Large volume gas irradiation procedure developed at The University of Texas at Austin

A large volume, in-core gas irradiation technique was developed at The University of Texas at Austin MARK II TRIGA reactor to produce a sample of ⁴²Ar with an activity above 1 mBq. The method requires a large volume, 1.4 L, of natural Ar gas (99.6003 % ⁴⁰Ar) at about 1 atm and three 12 h irradiation periods. The production of ⁴²Ar requires a double capture to be produced from the stable ⁴⁰Ar isotope. This method produced 940 kBq of ³⁹Ar, 3.08 MBq ³⁷Ar, 114 GBq ⁴¹Ar, and 0.311 Bq ⁴²Ar at the end of the final irradiation period.     

Production of <Superscript>37</Superscript>Ar in The University of Texas TRIGA reactor facility

The detection of ³⁷Ar is important for On-Site Inspections (OSI) for the Comprehensive Nuclear-Test-Ban Treaty monitoring. In an underground nuclear explosion this radionuclide is produced by ⁴⁰Ca(n,α)³⁷Ar reaction in surrounding soil and rock. With a half-life of 35 days, ³⁷Ar provides a signal useful for confirming the location of an underground nuclear event. An ultra-low-background proportional counter developed by Pacific Northwest National Laboratory is used to detect ³⁷Ar, which decays via electron capture. The irradiation of Ar gas at natural enrichment in the 3L facility within the Mark II TRIGA reactor facility at The University of Texas at Austin provides a source of ³⁷Ar for the calibration of the detector. The ⁴¹Ar activity is measured by the gamma activity using an HPGe detector after the sample is removed from the core. Using the ⁴¹Ar/³⁷Ar production ratio and the ⁴¹Ar activity, the amount of ³⁷Ar created is calculated. The ⁴¹Ar decays quickly (half-life of 109.34 min) leaving a radioactive sample of high purity ³⁷Ar and only trace levels of ³⁹Ar.     

Average cross-sections for (n,p) reactions on calcium in a fission-type reactor spectrum

The average cross-section in a fission-type reactor spectrum \(\bar \sigma _F\) was experimentally determined for the reactions⁴²Ca(n, p)⁴²K,⁴³Ca(n, p)⁴³K and⁴⁴Ca(n, p)⁴⁴K. Calcium carbonate samples and fast neutron flux monitors were irradiated with and without cadmium shielding in the Thetis reactor (Institute for Nuclear Sciences, Rijksuniversiteit, Gent). The potassium activities induced in the calcium carbonate samples were separated and purified by tetraphenylborate precipitation, after which they were measured with a Ge(Li)-detector of calibrated detection efficiency. On the basis of \(\bar \sigma _F = 0.64\) mb for the reaction²⁷Al(n, α)²⁴Na, the average cross-sections were as follows:⁴²Ca(n, p)⁴²K: 2.82±0.07mb;⁴³Ca(n, p)⁴³K: 1.89±0.05 mb;⁴⁴Ca(n, p)⁴⁴Ca(n, p)⁴⁴K: 0.065±0.003 mb.     

Feasibility study for production of 99mTc by neutron irradiation of MoO3 in a 250 kW TRIGA Mark II reactor

The subject of this paper is to explore the possibility to obtain ^99mTc from activation of ⁹⁸Mo, using the TRIGA Mark II low flux research reactor (Vienna, Austria). Irradiation of both natural and enriched in ⁹⁸Mo molybdenum oxides was compared. Aims of this work included the determination of neutron fluxes and ⁹⁸Mo(n, γ)⁹⁹Mo reaction effective cross section in the TRIGA Mark II reactor irradiation channels, calculation of ⁹⁹Mo specific activities, determination of optimal irradiation conditions for the subsequent ^99mTc separation from MoO₃ targets using concentrating technologies.     

Contributions to the 37Ar background by research reactor operations

Radioargon has been identified as a useful nuclide for verifying compliance with the Comprehensive Nuclear-Test-Ban Treaty. Use of ³⁷Ar to identify a nuclear explosion requires quantification of contributions to the ³⁷Ar background at a potential measurement site. A method of estimating ³⁷Ar release activities using isotopes of radioxenon and radioargon has been developed in this paper. Numerical solutions to the system of equations describing air-activation in a reactor were used to determine ratios of release activities for ¹³⁵Xe/¹³³Xe, ^133mXe/^131mXe, and ³⁷Ar /⁴¹Ar as function of irradiation time and off-gas residence time prior to measurement and release. Published radioactive noble gas effluent data for the High Flux Isotope Reactor, HFIR (ORNL) from the year 1996 to 2010 were compiled as a test data set to predict the ³⁷Ar release on a yearly basis. An average ³⁷Ar release rate of 1.86 × 10¹⁰ Bq per year was calculated. The estimated release rate was used as a source term for atmospheric transport to run a test case for ³⁷Ar release over a typical HFIR operation cycle. Results showed that ground-level concentrations of ³⁷Ar did not exceed the minimum detectable concentration for a ³⁷Ar field measurement system beyond the immediate vicinity of the release point.     

