Use of very short-lived nuclides in nondestructive activation analysis with a fast shuttle rabbit

An equation for the dead-time correction of measurements of very short-lived isotopes is derived. As an example, this treatment is applied in the measurement of 7.2 sec^197m Au in the presence of 65 h¹⁹⁸Au.     

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.     

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.     

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).     

Activation analysis with short-lived nuclides in aerosol physics

Although Neutron Activation Analysis is usually not very common in aerosol physics, there are fields of application which seem to be rather successful. In general it is shown which properties activable aerosols should have, how they can be produced and how aerosol samples might be drawn. By use of special aerosol separators not only the mass-concentration but also the size-distribution of the aerosol can be determinated. Based on two studies, the utility of activable aerosols is demonstrated: Calibration and test of a simple discontinously working aerosol monitor for the off-gass system of isotope hoods; dynamic o radioactive ionized aerosols in a sealed room. Finally a general survey of further applications of activable aerosols is given.     

New perspectives for very short-lived neutron activation analysis

Recent attempts to improve the performance of very short-lived neutron activation analysis are reviewed. It is shown that the combination of an intense cold neutron beam from a research reactor with a beam chopper offers higher signal-to-background ratio, more accurate timing and much simpler sample handling than conventional cyclic activation analysis. Application of a digital spectrum analyzer in data list mode allows for easy determination of the half-life. Hence, time-resolved activation analysis utilizing energy and time information becomes practical. This revised version was published online in July 2006 with corrections to the Cover Date.     

Precision high-speed neutron activation analysis via very short-lived activities

An automated, highly reproducible fast-transfer system (0.36±0.01 sec) has been developed, an oscillator/multichannel-scaling system has been developed to follow rapidly-changing spectrometer dead-times, the mathematics has been developed, and the data processing steps have been computerized. Three induced activities have been studied in some detail:^207mPb (0.80 sec),^38mCl (0.70 sec) and²⁰F (11.03 sec). Both steady-state and high-intensity pulsed reactor irradiations, with and without a Cd liner, have been used. The dead-time correction method has been carefully checked, and the overall method has been tested by the analysis of two NBS Standard Reference Materials: orchard leaves (for Cl and Pb) and bovine liver (for Cl). This paper represents a portion of the Ph. D. thesis of D. A. MILLER.     

Trace elements of coal,coal ashes and fly ashes by activation analysis with short-lived nuclides

On irradiation with neutrons, some of the interesting trace elements in coal, coal ash and fly ash produce short-lived nuclides which may be determined—together with some of the matrix elements—by activation analysis. This enables the characterization of samples. To find out the distribution of elements in the gaseous or aerosol exhaust of fossil-fired power plants, we simulated the combustion in a quartz apparatus containing a cold trap, using the combustion temperature (780 °C) employed for the standard ash determination. High Se values were found in the cold trap deposits from black coal from Poland. Halogens were also found in the deposits.     

Instrumental activation analysis of coal and fly ash with thermal and epithermal neutrons and short-lived nuclides

Instrumental neutron activation analysis is applied to the determination of about 25 elements in coals and fly ash by means of nuclides with half-lives of less than 48 h ; thermal and epithermal irradiations are used. The results indicate that epithermal activation is preferable for twelve of the elements (Ga, As, Br, Sr, In, Cs, Ba, La, Sm, Ho, W and U). Data for SRM 1632 (coal) and SRM 1633 (fly ash) compare favorably with the results obtained by other investigators.     

Recent instrumental neutron activation analysis studies utilizing very short-lived activities

The advantages and disadvantages of utilizing very short-lived induced activities (half lives in the range of 0.3 sec to 60 sec) in neutron activation analysis are reviewed. Results obtained with the recently described fast-transfer system and deadtime correction system are presented. They include results for 12 elements (F, S, Cl, Sc, Ge, Se, Br, Y, Zr, Ba, W, Pb), in both steady-state and high-intensity pulse irradiations, in both unlined and cadmium-lined irradiation positions. The half lives of the 12 species studied range from 0.3 sec to 18.7 sec. Some further aspects of the deadtime correction system are discussed.     

Use of cyclotron-produced fast neutrons in activation analysis

The determination of 15 elements: Pb, Sr, Ba, ti, Ca, Sc, Cs, Zr, Rb, Cr, Se, Ni, Y, Co and Zn was investigated by fast neutron activation analysis using 80 MeV deuterons on various environmental samples. Detection limits of these elements from interference-free spectra were calculated.     

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.     

Catching conditions of a disease with nondestructive activation analysis of hair

In this study, we aimed to recognize the body abnormalities through determining the metallic balance of hair. We determinated multiple elements of patients hair with acute chromium poisoning by burn from the worst clinical condition to complete recovery. Elements determined were Al, Au, Br, Ca, Cl, Co, Cr, Cu, Fe, Hg, I, K, Mg, Mn, Na, S, Se, V and Zn by mondestractive neutron activation analysis. Comparing the clinical findings of a patient with acute chromium poisoning and metallic balance of his hair, we demonstrated that the metallic balance returned to the normal range with recovery from sickness, which suggested a promising possiblity to utilize this as one parameter indicative of clinical state.     

