Neutron-irradiated Targets Research Articles

Steady-State Mechanical Analysis for Target Assembly in the Material Plasma Exposure eXperiment Facility

The Material Plasma Exposure eXperiment (MPEX) steady-state linear plasma facility is currently under design at Oak Ridge National Laboratory to expose target specimens to fusion divertor regimes. The neutron-irradiated target is actively cooled and remote handled in the MPEX facility for conducting plasma-material–interaction (PMI) experiments. In this study, the steady-state stresses in the target and target assembly system are investigated using two-dimensional (2-D) and three-dimensional (3-D) models to provide expected stresses/strains under the heat loads to which various system components would be exposed during MPEX operation. The calculated temperatures from the 2-D axisymmetric mechanical model were found to be in excellent agreement with those from the full 3-D thermohydraulic model, providing a strong model validation. Numerical simulation results for the steady-state mechanical model indicate nonuniform distributions for the temperature, stress, and deformation within the critical components. For the initial design, the deformation results indicate possible gap openings between contacting surfaces below the plasma-facing materials. To reduce the possibility of interfacial gap opening, the target assembly was slightly changed and evaluated using the 2-D stress model. Numerical simulation results indicate that the interfacial gap openings can be minimized without drastically changing the entire target assembly. The stress-strain conditions for the target will be further used to assess the appropriate operation during MPEX experiments and gain insight into materials science phenomena during PMI.

Evidence of lithium mobility under neutron irradiation

Understanding compositional and microstructural changes in functional intermetallic coatings is of great importance for fusion energy and nuclear materials applications. Tritium ( 3 H) and lithium ( 6 Li, 7 Li) transport within a neutron irradiated target rod employing an aluminide-coated austenitic stainless-steel cladding was investigated using state-of-the-art multimodal imaging. Specifically, a scanning electron microscope augmented with focused ion beam (SEM-FIB) was used to prepare lift-out samples of the irradiated coating for microanalysis. Scanning transmission electron microscopy (STEM) was used to acquire atomic-scale information on the coating surface microstructure, morphology, and composition. Atomic force microscopy (AFM) was used to determine lift-out dimensions nondestructively. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed the presence of carbonaceous species and unexpected lithium isotopic distributions in the irradiated tubing, suggesting light isotope mobility between internal target components during irradiation. SIMS chemical mapping of aluminide coatings at core midplane and lower core locations of the cladding shows that light isotopic (e.g., 3 H, 6 Li, 7 Li) distributions are different in the irradiated coating. Advance correlative imaging results suggest lithium transport during the tritium production process and give new insights into the fundamental transport mechanism within the target during irradiation and non-equilibrium conditions.

The Fission-Based 99Mo Production Process ROMOL-99 and Its Application to PINSTECH Islamabad

An innovative process for fission based99Mo production has been developed under Isotope Technologies Dresden (ITD) GmbH (former Hans Wälischmiller GmbH (HWM), Branch Office Dresden), and its functionality has been tested and proved at the Pakistan Institute of Nuclear Science and Technology (PINSTECH), Islamabad. Targets made from uranium aluminum alloy clad with aluminum were irradiated in the core of Pakistan Research Reactor-1 (PARR-1). In the mean time more than 50 batches of fission molybdenum-99 (99Mo) have been produced meeting the international purity/pharmacopoeia specifications using this ROMOL-99 process. The process is based on alkaline dissolution of the neutron irradiated targets in presence of NaNO3, chemically extracting the99Mo from various fission products and purifying the product by column chromatography. This ROMOL-99 process will be described in some detail.

A facility for fast-neutron irradiations at Jyväskylä and its use for nuclide cross-section measurements in fission

An efficient and reliable transport system for fast-neutron irradiations has been built at the Physics Department, Jyväskylä, Finland. It is constructed from commercial bicycle components and is driven by a computer-controlled stepping motor. It can be operated in single or cyclic mode. The neutron irradiated targets are moved within 1.2s (full stop to full stop) to a well-shielded position 3m away where they can be removed or directly investigated by γ spectroscopy. The system has been built with the aim to experimentally verify the calculated production rates of neutron-rich nuclei in the SPIRAL2 uranium target. However, the facility can be used for various kinds of fast-neutron irradiations, with a neutron spectrum up to 60MeV produced by stopping a deuteron beam of several μA in a thick target. Examples of applications are activation and integral cross-section measurements, evaluation of damages in materials and biological cells.

