Increasing Neutron Dose Research Articles

EPR spectroscopic characterization of neutron-irradiated nanocrystalline anatase particles

This study investigates the effects of neutron irradiation on nanocrystalline anatase (TiO₂) using electron paramagnetic resonance (EPR) spectroscopy. Neutron irradiation doses of 1.6 × 101⁵, 8 × 101⁵, 4 × 101⁶, and 2 × 101⁷ n/cm2 were applied to TiO₂ samples, and changes in the EPR spectra were analyzed to explore the transmutation of titanium (Ti) atoms into vanadium (V). The results reveal that the irradiation induces the conversion of 50Ti to 51V via neutron capture, accompanied by the formation of oxygen and titanium vacancies. The intensity of the EPR signal decreases with increasing neutron dose, indicating that the formation of 51V isotopes and other irradiation-induced effects influence the material's paramagnetic behavior. The study provides insights into the transmutation process and highlights the potential of neutron irradiation for modifying the properties of TiO₂, with implications for photocatalytic applications and radiation-resistant materials.

Effects of neutron radiation as cosmic radiation on food resources

One of the major challenges in deep space exploration are effects of cosmic rays on human body and soft error, but equally important are their effects on food resources. In this study, we focused on neutrons as the secondary particle in the deep space environment and investigated how they affect food resources. Fast neutron was irradiated by the RIKEN Accelerator-driven compact Neutron Source (RANS) on meat sample. Biochemical analysis was conducted to present concrete effects of cosmic rays on food in deep space environment. Oxidative and nitrative modifications of proteins were detected by the electrophoresis and Western blotting. The result shows that nitrative modification of tryptophan, which is an essential amino acid in protein, tended to increase with increasing neutron dose.

Swelling of Highly Neutron Irradiated Beryllium and Titanium Beryllide

The swelling of beryllium and titanium beryllide after irradiation at 70–750 °C to neutron fluences of (0.25–8) · 1022 cm−2 (E > 1 MeV) was measured using methods of immersion, dimension, and helium pycnometry. Dependences of the swelling on the irradiation temperature and neutron dose were plotted and analyzed. The dose dependences show linear dependences of the swelling for all irradiation temperatures except 70 °C, where the swelling rate varies, depending on increasing neutron dose. Be-7Ti shows much less swelling than pure Be. Irradiation at 430–750 °C to neutron fluence of 1.82 · 1022 cm−2 (E > 1 MeV) leads to swelling of Be at about 50%; for Be-7Ti, it is 2.7%. The microstructure study shows that the formation of bubbles and pores in beryllium occurs much more intense than in titanium beryllide.

Cold neutron radiation dose effects on a 6LiF:ZnS(Ag) neutron detector with wavelength shifting fibers and SiPM photodetector

A 6LiF:ZnS(Ag) based cold neutron detector with wavelength shifting (WLS) fibers and SiPM photodetector was developed at the NIST Center for Neutron Research for the CANDoR instrument (Chromatic Analysis Neutron Diffractometer or Reflectometer). A series of detectors were irradiated with neutron doses ranging between 1E+11 n/cm2 to 6E+12 n/cm2. It was found that the neutron absorbing 6Li isotope was not measurably depleted, but the photonic yield of the detector deteriorated with increasing neutron dose. Photonic yields were compared before and after neutron exposure by comparing pulse energy spectrum photopeaks before and after exposure. A typical detector used in the CANDoR instrument is expected to withstand a cumulative cold neutron dose of at least 1E+12 n/cm2 before degrading to an unfit state. The component parts of the detector could not be separated, so the degradation of the bulk scintillator and WLS fibers could not be gauged separately.

Neutron irradiation and forming gas anneal impact on β-Ga2O3 deep level defects

We used depth-resolved cathodoluminescence spectroscopy (DRCLS), absorption spectroscopy, and temperature-dependent Hall effect (TDH) measurements to study the effects of fluence dependent neutron irradiations on deep level defects and the associated changes of electrical properties of β-Ga2O3 grown by low pressure chemical vapor deposition and pulsed laser deposition. DRCLS enabled us to monitor systematic increases of three deep level defects after neutron irradiation which correlated with TDH measurements of significant free carrier removal and mobility decrease. The correlations between defect profiles and electrical property changes vs. irradiation dose link these dominant electrically active native point defects in Ga2O3 with their contributions to free carrier mobility, carrier density, and donor/acceptor depth profiles, further revealing their donor/acceptor electrical behavior and physical nature, consistent with the formation of compensating defects. After irradiation, temperature-dependent forming gas (FG) anneals were performed to reverse the radiation-induced damage and carrier removal. The evolution of defect concentrations with increasing neutron dose and their depth-resolved distributions with FG anneal temperature reveal an interplay between specific defects to control electronic properties.

