Β-ray Induced X-ray Spectrometry Research Articles

3D benchmark experiments of tritium in tungsten for tritium measurements by detecting β-ray induced X-rays

Tungsten is one of the most promising materials for plasma facing components (PFCs), and β-ray induced X-ray spectrometry (BIXS) is an important non-destructive method to obtain tritium depth profile and retention information for the development of PFCs, recovery of fuel and control of tritium safety in a fusion reactor. In this article, benchmark experiments to obtain tritium 3D profile in tungsten have been firstly performed using layer-by-layer chemical etching (LLCE) and imaging plate (IP) techniques. BIXS spectra have been detected at each layer. The average layer thickness of each erosion was controlled to be around 150 nm and 8 layers (the total thickness was 1.21 μm) were eroded, and the maximum uncertainty of tritium activity was 7.91 % in the LLCE experiments. Monte-Carlo simulations of BIXS spectra with Geant 4 code and four kinds of physical packages (Penelope, Livermore, EmStd. Opt1 and EmStd. Opt4) have been benchmarked against to the experimental results. Results show that all the four physical packages are not suitable to calculate the intensity of the BIXS spectra, and the current mode or cross sections should be improved to simulate the interaction between low electron/photon and tungsten accurately. However, the relative intensity of W-Mα peak and W-Lα can be simulated well using current physical packages such as EmStd. Opt4 and Livermore, which is a good indicator for tritium depth profile in tungsten.

Tritium analysis in zirconium film with BIXS and EBS: Generality test of Al thin film as the β-ray stopping layer in BIXS

The tritium analysis in tritium/deuterium-containing zirconium thin films was performed using elastic backscattering spectrometry (EBS) and β-ray induced X-ray spectrometry (BIXS). The EBS energy spectra were simulated with the SIMNRA program to obtain the tritium depth profiles and the total tritium contents in the samples. Two stopping powers used in the SIMNRA program were compared and it was shown that the SRIM stopping power in the simulations was better than the Ziegler/Biersack stopping power. In the BIXS that incorporated Monte Carlo simulation data, the β-ray stopping layers between the X-ray detector and the sample were Al thin film (BIXS-Al) and Ar gas (BIXS-Ar), respectively. The pile-up effects for BIXS X-ray spectra were corrected using Monte Carlo method for the first time. The tritium depth profiles and the total tritium contents in zirconium thin films obtained by the BIXS-Ar, BIXS-Al, EBS and the pressure, volume and temperature (PVT) method were compared. The possible reasons for the difference between the BIXS-Ar and BIXS-Al were discussed and the generality of Al thin film as the β-ray stopping layer was tested and a standard procedure of BIXS method for analyzing tritium-containing solid materials was proposed, in which the BIXS-Al method was recommended.

Tritium distribution analysis of Be limiter tiles from JET-ITER like wall campaigns using imaging plate technique and β-ray induced X-ray spectrometry

Tritium (T) distribution on the plasma-facing surfaces (PFSs) and inside castellation of Be limiter tiles from the JET tokamak with the ITER-like wall (ILW) was analyzed using imaging plate (IP) technique and β-ray induced X-ray spectrometry (BIXS). Regarding to PFSs, the outer poloidal limiter (OPL) showed significantly higher T concentrations than the inner wall guard limiter (IWGL) and upper dump plate (DP). The concentration of T on OPL was high at the central part. However, deuterium (D) and metallic impurities showed maximum concentration at the edges. This difference in distributions indicated different deposition and retention mechanisms between T and D. In contrast, deposition profiles of T concentrations on the castellated surfaces extended up to ∼ 5 mm into the gap, i.e. were similar to those of D and metallic impurities found by ion beam analysis.

BIXS for tritium analysis with Ar gas and Al thin film as β-ray stopping layers and comparison with EBS

β-ray induced X-ray spectrometry (BIXS) and elastic backscattering spectrometry (EBS) were utilized in this study for the tritium analysis of samples of tritium/deuterium-containing titanium films with thick Mo substrates. Using the BIXS method which incorporates Monte Carlo simulated data, we used Ar gas filler (BIXS-Ar) or placed Al film (BIXS-Al), respectively, between the sample and X-ray detector as β-ray stopping layers. Using the EBS method to confirm whether or not the tritium will volatilize under the impact of the proton beams, we conducted two measurements at the same point of the sample surfaces. A TiH film sample with thick Mo substrate was used in our EBS experiment to remove the influence of the Mo spectrum on the EBS experimental spectra of tritium/deuterium-containing samples. We well fit using the SIMNRA code the tritium and deuterium EBS spectra that were obtained by removing the Mo spectra. The tritium content and depth profiles in the titanium films were obtained via these different methods and the results were compared. It was found that the total tritium content measured using the EBS, BIXS-Al, and BIXS-Ar methods were in agreement within the experimental uncertainties, and the BIXS-Al method may be better at measuring the tritium depth profiles than the BIXS-Ar method.

