Preconcentration of silver from rocks by extraction with bismuth dibenzyldithiocarbamate prior to neutron activation analysis

The method developed for determining trace levels of silver in geological materials involves the extraction of silver with a toluene solution of bismuth dibenzyldithiocarbamate followed by neutron activation of the extract. At pH 2 and in the presence of 0.1M EDTA, silver is quantitatively extracted. Under these conditions only small amounts of copper are coextracted. The detection limits of silver for three different modes of neutron activation analysis: /three cycles with Ge/Li/ detector, one cycle with Ge/Li/ detector and one cycle with NaI/Tl/ detector/ were 12, 20 and 11 ng g^–1, respectively.     

Optimization of HANARO cold neutron induced prompt gamma activation analysis system by using Monte Carlo code

Prompt gamma activation analysis (PGAA) is a nuclear analytical technique for non-destructive determination of elemental and isotopic compositions. The principle of PGAA technique is based on detection of captured gamma-ray emitted from an analytical sample while being irradiated with neutrons. Use of a cold neutron beam guide greatly reduces the gamma-ray background at the analytical sample while maintaining a neutron capture rate is comparable to that of standard thermal neutron PGAA. A new cold neutron induced prompt gamma activation analysis (CN-PGAA) system has been under construction since April of 2009 at the HANARO Cold Neutron Building (KAERI, Republic of KOREA). In this study, the Compton suppression factor of the CN-PGAA system was estimated to be 5.5 using a ⁶⁰Co radioactive source in conjunction with the MCNPX simulations. Several parameters of the CN-PGAA system were studied to estimate and optimize the performance of the system: scintillation material in the guarded detector of a Compton suppression spectrometer (CSS); the relative positions of the HPGe detector and annular detector; and the distance between the HPGe detector and back catcher BGO detectors of the CSS. In addition, the neutron ray-trace simulation package, McStas, was adopted to predict the neutron flux and wavelength distribution at the end of the cold neutron beam guide. These results served as input for the MCNPX simulation of the CN-PGAA system.     

Characterization of prototype perforated semiconductor neutron detectors

Semiconductor detectors whose surfaces are coated with neutron-reactive material can be made to detect thermal neutrons, but with efficiencies only of a few percent. However, perforating the semiconductor material, filling the perforations with neutron-reactive material, and then coating the detector surface can lead to neutron detectors of much higher thermal neutron detection efficiencies, perhaps approaching or exceeding 50%. Several perforated semiconductor neutron detectors have been constructed, both for dosimetry and for position-sensitive neutron detection. The characterization of prototype devices based on these detectors is described.     

Analytical use of neutron-capture gamma-rays

Certain elements which are not possible to detect with conventional neutron activation analysis can be measured using thermal neutron-capture gamma-ray analysis. The use of a curved neutron guide at the High Flux Reactor, Grenoble, with a thermal neutron flux of 1.5·10¹⁰n·cm⁻²·sec⁻¹ and the advantage of a low-background counting system (Ge(Li) detector) far from the reactor core are described. Experimental detection limits of a number of elements are given for the low-energy and the high-energy regions. Some applications of the capture gamma-ray method in the whole energy range are studied and are briefly discussed.     

Design and evaluation of a TNA explosive-detection system to screen carry-on luggage

Thermal neutron analysis (TNA) technology has been used for the non-destructive detection of explosives. The system uses a relatively weak ²⁵²Cf neutron source (1.03·10⁷ n/s) and two 3"×3" NaI(Tl) detectors. The presence of explosives is confirmed via detection of the 10.83 MeV prompt gamma-ray associated with nitrogen decay. The MCNP4A code was used to simulate the neutron and gamma transport through the system. The thermal neutron flux in the activation position was measured using gold and indium foils. The measured thermal neutron flux was lower, by not more than 9.5%, than that of simulation. In this report the results of the preliminary tests on the system are described.     

Control of the hafnium content in Co samples by SSMS

Summary The production of ⁶⁰Co requires a strict control of the chemical composition of the cobalt before irradiation in order to avoid the activation of some undesirable elements and to constrain the presence of slow neutron poisons. A methodology by SSMS for the survey analysis of metallic Co prior to its irradiation in the nuclear reactor at Embalse (Cdba., Argentina) is described. The low detection limit attained for Hf (below 0.5 ppm) is outlined. The results obtained for some other impurities without a standard reference are compared with atomic emission spectrographic data and show satisfactory agreement.

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Kontrolle des Hafniumgehaltes in Cobaltproben durch SSMS

     

A technique for improved detection limit in indirect neutron activation determination of boron

Using vanadium as the activable element, an indirect cyclic neutron activation technique for determination of boron in aqueous solutions has been developed. Experimental arrangement consisted of a 5 Ci Pu?Be based neutron irradiator and a 7.5 cm × 7.5 cm NaI/Tl/ detector. Recycling of vanadium between the irradiation source and the detector produced improved detection limit and sensitivity.     

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.     

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.     

Determination of titanium in bauxite: A comparison of neutron activation analysis with the X-ray fluorescence method

The determination of the titanium content of bauxite samples of various origin was studied by thermal neutron activation and X-ray analysis. A²⁵²Cf-fission neutron source and a Ge(Li) detector as well as a³H exciting source and a Si(Li) detector were used in the investigations. Within equal measuring times and with a sample weight of 8 g the sensitivity of the activation method is 0.35 w% Ti with an absolute statistical error less than 10%, while that of the X-ray method is 0.06 w% Ti and the absolute statistical error does not exceed 5%.     

