14 MeV neutron reactions producing gamma-ray emitting nuclides with half-lives below 3 seconds

Fast neutron activation analysis (FNAA) experiments were performed using a Cockroft-Walton neutron generator and a fast pneumatic rabbit system with a sample transport time of 120 ms. With this facility cyclic activations of¹⁸O, Zr, Ba and Pb leading to the short-lived reaction products¹⁵C,^90mZr,^136mBa and^207mPb were investigated. Derived from these measurements the analytical sensitivities of the involved reactions will be discussed.     

Cross-sections of 14 MeV neutron reactions on phosphorus and calcium

Cross-section values for 14.7 MeV neutrons are measured for the following reactions: $$\begin{gathered} ^{31} P(n,\alpha )^{28} Al,(132 \pm 10)mb;^{42} Ca(n,p)^{42} K,(173 \pm 19)mb; \hfill \\ ^{43} Ca(n,p)^{43} K,(111 \pm 9)mb;^{44} Ca(n,p)^{44} K,(42 \pm 2)mb; \hfill \\ ^{44} Ca(n,\alpha )^{41} Ar,(27 \pm 2)mb;^{48} Ca(n,2n)^{47} Ca,(616 \pm 54)mb. \hfill \\ \end{gathered}$$ An analysis of available cross-section data for these reactions is performed and preferred mean values for each reaction are given.     

14 MeV neutron activation analysis using short-lived products

Cyclic activation using pneumatic shuttling system and switch off and on the neutron source and detector are described in order to eliminate some uncertainties by the provision of more accurate timing, the measurement of the effective activating neutron flux and the correction for the detection system dead time.     

An automated neutron activation system for short-lived nuclides

The present paper describes an attempt to create a reliable and easy to use system for neutron activation with short-lived nuclides, suitable to be used with several irradiation and counting procedures in instrumental neutron activation analysis (INAA) at the Portuguese Research Reactor. This system can become very useful for a large community within LNETI, as well as other national institutes and universities, particularly for those involved in studies where the analysis of a large number of samples is required. Selenium determination has been performed, through the short-lived nuclide^77mSe, as an example of the reliability of the system.     

Epithermal neutron activation analysis of short-lived nuclides in geological material

The cadmium ratios of 52 short-lived nuclides have been measured. Epithermal neutron irradiation reduces the activities of²⁰F,²⁷Mg,²⁸Al,³⁸Cl,⁴⁹Ca,^46mSc,⁵¹Ti,⁵⁶Mn and⁶⁶Cu by factors of 20–30. The calculated improvements in detection limits for Ga, Br, Rb, Y, Mo, Rh, Pd, Ag, In, Sn, Sb, I, Ba, Nd, Sm, Gd, Dy, Er, Yb, Hf, W, Re, Pt, Au, Th and U are in the range 1–6. Hafnium was measured in USGS rocks: AGV-1 (4.9 μg g⁻¹), G-2 (7.5 μg g⁻¹) and GSP-1 (14.7 μg g⁻¹) and IAEA standards: SOIL-5 (6.3 μg g⁻¹ and SL-1 (4.6 μg g⁻¹). CCRMP reference concentrates PTC and PTM were analysed for rhodium (1.1 and 0.75 μg g⁻¹, respectively) and silver (69 and 5.8 μg g⁻¹, respectively).     

Cross-sections of (n,p) reaction at a neutron energy of 14–15 MeV

The (n,p) reaction cross-sections induced by 14–15 MeV neutrons have been analyzed on the basis of available data taken from the literature, using the multiple regression technique. An empirical formula describing the dependence of (n,p) reaction cross-sections on 5 parameters: neutron (N) and proton (Z) number, asymmetry factor ((N–Z)/A) where A=N+Z, neutron and proton binding energies (B_n, B_p) has been found. Its validity is checked and discussed.     

Counting statistics of short-lived nuclides

The well-known Poisson formula for counting statistics is generalized to the situation where the radioactive source studied, with mean lifetime 1/λ, decays apprecialy during the total time of observation T. A general expression is given for the modified probability_λP(k) of observing k events in a short time interval t_o=T/n, where the results are averaged over the period of observation T. This corresponds to the experimental distribution which is obtained by pooling together all the n≫1 individual measurements of k made with a given source. The deviation from the simple Poisson law, which neglects decay, depends essentially on the quantity ν=λ·T. If ν is of the order of unity, the deformation is strong enough that it can serve as the basis of a new method for measuring the half-life of the nuclide involved. Invited paper.     

Precision in 14 MeV neutron activation analysis

The errors of analysis due to the different parameters involved in 14 MeV neutron activation analysis method are studied. Formulae to calculate these erros have been developed when possible. Otherwise they have been evaluated for special experimental situations. Special cases where some parameters become critical, as far as precision is concerned, have been mentioned.     

Spatial neutron flux distributions around A 14 MeV neutron generator

The neutron flux distribution in the vicinity of 30, 20 and 10 mm diameter targets is measured by irradiating concentric ring-type iron monitors at different distances from the target and counting the induced⁵⁶Mn activity. Considering the many uncertainties, satisfactory agreement was found between theory and experiment. Aspirant of the N.F.W.O.     

14 MeV neutron activation analysis of gold jewellery

Samples of nominal 18 carat and 21 carat gold jewelleries from the local market were non-destructively bulk analyzed using neutron activation analysis. Neutrons of 14 MeV energy were used with a fast pneumatic sample transfer system. The actual gold contents, as well as the composition of the base metals in these samples were determined. The fast neutron activation was found to be an efficient, quick and accurate method of characterizing the precious metal objects routinely in bulk, with a large sample throughput. The results demonstrate the commercial availability of the technique for non-destructive bulk analysis of precious metal objects.     