Effects of activation products on tritium measurements for tungsten in fusion reactors

Influence of neutron activated products (NAPs) is one of the primary problems for tritium measurements in tungsten as plasma-facing materials (PFMs). Both Monte Carlo simulation was introduced to calculate the amount of NAPs after different decay time and at different location of the divertor in detail. Then, the effects of NAPs on the commonly used tritium measurement methods for PFMs, including chemical etching method, β-ray induced X-ray spectrometry, tritium imaging plate technique and tritium calorimeter, have been evaluated quantitatively for PFM samples with different tritium depth profile, sample thickness and sample cooling time. Results indicate that more than one hundred kinds of NAPs would generate through the irradiation of fusion neutrons and NAPs with half-lives shorter than 1E-03 year and large activities, such as W-187, W-183 m etc., account for a substantial part of total activity directly after exposure and their amounts rapidly decrease to negligible as decay time increases. However, within cooling time from 3 to 60 months, the influence of tritium measurements is barely dominated by W-185, W-181, Ta-182 and Ta-179. In addition, it is found that the influence of NAPs on chemical etching method is the minimum while the other three approaches are still strongly affected by NAPs after several months. And it usually takes several years to let the signal from NAPs become acceptable comparing with signal from tritium in measurements.

Tritium distributions on W-coated divertor tiles used in the third JET ITER-like wall campaign

Tritium (T) distributions on tungsten (W)-coated plasma-facing tiles used in the third ITER-like wall campaign (2015–2016) of the Joint European Torus (JET) were examined by means of an imaging plate technique and β-ray induced x-ray spectrometry, and they were compared with the distributions after the second (2013–2014) campaign. Strong enrichment of T in beryllium (Be) deposition layers was observed after the second campaign. In contrast, T distributions after the third campaign was more uniform though Be deposition layers were visually recognized. The one of the possible explanations is enhanced desorption of T from Be deposition layers due to higher tile temperatures caused by higher energy input in the third campaign.

Thermal Release Behavior of Tritium from Tungsten After Implantation by Glow Discharge

Tritium release behavior in a tungsten sample after exposing to tritium ions with energy about 200 eV created by glow discharge has been studied by both β-ray–induced X-ray spectrometry (BIXS) and imaging plate (IP). The tungsten sample was heated stepwise in a vacuum vessel at temperatures from 400 to 1000 K in experiments, and results obtained from both BIXS and IP measurements showed that the amount of tritium absorbed on the sample surface decreased more than 97% after heating at 800 K. Both intensity and shape of the measured X-ray spectrum have been specified to estimate the change of the tritium depth profile after each heat treatment. Besides, the Monte Carlo Stopping and Range of Ions in Matter (SRIM) code has been introduced to calculate the initial tritium depth profile just after being irradiated by glow discharge. Analysis shows that tritium atoms locate around 3 nm in depth before annealing, and tritium distribution becomes uniform in the near-surface layers (around several nanometers) gradually after heat treatment. At about 800 K, the relative tritium concentration in the near-surface layers reaches its maximum value compared with tritium in the deeper part of the tungsten sample. Then more and more tritium diffuses deeper into the sample as the temperature increases.

Tritium analysis of divertor tiles used in JET ITER-like wall campaigns by means of β-ray induced x-ray spectrometry

Energy spectra of β-ray induced x-rays from divertor tiles used in ITER-like wall campaigns of the Joint European Torus were measured to examine tritium (T) penetration into tungsten (W) layers. The penetration depth of T evaluated from the intensity ratio of W(Lα) x-rays to W(Mα) x-rays showed clear correlation with poloidal position; the penetration depth at the upper divertor region reached several micrometers, while that at the lower divertor region was less than 500 nm. The deep penetration at the upper part was ascribed to the implantation of high energy T produced by DD fusion reactions. The poloidal distribution of total x-ray intensity indicated higher T retention in the inboard side than the outboard side of the divertor region.