Determination of impurity radionuclides in 131Cs solutions

The radiochemical purity of a 131 Cs solution used in brachytherapy is studied. After separating 131 Cs from the neutron irradiated targets BaO, Ba(NO 3 ) 2 , and BaCO 3 , the contribution of impurities was evaluated: 0.015% for 124 Sb and 0.012% for 132 Cs. The contribution of the parent 131 Ba to cesium solutions was, on average, 0.0067% for BaO, 0.01% for Ba(NO 3 ) 2 , and 0.011% for BaCO 3 . Brachytherapeutic treatment methods for cancer are widely used in nuclear medicine. The essence of brachytherapy lies in the fact that several tens of microsources of ionizing radiation are introduced into tissue tumors using special needles without any surgical intervention. The microsources are small titanium capsules‐grains containing a radionuclide which possesses definite nuclear characteristics, such as the presence of low-energy radiation for effective action on a tumor and absence of high-energy radiation to prevent damage to healthy tissue. Radiation sources based on 131 Cs were first used in 2004 in clinics in the USA and it was determined that 131 Cs suppresses the growth of cancer cells more quickly and effectively than 125 I and 103 Pd, which are used now [1, 2]. Radiation microsources based on 131 Cs have proven themselves well

Unique challenges with recent gamma spectroscopy measurements at Los Alamos National Laboratory

A variety of unique radioactive samples have been measured recently at Los Alamos National Laboratory (LANL) using an electrically-cooled high-purity germanium detector. In each case the purpose of the measurements included one or more of the following objectives: (1) an accurate determination of the isotopic weight fractions of different plutonium or uranium materials; (2) an accurate determination of the isotopic quantity in the absence of relevant calibration standards; and (3) a qualitative determination of various sample impurities for additional forensic information. This paper discusses how simple modifications to the PC-FRAM parameter sets enabled a better determination of the isotopic content of the following samples: (1) high-purity plutonium metal, (2) plutonium-beryllium (PuBe) neutron sources, (3) neutron-irradiated natural uranium, and (4) re-processed HEU fuel with elevated 236U content. The isotopic quantity in a variety of samples was determined using a combination of the Spectral Nondestructive Assay Platform (SNAP™) routine from Eberline Services and the Monte Carlo Neutral Particle (MCNP) code developed at LANL. The non-traditional sources that were quantified with these gamma ray modeling codes included dozens of neutron-irradiated targets of natural uranium, several plutonium-beryllium neutron sources, and three high-purity samples of plutonium metal.

Separation of no-carrier-added arsenic-77 from neutron irradiated germanium

Arsenic-77 ( T 1/2 =1.6 d) was produced by irradiating natural germanium in Pakistan Research Reactor-1. The nuclear reaction 76 Ge( n ,γ) produces 77 Ge, which decays by emission of β - particles into 77 As. The neutron irradiated target was dissolved in aqua regia, excess of acid was removed by evaporation and finally the solution in basic media was passed through hydrous zirconium oxide (HZO) column. The Ge was quantitatively retained on HZO, while 77 As was present in the effluent. More than 90% 77 As was recovered. The chemical impurity of Ge in 77 As was <0.01 μg/mL.

Chemical stabilization of recoil 56Mn in MnSO4-KClO4 mixed crystals following (n, γ) process

