Ovidiu Toader

Conducting Well‐Controlled Ion Irradiations To Understand Neutron Irradiation Effects In Materials

A firm understanding of the effect of radiation on materials is required to develop predictive models of materials behavior in‐reactor and provide a foundation for creating new, more radiation‐tolerant materials. Ion irradiation can serve this purpose for nuclear reactor components and is becoming a key element of materials development for advanced nuclear reactors. Ion irradiations can be conducted quickly, at low cost, and with precise control over irradiation temperature, temperature uniformity, dose rate, dose uniformity and total dose. During proton irradiations the 2σ (twice the standard deviation) of the sample temperature is generally below ∼7 °C, the dose rate variation ∼3%, the dose uncertainty ∼3%, and there is an excellent temperature and dose uniformity across the irradiated area. In this article, we describe the experimental setup and irradiation procedure used to conduct well‐controlled ion irradiations at the University of Michigan.A firm understanding of the effect of radiation on materials is required to develop predictive models of materials behavior in‐reactor and provide a foundation for creating new, more radiation‐tolerant materials. Ion irradiation can serve this purpose for nuclear reactor components and is becoming a key element of materials development for advanced nuclear reactors. Ion irradiations can be conducted quickly, at low cost, and with precise control over irradiation temperature, temperature uniformity, dose rate, dose uniformity and total dose. During proton irradiations the 2σ (twice the standard deviation) of the sample temperature is generally below ∼7 °C, the dose rate variation ∼3%, the dose uncertainty ∼3%, and there is an excellent temperature and dose uniformity across the irradiated area. In this article, we describe the experimental setup and irradiation procedure used to conduct well‐controlled ion irradiations at the University of Michigan.

Remote Monitoring and Control of Irradiation Experiments

As computer technology plays an increasing important role in particle accelerator facilities, instrumentation systems can be expected to include web connections and other remote capability features. The Michigan Ion Beam Laboratory at the University of Michigan in Ann Arbor has developed remote monitor and control capability by using a combination of commercial software packages and in‐house software development. Irradiation parameters such as ion current on the samples and apertures, sample temperature read from an optical pyrometer, and chamber pressure can all be accessed and monitored remotely through a web site, as can ion source parameters such as power supply currents and voltages or feed gas pressure. With administrator permission, the control parameters of the ion source or the readouts from the irradiation stage can be modified in real time during an experiment. A description will be given of the various ways in which this type of remote monitoring and control has been accomplished at the Michig...

A high intensity radiation effects facility

The facility of the Michigan Ion Beam Laboratory at the University of Michigan has been upgraded to conduct high intensity radiation effects studies on materials. This upgrade is necessary to pursue higher radiation damage levels than the studies previously conducted. To achieve this capability a new volume ion source was installed which can produce several times more H− current than the previous duoplasmatron. We will describe the objectives of the research and the facility as well as applications to a variety of radiation damage problems.

Modification in surface properties of poly-allyl-diglycol-carbonate (CR-39) implanted by Au+ ions at different fluences

Abstract Ion implantation has a potential to modify the surface properties and to produce thin conductive layers in insulating polymers. For this purpose, poly-allyl-diglycol-carbonate (CR-39) was implanted by 400 keV Au+ ions with ion fluences ranging from 5 × 1013 ions/cm2 to 5 × 1015 ions/cm2. The chemical, morphological and optical properties of implanted CR-39 were analyzed using Raman, Fourier transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM) and UV-Vis spectroscopy. The electrical conductivity of implanted samples was determined through four-point probe technique. Raman spectroscopy revealed the formation of carbonaceous structures in the implanted layer of CR-39. From FT-IR spectroscopy analysis, changes in functional groups of CR-39 after ion implantation were observed. AFM studies revealed that morphology and surface roughness of implanted samples depend on the fluence of Au ions. The optical band gap of implanted samples decreased from 3.15 eV (for pristine) to 1.05 eV (for sample implanted at 5 × 1015 ions/cm2). The electrical conductivity was observed to increase with the ion fluence. It is suggested that due to an increase in ion fluence, the carbonaceous structures formed in the implanted region are responsible for the increase in electrical conductivity.

A Multi-Pinhole Faraday Cup Device for Measurement of Discrete Charge Distribution of Heavy and Light Ions

A new multi-pinhole Faraday cup (MPFC) device was designed, fabricated and tested to measure ion beam uniformity over a range of centimeters. There are 32 collectors within the device, and each of those is used as an individual Faraday cup to measure a fraction of the beam current. Experimental data show that the device is capable of measuring a charged particles distribution - either in the form of a raster scanned focused beam or a defocused beam.

Simulation of ion beam transport through the 400 Kv ion implanter at Michigan Ion Beam Laboratory

The Michigan Ion Beam Laboratory houses a 400 kV ion implanter. An application that simulates the ion beam trajectories through the implanter from the ion source to the target was developed using the SIMION® code. The goals were to have a tool to develop an intuitive understanding of abstract physics phenomena and diagnose ion trajectories. Using this application, new implanter users of different fields in science quickly understand how the machine works and quickly learn to operate it. In this article we describe the implanter simulation application and compare the parameters of the implanter components obtained from the simulations with the measured ones. The overall agreement between the simulated and measured values of magnetic fields and electric potentials is ∼10%.

Surface analysis for students in Nuclear Engineering and Radiological Sciences

Students in Nuclear Engineering and Radiological Sciences at the University of Michigan are required to learn about the various applications of radiation. Because of the broad applicability of accelerators to surface analysis, one of these courses includes a laboratory session on surface analysis techniques such as Rutherford Backscattering Analysis (RBS) and Nuclear Reaction Analysis (NRA). In this laboratory session, the students determine the concentration of nitrogen atoms in various targets using RBS and NRA by way of the 14N(d,α)12C reaction. The laboratory is conducted in a hands‐on format in which the students conduct the experiment and take the data. This paper describes the approach to teaching the theory and experimental methods behind the techniques, the conduct of the experiment and the analysis of the data.