Validation of a loss-free counting system for neutron activation analysis with short-lived indicators

The use of loss-free counting systems makes possible the exact correction for pile-up and dead-time losses during counting of a mixture of short-lived radionuclides even at very high count rates. However, counting statistics cannot be calculated by taking into account only the Poisson distribution of the incoming -quanta, such as is done in existing computer programs for -spectrometry. At moderate count rates Müller statistic was found to account for the observed variability between duplicate countings; however, at higher count rates the variability of weighing factors was found to be significant in comparison with the Müller statistic. While counting statistics could not be correctly estimated for short-lived species, experiments showed excellent accuracy for initial dead times up to 90%.     

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.     

Selection of short-lived isotopes for activation analysis with respect to sensitivity

During the last decade the use of short-lived isotopes in activation analysis has exploded, owing to the application of high resolution gamma-ray spectrometry. Complex spectra can in fact be resolved without the need for chemical separations. The application of cyclic activation-counting enables the use of isotopes with half-lives below 10 seconds. These short-lived isotopes can be produced by different activation processes. As neutron sources one can distinguish reactors, generators for 14 MeV or high energy machines such as cyclotrons and isotopic neutron sources. High energy photons can be produced by interaction of an energetic electron beam with a target, giving rise to an intense bremsstrahlung spectrum with maximum energy from 10 up to 70 MeV. While these photons induce several types of threshold reactions, lower energetic photons are used for resonance activation producing metastable isomers. More and more also charged particles (p, d,³He, α) are being used as projectiles to produce radioactive isotopes that can be measured in activation analysis. In the present paper a concise compilation is made of the nuclear reactions, applicable in activation analysis of minor or trace constituents using gamma emitting isotopes with half-lived smaller than 1 hour. Activations of all naturally occurring elements, except the noble gases, with Z values ranging from 9 to 92 have been considered. The reactions resulting in the most sensitive gammaspectroscopic determinations have been selected and are tabulated per element, together with the appropriate cross section and the resonance integral if significant for neutron reactions, the cross section at the giant resonance energy for the photon and at the maximum of the excitation function for the charged particle reactions and the threshold energy for all threshold reactions. For each isotope produced the half-life and the major gamma-ray energy is given. Finally calculated or experimental sensitivities have been compiled from a number of references, as the emission rate per second of the most intense gamma-ray, at the end of a 1 minute irradiation under well-defined circumstances for 1 microgram of the element. When cyclic activation has been applied it is indicated. These data are provided for more than 200 nuclear reactions. It appears that the majority of the 70 elements constacred can in some way be determined with a high sensitivity after such a short irradiation. Only for the elements Tm and Tb no reaction yielding a short-lived isotope with a reasonable sensitivity could be found. Both elements can however very sensitively be determined after a longer neutron irradiation. For a number of elements activation analysis by means of the middle-long-lived isotopes (2 hours to 3 days) is the most sensitive even after a 1 minute irradiation and immediate count (Mn, Ga, As, Sr, Ru, La, Eu, Ho, Lu, Os and Au). But for all other elements the highest gamma emission rate results from isotopes with half-lives shorter than 1 hour. Extremely high counting rates are obtained after thermal reactor neutron activation for Na, Sc, V, Co, Se, Rh, Ag, In, Eu, Dy, Er and Hf. For a number of elements the selectivity of the analysis can however largely be enhanced by irradiation under Cd-cover. High σ₀ ratios exist in fact for activation of medium and high Z elements such as Nb, Rb, Rh, Sn, Sb, Ba, Ce, Lu, Ta, Os, Hg and U. For some elements activation with reactor fission neutrons or 14 MeV neutrons provides an interesting sensitivity for a threshold reaction or the production of an isomer (F, Si, P, Cl, Ca, Cr, Se, Y, Ba, Ce, Pr, Bi, Pb). Cyclic activation and counting of very short-lived isotopes has been applied advantageously in the ng to μg range for a number of elements. Also cyclic activation with a 14 MeV generator has recently been studied. Low energy photon activation analysis allows selective production of metastable isomers of Se, Br, Ag, Er, Hf, Ir and Au, while high energetic photon production analysis yields high specific activities for elements such as K, Cr, Se, Br, Mo, Pr, Nd, Ho and allows interesting determinations of Mg, Cl, Si, Cr, Fe, Zr and Pb. Also charged particle activation can be used with surprisingly high sensitivity for some medium and high Z elements (Cr, Y, Se, Br, Zr, Mo, La, Ta, V). The intensity of the irradiation is in these cases mostly only limited by the properties of the sample itself, such as heat transfer and matrix activity. Examples of the compilation will be discussed and applications shown.     

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.