Neutron activation analysis using thermal or superthermal neutrons with the capture reaction (n, γ) is widely used to determine trace quantities of the elements in most biomedical materials, but it does not permit determining the content of the main elements (C, H, N, and O). An advantage of activation analysis using fast (14 MeV) neutrons lies in the possibility of determining nitrogen and oxygen according to the nuclear reactions (n, p) and (n, α) [1]. One of the most important applications of this method is determining protein in biomedical materials [2][3][4][5][6].A variant of using fast neutrons for determining the nitrogen content and through the nitrogen the protein content in certain kinds of grain and pulse crops has been developed [7]. To prevent errors associated with the instability of the fast-neutron flux and the irradiation geometry for samples and standard materials, the flux was monitored with an activation detector.Nitrogen in grain crops was determined with the reaction 14 N(n, 2n) 13 N, which product is a positron emitter with T 1/2 = 9.98 min, accompanied by annihilation γ-rays with energy E = 511 keV (100.62%).The mass m of nitrogen in the irradiated material was calculated from the induced activity A = 6.023·10 23 kmθM -1 σΦ[1 -exp (-λt irr )]exp (-λt cd ),where k is the detected radiation fraction; θ is the abundance of 14 N (99.635%); M is the molecular mass of nitrogen; σ is the reaction cross-section (0.0058 b); Φ is the neutron flux; λ is the decay constant; and t irr and t cd are the durations of irradiation and cool-down of the irradiated material, respectively. The activity with respect to the number of recorded counts is usually found from the relationwhere I is the number of recorded counts, ω is the detection efficiency for γ rays, and ε is a geometric factor. For the same irradiation and cool-down time for the sample and standard,where the indices refer to the sample (s) and the standard (st). For monitors (m) which are irradiated together with a sample and standard, I m.s /I m.st = (m m.s Φ m.s )/(m m.st Φ m.st ).
Nitrogen and phosphorus are the most important macronutrients among 17 nutrients required for optimal plant growth and reproduction. These elements are always present in cereal crops and play a determining role in the quality of plant products. For this reason, methods for determining their content simultaneously are of immediate interest in connection with monitoring grain quality.Fast neutron activation analysis is the most suitable method for determining nitrogen and phosphorus content in grain, pulse, and other agricultural crops [1,2]. This article presents the results of additional studies of a method for simultaneous determination of nitrogen and phosphorus in grain, pulse, hulled, and kernel crops using the NG-150 neutron generator at the Institute of Nuclear Physics of the Academy of Sciences of the Republic of Uzbekistan [2][3][4].The nuclear reaction 31 P(n, α) 28 Al was used to determine phosphorus content (Table 1). Aluminum is used as a monitor for checking the neutron flux [2]. The nuclear reaction 28 Si(n, p) 28 Al is an interfering reaction when determining phosphorus, and the reaction 29 Si(n, p) 29 Al is used to take account of this interfering effect on the method [5].The neutron activation method was developed to determine the nitrogen and phosphorus content in samples of certain grain, pulse, hulled, and kernel crops -wheat, millet, beans, buckwheat, dried apricots, apricots, pistachios, and peaches. Samples with mass 19-22 g were weighed and packed in 40 mm in diameter, 35 mm high cylindrical polyethylene containers. A polyethylene top tightly sealed a container. A 35-50 mg, 0.1 mm thick aluminum monitor was secured to the top for monitoring the fast-neutron flux. Some nitrogen and phosphorus compounds served as comparison samples. The test procedure for standard nitrogen is described in detail in [2,3]. The phosphorus content in the plants is 0.1-0.6% [6]. For this reason, the comparison samples were prepared from compounds in which the phosphorus mass falls approximately within these limits. The samples were irradiated in identical fast neutron fluxes. The time regimes of irradiation of the samples and measurement of their induced activity were also identical. Figure 1 displays the dependence of the variation of the 28 Al activity (in this case the number of counts recordedthe area of the photo-peak of the γ-ray 1778.8 keV line) versus the phosphorus mass in the comparison samples. This dependence is rectilinear within the limits of the chosen phosphorus concentration range, whence it follows that the method can be used to determine correctly the content of the element in biological materials. It is evident that for some samples the deviation of the data from rectilinearity is substantial (>30%). Such a deviation could be due to possible mass losses as a result of long-term storage of chemical compounds or sorption of water from air. For this reason, compounds which fell on the rectilinear sections of the plot were used as the comparison samples. Thus, the approach for developing a method...
The yield of a radionuclide is an important physical quantity, determining the number of radioactive atoms in the irradiated samples. For low and intermediate energy protons and deuterons, 7 Be forms from lithium and boron in the nuclear reactions 7 Li (p, n), 10 B (p, α), 11 B (p, αn), 6 Li (d, n), 7 Li (d, 2n), 10 B (d, αn), 11 B (d, α2n). For purposes of using a cyclotron in activation analysis, the 7 Be yield obtained by irradiating targets with charged particles accelerated in the U-150 cyclotron at the Institute of Nuclear Physics of the Academy of Sciences of the Republic of Uzbekistan was investigated [1][2][3][4][5]. The yield of 7 Be in the reactions Li(d, n) and Be(d, n) was also measured at deuteron energies 25 and 40 MeV [5].Another method for obtaining 7 Be consists in using recoil protons and deuterons which form in a nuclear reactor as a result of (n, p) or (n, d) and elastic or inelastic scattering of fast neutrons interacting with hydrogen nuclei [6].The present article presents experimental results from a study of 7 Be production by irradiating natural lithium and boron by recoil protons and deuterons in a nuclear reactor.The radionuclide yield is given by the expression where A is the activity of the radionuclide at t cool = 0, λ is the decay constant, m is the mass of lithium or boron in the irradiated sample, and t irr is the duration of irradiation. The specific activity of 7 Be referred to unit mass of a chemical element in the irradiated sample was estimated from the relation A = N γ exp (-λt cool /(mt meas ωI γ ),where N γ is the number of measured counts, t meas is the duration of a measurement, η is a geometric detection factor, ω is the attention efficiency, I γ is the intensity of the gamma radiation, and t cool is the cooling time. 7 Be possesses a half-life which is suitable for measurements T 1/2 = 53.61 days and emitted gamma ray energy E γ =
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