Fast-neutron activation analysis with short-lived nuclides

At the GKSS Research Center Geesthacht, a new 14 MeV activation facility—a 5·10¹² n/s neutron generator combined with a fast rabbit system (KORONA)—is being installed. Homogeneous neutron flux at a level of 5·10¹⁰ n·cm⁻²·s⁻¹ and sample transfer times of 140 ms to a 16m distant detector station are characteristic features of the facility described in the paper. With special consideration of short-lived nuclides and including cyclic activation, the analytical prospects with the intense neutron source are discussed, and sensitivities for 78 elements are presented.     

Geometry errors in 14 MeV neutron activation analysis

The effects of inaccurate sample sizes and sample positioning on 14 MeV neutron activation analysis results are estimated for 30, 20 and 10 mm diameter targets. It appears that axial positioning is the most critical parameter and that using a larger tritium target will yield an overall improvement of the reproducibility. Aspirant of the N.F.W.O.     

Activation cross-section measurements for producing short-lived nuclei with 14 MeV neutrons—Ge, Pd, Yb

Activation cross sections for ⁷⁰Ge(n,p)⁷⁰Ga, ⁷⁴Ge(n,p)⁷⁴Ga, ¹⁰⁸Pd(n,p)¹⁰⁸Rh, ¹¹⁰Pd(n,α)¹⁰⁷Ru, and ¹⁷⁴Yb(n,p)¹⁷⁴Tm reactions producing short-lived nuclei with half-lives of several minutes were measured in the energy between 13.5 and 14.8 MeV using activation technique in this work. All cross-section values were relatively obtained on the basis of the standard cross section of ⁹³Nb(n,2n)^92mNb or ²⁷Al(n,α)²⁴Na, and the neutron energies were measured by the method of cross-sectional ratios for ⁹⁰Zr(n,2n)^89m+gZr to ⁹³Nb(n,2n)^92mNb reactions. Careful attention on corrections was paid to neutron irradiation and induced activities measurement. The measured results were discussed and compared with the previous works.     

An automatic NAA analyzer for short-lived nuclides

An automatic activation analyzer with sample changer, pneumatic transfer system and fast pulse counting with real time pulse pile-up and dead time compensation is described. Transfer times between 80 and 300 ms from irradiation position to measurement station can be obtained. Counting losses are corrected within 10% up to total count rates of 120 kc/s.     

Fast radiochemical separations for neutron-deficient short-lived nuclides

We review both simple and exotic radiochemical techniques used for the separation, purification, and analysis of neutron-deficient short-lived nuclides. These range from classical wet-chemical methods to automated and instrumental techniques. We give special attention to chemical adjuncts of the He-jet recoil-transport technique and to high-resolution mass spectrometry. We also review recent developments in biological applications, including¹³N production and use.     

Determination of ko-factors of short-lived nuclides (T≧1 min) by thermal neutron activation technique

The k_o,Au-factors for 11 short-lived nuclides with T less than 1 min have been determined by irradiating the samples with thermal neutrons in the reactor thermal column using the pneumatic transfer system. The results obtained experimentally, without any error induced by the fast component of the reactor neutron spectrum and uncertainties of nuclear related characteristics, are in good agreement with the calculated data.     

Calculated screening effect in 14 MeV neutron activation analysis

The screening effect produced by a sample upon a standard located behind it is calculated. Curves for the secreening effect as a function of the sample material and of the sample depth are given.     

Optimum sample shape for 14 MeV neutron activation analysis

Based on the criteria of the maximum induced activity, the problem of the optimum sample shape was analyzed for a given volume of sample. Its shape was assumed to be cylindrical and the optimum values for the height-to-diameter ratio (presented in the included tables) were calculated under various circumstances. Coaxial and perpendicular sample—target irradiation geometries were considered.     

Measurements of short-lived cosmogenic nuclides in rain samples

Summary Extremely low activity levels of cosmic ray induced nuclides have been measured in freshly precipitated rainwater by quick chemical separation coupled with ultra low background gamma-spectrometry. The nuclides detected were ³⁸S (T_1/2 = 2.83 h)-³⁸Cl (37.2 m), ³⁹Cl (55.6 m), ²⁴Na (14.96 h), ²⁸Mg (20.9 h), ⁷Be (53.3 d) and ²²Na (2.602 y). The number of atoms in rain water were evaluated to be ranging from 400-1900 l^-1 for ³⁹Cl (n = 6, mean: 1200), 30-1500 l^-1 for ²⁴Na (n = 16, mean: 520), 80-600 l^-1 for ²⁸Mg (n = 13, mean: 260), 1 ^. 10⁶-4 ^. 10⁷ l^-1 for 7Be (n = 16, mean: 7 ^. 10⁶) and 2 ^. 10³-1 ^. 10⁵ l^-1 for ²²Na (n = 9, mean: 2 ^. 10⁴). Measurements of activity levels and activity ratios of short-lived cosmic-ray induced short-lived nuclides will open new method to understand atmospheric processes occurred at the altitude of rain cloud.     

14.8 MeV neutron activation cross-sections for (n,p) and (n, α) reactions of some rare earth nuclides

The activation cross-sections for sixteen (n, p) and (n, α) reactions on rare earth nuclides were measured at 14.8 MeV neutron energy. A Ge(Li) detector was used for the radioactivity measurements. The measured cross-sections are compared with the semi-empirical predictions of LEVKOVSKII³ and BAYHURST and PRESTWOOD.¹⁶