High Level Tritiated Water Monitoring by Bremsstrahlung Counting Using a Silicon Drift Detector

The β-ray induced X-ray spectrometry (BIXS) is a promising technique to monitor the tritium concentration in a fuel cycle of a fusion reactor. For in-situ measurements of high level tritiated water by bremsstrahlung counting, the characteristics of a low-noise silicon drift detector (SDD) have been examined at the Tritium Laboratory Karlsruhe (TLK). In static measurements with constant sample volume and tritium concentration, the bremsstrahlung spectra of tritiated water samples in a concentration range of 0.02 to 15 MBq/ml have been observed. The volume has been kept constant at 5 cm3. The observed spectra are well above the noise threshold. In addition to X-rays induced by β-rays, the spectra feature X-ray fluorescence peaks of the surrounding materials. No indications of memory effects have been observed. A linear relation between the X-ray intensity and the tritium concentration was obtained and the lower detection limit of the setup has been determined to 1 MBq ml-1, assessed by the Currie criterion. In addition, the spectra obtained experimentally could be reproduced with high agreement by Monte-Carlo simulations using the Geant4-toolkit. It was found that the present detection system is applicable to non-invasive measurements of high-level tritiated water and the SDD is a convenient tool to detect the low energy bremsstrahlung X-rays.

Measurements of inner-shell characteristic X-ray yields of thick W, Mo and Zr targets by low-energy electron impact and comparison with Monte Carlo simulations

Inner-shell characteristic X-ray yields are one of the important ingredients in the β-ray induced X-ray spectrometry (BIXS) technique which can be used to perform tritium content and depth distribution analyses in plasma facing materials (PLMs) and other tritium-containing materials, such as W, Mo, Zr. In this paper, the measurements of K, L, M-shell X-ray yields Y(E) of pure thick W (Z=74), Mo (Z=42) and Zr (Z=40) element targets produced by electron impact in the energy range of 5–29keV are presented. The experimental data for Y(E) are compared with the corresponding predictions from Monte Carlo (MC) calculations using the general purpose MC code PENELOPE. In general, a good agreement is obtained between the experiment and the MC calculations for the variation of Y(E) with the impact energy both in shape and in magnitude with ∼10%. The effect of uncertainty of inner-shell characteristic X-ray yields on the BIXS technique is also discussed.

Characterization of Tritium Retention in Plasma Sprayed B4C/Mo Coatings

Quantification of the amount and depth of tritium retained on plasma facing materials(PFMs) surface is of great importance for selecting PFMs with high safety in the nuclear system. In the present study, potential PFMs of B4 C/Mo coatings were prepared and the depth profiles of tritium in the coatings were measured both by imaging plate(IP) technique and β-ray induced X-ray spectrometry(BIXS). The IP images showed that the amount of adsorbed tritium in the coatings followed the order of B4 C BM15 BM5 Mo, which was along with the X-ray spectra also illustrating that most tritium penetrated into the bulk of the B4 C coating while on the surface only for the other three coatings. The cross-sectional morphologies of the coatings were observed by scanning electron microscope(SEM), which demonstrated that B4 C coatings had the highest porosity while the other three coatings were denser despite of the existence of smaller-sized pores and cracks. All the results suggest that pores and microcracks in the as-sprayed coatings provide passageway for tritium penetration and adsorption, which are the key factors that affect the amount of tritium adsorbed. Furthermore, the content of Ti contamination in the coatings also plays an important role in controlling tritium adsorption.

Tritium retention in nanostructured tungsten with large effective surface area

Abstract Tungsten specimens with fiberform nanostructure (Nano-W) were prepared by exposure to helium plasma in the divertor plasma simulator NAGDIS-II with different amounts of helium fluence. For comparison, tungsten specimens with smooth surface (Polished-W) were also prepared. Surface area of Nano-W was measured by using Brunauer, Emmet and Teller (B.E.T.) method. Tritium retention of Nano-W and Polished-W was investigated by an imaging plate (IP) and β-ray induced X-ray spectrometry (BIXS) technique exposure to mixture gas of deuterium and tritium. It was found that surface area of Nano-W was significantly larger than that of Polished-W and increased in proportion to the amount of helium irradiation. On the other hand, tritium retention showed a saturation trend when the helium fluence was higher than 5.0 × 1025 m−2.

