluminium (196) and in any matrix (197)(198)(199)(200)(201)(186). The problem has been reviewed in some detail by Adams et al. (202), Nargolwalla and Przybylowicz (203) and by Cornells et al. (204). On condition that a suitable 0-shielding is used, so that no P-rays are detected, systematic errors may... 

Classical methods such as reducing fusion or 14 MeV neutron activation analysis are only able, under optimal circumstances, to carry out routine control analyses. In most cases this means "YES/NO-analyses" with a sensitivity of approximately 0.5 ig/g. Activation analysis with photons or charged particles allows to determine concentrations of 0.1 tg/g or below. These developments led... 

The analysis of oxygen in titanium, zirconium and their alloys was the subject of several round robins within BCR, which led to the certification of five reference materials (133)(278)(239). These reference materials (Table VII-29) are essentially based on 14 MeV neutron activation analysis and reducing fusion which both allow precisions and accuracies of 3 to 5 % in the range 500 to 1750 /ig/g. Basically the most interesting method at these higher concentration levels has been up to now 14 MeV neutron activation analysis. This method has really been used as a reference method in the BCR programme, and has substantially contributed to the development of reducing fusion to its present level of accuracy. 

The same conclusions are valid for zircaloy. A batch of this material (diameter 13 mm) has been recently analysed within BCR, with the results listed in Table VII-30. 14 MeV neutron activation analysis was not applied, due to the limited diameter of the material. 

From round robins organized by EURISOTOP in the early seventies, it appeared that the determination of oxygen at concentrations of 20 to 30 nq/g by reducing fusion, 14 MeV neutron activation analysis, charged particle and... 

Generally the oxygen content of tungsten is still lower than the one of molybdenum. This was confirmed in several round robins organized within BCR since 1972 (282). Table VII-34 summarizes the results obtained in the last one. It appears that more classical methods such as reducing fusion and 14 MeV neutron activation analysis are of limited use, especially due to surface contamination problems originating from cracks produced in sample shaping. 

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