Summary Stabilization of recoil 56Mn in mixed crystals of MnSO4KClO4 was studied with especial emphasis on isothermal annealing of neutron irradiated target. The results showed that *MnO4 - yield (%) varies linearly with the increase in perchlorate concentration from 0.100 to 0.500 mol fraction, reaching a maximum value of (89.0 ± 1.1)%. However, the value of intercept (P 0) obtained was (63.0 ± 1.2)%. Isothermal annealing of 56Mn in the present mixed crystal (MnSO4KClO4) of the two molar concentrations (i.e., 0.100 and 0.500 mol fraction) of perchlorate was studied at different temperatures for a desired length of time. The retention values increased with increasing temperature and time of annealing for both the samples. The values found for the two concentrations were (67.0 ± 1.0)% and (89.0 ± 1.1)%, respectively, at room temperature. Retention value increased gradually in the beginning but slowed down with a lapse of time and finally attained saturation within about 20 min of heating at 373 K in both cases. Limiting saturations were found to be (86.0 ± 1.0)% (max) for 0.100 molar concentration and (96.0 ± 0.8)% (max) for 0.500 molar concentration. The rate of annealing was found to increase while the extent of annealing decreased. The recoil re-entry process obeys first order rate law and the energies of activation for the system (MnSO4KClO4) computed from the classical Arrhenius plots were found to be 0.15 ± 0.05 eV for 0.1 molar ratio and (2.5 ± 0.06)×10-2 eV for 0.5 molar ratio. The low value of activation energy indicates that there is a recombination of recoil fragments and participation of defect controlled reactions in thermal annealing, leading to higher saturation retention in 0.500 molar ratio. The results obtained are discussed in the light of vacancies created by the dopant and helping in the proposed recoils stabilization mechanism.

A novel, very compact 1.0 MV singletron™ accelerator

Recently, a novel 1 MV terminal voltage, single ended accelerator has been put into operation at the Institute of Advanced Energy, Kyoto University, Japan. The coaxial Singletron™, in which three new technologies are made successfully for practical use, is characterised by a very small footprint of 1×2 m 2 and has been designed by High Voltage Engineering Europa B.V. It is part of an experimental set-up called DuET. The accelerator will be applied to simulate atom transmutation in neutron irradiated target materials in nuclear fusion material research. The accelerator is capable of delivering high brightness beams of e.g. hydrogen and helium. A typical brightness of >10 A m −2 rad −2 eV −1 was measured for a∼20 μA, 1 MeV H + beam. Initial test showed stable operation at 1 MV terminal voltage for three consecutive days with currents of 20 μA He + when the terminal was cooled directly.

Cross sections of neon isotopes induced by 5, 7, 16, and 19 MeV neutrons

Neutron-irradiated targets of natural magnesium have been analyzed by mass spectrometry in order to determine the excitation functions of neon from the energy threshold up to 20 MeV. Production cross sections of {sup 20,21,22}Ne isotopes were measured at 5.20, 7.00, 16.20, and 19.05 MeV.

Determination of Se, Cd, and Hg in an aquatic environment of Bombay by substoichiometric neutron activation analysis

The toxicity of Se, Cd, and Hg as environmental pollutants and the impact of these elements on the aquatic ecosystem is undisputed. The present paper reports an investigation of the concentration of Cd, Se, and Hg in an aquatic environment of a large metropolitan city like Bombay. As the toxicity of these elements manifests itself at micro and submicro levels, the very sensitive technique of neutron activation analysis was employed. A sequential substoichiometric extraction technique for the separation of radiochemically pure203Hg,75Se, and115–115mCd from the neutron irradiated target has also been employed.

The reaction Mg(n,α)Ne at 14.1 and 14.7 MeV: cross sections and implications for meteorites

Mass spectrometric analyses of neutron-irradiated targets of natural magnesium yield cross sections of59 ± 14,160 ± 8, and11.0 ± 3.3mb for 20Ne, 21Ne, and 22Ne, respectively, at 14.1 MeV and of94 ± 8,152 ± 12, and13.0 ± 2.0mb at 14.7 MeV. With the incorporation of these cross sections, calculations modeling cosmic-ray interactions in stony meteoroids of radii 20 and 26 cm predict that between the surface and center the 22Ne/ 21Ne ratio falls more than 10% while the 21Ne production rate rises about 30%. The reaction 24Mg(n,α) 21Ne predominantly controls these trends: the 22Ne/ 21Ne ratio due to magnesium decreases over 15% while that due to silicon remains constant with increasing depth. The calculations are compared with published neon measurements for the Keyes and St. Séverin meteorites.