The Ruđer Bošković Institute is the largest research institute in Croatia, covering a broad spectrum of basic and applied research areas with a very long history of nuclear research. The first 200 kV Cockroft Walton accelerator was built locally in 1956. and has been operated mostly as a neutron generator using 2H(d,n)3He and later 3H(d,n)α reactions. In the 15 years of its operation, students completed more than 30 Masters and Ph.D. thesis. In 1962. RBI installed 20 MeV deuterons cyclotron and today are in operations 18 MeV proton cyclotron for PET isotopes, 6 MV EN Tandem and 1 MV Tandetron with plans to install additional 6MV Tandem to replace 1MV in less than two years’ time.
The Laboratory for Ion Beam Interactions – LIBI group performs basic and interdisciplinary research concerning interactions of ion beams with matter and develop methods to characterize and modify the properties of matter, with emphasis on nanostructure research with fundamental processes: stopping of ions in solids and related effects, inner shell ionization and X-ray emission processes, ion scattering and nuclear reactions.
Accelerator-based technologies are associated with a broad range of applications that have societal and technological impacts particularly in material characterization and material modifications. The utilization of accelerators enhances innovation in areas such as materials research, cultural heritage, environment, biomedicine, forensics, energy, health, and natural resources. Recently LIBI implemented innovation management activities from the idea generation to the commercialization potential definition.
The developments in technologies and acquired knowledge that can be transferred to the others are done in the area of and design and constructions of end-stations and data acquisition and control software and hardware. Recently, the internal developments of custom-made technologies are:
- Time-of-Flight Elastic Recoil Detection Analysis (TOF ERDA) chamber;
- High energy Resolution Particle induced X-ray emission HR PIXE at the ion microprobe;
- Custom made data acquisition system for ion beam analysis.
Time-of-Flight Elastic Recoil Detection Analysis (TOF-ERDA) is a well-established and powerful ion beam analytical (IBA) technique used for quantitative depth profiling of light and medium mass elements, in both, light and heavy matrices. It is based on the coincidence measurement of the energy and time-of-flight of the atoms from the target recoiled by primary heavy ions such as Cl, I, Au, etc. Coincidence measurement enables to separate all elements by energy and mass, including the hydrogen. Time/energy spectra are converted to depth profiles using the known relation of energy loss by the unit of length of the ions in the sample (stopping power). Because of the high stopping power of the primary heavy ions, thin
films with the thickness of ~ 500 nm can be analysed. The depth resolution of few nm at the surface can be achieved for C, N and O (with a sensitivity of 0.1 %.), and ~ 10 nm for H (with sensitivity of ~100 ppm). Contrary to silicon particle detectors used in the standard IBA, the efficiency of the carbon-foil time detectors in TOF system depends on the energy of analysing recoil atoms (i.e. electronic stopping power in the C foil) and it is less than 100% for the lightest elements. This is particularly critical for hydrogen where detection efficiency can be drastically reduced (~ 10%). To improve the detection efficiency of TOF ERDA for H, the electron emission of C foils has been enhanced by evaporating a thin LiF layer on them, which improved significantly detection efficiency for H, making TOF ERDA spectrometer more suitable for hydrogen analysis.
Due to the excellent performances of TOF-ERDA spectrometer, RBI is recognised by the companies INFINEON and ARM as their reference laboratory for the characterization of their products – thin films. The technology transfer with National Centre of Scientific Research “Demokritos„ Institute of Nuclear and Particle physics, Greece is agreed with the planned realization of the technology transfer by the end of 2021. together with the data acquisition software.
Particle induced X-ray emission (PIXE) technique is a routine tool for elemental concentration determination in samples irradiated with MeV energy protons. Small variations of X-ray intensities and shifts in X-ray energy due to chemical effects can be detected also with energy dispersive detectors like Si(Li), Ge and/or SDD, but they are usually ignored. Wavelength dispersive spectrometers unfold the fine structure of X-ray spectra enabling the chemical speciation studies with high resolution PIXE (HR PIXE).
We designed and constructed a downsized wavelength dispersive X-ray (WDX) spectrometer dedicated for microscopic samples utilizing the microscopic beam of our ion microprobe. A dedicated vacuum chamber, housing the flat diffraction crystal, sample holder and CCD X-ray detector, was constructed and positioned behind the main ion microprobe chamber. Its high resolution of the order of 1 eV enables separation of X-ray lines which usually overlap in ED spectra (for example K lines of sulfur and M lines of Hg and/or Pb). Spectrometer’s capabilities in chemical speciation studies are already demonstrated: (i) on the high-resolution Si Kα and Kβ X-ray spectra for several silicon compounds irradiated with 2 MeV protons and (ii) in the multiple ionization study of Kα X-ray lines of Mg and Al irradiated with 3, 4 and 5 MeV helium ions. The influence of the multiple ionization satellites on X-ray spectra of light elements (Mg, Al) is important in the analysis of X-ray spectra obtained with APXS (Alpha particle X-ray Spectrometer) installed on Mars Exploration rover.
Some of the drawbacks of the current spectrometer will be solved within the ongoing Croatian Science Foundation project in which the new, upgraded spectrometer will be constructed. SDD and SB detectors will be implemented into a new WDX chamber enabling the collection of 2D PIXE and RBS maps before the acquisition of HR PIXE spectra on the specific regions of the sample and technology transfer is agreed and delivered at Centro Nacional de Aceleradores, Sevilla, Spain with the installation planned by the end of 2021. together with the data acquisition software.
Custom made data acquisition system with target positioning & beam scanning software
In order to cover the wide variety of requirements set by each IBA techniques, a flexible data acquisition and control system was developed based on a Xilinx FPGA with custom made FMC add-on boards. This allows one system to connect and control beam modification devices, such as ion beam optics elements, and simultaneously collect data from multiple detectors. The reprogrammable nature of the FPGA is taken advantage of to give the acquisition system the ability to adapt to the experimental conditions set by the user. Once the user sets the parameters, the FPGA reprograms itself in the background without any additional user input.
Furthermore, the acquisition hardware is controlled by RBI’s SPECTOR software which is currently being upgraded to adopt a Common Data Format for IBA analysis. The standardization of the acquisition system and control software allows for one system to be used on all beamlines. Additionally, a technology transfer for this acquisition system was agreed with National Centre of Scientific Research “Demokritos”.
More can be found on our web page https://www.irb.hr/eng/Divisions/Division-of-Experimental-Physics/Laboratory-for-ion-beam-interactions.