Lund Nuclear Microprobe Research Articles

Applications of SU-8 in the development of a Single Ion Hit Facility

The Lund Nuclear Microprobe (LNM) has been adapted to be used as a Single Ion Hit Facility (SIHF) for proton cell irradiation experiments at low dose. In order to test the capabilities of the system, Ni dot arrays and artificial cells have been fabricated with the photopolymer SU-8 and common lithographic techniques. The primary purpose of the Ni dot arrays was to determine the targeting accuracy of the beam in vacuum and in air. Additionally, this sample was employed to evaluate the system performance during cell target irradiation experiments. The Ni dot arrays were also used for beam characterization. The artificial cells were originally fabricated to test the software for cell recognition and localization, developed and implemented at the LNM. However, this sample became very functional to make small adjustments at the irradiation chamber for cell irradiation experiments. A description of the samples, fabrication procedure and applications are presented in this paper.

First results from the Lund NMP particle detector system

The design and first results from a Double Sided Silicon Strip Detector (DSSSD) recently installed at the Lund Nuclear Microprobe facility (NMP) are presented. The detector has 64 sector strips and 32 ring strips, which in combination give more than 2000 detector cells, each with characteristics comparable with a standard surface barrier detector (SBD). The detector has been tested both with radioactive sources and with different ion beams and energies. The most striking features are the high rate virtually pile-up free operation and also the possibility of detailed measurement of angular distributions.

Characterisation of a pre-cell hit detector to be used in single cell irradiation experiments at the Lund Nuclear Microprobe

This paper describes the characterisation of an ultra-thin silicon semiconductor Δ E detector to be used as a pre-cell ion hit detector in single ion experiments on individual, living cells. The characteristics of interest for this specific application are the hit detection efficiency, which has to be close to 100% to enable bombardment with either a single ion or a counted number of ions, the beam spreading, which should be as small as possible to maintain the targeting accuracy, and the vacuum tightness, since the detector is intended, if possible, to be used simultaneously as vacuum window. The hit detection efficiency was shown to be above 99% when detecting alpha particles or 2 MeV protons, the increase in beam size was about 1 μm and the vacuum tightness was comparable to that of the Si 3N 4 wafer which is normally used as vacuum window, thus the Δ E detector fulfils the main criteria to function properly as a single ion hit detector.

Evaluation of a pre-cell hit detector for the future single ion hit facility in Lund

Currently, a single ion hit facility, for irradiation of single cells with single, light MeV ions is under development at the Lund Nuclear Microprobe. In this paper, a novel approach to the ion detection issue is presented. A silicon detector, a type utilized at other facilities for post-cell ion detection, has been investigated as a possible option for pre-cell hit detection. If proven successful, this detector could possibly also be used simultaneously as vacuum window.The first experiments carried out on the 9μm thick silicon detector, with an area of 4mm2, have been aimed at investigations of signal-to-noise ratio and efficiency. The results thus far reveal a low noise level and a noise distribution, which is well separated from the signal peak. However, the efficiency remains a problem, since at present it is far from the required 100%.

Development of a microtomography system at the Lund sub-micron beamline

A system for ion beam tomography has been implemented in conjunction with the new sub-micron beamline at the Lund Nuclear Microprobe laboratory. The first version of the system is dedicated to STIM (scanning transmission ion microscopy) tomography for three-dimensional mass density analysis, but future development will allow also PIXE (particle induced X-ray emission) tomography for elemental analysis of micrometer-sized samples. The PIXE tomography will gain from the 8-element large area HPGe X-ray detector (100mm2 for each element) at the low beam currents inherited with a sub-micrometer beam spot size.In this work, the first results are presented together with a detailed description of the developed system, including computer control of the sample rotation. The reconstruction technique, as well as potential tomography applications is briefly discussed.

The Lund Nuclear Microprobe sub-micron set-up. Part I: Ion optics calculation

A new beam line for generating a sub-micron beam spot for high-resolution nuclear microprobe applications has been constructed at the Lund nuclear microprobe facility. In this paper, the first in a series of three, a detailed theoretical investigation of different focusing systems is presented based on calculations performed with the computer programs PRAM and OXTRACE. Comparison is made between a doublet, a triplet, a quadruplet and a split quadruplet (two-stage focusing). For the split quadruplet all four quadrupole magnets were uncoupled.The conclusion from the calculations was that to obtain the smallest possible beam, the two-stage focusing system should be used. Such a focusing system (a doublet at each stage) has been chosen for the new sub-micron set-up at the Lund NMP laboratory. The first stage focuses the beam in an intermediate chamber, which has a high-resolution optical viewing system facilitating more control over the beam spot. This real image of the first stage is then used as a virtual object for the second stage.

The Lund Nuclear Microprobe sub-micron set-up. Part III: Sample stage, optical imaging and detector configuration in the experimental chamber

A new sub-micron beamline for high-resolution nuclear microprobe applications has been constructed at the Lund nuclear microprobe facility. The design and construction of the main experimental chamber, sample viewing system and computer controlled precision sample stage movement is presented in this paper.The chamber is especially designed for using a large area annular HPGe detector. The advantages with such a large area detector are discussed and illustrated. In addition the quality of the optical viewing and the precision sample stage is discussed.