Dating of mineral samples through activation analysis of argon

Mass Spectrometry has been the usual method to determine Ar concentrations in mineral samples for dating them through the⁴⁰Ar/⁴⁰K ratio. This technique has been replaced since 1966 by measurement of⁴⁰Ar/³⁹Ar ratio, after artificial production of³⁹Ar from the³⁹K(n,p)³⁹Ar reaction produced in the fast neutron flux of a nuclear reactor. This method requires the fusion of the sample by incremental heating until reaching a temperature of 1000°C in order to get the total release of both argon isotopes. In principle, it should be possible to determine the⁴⁰Ar/⁴⁰K ratio by activation analysis in an easier, non-destructive way, but it presents the following drawbacks: manufacture of argon standards; usual low ratio peak/Compton distribution for both peaks: 1.29 Mev and 1.52 Mev (⁴¹Ar and⁴²K respectively), since potassium minerals are usually very rich in sodium, manganese and chlorine; reaction⁴¹K(n,p)⁴¹Ar induced by fast neutrons present in the thermal flux; and possible contamination of the samples and standards with atmospheric⁴⁰Ar (99.6% of elementary Ar, whose proportion in the atmosphere at sea level is 0.93%). This paper describes how these problems may be solved, also determining the limits of Ar and K concentration related to Compton distribution, in our experimental conditions.     

Determination of the fission averaged cross sections of some threshold reactions induced on chlorine, potassium, and calcium, and their role in the development of self-validated methods of neutron activation analysis

The feasibility of validating data obtained in the determination of chlorine, potassium, and calcium by neutron capture activation analysis, through their determination using threshold reactions has been studied. To this purpose the authors experimentally determined the following fission neutron spectrum averaged cross sections (in mb):³⁷Cl(n,p)³⁷S, 0.234±0.015;⁴¹K(n,α)³⁸Cl, 0.740±0.044;⁴²Ca(n,p)⁴²K, 3.09±0.22;⁴³Ca(n,p)⁴³K, 2.27±0.12;⁴⁴Ca(n,p)⁴⁴K, 0.074±0.013. The application of these values to the analysis of some reference materials are presented. Also, the problem of mutual interferences has been addressed for the following pairs:³⁶S(n,Γ)³⁷S and³⁷Cl(n,p)³⁷S;³⁷Cl(n,Γ)³⁸Cl and⁴¹K(n,α)³⁸Cl;⁴¹K(n,ψ)⁴²K and⁴²Ca(n,p)⁴²K.     

Characterization of the neutron flux gradients in typical irradiation channels of a TRIGA Mark II reactor

The neutron distribution in a defined volume (gradient) for different matrices (air, water, cellulose, biological material and silicon dioxide) in two typical irradiation channels (pneumatic tube (PT) and IC40-channel in the carousel facility) in the TRIGA Mark II reactor at the Joef Stefan Institute (IJS) was studied. Our experiment was based on inserting Fe wires (flux monitors) into the chosen matrices. The wires were cut into small pieces after irradiation and the induced activities of ⁵⁹Fe measured. The results showed that for the studied geometry the average spatial thermal neutron flux inhomogeneities (for five studied matrices) are about 2.3% in the PT-channel and about 2.9% in the IC40-channel.     

Application of neutron activation analysis to the measurement of isotope abundance shifts in calcium and potassium

A simple method for the measurement by neutron activation analysis of the isotopic abundance shifts of⁴⁴Ca and⁴¹K in compounds of low volatility is described. Extraction and measurement procedures for the radioactive argon isotopes (³⁷Ar,³⁹Ar and⁴¹Ar produced by (n, α) and (n, p) reactions are also given. The results obtained demonstrate that the accuracy for the measurement of δ⁴⁴Ca is better than by the mass spectrometric method; in the case of δ⁴¹K measurement the accuracy is the same as that obtained with the mass spectrometer. Interfering reactions which yield other rare gases, and their relative contribution to the error in the measurement of δ values are also discussed.     

