Non-destructive analysis of objects using neutron resonance capture

Summary In this paper we discuss an analytical method, neutron-resonance-capture-analysis (NRCA), which uses the energies of resonances to recognize elements. These resonances are observed by the time-of-flight technique using a pulsed neutron beam at the GELINA facility in Geel (Belgium). The prompt γ-radiation, emitted after a neutron is captured, is used to signal that capture occurred. Areas of resonance peaks are used to evaluate the elemental composition of objects and materials quantitatively. A comparison of NRCA and PGAA is made and elucidated with experimental data resulting from measurements of bronze artefacts at GELINA and at the Budapest Neutron Centre.     

Non-destructive bulk analysis of the Buggenum sword by neutron resonance capture analysis and neutron diffraction

Two neutron based techniques, neutron resonance capture analysis (NRCA) and time-of-flight neutron-diffraction (TOF-ND) have been used to determine the elemental composition and structure of a precious and very well preserved all-metal sword from the Bronze Age. This Buggenum sword was on loan from the National Museum of Antiquities (NMA) in Leiden (NL). NRCA and TOF-ND experiments have been carried out at a number of more or less identical positions of the sword. The tin-bronze ratio and the relative amounts of some minor elements (Sb, As, Ag, In) have been determined. The results of neutron diffraction measurements showed considerable tin-segregation, and clear indications of hardening on the edges of the blade. In addition, radiographs using Bremsstrahlung revealed the construction of the hilt–blade connection. The work was carried out at the EC Joint Research Centre IRMM in Geel (B) and at the ISIS facility of the Rutherford Appleton Laboratory (UK).     

Determination of palladium in gasoline by neutron activation analysis and automated column extraction

Palladium in gasoline was determined by means of neutron activation analysis (NAA) and selective sorbent extraction. Unleaded gasoline consistent with DIN EN 228, RON 95 was irradiated at a thermal neutron flux of phith = 1.68 x 10(13)s(-1)cm(-2) and an epithermal neutron flux of 3.32 x 10(11)s(-1)cm(-2) for t(irr) = 12 h. The irradiated gasoline was digested with nitric acid and palladium was then separated as N,N-diethyl-N'-benzoylthiourea complex by an automated column pre-concentration procedure. The eluate of 50 microL was dried on a filter paper and the 88.03 keV photons resulting from the decay of 109Pd were detected in a low level HPGe spectrometer with an efficiency of 35.5%. Severe interferences with other matrix constituents, especially 82Br could be overcome and the detection limit for palladium was improved to 3.4 ng/L at a confidence level of 90%. Although the analytical procedure applied yielded the lowest detection limit for palladium obtained in gasoline up to now, no indications for the presence of palladium were found.     

Preparation and Pharmacokinetic Evaluation of Iodine-125 Labeled Alphamethyl-L-Tyrosine

A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of ⁶⁰Co and ¹⁵²Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120–1400 keV. Second, a PGNAA system consisting of a light-water moderated ²⁵²Cf (1.06 g) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the ²⁵²Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 g/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model.     

Depth profiling of titanium using a resonance in 48Ti(p,γ)49V nuclear reaction

Depth profiling of titanium using the resonances at 1,007, 1,013 and 1,362 keV in ⁴⁸Ti(p,γ)⁴⁹V nuclear reaction (E _γ  = 7.9 MeV) has been investigated. The resonance at 1,362 keV with a detection sensitivity of ~5.1 × 10²⁰ at. cm^?3 (~ 1 at.%), probing depth of ~800 nm and a depth resolution of ~24 nm in silicon is best suited for analytical applications. Lower probing depth and lesser detection sensitivity are the major limitations of the two other resonances. The applicability of the resonance at 1,362 keV is demonstrated by depth profiling Ti in Pd (32 nm)/Ti (57 nm)/Mg (300 nm)/Ti (57 nm)/Si multi-layered coating.     

Fast non-destructive determination of iron and sulphur in coal by means of neutron radiative capture

The possibility of determination of iron and sulphur in large-scale samples of coal /20–50 kg/, based on process /n, /, was evaluated. The spectral lines of the doublet 7631 keV and 7645 keV were used for the determination of iron, while the line at 5421 keV was used for the determination of sulphur. The neutron source was²⁵²Cf /total neutron emission at 2.5×10⁷ s^–1/ located additionally in D₂O moderator. A Ge/Li/ detector was used for gamma radiation detection. The calibration dependencies of the analyzer were linear. In exposure times of up to 1 h, the detection limits of 0.34% and 0.64% and accuracies of 0.25% and 0.4% have been achieved in case of iron and sulphur, respectively.     

Possible use of low voltage accelerators in PIXE analysis

A low energy (200 keV) accelerator routinely used as a neutron generator has been modified and a procedure established to extend the use to include proton induced X-ray emission (PIXE) analytical method. With these modifications, the generator has been used to measure the proton induced X-ray emission cross sections for twenty-eight elements ranging from aluminium to lead at 160 keV bombarding energy. Using these cross sections, the minimum detection limits for trace element determination in a rock matrix of average atomic number 13 have been evaluated.     

