A software counting loss correction method for neutron activation analysis with short-lived radionuclides

A method has been developed for the correction of counting losses in NAA for the case of a mixture of short-lived radionuclides. It is applicable to systems with Ge detectors and Wilkinson or successive approximation ADC's and will correct losses from pulse pileup and ADC dead time up to 90%. The losses are modeled as a constant plus time-dependent terms expressed as a fourth order polynomial function of the count rates of the short-lived radionuclides. The correction factors are calculated iteratively using the peak areas of the short-lived radionuclides in the spectrum and the average losses as given by the difference between the live time and true time clocks of the MCA. To calibrate the system a measurement is performed for each short-lived nuclide. In a test where the dead time varied from 70% at the start of the measurement to 13% at the end, the measured activities were corrected with an accuracy of 1%.     

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.     

An automated gamma-ray counting system for fast neutron activation analysis

An automated gamma-ray counting system was designed and built for use in counting long-lived nuclides (T>hr) produced during analysis by fast neutron activation. The system is mechanically simple, vet interfaced to sophisticated control and counting equipment for completely automated counting.     

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.     

Anticoincidence counting further improves detection limits of short-lived products by pseudo-cyclic instrumental neutron activation analysis

A systematic investigation was carried out on the merits and limitations of anticoincidence counting for short-lived radionuclides (t _1/2 < 75 s) used in instrumental neutron activation analysis (INAA) and pseudo-cyclic INAA (PC-INAA) methods for single as well as simultaneous multielement determinations in botanical and nutritional reference materials. The list of radionuclides of interest included: ¹⁰⁸Ag, ¹¹⁰Ag, ^165mDy, ²⁰F, ^75mGe, ^179mHf, ^86mRb, ^46mSc, ^77mSe, and ^177mYb. Precision and accuracy of measurements were good, and detection limits were of the order of µg kg^?1.     

Fast neutron activation analysis using short-lived radionuclides

Fast neutron activation analysis experiments were performed to investigate the analytical possibilities and prospective utilization of short-lived activation products. A rapid pneumatic transfer system for use with neutron generators has been installed and applied for detecting radionuclides with a half-life from 300 ms to 20 s. The transport time for samples of total mass of 1–4 g is between 130 and 160 ms for pressurized air of 0.1–0.4 MPa. The reproducibility of transport times is less than 2%. The employed method of correcting time-dependent counting losses is based on the virtual pulse generator principle. The measuring equipment consists of CAMAC modules and a special gating circuit. Typical time distributions of counting losses are presented. The same 14 elements were studied by the conventional activation method (single irradiation and single counting) by both a typical pneumatic transport system (run time 3 s) and the fast pneumatic transport facility. Furthermore, the influence of the cyclic activation technique on the elemental sensitivities was investigated.     

Monitoring of neutron flux changes in short-lived neutron activation analysis

It is well known variations in neutron fluxes can adversely affect the final result in neutron activation analysis. The monitoring of neutron flux changes are usually described for medium and long-lived NAA using foils of cobalt, gold, zirconium, etc. However, for short-lived neutron activation analysis there appears to be no systematic study of the variations of the neutron flux. With our new automatic pneumatic system, where irradiation timing, decay and counting and position are very reproducible, we have performed a series of experiments using thermal and epithermal neutrons using aluminum wire as a monitor to monitor the neutron fluxes. Our experiments confirm that neutron flux fluctuations in the worst case can be up to ±12 % with a SD of 2–3 %. This effect can be seen regardless of the irradiation time and must be taken into consideration to achieve the best result.     

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.     

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.     