Neutron flux variability at the TRIGA MARK II reactor,Ljubljana, as a parameter with applying the ko-method of NAA

Neutron-flux behaviour during irradiation should be known when applying the k_o-method of neutron activation analysis /NAA/. During two 100-hour operating periods of the TRIGA MARK II reactor, Ljubljana, the flux was measured by means of a¹⁹⁷Au/n,/¹⁹⁸Au monitor /E=411.8 keV/. Cadmium-covered irradiations were also performed to obtain the epithermal flux and thermal-to-epithermal flux ratio variations. Consistency was found between these results and the reactor operators' logbook record.     

Dielectric loss of neutron-irradiated nanocrystalline silicon carbide (3C-SiC) as a function of frequency and temperature

At the present work, nanocrystalline 3C-SiC has been irradiated by neutron flux (2 × 10¹³ n·cm⁻²s⁻¹) up to 20 h in a TRIGA Mark II type research reactor. The dielectric loss of nanocrystalline 3C-SiC was studied comparatively before and after neutron irradiation. The increased dielectric loss was clearly observed after neutron irradiation in both f(tanδ) ∼ f(f) and f(tanδ) ∼ f(T) plots. Furthermore, slope observed on the f(tanδ) ∼ f(f) plots at certain values of the frequency. Dielectric loss increasing and shifted slope explained by the neutron transmutation, dangling bonds, the formation of the defects or additional charge carriers. Moreover, the mechanism of all effects obtained from the experiments was explained by the polarization approach.     

The single-comparator method in thermal neutron activation analysis extended for some (n,p) reactions

From experimental studies of the rate of the reactions⁴⁷Ti(n, p)⁴⁷Sc,⁴⁸Ti(n, p)⁴⁸Sc and⁵⁸Ni(n, p)⁵⁸Co in four nuclear reactors, it is concluded that for the irradiation positions of the light water moderated reactors BR2 (Mol, Belgium) and HFR (Petten, Netherlands) a simple empirical relation exists between the fast neutron flux on the one hand and the thermal and epithermal neutron flux on the other. The graphite moderated reactor BR1 (Mol, Belgium) and the heavy water reactor FRJ2 (Jülich, Federal Republic of Germany), however, have relatively much lower fast fluxes and their irradiation facilities do not obey the empirical relation determined.     

Determination of neutron flux parameters in PUSPATI TRIGA Mark II Research Reactor, Malaysia

In standardization NAA, it is necessary to characterize the neutron spectrum parameters such as epithermal neutron flux shape factor (α), thermal to epithermal neutron flux ratio (f), thermal neutron flux (φ _th) and epithermal neutron flux (φ _epi) in the irradiation facility to determine the concentration of an element in the sample using absolute and k ₀ standardization methods. The α and f were determined using Cd-ratio multi monitor method using experimental data obtained in PUSPATI TRIGA Mark II research reactor at four irradiation positions (10, 20, 30 and 40) of the rotary rack. The calculated values of α and f ranged from 0.006 to 0.0281 and 18.56 to 19.12 respectively. The average values of φ _th and φ _epi were found as 2.33 × 10¹² and 1.23 × 10¹¹ n cm^?2 s^?1 respectively. Moreover, a comparison of the neutron flux parameters in the present study shows an acceptable level of consistency with those of previous studies.     

Preparation of radio-Sm by neutron activation for accelerator mass spectrometry

Field measurement of isotopic ratios may be used to fingerprint an element’s origin, be it from commercial power, industrial, medical or historical weapons fallout. Samples of samarium radionuclides were prepared by neutron activation for subsequent analysis using accelerator mass spectrometry (AMS). High purity samarium (III) oxide powder was irradiated in the University of Texas at Austin TRIGA reactor to a total neutron fluence of 5 × 10¹⁵ cm^?2. An initial determination of the isotopic ratios was made using activation calculations with a BURN card in an MCNPX-based model of the TRIGA core. Experimental validation of the MCNP results was achieved by analyzing gamma spectra of the irradiated oxide powers after irradiation. Subsequent measurement of ¹⁵¹Sm will be conducted at the CAMS facility at LLNL demonstrating the first measurement of this isotope at this facility.     

Multi-element determination in sandstone rock by instrumental neutron activation analysis

Summary Instrumental neutron activation analysis (INAA) was used for the qualitative and quantitative analysis of sandstone samples of Aswan area, in South Egypt. The samples were properly prepared together with standards and simultaneously irradiated by a neutron flux of 7 ^. 10¹¹ n ^. cm^-2.s^-1. in the TRIGA research reactor facilities in Mainz. The gamma-spectra from a hyperpure germanium HPGe detector were analyzed. The present study provides the basic data of elemental concentrations of a sandstone rock. The following elements have been determined: Na, K, Fe, Sc, Cr, Co, Zr, Ce, La, Nd, Sm, Eu, Yb, Lu, Hf, Ta, Th and U. Energy dispersive X-ray fluorescence (EDXRF) was used for comparison and to detect elements which can be detected only by this method.     