Correlation between locally deformed structure and oxide film properties in austenitic stainless steel irradiated with neutrons

To elucidate the mechanism of irradiation-assisted stress corrosion cracking (IASCC) in high-temperature water for neutron-irradiated austenitic stainless steels (SSs), the locally deformed structures, the oxide films formed on the deformed areas, and their correlation were investigated. Tensile specimens made of irradiated 316L SSs were strained 0.1%–2% at room temperature or at 563 K, and the surface structures and crystal misorientation among grains were evaluated. The strained specimens were immersed in high-temperature water, and the microstructures of the oxide films on the locally deformed areas were observed. The appearance of visible step structures on the specimens' surface depended on the neutron dose and the applied strain. The surface oxides were observed to be prone to increase in thickness around grain boundaries (GBs) with increasing neutron dose and increasing local strain at the GBs. No penetrative oxidation was observed along GBs or along surface steps.

Effects of high neutron doses and duration of the chemical etching on the optical properties of CR-39

Effects of the duration of chemical etching on the transmittance, absorbance and optical band gap width of the CR-39 (Polyallyl diglycol carbonate) detectors irradiated to high neutron doses (12.7, 22.1, 36.0 and 43.5Sv) were studied. The neutrons were produced by bombardment of a thick Be target with 12MeV protons of different fluences. The unirradiated and neutron-irradiated CR-39 detectors were subjected to a stepwise chemical etching at 1h intervals. After each step, the transmission spectra of the detectors were recorded in the range from 200 to 900nm, and the absorbances and optical band gap widths were determined. The effect of the etching on the light transmittance of unirradiated detectors was insignificant, whereas it was very significant in the case of the irradiated detectors. The dependence of the optical absorbance on the neutron dose is linear at short etching periods, but exponential at longer ones. The optical band gap narrows with increasing etching time. It is more significant for the irradiated dosimeters than for the unirradiated ones. The rate of the narrowing of the optical band gap with increasing neutron dose increases with increasing duration of the etching.

Effects of neutron irradiation on optical and chemical properties of CR-39: Potential application in neutron dosimetry

Effects of high-dose neutron irradiation on chemical and optical properties of CR-39 were studied using FTIR (Fourier Transform Infrared) and UV–vis (Ultraviolet–Visible) spectroscopy. The primary goal was to find a correlation between the neutron dose and the corresponding changes in the optical and chemical properties of CR-39 resulted from the neutron irradiation. The neutrons were produced by bombarding a thick Be target with 22-MeV protons. In the FTIR spectra, prominent absorbance peaks were observed at 1735cm−1 (CO stretching), 1230cm−1(C–O–C stretching), and 783cm−1(C–H bending), the intensities of which decreased with increasing neutron dose. The optical absorbance in the visible range increased linearly with the neutron dose. Empirical relations were established to estimate neutron doses from these optical properties. This technique is particularly useful in measuring high doses, where track analysis with an optical microscope is difficult because of track overlapping.

Radiation-induced stress relaxation in high temperature water of type 316L stainless steel evaluated by neutron diffraction

Weld beads on plate specimens made of type 316L stainless steel were neutron-irradiated up to about 2.5 × 10 25 n/m 2 ( E > 1 MeV) at 561 K in the Japan Material Testing Reactor (JMTR). Residual stresses of the specimens were measured by the neutron diffraction method, and the radiation-induced stress relaxation was evaluated. The values of σ x residual stress (transverse to the weld bead) and σ y residual stress (longitudinal to the weld bead) decreased with increasing neutron dose. The tendency of the stress relaxation was almost the same as previously published data, which were obtained for type 304 stainless steel. From this result, it was considered that there was no steel type dependence on radiation-induced stress relaxation. The neutron irradiation dose dependence of the stress relaxation was examined using an equation derived from the irradiation creep equation. The coefficient of the stress relaxation equation was obtained, and the value was 1.4 (×10 −6/MPa/dpa). This value was smaller than that of nickel alloy.

Positron annihilation coincidence Doppler broadening measurements of irradiation-induced precipitation in Ni-Sn alloys

Irradiation-induced precipitation in Ni-Sn binary alloys was examined by positron annihilation coincidence Doppler broadening (CDB) and lifetime measurements, and the correlation between precipitation and void growth was studied. S-W plots obtained from CDB measurements of pure Ni and Ni-Sn alloys were compared. The change in S-W plots in Ni-0.05at.%Sn with increasing neutron dose was nearly the same as that of pure Ni, while that of Ni-0.3at.%Sn and Ni-2at.%Sn deviated from that of pure Ni. Precipitation of Ni3Sn was detected after annealing of Ni-2at.%Sn, and the precipitation was promoted by irradiation. In Ni-0.3at.%Sn, no precipitation was detected after an 1173 K heat treatment, but irradiation-induced precipitation did occur. The precipitation and the frequency of one-dimensional motion of interstitial clusters were closely correlated, and the clusters and vacancies annihilated each other. The precipitation suppressed void growth.

