Measurements of the neutron spectra from the 7Li(p,n) accelerator based neutron source: Position and angular dependences

Thick target ⁷Li(p,n) neutron spectra were measured using a ³He ion chamber in the proton energy range of 1.95 to 2.30 MeV. The fast neutron spectra were collected for various distances from the lithium target as well as for various neutron emission angles. By unfolding the ³He raw data with the iterative van Cittert algorithm, the neutron fluence spectra were obtained. The ³He measured neutron spectra were compared with both analytically computed and Monte Carlo simulated spectra to account for neutron scatterings in the lithium target assembly and in the experimental area. To verify the accuracy of the neutron dose computation, the fast neutron kerma was obtained for each neutron spectrum using the fluence to kerma conversion coefficients and was compared with the measured neutron dose using tissue-equivalent proportional counters. In the position dependence investigation at the 0° emission angle, the analytically computed neutron kerma overestimates the experimental kerma by a factor of two mainly due to neutron moderation. The corresponding neutron kerma from the ³He measured spectra were in agreement with the neutron doses measured using tissue-equivalent proportional counters within 20% for lower proton energies, but the discrepancy increased to ～50% for higher proton energies. In the angular distribution investigation, a notable discrepancy between measured and computed neutron spectra were observed due to the neutron scattering effects in the target assembly and experimental room.     

Detection and identification of explosives and illicit drugs using neutron based techniques

Some methods developed in collaboration between the ATOMKI and IEP for bulk hydrogen analysis and for the detection and identification of illicit drugs are presented. Advantages and limitations of neutron techniques (reflection, transmission, elastic and inelastic scatterings, leakage spectra and angular yields of Be(d,n), Pu–Be, D–D, D–T and ²⁵²Cf neutrons transmitted from thick samples, effects of hidden materials) are discussed.     

Performance comparison of an 241Am-Be neutron source-based PGNAA setup with the KFUPM PGNAA setup

Monte Carlo calculations have been carried out to compare the performance of an ²⁴¹Am-Be neutron source-based prompt gamma neutron activation analysis (PGNAA) setup with that of the 2.8 MeV neutron-based PGNAA setup at King Fahd University of Petroleum and Minerals (KFUPM) to analyze Portland cement samples. This work is a part of a wide Monte Carlo studies being conducted at KFUPM in search of a more efficient neutron source for its 2.8 MeV neutrons, from the D(d,n) reaction, based PGNAA facility. In this study an ²⁴¹Am-Be neutron source-based PGNAA setup was simulated. For comparison, the diameter of a cylindrical external moderator of the ²⁴¹Am-Be neutron source, based PGNAA setup, was assumed to be similar to that used in the KFUPM PGNAA setup. The results of this study revealed that although the optimum geometry of the ²⁴¹Am-Be neutron source-based setup is similar to that of the KFUPM PGNAA facility, the performance of the ²⁴¹Am-Be neutron source-based setup is slightly poorer than that of the 2.8 MeV neutron-based setup. This revised version was published online in July 2006 with corrections to the Cover Date.     

A method for bulk hydrogen analysis based on transmission and back scattering of fast neutrons

A method was proposed for bulk hydrogen analysis. It is based on simultaneous detection of transmitted fast neutrons and back scattered thermal neutrons from the investigated samples by ³He detectors. The fast neutron beams were obtained from ²⁵²Cf and Pu–Be neutron sources. The experimental set-up as well as samples preparation were described. Incident thermal neutrons beams obtained from either ²⁵²Cf or Pu–Be sources, were used to investigate the samples by neutron backscattering. The results obtained from transmission and backscattering of fast neutrons were compared and discussed. The advantage and capabilities of the proposed method were presented. The results obtained using fast neutron beams are more sensitive than those obtained using thermal neutron beams. Validation procedures were proposed to credit the results.     

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.     

The application of NAA with irradiation at reduced temperature for the study of element losses during pretreatment of biological samples

The neutron capture gamma-ray spectroscopy facility assembled at the Institute of Radiochemistry, KfK (for analytical purposes) using a²⁵²Cf neutron source with a strength of 6·10⁷ n/s, has been used to check its applicability and sensitivity for quantitative analyses of ores. The analysis of Sm, Cd and Mn in phosphate and monazite rock samples has been carried out. The results from this study show a variation of about 25% from the values determined by RNAA method. This discrepancy could be mainly due to the low signal-to-background ratio observed which is caused by (i) scattering of the source gammarays by the target, and (ii) interference from the 2223.1 keV neutron capture hydrogen gamma-rays produced by the moderated materials and from their compton scattering in the detector. To overcome these difficulties we suggest to introduce a 2.5 cm thick polyethylene sheet between the detector⁶Li-cap shielding and the target as well as to increase the detection solid angle. Also the strength of the²⁵²Cf neutron source should be increased by an order of magnitude and the neutron beam should be collimated to obtain the optimal thermal neutron flux with a low level of²⁵²Cf gamma-rays. This can be achieved by setting up between the neutron source and the target a conical polyethylene collimator with a thickness of 10 cm containing a 1 cm thick lead sheet.     