Cross-sections of 14 MeV neutron reactions on phosphorus and calcium

Cross-section values for 14.7 MeV neutrons are measured for the following reactions: $$\begin{gathered} ^{31} P(n,\alpha )^{28} Al,(132 \pm 10)mb;^{42} Ca(n,p)^{42} K,(173 \pm 19)mb; \hfill \\ ^{43} Ca(n,p)^{43} K,(111 \pm 9)mb;^{44} Ca(n,p)^{44} K,(42 \pm 2)mb; \hfill \\ ^{44} Ca(n,\alpha )^{41} Ar,(27 \pm 2)mb;^{48} Ca(n,2n)^{47} Ca,(616 \pm 54)mb. \hfill \\ \end{gathered}$$ An analysis of available cross-section data for these reactions is performed and preferred mean values for each reaction are given.     

Preliminary study of trace elements in human brain tumor tissues by instrumental neutron activation analysis

Elemental profiles of brain tumor tissues from 15 patients of astrocytomas (grade I–III) and normal human brain tissues of 23 male age matched autopsies as controls have been studied by instrumental neutron activation analysis. The SLOWPOKE reactor with a thermal neutron flux of 8·10¹¹n·cm^–2·s^–1 and swimming pool type reactor with a thermal neutron flux of 1·10¹³n·cm^–2·s^–1 were used for short and long irradiation of samples, respectively. Spectrophotometry was only used for analyzing phosphorus. A total of 18 elements Se, Na, K, Br, Cl, Mn, Mg, S, Ca, Cu, Hg, Cr, Fe, Rb, Zn, Co, Sc and P has been determined for this purpose. The reliability of methods has been checked by analyzing biological standard reference materials horse kidney (IAEA H-8) and bovine liver (NBS SRM 1577a). The analytical results showed that compared with the normal brain tissues, concentrations of Ca, Fe, Cu, Zn, Se, Mn, Br and Sc were significantly higher in tumor tissues (P<0.01) and concentrations of Rb, K and P were lower, while no differences for contents of Mg, S, Cr, Hg, Na and Cl were observed. A negative correlation between P and Ca in malignant and normal brain tissues was observed.     

A search for losses of chemical elements during freeze-drying of biological materials

Possible losses of seven chemical elements were investigated in biological tissues during freeze-drying in vacuum. Thyroid glands were taken during post-mortem examination of 23 people died of different diseases. Instrumental neutron activation analysis (INAA) was used to estimate contents of Br, Ca, Cl, I, K, Mg, and Na. The nuclear reator vertical channel with flux density of 1.2·10¹³n·cm^–2·s^–1 was used for neutron irradiation. The analysis was carried out using short-lived radionuclides induced in samples after neutron irradiation. Then thyroids were freeze-dried at below 0 °C in vaccum up to the constant mass (lyophilisation) and then homogenized. Samples of lyophilised and homogenized tissues were again studied by INAA. The lack of difference between the results of the analysis before and after lyophilisation is an evedence of no loss of Br, Ca, Cl, I, K, Mg and Na during freeze-drying of biotissues in vaccum.     

Determination of trace elements in high purity copper by INAA, GFAAS and ICP/AES

Trace impurity elements in high purity copper metal (4 mine class) put on the market were analyzed by Instrumental Neutron Activation Analysis (INAA) and the results compared with those from Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS) and Inductively Coupled Plasma Atomic Emission Spectrophotometry (ICP-AES). The sample irradiation was done at the irradiation facilities (thermal neutron flux, 5·10¹² n·cm⁻²·s⁻¹) of the TRIGA Mark-III research reactor in the Korea Atomic Energy Research Institute. Four unalloyed copper standards (NIST SRM # 393, 394, 395 and 398) were used to identify the accuracy and precision of the analytical procedure. The homogeneity of samples was assessed by means of the elements such as Ag, As, Co, Sb, Se and Zn. The analytical results of INAA, GFAAS and ICP-AES were in good agreement within expected uncertainties each other and showed the possibility of using them for the analytical quality control.     

Determination of trace elements in biological materials by neutron activation and extraction with TOPO

Solvent extraction with TOPO from 6M hydrochloric acid is proposed as a method for the elimination of interfering activities in neutron activation analysis of biological material for trace elements. By this procedure²⁴Na,⁴²K,³²P,⁸²Br, and⁴⁷Ca are efficiently removed, and a number of trace element activities can be measured by Ge(Li) spectrometry. Chemical yields are determined by re-activation. Data for Cu, Zn, Mo, and Cd in two biological standards are presented.