Perspectives on radiation effects in nickel-base alloys for applications in advanced reactors

Because of their superior high temperature strength and corrosion properties, a set of Ni-base alloys has been proposed for various in-core applications in Gen IV reactor systems. However, irradiation-performance data for these alloys is either limited or non-existent. A review is presented of the irradiation-performance of a group of Ni-base alloys based upon data from fast breeder reactor programs conducted in the 1975–1985 timeframe with emphasis on the mechanisms involved in the loss of high temperature ductility and the breakdown in swelling resistance with increasing neutron dose. The implications of these data for the performance of the Gen IV Ni-base alloys are discussed and possible pathways to mitigate the effects of irradiation on alloy performance are outlined. A radical approach to designing radiation damage-resistant Ni alloys based upon recent advances in mechanical alloying is also described.

IASCC Initiation in Highly Irradiated Stainless Steels under Uniaxial Constant Load Conditions

Uniaxial constant load tests in 320°C simulated PWR primary water were conducted for cold-worked SUS316 stainless steels irradiated to 30–73 dpa. IASCC failure occurred within ∼100 h at applied stresses of 470–752MPa. The time-to-failure decreased with increasing neutron dose and applied stress. A compilation of literature data obtained using ring compression tests indicated that the results of ring compression tests for IASCC initiation were similar to those of uniaxial tensile tests. The border stress for IASCC failure decreased with increasing dose and saturated at ∼400 MPa at ∼30 dpa. This behavior was similar to that of radiation-induced material changes, such as hardness or grain boundary segregation.

Static strain aging and dislocation–impurity interactions in irradiated mild steel

Interactions between dislocations and interstitial impurity atoms lead to strain aging phenomenon in ferritic steels that are affected by the defects produced during neutron radiation exposure. We present here results on static strain aging in a silicon-killed mild steel before and after neutron irradiation. It is noted that the degree of strain aging (as measured by the yield point following restraining) decreased with increasing neutron dose resulting in essentially non-aging type at the highest dose (∼10 19 n/cm 2). The strain aging kinetics were investigated using data at various aging temperatures and were found to be unaffected by the neutron radiation exposure. These experimental results are compared to those observed in dry hydrogen treated (partially denitrided) samples and are correlated with models on Cottrell locking.

IASCC Initiation in Highly Irradiated Stainless Steels under Uniaxial Constant Load Conditions

Uniaxial constant load tests in 320°C simulated PWR primary water were conducted for cold-worked SUS316 stainless steels irradiated to 30–73 dpa. IASCC failure occurred within ∼100 h at applied stresses of 470–752MPa. The time-to-failure decreased with increasing neutron dose and applied stress. A compilation of literature data obtained using ring compression tests indicated that the results of ring compression tests for IASCC initiation were similar to those of uniaxial tensile tests. The border stress for IASCC failure decreased with increasing dose and saturated at ∼400 MPa at ∼30 dpa. This behavior was similar to that of radiation-induced material changes, such as hardness or grain boundary segregation.

Vacancy Clusters in Germanium

Fast neutron irradiation of germanium has been used to study vacancy reactions and vacancy clustering in germanium as a model system to understand ion implantation and the vacancy reactions which are responsible for the apparently low n-type doping ceiling in implanted germanium. It is found that at low neutron doses (~1011cm-2) the damage produced is very similar to that resulting from electron or gamma irradiation whereas at higher doses (> 1013cm-2) the damage is similar to that resulting from ion implantation as observed in the region near the peak of a doping implant. Electrical measurements including CV profiling, spreading resistance, Deep- Level Transient-Spectroscopy and high resolution Laplace Deep-Level Transient-Spectroscopy have been used in conjunction with positron annihilation and annealing studies. In germanium most radiation and implantation defects are acceptor like and in n-type material the vacancy is negatively charged. In consequence the coulombic repulsion between two vacancies and between vacancies and other radiation-induced defects mitigates against the formation of complexes so that simple defects such as the vacancy donor pair predominate. However in the case of ion implantation and neutron irradiation it is postulated that localized high concentrations of acceptor like defects produce regions of type inversion in which the vacancy is neutral and can combine with itself or with other radiation induced acceptor like defects. In this paper the progression from simple damage to complex damage with increasing neutron dose is examined.