Resonance activation analysis of iodine

Resonance neutron activation and gamma-ray spectrometry were used to determine traces of iodine in biological materials. The method developed is purely instrumental and fairly rapid. The major interfering activities of²⁴Na,³⁸Cl,³⁶Mn and⁸²Br were significantly reduced by irradiating the samples inside a shield of Cd, NaCl, MnBr₂ and MnO₂. Neutrons with energies close to the resonances of Na, Cl, Mn and Br were absorbed in the shield and did not activate the sample while neutrons with energies close to the resonances of iodine were not absorbed appreciably. Thus the activity of¹²⁸I was enhanced relative to the interfering activities. The 442 keV gamma of¹²⁸I (T=25 min) was measured using a high-resolution Ge(Li) detector and a multichannel analyzer. Sensitivity of 0.05 ppm was obtained.     

Detection of background thermal neutrons in a modified low-background germanium gamma-ray spectrometer

Journal of Radioanalytical and Nuclear Chemistry - The paper presents the detection of background neutrons using the 558.4 keV gamma line emitted from excited 114Cd nuclei after neutron...     

Non-destructive assay technique for the determination of <Superscript>238</Superscript>U/<Superscript>232</Superscript>Th ratio in the mixed oxides of uranium and thorium using prompt gamma-ray neutron activation

A non-destructive assay technique based on prompt gamma-ray neutron activation analysis for the determination of ²³⁸U to ²³²Th ratio in the mixed oxide fuel materials has been established. The method uses closely spaced high energy gamma-rays in the region of 4000 keV to 4150 keV enabling it to be applied for samples of any geometry and thickness without having any correction for gamma-ray attenuations and detection efficiencies.     

Determination of palladium by chemical neutron activation analysis using low energy photon spectrometry

A chemical neutron activation analysis method to determine trace amounts of palladium present in the uranium ores has been developed. Palladium was concentrated on an anionic exchanger to purify from large amounts of uranium, iron and copper that were present in the ore. The resin in which Pd was adsorbed was neutron irradiated and the activation product¹⁰⁹Pd was assayed through its daughter^109mAg by low energy photon spectrometry to estimate palladium. Both the 88 keV gamma-line and the 22 keV X-ray line (arising out of the internal transition of^109mAg) were used to arrive at the concentration values by a standard comparison technique. A thin window Si(Li) detector and an HPGe detector were used for the radioactive assay. Detection limits and the advantage of using the X-ray line of Ag over that of the gamma-line were discussed. An absolute detection limit of 0.12·10⁻⁹ g could be arrived at by the use of the 22.10 keV X-ray line in an interference-free condition.     

Determination of palladium in gasoline by neutron activation analysis and automated column extraction

^? Palladium in gasoline was determined by means of neutron activation analysis (NAA) and selective sorbent extraction. Unleaded gasoline consistent with DIN EN 228, RON 95 was irradiated at a thermal neutron flux of Φ_th = 1.68 · 10¹³s^–1cm^–2 and an epithermal neutron flux of 3.32 · 10¹¹s^–1cm^–2 for t_irr = 12 h. The irradiated gasoline was digested with nitric acid and palladium was then separated as N,N-diethyl-N’-benzoylthiourea complex by an automated column pre-concentration procedure. The eluate of 50 μL was dried on a filter paper and the 88.03 keV photons resulting from the decay of ¹⁰⁹Pd were detected in a low level HPGe spectrometer with an efficiency of 35.5%. Severe interferences with other matrix constituents, especially ⁸²Br could be overcome and the detection limit for palladium was improved to 3.4 ng/L at a confidence level of 90%. Although the analytical procedure applied yielded the lowest detection limit for palladium obtained in gasoline up to now, no indications for the presence of palladium were found.     

Improvement ofin vivoneutron activation analysis of Mn using a 4p NaI(Tl) detector array

Summary Manganese contents in hand phantoms were analyzed by in vivo neutron activation analysis using a 4p NaI(Tl) detector array. Solution-type phantoms with varying amount of Mn and fixed amounts of physiological normal elements (Na, Cl, Ca) were prepared in a cylindrical shape to simulate fisted hands and were irradiated with the ⁷Li(p,n) neutron beam. The proton energy and polyethlyene cavity were set at optimized conditions established before. The g-ray spectra were accumulated under the anticoincidence mode. The calibration was done both for the 847 keV full-energy peak area and for the total area of ⁵⁶Mn, which is defined as the total number of counts anywhere in the g-ray spectrum from ⁵⁶Mn. From the analysis of the 847 keV peak, the Mn detection limit has been improved by a factor of 1.6 compared to the previous feasibility test thanks to a significant gain in the g-ray detection efficiency. Further improvement by a factor of 1.2 was identified when the total area of ⁵⁶Mn was used for the calibration. The final sensitivity and detection limit for a 20 mSv hand dose reached 12,050 counts/mg Mn, and 86 mg, respectively. The overall improvement achieved in this study will be a considerable contribution toward realization of the clinical application.     