Comparison of reconstruction methods of depth distribution of tritium in materials based on BIXS

Three reconstruction methods based on Tikhonov regularization are used to solve the ill-posed inverse problem when incorporating Monte Carlo calculations into the β-ray induced X-ray spectrometry (BIXS) for analyzing the tritium content and depth distribution in the material surface. These methods are implemented by the GENEREG, CONTIN and REGUTOOLS codes, respectively. The tritium sample is assumed to be a molybdenum slab of 5 μm thickness, and an argon gas of 5 mm thickness is filled in front of the molybdenum slab. The Monte Carlo code PENELOPE is used to simulate the X-ray energy spectra induced by tritium’s β-decays. The reconstruction results for tritium depth distributions by these three codes are compared and the comparison shows that the code GENEREG can give satisfactory results. Some discussions are made.

Reconstruction of depth distribution of tritium in materials by β-ray induced X-ray spectrometry

Monte Carlo calculations, instead of the analytical method, are incorporated into the β-ray induced X-ray spectrometry for analyzing the tritium content and depth distribution in the near surface. This improvement makes the β-ray induced X-ray spectrometry for tritium analysis be able to take into account the physics processes more accurately and be utilized more flexibly. The inverse problem involved is treated by using the Tikhonov regularization method and classical molecular dynamics method. The results concerned are discussed.

Effect of Water Vapor on Tritium Decontamination of Stainless Steel 316

ABSTRACTTo establish efficient decontamination methods for tritium-contaminated stainless steels, the desorption of tritium was studied for SS-316 in dry and wet argon gas carriers at different temperatures. The specimen was exposed to tritium at 523 K for 3 hours. The tritium inventory was in a range from 2 to 12 MBq. The desorption at elevated temperatures was measured by using a liquid scintillation counter. In addition, the tritium depth profiles in the specimen were evaluated by β-ray induced X-ray spectrometry. It was found that the decontamination efficiency was enhanced by the presence of moisture. This effect was ascribed to the isotope exchange reaction on the surface. The depth profile measurements revealed the presence of tritium-rich subsurface layer and the bulk with lower tritium concentration. The majority of tritium was, however, found in the bulk, indicating that extraction of bulk tritium is essential for the decontamination of SS-316 exposed to tritium at high temperatures.

Nondestructive measurement of surface tritium by β-ray induced X-ray spectrometry (BIXS)

Abstract Applicability of a newly developed β-ray induced X-ray spectrometry (BIXS) has been examined to measure nondestructively tritium retained on/in the graphite samples. Examination was carried out by using the graphite plates irradiated with tritium ions and an ALT-II limiter tile exposed to D-plasmas in TEXTOR. For the former samples, a sharp intense peak and a broad weak peak appeared clearly in the spectra; the former peak was attributed to the characteristic X-rays from argon used as a working gas, and the latter peak was assigned to the bremsstrahlung X-rays from sub-surface layers of graphite. On the other hand, for the latter sample, a rather weak characteristic X-ray peak was observed along with a diminutive bremsstrahlung X-ray peak. Although the intensities of those X-rays differed from spot to spot, the tritium levels retained on the limiter tile were determined to be 58–132 Bq / cm 2 . It was concluded, therefore, that valuable information on the amount and the distribution of tritium retained on/in the wall materials can be nondestructively obtained by using the BIXS.

In situ observation of tritium interactions with Pd and Zr by β-ray induced X-ray spectrometry

A newly developed technique, β-ray induced X-ray spectrometry (BIXS), was applied to in situ and real-time measurements of depth profiles of tritium in palladium and zirconium. Two distinct spectra were detected by BIXS, one due to the characteristic X-rays giving rise to a sharp intense peak; and the other due to the bremsstrahlung X-rays leading to a broad weak peak. The intensities of these peaks for palladium decreased with time at room temperature, while they were almost constant for the Zr-sample at room temperature. Heating the Zr-sample, however, caused similar changes in the spectra as those for palladium at room temperature. It was found that these phenomena are due to the diffusion of tritium into the bulk regions, causing a reduction of the tritium concentration in the sub-surface layers of the samples. All of the observed β-ray induced X-ray spectra could be reproduced well by computer simulation by assuming respective depth profiles of tritium in the samples. It was confirmed that BIXS is quite useful to analyze the dynamic transport behavior of tritium in materials.