Nanostructural evolution in surveillance test specimens of a commercial nuclear reactor pressure vessel studied by three-dimensional atom probe and positron annihilation

The nanostructural evolution of irradiation-induced Cu-rich nanoprecipitates (CRNPs) and vacancy clusters in surveillance test specimens of in-service commercial nuclear reactor pressure vessel steel welds of Doel-1 and Doel-2 are revealed by combining the three-dimensional local electrode atom probe and positron annihilation techniques. In both medium (0.13 wt.%) and high (0.30 wt.%) Cu welds, the CRNPs are found to form readily at the very beginning of the reactor lifetime. Thereafter, during the subsequent 30 years of operation, the residual Cu concentration in the matrix shows a slight decrease while the CRNPs coarsen. On the other hand, small vacancy clusters of V 3–V 4 start appearing after the initial Cu precipitation and accumulate steadily with increasing neutron dose. The observed nanostructural evolution is shown to provide unique and fundamental information about the mechanisms of the irradiation-induced embrittlement of these specific materials.

Effect of neutron radiation on the photoelectric parameters of p-n-InSe structures

The effect of irradiation with fast reactor neutrons at an effective energy of 1 MeV and a fluence within Φ = 1 × 1014−5 × 1015 n/cm2 on the photoelectric parameters of p-n-InSe homojunctions obtained in direct optical contact between p- and n-type semiconductors has been studied. The exposure to fast neutrons leads to an increase in the rectification coefficient and the diode ideality factor of the current-voltage characteristics with increasing neutron dose. No significant changes have been observed in the photosensitivity spectra of p-n-InSe structures irradiated to various doses, which allows these structures to be recommended for the creation of radiation-resistant photodetectors.

Dependence of Barkhausen noise in the neutron irradiated reactor pressure vessel steel

Barkhausen noise (BN) and ferromagnetic resonance (FMR) experiments were conducted in the neutron irradiated commercial nuclear pressure vessel steel. The energy of BN decreased by neutron irradiation and the rates increased with increasing neutron dose. The resonance field and linewidth determined from FMR spectra increased with increasing neutron dose. The experimental results were explained as domain wall pinning of irradiation induced precipitates and change of anisotropy energy associated with neutron irradiation.

A model describing neutron irradiation-induced segregation to grain boundaries in dilute alloys

A model describing neutron irradiation-induced grain boundary segregation at a given temperature is established for dilute alloys based on a complex diffusion mechanism and combined with Mc-Lean’s equilibrium segregation model. In the model, irradiation-enhanced solute diffusion is taken into consideration. The diffusion equations are more rigorously solved than in earlier models, so that an accurate definition of the grain boundary solute concentration is given as a function of time. The effect of the temperature dependence of dislocation density is accommodated and the estimation method for complex diffusion is reappraised. Theoretical predictions are made for segregation of phosphorus in neutron-irradiatedα-Fe. There exists a transition temperature below which combined irradiation-induced nonequilibrium and irradiation-enhanced equilibrium segregation is dominant and above which thermal equilibrium segregation is dominant. The peaks in the temperature dependence of segregation shift to lower temperatures with decreasing neutron dose rate and/or increasing neutron dose. The combined radiation-induced nonequilibrium and radiation-enhanced equilibrium peak segregation temperature is about 150 °C forP grain boundary segregation in neutron-irradiatedα-Fe at dose rate=10−6 dpa/s and dose=1 dpa. The thermal equilibrium segregation peak is around 550 °C for the same conditions. Comparison of some experimental and predicted results shows that the predictions are generally consistent with the observations.

A statistical model for the analysis and prediction of the effect of neutron irradiation on Charpy impact energy curves

The structural integrity safety assessments of nuclear reactor pressure vessels are based, in part, on a prediction of the effect of neutron irradiation on material properties. Databases which monitor this effect are often made up of Charpy absorbed energy measurements. This article presents a generally applicable, new and statistically rigorous method of analysis in which any prior belief as to the form of the material specific, irradiation damage mechanisms can be included. The analytic strategy described can provide predictions of best estimate and confidence limits for use in safety cases. The Charpy absorbed energy measurements obtained over a wide range of temperatures follow a sigmoidal curve which has been modelled by a three parameter curve with the same functional form as a relationship for the Burr distribution function. Charpy transition curves obtained as part of the surveillance of radiation damage of nuclear reactor materials, are found to be displaced to higher temperatures and change their appearance with increasing neutron dose. These changes have been examined by multiple regression analysis of Charpy data using the maximum likelihood estimation method. Relationships which describe the dependence of the upper shelf Charpy energy and the parameters of Burr distribution on irradiation dose and temperature have been derived and linked to the physical processes of irradiation damage. As an illustration of the method, the analysis of a set of Charpy data for nuclear reactor pressure vessel steels is described.