Conversion Electron Moessbauer Spectroscopie Studies on Ion Implanted Iron Layers

Conversion electron Moessbauer spectroscopy (CEMS) is a method very suitable for the study of ion implanted iron. It is demonstrated on nitrogen and phosphorus implanted iron layers. Using this technique not the 14.4-keV-gamma-rays as in the case of the conventional Moessbauer transmission experiments but the conversion and Auger electrons are detected. These electrons have a maximum energy of 7.3 keV. The Moessbauer signal can be obtained from a surface layer of about 300 nm. But the main fraction of the signal, namely 65%, comes from the first 50 nm. This range is just interesting for ion implantation. Depending on the test conditions different iron nitrides are formed by the nitrogen implantation and the phosphorus implantation can result in both amorphization and compound formation in the implanted layer.     

The effect of thermal reactor neutron irradiation on semi-insulating GaN

Semi-insulating Gallium nitride was irradiated by fast and thermal neutrons with fluences from 10¹⁴ to 10¹⁶ n/cm². Depth-resolved cathodoluminescence spectroscopy was used to determine defects changes before and after irradiation. The results revealed two kinds of defects affected near-band emission recombination from two opposite directions. One was attributed to irradiation-induced N vacancies that contribute to near-band emission recombination. Another was attributed to irradiation-induced deep level defects that contribute to sub-band gap recombination and thus decrease the near-band emission recombination.     

Swift heavy ion irradiation-induced modifications in structural and electrical properties of Y3+-substituted yttrium iron garnet

The consequences of 50 MeV Li³⁺ ion irradiation (fluence: 5×10¹³ ions/cm²) on the structural and electrical properties of the Y_3+xFe_5?xO₁₂ (x=0.0, 0.2, 0.4 and 0.6) garnet system have been investigated over the temperature range of 300–673 K. It is found that the percentage formation of an additional yttrium orthoferrite phase observed along with the bcc garnet phase considerably reduces for x=0.4 and 0.6 compositions after swift heavy ion (SHI) irradiation. The nature of thermal variation of DC resistivity curves for x=0.0 and 0.2 compositions is different from that for x=0.4 and 0.6 compositions. The SHI irradiation influences the magnitude of DC resistivity and conduction mechanism for the single-phase compositions while for mixed-phase compositions they remain unaffected. The results have been explained in the light of replacement of magnetic (5μ_B), smaller (0.64 Å), Fe³⁺ ion by nonmagnetic (0μ_B), larger (0.89 Å), Y³⁺ ion, the presence of the yttrium orthoferrite phase and swift heavy ion irradiation-induced paramagnetic centers in the system.     

Ionizing radiation effects on electrical and reliability characteristics of sputtered Ta2O5/Si interface

This paper describes the effect of ionizing radiation on the interface properties of Al/Ta₂O₅/Si metal oxide semiconductor (MOS) capacitors using capacitance–voltage (C–V) and current–voltage (I–V) characteristics. The devices were irradiated with X-rays at different doses ranging from 100?rad to 1?Mrad. The leakage behavior, which is an important parameter for memory applications of Al/Ta₂O₅/Si MOS capacitors, along with interface properties such as effective oxide charges and interface trap density with and without irradiation has been investigated. Lower accumulation capacitance and shift in flat band voltage toward negative value were observed in annealed devices after exposure to radiation. The increase in interfacial oxide layer thickness after irradiation was confirmed by Rutherford Back Scattering measurement. The effect of post-deposition annealing on the electrical behavior of Ta₂O₅ MOS capacitors was also investigated. Improved electrical and interface properties were obtained for samples deposited in N₂ ambient. The density of interface trap states (D_it) at Ta₂O₅/Si interface sputtered in pure argon ambient was higher compared to samples reactively sputtered in nitrogen-containing plasma. Our results show that reactive sputtering in nitrogen-containing plasma is a promising approach to improve the radiation hardness of Ta₂O₅/Si MOS devices.     