Determination of boron in materials by cold neutron prompt gamma-ray activation analysis

An instrument for cold neutron prompt gamma-ray activation analysis (PGAA), located at the NIST Center for Neutron Research (NCNR), has proven useful for the measurement of boron in a variety of materials. Neutrons, moderated by passage through liquid hydrogen at 20 K, pass through a (58)Ni coated guide to the PGAA station in the cold neutron guide hall of the NCNR. The thermal equivalent neutron fluence rate at the sample position is 9 x 10(8) cm(-2) s(-1). Prompt gamma rays are measured by a cadmium- and lead-shielded high-purity germanium detector. The instrument has been used to measure boron mass fractions in minerals, in NIST SRM 2175 (Refractory Alloy MP-35-N) for certification of boron, and most recently in semiconductor-grade silicon. The limit of detection for boron in many materials is <10 ng g(-1).     

The internal comparator method

An internal comparator method is proposed which offers reliable instrumental neutron activation analysis (INAA) results for samples with an irregular geometry and/or measured at the closest position to the Ge detector. Because the selected internal comparator in the sample analyzed will receive exactly the same thermal neutron flux as the other components, this method can be applied to the INAA of materials suffering from thermal neutron self-shielding. To apply the internal comparator method, the k₀-method must be installed and the analytes, including the internal comparator, should be homogeneously distributed in the test portion.     

Instrumental neutron activation analysis of some ancient punchmark coins from India

A nondestructive instrumental neutron activation analysis technique is applied for the analysis of precious ancient punchmark coins. Coins ranging between 8th century B.C. to 2nd century B.C. were irradiated with thermal neutrons in a²⁵²Cf neutron source facility and analyzed by comparator method of instrumental neutron activation analysis, using high purity germanium detector coupled to a multichannel analyzer, the activities being measured at photopeak energies of the corresponding radioisotopes. It is observed that punchmark coins are mainly of two types: copper or silver based. Other elements present in varying proportions are gold, arsenic and antimony.     

Perforated diode neutron detector modules fabricated from high-purity silicon

Compact neutron detectors are being designed and tested for use as low-power real-time personnel dosimeters. The neutron detectors are pin diodes that are mass produced from high-purity Si wafers. Each detector has thousands of circular perforations etched vertically into the device. The perforations are backfilled with ⁶LiF to make the pin diodes sensitive to thermal neutrons. The prototype devices deliver 4.7% thermal neutron detection efficiency while operating on only 15 V, showing a 9% increase in efficiency over identical planar devices.     

The soil moisture and its effect on the detection of buried hydrogenous material by neutron backscattering technique

Among the available nuclear techniques, the neutron backscattering technique, based on the detection of the produced thermal neutrons, is thought to be the most promising for landmine detections.The results obtained from Monte Carlo simulation were used for selection of BF₃ detector and Am–Be neutron source shielding. In addition, soil moisture was discussed as a limitation of the neutron backscattering technique. It was experimentally found that this technique is useful for soil whose water content is lower than 14%.     

Multiple prompt gamma-ray analysis and construction of its beam line

By combining neutron activation analysis with multiple gamma-ray detection (gamma-gamma coincidence), we have proved better sensitivity and resolution for the trace element analysis than the ordinary single gamma-ray detection method. We now try to apply the multiple gamma-ray detection method to the prompt gamma ray analysis (PGA). We have established a new cold neutron beam line for PGA in Japan Research Reactor, JRR-3M, at Tokai establishment of Japan Atomic Energy Research Institute (JAERI). It consists of a beam shutter, a beam attenuator, a gamma-ray detector array, a sample changer, and a beam stopper. We construct a high-efficiency gamma-ray detector array specially designed for this purpose. Its performance has been evaluated with the Monte Carlo simulation code, GEANT 4.5.0.     

Decreasing the detection limits to ppq levels for high purity silicon analysis by instrumental neutron activation analysis with kilogram sampling weight

The amount of silicon sample used in instrumental neutron activation analysis (INAA) is generally less than twenty grams and the detection limits are in the range of ppb to ppt. The detection limits can be decreased further in several ways. Increasing neutron flux density, extending irradiation period and/or using more effective detector can improve the detection limits to some extent. Increasing sample weight, however, is a more feasible way to decrease the detection limits by a factor of hundreds with no new investment in existing irradiation/counting systems. In this work, two 8-inch high-purity silicon samples were analyzed by INAA to evaluate the validity and limitations of this concept in respect to neutron flux inhomogeneity, neutron shielding and -ray counting efficiency.     

Destructive and nondestructive analysis of some elements in tissue and environmental samples by thermal neutron activation analysis technique

A rapid and selective method has been developed and applied for determining elements present in tissue and environmental samples by both destructive and nondestructive activation analysis. Nondestructive activation analysis involves the irradiation of the sample and standard of the elements such as Mn, Na, and K with thermal neutrons from²⁵²Cf neutron source followed by radioassay of the (n,r) products on a HPGe detector coupled to a PC-based MCA. Elements are determined by irradiating the samples in the thermal neutron flux of the CIRUS reactor and radiochemically separating the isotopes of interest using substoichiometric extraction and precipitation technique. The statistical evaluation of the method with respect to accuracy and precision of the method and its sensitivity are discussed.     

Boron distribution measurement in metals by neutron induced radiography

The neutron induced microscopic radiography is a suitable method to detect boron content and distribution in metallic materials. For the research reactor KRR-2, the optimum thermal neutron fluence for various amount of boron content, the background effect due to fast neutron and -ray to the minimum detection limit of boron content, as well as the optimum-etching condition of the solid state nuclear track detector were determined.