Prompt gamma neutron activation analysis of boron with a 241Am-Be neutron source

A prompt gamma neutron activation analysis (PGAA) setup installed at ANRTC has been used to analyze boron. It consists of a 22.6% REGe detector and a 740 GBq ²⁴¹Am-Be neutron source moderated with water and paraffin. At the sample irradiation position, the thermal neutron fluence rate measured was 2.36·10⁴ n·m^–2· s^–1 and the corresponding Cd-ratio was 22 for gold monitor. The absolute detection efficiency in the range of 120–1500 keV was determined using ¹⁵²Eu standard solution. The sensitivity and detection limit for standard boric acid samples has been determined. The boron content in boric acid prepared from Turkish borate ores is measured to be 15.91±0.46% wt.     

Prompt gamma neutron activation analysis of boron with a 241Am-Be neutron source

A prompt gamma neutron activation analysis (PGAA) setup installed at ANRTC has been used to analyze boron. It consists of a 22.6% REGe detector and a 740 GBq ²⁴¹Am-Be neutron source moderated with water and paraffin. At the sample irradiation position, the thermal neutron fluence rate measured was 2.36·10⁴ n·m^–2· s^–1 and the corresponding Cd-ratio was 22 for gold monitor. The absolute detection efficiency in the range of 120–1500 keV was determined using ¹⁵²Eu standard solution. The sensitivity and detection limit for standard boric acid samples has been determined. The boron content in boric acid prepared from Turkish borate ores is measured to be 15.91±0.46% wt.     

A compilation of precisely determined gamma-transition energies of radionuclides produced by reactor irradiation

The gamma ray energies of nearly all radionuclides formed by reactor neutron irradiation have been determined using high resolution Ge(Li) spectrometry. The re-producibility of the determinations is demonstrated and, to estimate the accuracy of the measurements, the results are compared with those of other investigators. In the energy range from 80 to about 1400 keV the accuracy for the most abundant gamma rays is better than 0.2 keV. The energies of gamma transitions above 1400 KeV may be less accurate. The data are compiled in an atomic number and in a photon energy sequence. A table of characteristic X-rays is also included. The tables are intended to be helpful in the identification of isotopes in neutron activation analysis. Reprints of this compilation can be ordered from the Co-ordinating Editor (price: 2 US $).     

Application of fast solvent extraction processes to studies of exotic nuclides

The nucleus²³Na has been investigated by studying the primary γ-rays emitted from 53 keV neutron capture in it using a high resolution and high efficiency (100%) HPGe detector and NaI(T1) detector for anti-Compton. 24 primary γ-rays were placed in the²⁴Na, in which 3 primary γ-rays were new ones from a (n, γ) reaction, and reported for the first time. In order to obtain an exact energy calibration within 7 MeV,⁵⁶Fe(n,γ)⁵⁷Fe reaction was used at thermal neutron energy. Intensity calibration was obtained from the²⁷Al(p,γ)²⁸Si reaction atE _p=2046 keV. The neutron binding energy of²⁴Na was determined to be 6959.75 keV.     

Cumulative neutron activation of short-lived radionuclides for the analysis of large samples in mineral exploration

Cumulative neutron activation is used to determine mg/kg concentrations of gold in rock samples, weighing 10 g. Twenty 0.5 g replicates are irradiated in an epithermal-neutron flux for 5 s and counted for 14 s. The twenty spectra are summed, and gold is measured with the 279 keV gamma-ray of^197mAu (7.2 s). Total analysis time for a 10 g sample is 400 s and detection limits around 2 mg/kg are achieved in gold ores, sulfides and silicates.     

Determination of arsenic and gallium in standard materials by instrumental epithermal neutron activation analysis

Epithennal neutron activation analysis has been applied to the determination of arsenic and gallium in standard materials at trace concentrations. The reduction of ²⁴Na activity compared to thermal neutron activation is advantageous. Arsenic detection limits (1σ) are 0.04 and 0.015 μg for inorganic and organic materials, respectively. The corresponding gallium detection limits, for the best cases, are 0.13 and 0.29 μg. Gallium determinations with the 834-keV photopeak of ⁷²Ga suffered interferences attributed to the threshold reaction ⁵⁴Fe(n,p) ⁵⁴Mn; the less intense ⁷²Ga peaks at 629 and 2200 keV provided quantitative results for all samples tested. Gallium detection limits with the less intense, but more reliable 629-keV peak were 0.9 and 0.1 μg for inorganic and organic materials, respectively. Arsenic determinations are best performed with the more intense ⁷⁶As 559-keV line, as the 657-keV line has an unknown interference.     

Do we need radiochemical separation in activation analysis?

The optimization of neutron activation analysis with regard to detection limit and uncertainty of measurement using physical and chemical means is reviewed. Using selected examples it is demonstrated that radiochemical separation is the most effective means of optimization, especially in neutron activation analysis, because it yields the lowest detection limits and uncertainties. This revised version was published online in July 2006 with corrections to the Cover Date.