Determination of k 0-factors and validation of k 0-INAA for short-lived nuclides

For standardization of k ₀-based instrumental neutron activation analysis, k ₀-factors for short-lived nuclides (half-lives—11 s to 37 min) of elements F, Se, Sc, Al, V, Ti, Cu, Ca, Mg, I, and Cl with respect to gold (¹⁹⁷Au) were determined using pneumatic carrier facility (PCF) at CIRUS reactor of BARC, Mumbai. Characterization of PCF was carried out by cadmium-ratio method using Au and Zr. The experimental k ₀-factors of the isotopes were found to be in good agreement with the recommended k ₀-factors in most of the cases, as evident from the values of % error and U-score at 95% confidence level. The method was validated by determining concentrations of elements through their short-lived nuclides in one type of the synthetic multielement standards (SMELS-I) obtained from SCK-CEN, Belgium. The method was also applied for determination of concentrations of some of the elements in two reference materials of IAEA, SL-3, and SL-1.     

In-beam determination of k0 factors for short-lived nuclides

The prompt -activation analysis (PGAA) facility at Budapest Research Reactor offers a unique possibility to perform in-beam measurements. Several k ₀ factors for decay -lines of short-lived nuclides have been determined accurately by means of in-beam activation. The present values compare well with literature data. New k ₀ factors are proposed for ^24mNa and ^60mCo.     

Determination of Q 0 and k 0 factors for 75Se

Since the initial determination of the Q ₀ and k ₀ factors for ⁷⁵Se systematic errors in Se determination in various matrices have been noticed by several users of the k ₀ method. A number of publications have been made on this subject, resulting in different k ₀ and Q ₀ values for this radio-isotope. This work consists of a re-determination of Q ₀ and k ₀ values for ⁷⁵Se using the bare and Cd-ratio methods making use of three different irradiation channels from the BR1 reactor. For this re-determination three different kinds of standards were used: a pure Se powder standard, an ICP standard solution and pure Se shots. Results were compared with previously published literary data. Differences in k ₀ with the official published data ranging from 3.5 to 12 % were observed and potential reasons for this discrepancy are discussed. A good consistency with recent work was found. The impact on recent certification and intercomparison exercises demonstrates the effectiveness of the newly proposed values.     

Neutron spectrum correction of k0-factors for k0-based neutron-induced prompt gamma-ray analysis

Neutron spectrum correction has been attempted for the k₀-factors of the non-1/v elements which are affected neutron spectrum difference. Effective g-factors and Westcott g-factors, which are neutron spectrum correction factors obtained from an actual neutron spectrum and the Maxwellian distribution, respectively, for the non-1/v elements were calculated using their neutron cross section data of JENDEL-3.2. The neutron spectrum correction was made for the measured k₀-factors of the non-1/v elements such as Cd, Sm and Gd with the cold and thermal guided neutron beams of JRR-3M using the g-factors. The corrected k₀-factors between the cold and thermal neutron beams using both g-factors for both neutron beams agreed well for Cd. However, 9 to 44% deviations have been found for Sm and Gd, respectively.     

Determination and evaluation of fission k0-factors for correctionof the 235U(n,f) interference in k0-NAA

In order to provide a tailored solution for the correction of the ²³⁵U interference in k₀-NAA, fission k₀-factors for the analytically relevant radionuclides/gamma-lines (versus gold as the comparator), are experimentally determined in four channels of the Gent THETIS reactor. A comparison is made with former data from the literature. The new evaluated results are to be implemented in the forthcoming upgrade of the DSMKayzero software package for k₀-NAA.     

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.     

Measurement of k 0 and Q 0 values for iridium isotopes

There is an increasing demand for the chemical analysis of new materials containing iridium. The k ₀-method is an excellent method for the analysis of new materials but measured k ₀-values and Q ₀-values have been lacking for ¹⁹¹Ir(n,γ)¹⁹²Ir, which offers greater sensitivity than ¹⁹³Ir(n,γ)¹⁹⁴Ir. In this work, the Q ₀-values were determined for the two reactions by the two-channel method, using five irradiation channels in two research reactors in Belgium and Canada. These measured Q ₀-values enabled the first determination of the resonance neutron Cd transmission factors for these two capture reactions, confirming suspicions that they are much less than unity. At the two laboratories, k ₀-values were measured for ¹⁹²Ir and ¹⁹⁴Ir and there was good agreement between the two laboratories. The k ₀-values for ¹⁹²Ir are original measurements, while those for ¹⁹⁴Ir are in good agreement with previously published values.     

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.     

The k0 and Q0 Values for the Zr-Isotopes: A Re-Investigation

The activities associated with the nuclear fuel cycle include uranium mining, enrichment and fuel fabrication, reprocessing and recycling of the spent fuel and management of nuclear waste. In this paper the nuclear fuel cycle strategies followed and envisages of the future directions are discussed.     

Cross-sections of 14 MeV neutron reactions producing short-lived nuclides

The cross-sections for the production of the short-lived nuclides:^26mAl,^197mAu,^136mBa,^79mBr,^139mCe,³⁴Cl,^167mEr,^114m3In,^114m2In,^38mK,^38mCl,²⁶Na,²⁰F,¹⁹²Re,^207mPb,^203mPb,^46mSc,^183mW,^90mZr obtained from (n, 2n), (n, n′), (n, alpha), (n,p) reactions using 14 MeV neutrons, were evaluated by the activation method. The experimental results of this work were compared with those obtained by other authors.     