Biomedical neutron research at the Californium User Facility for Neutron Science

The Californium User Facility for Neutron Science has been established at Oak Ridge National Laboratory (ORNL). The Californium Use Facility (CUF) is a part of the larger Californium Facility, which fabricates and stores compact²⁵²Cf neutron sources for worldwide distribution. The CUF can provide a cost-effective option for research with²⁵²Cf sources. Three projects at the CUF that demonstrate the versatility of²⁵²Cf for biological and biomedical neutron-based research are described: future establishment of a²⁵²Cf-based neutron activation analysis system, ongoing work to produce miniature high-intensity, remotely afterloaded²⁵²Cf sources for tumors therapy, and a recent experiment that irradiated living human lung cancer cells impregnated with experimental boron compounds to test their effectiveness for boron neutron capture therapy.     

Spectra and dose with ANN of 252Cf, 241Am–Be, and 239Pu–Be

Artificial neural networks have been applied to unfold the neutron spectra and to calculate the effective dose, the ambient equivalent dose, and the personal dose equivalent for ²⁵²Cf, ²⁴¹Am–Be, and ²³⁹Pu–Be neutron sources. The count rates that these neutron sources produce in a Bonner Sphere Spectrometer with a ⁶LiI(Eu) were utilized as input in both artificial neural networks. Spectra and the ambient dose equivalent were also obtained with BUNKIUT code and the UTA4 response matrix. With both procedures spectra and ambient dose equivalent agrees in less than 10%. The Artificial neural network technology is an alternative procedure to unfold neutron spectra and to perform neutron dosimetry.     

Determination of <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-values for some elements in neutron capture gamma-ray for prompt gamma activation analysis

Exploration and modification of data for k ₀-PGAA (prompt γ-ray activation analysis) values used as standards for k ₀ standardization are needed. An integrated system has been installed and calibrated in Hot Laboratories Center for PGAA, using ²⁵²Cf isotopic neutron source with neutron flux of 6.16E8 n/cm² s. The prompt k ₀-factors of about 12 elements were determined versus the 1951.1 keV γ-ray of the ³⁵Cl, as well as analyzing crude oil and oil product samples. The concentrations of the elements in crude oil H, B, Mg, Al, Na, Si, P, S, Cl, V and Cd were 1.18E5, 0.084, 5.48E2, 8.45E2 4.88E2, 1.62E2, 3.72E2, 8.2, 144.3, 393 and 209.2 ppm while in oil product samples were 1.32E5, 5.87, 4.56E2, 4.22E2, 7.16E3, 699, 157, 8.74, 492.3, 61 and 198.2 ppm. Validation of the k ₀-PGAA was applied in analyzing standard IAEA reference material (soil-7) which give good agreement with the literature data. The ²⁵²Cf neutron beam in radiation position was characterized by the cadmium-ratio method, and found that the cadmium ratio (f), was 160.     

A study on neutron energy spectrum estimation by LaBr3:Ce detector

A novel approach to estimation of neutron energy spectrum by LaBr₃:Ce detector which was usually used for gamma rays measurement was presented. In this approach, energy distribution of the neutron flux was devided into several bins, and simultaneous equations of these bins were setup based on the net counts of gamma peaks induced by neutron inelastic scattering with LaBr₃:Ce detector. With these equations, the neutron energy spectrum was derived by a deconvolution algorithm. This approach was tested using a 3 in.?×?3 in. LaBr₃:Ce detector exposured to an ²⁴¹Am-Be neutron source and proved practicable.

     

Single electron capture by C3+ ions in He,Ne and Ar

Translational energy spectra have been obtained for 6 keV C²⁺ ions resulting from single-electron capture by 6 keV C³⁺ ions in collision with He, Ne and Ar. Our data for He and Ne are in good agreement with previous measurements, while data for the Ar target have not appeared in the literature. The spectrum for C³⁺ in Ar is complex and appears to contain many strong spectral features which involve capture with excitation of the target product ion in Ar⁺.     

The application of a252Cf neutron multiplier for routine instrumental neutron activation analysis

The successful application of instrumental neutron activation analysis for routine determinations depends on the ability to produce accurate and precise analytical results in a relatively short time. An important factor in obtaining the desired speed has been the availability of a low-cost, moderate-flux neutron source for on-site use. The²⁵²Cf neutron multiplier (CFX), designed and constructed by Intelcom Rad Tech Corporation of San Diego, California, is a subcritical assembly capable of continuous, stable operation and has provided us with the ability to determine more than 35 elements as major and minor components. The CFX produces a thermal neutron flux of ∼2×10³ n/cm²-sec by a 100-fold multiplication of the neutrons emitted from a 1 mg²⁵²Cf source. Of particular importance in its application at Kodak has been the determination of the halogens Cl, Br, and I, both singly and simultaneously, in various matrices including photographic materials.     