The impact of scaling on single event upset in 6T and 12T SRAMs from 130 to 22 nm CMOS technology

ABSTRACT

As transistor sizes scale down to nanometres dimensions, CMOS circuits become more sensitive to radiation. High-performance static random access memory (SRAM) cells are prone to radiation-induced single event upsets (SEU) which come from the natural space environment. The SEU generates a soft error in the transistor due to the strike of an ionizing particle. Thus, this paper compares the endurance of 12T SRAM and 6T SRAM circuit on 130 up to 22?nm CMOS technology towards SEU. Besides that, this paper discusses the trend of critical linear energy transfer (LET) and collected charge due to technology scaling for the respective circuit. The critical LET (LETcrit) and critical charge (Qcrit) of 6T are approximately 50% lower compared with 12T SRAMs.     

ESR response of gamma-irradiated sulfamethazine

In the present work, characteristic features of the radiolytical intermediates produced in gamma-irradiated solid sulfamethazine (SMH) were investigated by electron spin resonance (ESR) spectroscopy. The heights of the resonance peaks, measured with respect to the spectrum baseline, were used to monitor microwave saturation, temperature and time-dependent kinetic features of the radical species contributing to the formation of recorded experimental ESR spectra. Three species having different spectroscopic and kinetic features were observed to be produced in gamma-irradiated SMH. SO₂, which is the most sensitive group of radiation in the SMH molecule, was found to be at the origin of radiation-produced ionic radical species. Based on the experimental results derived from the present study, the applicability of ESR spectroscopy to radiosterilization of SMH was discussed. In the dose range of interest (0.5–10 kGy), the radiation yield of solid SMH was calculated to be very low (G=0.45) compared with those obtained for sulfonamide aqueous solutions (G=3.5–5.1). Based on these findings, it was concluded that SMH and SMH-containing drugs could be safely sterilized by gamma radiation and that ESR spectroscopy could be successfully used as a potential technique for monitoring their radiosterilization.     

Radiation hardness of gas discharge tubes and avalanche diodes used for transient voltage suppression

The widespread use of gas discharge tubes (GDTs) and avalanche diodes for transient voltage suppression (TVS) in many cases results in their exposure to ionizing radiation. The aim of this paper is to investigate the influence of irradiation on these TVS devices’ characteristics, by exposing them to a combined neutron/gamma radiation field. Experimental results show that irradiation of TVS diodes causes a lasting degradation of their protective characteristics. On the other hand, GDTs exhibit a temporary change of performance. The observed effects are presented with the accompanying theoretical interpretations, based on the interaction of radiation with materials constituting the investigated devices.     

Density effects of heavy-ion stopping power in high temperature matter

Abstract

The stopping power and range for Xe ions in high temperature matter (partially ionized plasmas) have been calculated using the dielectric response function method. Calculations have been made for a target matter Al (Z = 13) over a wide range of temperatures and densities considering a finite temperature model. The stopping powers obtained have smaller values in comparison with those of a zero temperature model. The stopping power strongly depends on the density and temperature of the target material, and the projectile ion energy.     

Peculiarities of heavy ion channeling

Abstract

Depth distributions of implanted Mg⁺- and Ca⁺-ions and the corresponding radiation damage were studied for different channeling orientations of silicon crystals. The shape of the implantation profiles is discussed by using simple models for dechanneling and energy loss processes. A correlation between dechanneling, damage production and depth distributions of the channeled ions could be observed. This correlation is seen by the maxima shifts in damage and implanted ion distributions between channel and random incidence.     

Use of the EUR LiB 15/5 data set for radiation shielding calculations in iron

Abstract

The shielding effect of an iron sphere assembly has been tested for a Pu-α-Be neutron source placed in the center of the shield assembly. Emergent neutron and gamma spectra were measured with a stilbene scintillation counter. Discrimination between neutrons and gammas was achieved by the pulse shape discrimination technique based on the zero crossing method. Calculations have been made using the one-dimensional transport code ANISN-Westinghouse version (ANISN-W) and the EUR LiB 15/5 cross section data set. The agreement between measurements and calculations indicates that the cross section set and the calculation model are suitable for studying the iron shielding experiments over the neutron energy range 1.35–10 MeV and the gamma energy range 0.3–6 MeV. Total macroscopic cross sections for fast neutrons, linear attenuation coefficients for gamma rays and half-value thicknesses for neutrons and gammas for the whole energy range and at different energies have been obtained.