Trends in instrumentation for activation analysis of short-lived nuclides

This paper reports on the last year's two major activities of our nuclear instrumentation group it the field of high rate and high resolution gamma spectrometry which were mainly devoted to the needs of activation analysis of short-lived nuclides. The first of the projects was the completion of a state-of-the-art spectrometry system for very high counting rates which has been installed at the fast inrradiation and transport facility of the TRIGA reactor and now is the main instrument for the short-lived work of our radiochemistry group. Based on a laboratory-designed gated integrator pulse processing system and equipped with an Ortec Gamma-X detector of 20% relative efficiency with cooled FET and transistor reset preamplifier, it exhibits a basic resolution of 2.3 keV at 1332 keV which at a counting rate of 1.1 million cps of⁶⁰Co degrades to 3.4 keV. An essential feature of the system is a novel quantitative pileup rejector of the pulse counting type which has been specially designed for high rejection efficiency and at the same time, for the reliable exemption of valid events, and thus is a necessary prerequisite for quantitative real-time correction of counting losses by means of the Virtual Pulse Generator method. The second project included the successful implementation of the novel Preloaded Filter Technique (applied for patent), a new method for high resolution and high throughput processing of nuclear detector signals which, in contrast to conventional techniques, does not rely on a fixed pulse processing time per event which up to now was the main reason for pulse pileup and limited throughput, but, at the latest, terminates the filtering process of an individual event at the instant of arrival of the next event which results in optimized throughput and, at the same time, in a self-adapting, counting rate dependent shaping time. To that aim, the delta-noise filter of the system must be preloaded with the best estimate of the final result of the filtering process which is simply the unfiltered signal amplitude, to make sure that at the instant of termination of the filtering process the output of the filter deviates from the final value not more than by the decaying noise amplitude. Complemented by counting rate dependent step-noise filtering, this technique made possible the creation of a spectrometry system for all purposes which at low to medium counting rates is comparable to the best of the semi-Gaussian amplifiers and at high counting rates to the gated integrator. An experimental implementation of the Preloaded Filter combined with an Ortec Gamma-X detector of 15% relative efficiency resulted in a basic resolution of 1.9 keV at 1332 keV at a counting rate of 5000 cps slowly degrading to 3.2 keV at a counting rate of 650 000 cps of⁶⁰Co.     

The recommended k0-factors for neutron-induced prompt gamma-ray analysis and the prompt gamma-ray emission probabilities

Recommended k ₀-factors for gamma-lines of 24 elements useful for neutron-induced prompt gamma-ray analysis (PGA) and which are not influenced by neutron spectrum differences were obtained from the k ₀-factors measured with the cold and thermal neutron guided beams of JRR-3M, by statistical calculation. The prompt gamma-ray emission probabilities were derived from the recommended k ₀-factors using atomic weight, isotopic abundance and thermal neutron capture cross section all related to the k ₀-factors, for which one can obtain accurate data. The derived gamma-ray emission probabilities for the light elements (H to Ca) agreed well within ±10% with those of the ENSDF values, which reflect recent data while the agreement for heavy elements (Ti to Pb) was ±40% with those of the ENSDF, which are still composed of old data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Use of k0 concept to corrections for interferences from fissionable nuclides in reactor NAA

A neutron spectrum-independent compound nuclear constant, Ik_o, is proposed for fission interference corrections in reactor NAA by parametric method. Ik₀ values for eight major fission interference cases, belonging to three different types, have been determined in six irradiation positions (with _th/ _e 13,7–134) of three research reactors in our Institute. The general agreement among experimental Ik₀ 's from different irradiation positions and between experimental and calculated Ik₀ values for the same interference case verifies the validity of the method. Calculated Ik₀ values for all the possible fission interferences are tabulated. Interferences from²³⁸U(n,) and²³²Th(n,) reactions and reactor fast neutron induced²³⁸U(n, f) and²³²Th(n, f) reactions are discussed.     

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).     

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.     

Determination of 237Np by k0 RNAA

The determination of very low concentrations of ²³⁷Np is of key-interest for environmental monitoring. The application of the k ₀-method to neutron activation analysis was not possible so far, since the k ₀-parameters were lacking. The parameters required for the k ₀-method are: the effective resonance energy r, the resonance integral (1/E) to 2200 m^.s^-1 cross section ratio Q ₀, and the k ₀ values. In this work, the experimental values of these parameters were determined by using two nuclear reactors with very different flux characteristics.     

Is the k0 method accurate for elements with high Q0 values?

With a SLOWPOKE reactor, activation by epithermal neutrons is more important than for most other reactors. It was therefore undertaken to verify the accuracy of the k ₀ method for all elements with high Q ₀ values. Accurate standards of 40 elements were prepared and irradiated in the inner and outer irradiation sites of the Ecole Polytechnique SLOWPOKE reactor and then counted 10 cm from a 29% germanium detector and the amount of element in each case was calculated from the gamma-ray spectrum using the k ₀ method. For 13 nuclides with high Q ₀ values the results differed from the expected amounts by more than 5%, which suggests that measurements of new k ₀ and Q ₀ values are needed.     

Automatic stabilization of relative counting losses in gamma-ray spectrometry of short-lived nuclides

An electronic circuit for the stabilization of the relative counting losses due to dead time and pile-up effects is described. The circuit consists of two independent channel: for stabilization of dead time and pile-up, respectively. The stabilizer (circuit) receives continously information on temporary dead time and pile-up in a spectrometer and owing to feed back the relative counting losses (in peaks) are constant during the measuring time and can be easily calculated. Patent pending.