Instrumental neutron activation determination of rare earth,noble and other elements in mineral raw materials of The Socialist Republic of Vietnam

The possibilities of multielement neutron activation analysis of the mineral raw materials of the Socialist Republic of Vietnam, have been studied. Samples were activated by a²⁵²Cf neutron source (yield 4·10⁹ n·s^–1). The induced activity was measured by coaxial Ge(Li) and planar Ge detectors. The content of gold, thorium, uranium, rare earths and other elements, was determined and evaluated in ores and concentrates by an absolute method.     

Application of an image scanner for determination of boron in glass by a nuclear track technique

For boron concentration in the range of 010%, a 600 g²⁵²Cf neutron source was used for thermal neutron irradiation. As for the track counting technique, a visual observation method by human eye and an automatic counting method with an image scanner showed a good agreement between the determinations by both methods. The latter is useful for improving accuracy in elemental determination by using the nuclear track technique because it gives reproducible count values which are free from human error in comparison with the former.     

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.     

Fabrication of 50-mg252Cf neutron sources for the FDA activation analysis facility

The Transuranium Processing Plant (TPP) at the Oak Ridge National Laboratory (ORNL) has been requested by the Food and Drug Administration (FDA) to furnish 200 mg of²⁵²Cf for use in their new activation analysis facility. This paper discusses the procedure to be employed in fabricating the californium into four neutron sources, each containing a nominal 50-mg of²⁵²Cf. The completed neutron sources will be assayed using a precision fast-neutron counter, decontaminated and loaded into a concreete-shielded shipping container weighing 10.7 Mg for shipment to the FDA facility located at Howard University in Washington, D. C.Research sponsored by the Office of Basic Energy Sciences, U. S. Department of Energy, under contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.     

The comparison of four neutron sources for Prompt Gamma Neutron Activation Analysis (PGNAA) in vivo detections of boron

A Prompt Gamma Ray Neutron Activation Analysis (PGNAA) system, incorporating an isotopic neutron source has been simulated using the MCNPX Monte Carlo code. In order to improve the signal to noise ratio different collimators and a filter were placed between the neutron source and the object. The effect of the positioning of the neutron beam and the detector relative to the object has been studied. In this work the optimisation procedure is demonstrated for boron. Monte Carlo calculations were carried out to compare the performance of the proposed PGNAA system using four different neutron sources (²⁴¹Am/Be, ²⁵²Cf, ²⁴¹Am/B, and DT neutron generator). Among the different systems the ²⁵²Cf neutron based PGNAA system has the best performance.     

Cross-sections for formation of <Superscript>178m2</Superscript>Hf and <Superscript>179m2</Superscript>Hf through reactions on natural hafnium at neutron energy 14.8 ± 0.2 MeV

The cross sections for formation of metastable state of ¹⁷⁸Hf (^178m2Hf, 574.215 keV, 31 y) and ¹⁷⁹Hf (^179m2Hf, 362.55 keV, 25.05 d) through reactions induced by 14.8 ± 0.2 MeV neutrons on natural hafnium were measured for the first time. The monoenergetic neutron beam was produced via the ³H(d, n)⁴He reaction on ZF-300-II Intense Neutron Generator at Lanzhou University. Induced gamma activities were measured by a gamma-ray spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The neutron fluence were determined by the cross section of ⁹³Nb(n, 2n)^92mNb reaction. The neutron energy in the measurement were by the cross section ratios of ⁹⁰Zr(n, 2n)^89m+gZr and ⁹³Nb(n, 2n)^92mNb reactions.     

A quick method for the determination of the Al/Si weight ratio in alumino-silicates using an Am-Be neutron source

An irradiation procedure with fast and thermal neutrons from a 5 Ci Am-Be isotopic neutron source irradiation facility in combination with a 3'3' NaI(Tl) detector system has been used to determine Al/Si weight ratios in alumino-silicates. Samples were irradiated with and without Cd cover for 10 minutes and counted for 10 minutes after a waiting time of 1 minute. The peak area analysis of the 1779 keV gamma-ray line of ²⁸Al product radionuclide produced via ²⁷Al(n,γ)²⁸Al and ²⁸Si(n,p)²⁸Al reactions in combination with the neutron flux parameter at the irradiation site and nuclear data were used to determine Al/Si ratios. Due to discrepancy in literature data, Am-Be neutron source spectrum averaged cross sections of (n,p) reactions on ²⁷Al, ²⁸Si and ⁵⁶Fe were determined by the activation technique using ¹¹⁵In(n,n')^115mIn as the fast neutron flux monitor reaction. The method was tested using mixtures of high-purity Al₂O₃ and SiO₂ with known weight ratios of Al/Si and validated by a certified reference material BCS-CRM 348 (Ball Clay). Results are presented for bentonite, kaolin, bauxite, feldspar and ball clay samples from Nigeria. The method is non-destructive, rapid and suitable for use in-situ for large-scale exploration works and industrial process control. This revised version was published online in July 2006 with corrections to the Cover Date.