Validation experiment for large-sample prompt-gamma neutron activation analysis

A method is proposed for the implementation of large-sample prompt-gamma neutron activation analysis (LS-PGNAA). The method was tested with four different sample materials at the thermal PGNAA facility at JAERI, Japan. The macroscopic scattering cross section (Σ _s) and absorption cross section (Σ _a) of the samples were determined by monitoring the neutron flux in four positions just outside the sample container. With the Σ _s and Σ _a determined, the spatial neutron density distribution [n(r)] inside the sample material was derived. Taking n(r) and the gamma-ray self-absorption into account simultaneously, the effective geometric gamma-ray detection efficiency for large samples as a function of gamma-ray energy was calculated. Taking silicon as test element, the concentrations found agreed to within 7% with the known concentrations in the four sample materials examined, both when using relative standardization and with absolute standardization.     

Compton suppression spectrometry for analysis of short-lived neutron activation products in foods

Compton suppression spectrometry was used to analyze foods for elements with short-lived neutron activation products (half-lives of about 2 minutes to 1.5 days). Analysis conditions were optimized to provide quality assurance analyses for iodine in FDA’s Total Diet Study. Iodine mass fractions (0.075 to 2.03 mg/kg) were measured in 19 of 42 foods analyzed, with limits of detection (LODs) ranging from 0.03 to 1.4 mg/kg, mostly depending on NaCl content. LODs were lowered by up to a factor of 2 for 16 elements. Suppression factors ranged from about 2 to 8 over the energy range 400 to 3200 keV.     

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).     

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.     

The perfection of loss-free counting

Pileup losses in nuclear pulse spectrometry also depend on energy as lower energies produce narrower pulses which in turn have better chances to avoid pulse pileup. Consequently, in our present system individual energy-dependent pileup correction factors are calculated for all events, making it what very probably may be called the first perfect implementation of Loss-Free Counting. Temporal response and quantitative performance of the new system are tested over the whole range of counting rates (up to 10⁶ c/s) and counting losses (up to 99%) by means of short-lived isomeric transitions and a fast rabbit system.     

A cyclic neutron activation system using an isotopic neutron source for the measurement of short-lived isotopes

The design and construction of an activation analysis system using an isotopic neutron source which allows the measurement of prompt and delay gamma-rays, in conventional activation and cyclic activation modes, is briefly described with emphasis laid on its flexibility, transportability and low cost. Photon spectra obtained from the irrdiation of large samples under prompt, delay and cyclic conditions using both NaI(Tl) and Ge(Li) detectors are presented and described with respect to ‘in-vivo’ neutron activation analysis and the measurement of N, O, Na, P, Cl and Cd. It is pointed out that, despite the attractive possiblity of measuring Se in liver, ‘in-vivo’, by cyclic activation analysis, the system may potentially prove a very useful tool for industrial and other non-medical applications.     

Errors in instrumental neutron activation analysis based on short-lived radionuclides

Accuracy and precision of instrumental neutron activation analysis, based on short-lived radionuclides, are considered. Equations are derived for both quantitives as a function of concentration and features of the γ-ray spectrum. The determination of vanadium by way of⁵²V(T=3.75 min) is used as an example.     

Application of anti-Compton counting in instrumental neutron activation analysis

The inherent advantage of anti-coincidence counting of low-level radioactivity is defined in terms of changes in the limits of decision, detection and determination. It appears that the advantage factor can be expressed in the experimentally observed reductions of peak area, compton continuum and natural background. For an array equipped with a sample changer the advantage factor for interference by the compton continuum is4, while that for interference by the natural background amounts to 3. By sacrificing the sample changer and closing its gap with a Nal-plug, additional factors of 1.5 and 2 can be obtained for compton and natural background respectively.     

Review of loss-free counting in nuclear spectroscopy

This paper is a review of techniques for real-time correction of counting losses in nuclear pulse spectroscopy which became known under the name of loss-free counting (LFC).     

An activation analysis system for short-lived radioisotopes including automatic dead-time corrections with a microcomputer

A system based on an IBM-PC microcomputer coupled to a Canberra Series 80 multichannel analyser has been developed for activation analysis with short-lived radioisotopes. The data transfer program can store up to 77 gamma-ray spectra on a floppy disk. A spectrum analysis program, DVC, has been written to determine peak areas interactively, to correct the counting losses, and to calculate elemental concentrations.