The Lund Nuclear Microprobe sub-micron set-up. Part II: Beam line, focusing system and scanning

A new beam line for generating a sub-micron beam spot for high-resolution nuclear microprobe applications has been constructed at the Lund Nuclear Microprobe facility. The design and construction of the beam line, the quality test of the four high precision Oxford OM-52 Quadrupole magnets by the grid shadow method and the beam scanning system are presented in this paper.The beam line is designed for a two-stage focusing system using an independent doublet at each stage. The first stage focuses the beam in an intermediate chamber, which has a scanning system and a high resolution viewing system. The beam spot in the intermediate chamber is then used as the object for the second stage.Slit construction, vacuum system and beam control is discussed. Data illustrating the quadrupole quality and scanning capability are shown.

Hydrogen depth profiling by p–p scattering in nominally anhydrous minerals

Hydrogen has been shown to occur as a trace element in many nominally anhydrous minerals. The presence of hydrogen in several of the major minerals in the Earth’s mantle has received attention, due to the possibility that these phases provide a significant hydrogen reservoir. Recently an experimental and analytical procedure for hydrogen measurements in thin mineral samples by proton–proton scattering has been developed at the Lund Nuclear Microprobe facility. An annular surface barrier detector, divided in two insulated halves, is used to detect the scattered proton and the recoiled proton in coincidence. The summed energy of each detected proton pair can be used to produce depth profiles if the individual scattering angles are known. The easiest case is when only a small difference in energy between each detected proton pair is allowed, i.e. scattering angles very close to 45°. This limitation criterion considerably reduces the statistics. For this reason the analytical method has been expanded to use the full detector area (35–55°) and to identify the scattering angles individually for each hydrogen event.Nominally anhydrous minerals, both synthesized and of natural occurrence, with hydrogen concentrations from 10 to 100ppm have been analysed. Hydrous minerals, as well as Mylar foils were used as standards. Depth profiles show that intrinsic hydrogen can be distinguished from surface contaminations, e.g. water adsorbed on the sample surfaces.

An off-axis STIM procedure for precise mass determination and imaging

For the precise determination of the local mass density in thin samples analysed at the Lund Nuclear Microprobe, a modified version of off-axis STIM is described. An on-axis/off-axis geometry is used where a thin C-foil, placed behind the sample scatters protons into the particle detector. The advantage of this geometry compared to the off-axis case where particles are directly scattered from the sample into the particle detector is that the energy-loss spectrum acquired is less degraded. A spectral resolution comparable to on-axis STIM is achieved at a beam current high enough to allow for a simultaneous PIXE analysis (50–100 pA).

The beam blanking system for microlithography at Lund Nuclear Microprobe

A new beam blanking system was installed at the Lund Nuclear Microprobe and employed in proton beam lithography (PBL) for polymer microstructures fabrication. The blanker consists of two parallel plates connected to a high voltage generator. Measurement of the beam blanking time on a sample was performed by means of the standard PIXE system. The beam is blanked and returns to a sample within 200 ns. The blanking system is designed for the new sub-micrometer beamline under installation in the accelerator laboratory. A number of pilot MeV ion beam lithography experiments were performed to illustrate the possibility to use the blanking system in combination with the existing data acquisition and scanning system. A 2.5 MeV proton beam was used to irradiate 50 μm SU-8 negative resist. The blanker was shown to be a necessary part of the lithography system. It enables blanking between each pixel and hence fabrication of various patterns down to a single pixel. The blanker has significantly simplified beam control and enhanced process time and spatial resolution. Three-dimensional microstructures with 20:1 aspect ratio were fabricated.

Hydrogen analysis by p–p scattering in geological material

It has been concluded by geologists that a significant amount of hydrogen is stored as point defects in nominally anhydrous minerals. Determination of the amount of hydrogen bound in these minerals is a step towards determining the total water content of the earth mantle as well as comprehending its internal water cycle. The possibility to measure hydrogen in thin geological samples by elastic p–p scattering has been investigated at the Lund Nuclear Microprobe. In this work the development of the experimental procedure and standardisation of data analysis is described. Special emphasis has been put into doing the data analysis as simple as possible and at the same time applicable to all sorts of thin samples, even those of unknown nature. A special annular surface barrier detector composed of two insulated detector halves, which are read out simultaneously, is used to detect the recoiled proton and the scattered proton in coincidence. Conditions on the difference in time and energy of the detected particles, enables us to distinguish true hydrogen events from false or random ones. Homogeneous Mylar foils with known hydrogen content are used as reference material and enables determination of the total amount of hydrogen in the bulk of the geological samples as well as depth profiling, in order to separate contaminations in the surface from the bulk concentrations. The method has been tested with a 2.8 MeV proton beam on thin samples of both Muscovite, which is known to have a natural hydrogen concentration of about 0.5 wt%, and Pyroxene, which is a nominally anhydrous mineral.

Nuclear microprobe analysis of the selective boron uptake obtained with BPA in brain tumour tissue

The tumour selective ability of the boron compound boronophenylalanine (BPA), today used in Boron Neutron Capture Therapy in Sweden, has been investigated with the Lund Nuclear Microprobe. The tumour to tissue ratio of the boron concentration, as well as the location of boron within the cells, is critical for the efficiency of the therapy. It is desirable that the boron is accumulated as close as possible to the cell nucleus, since the alpha particles produced in the 10B(n,α) 7Li reaction only have a range of about 10 microns, i.e. a cell diameter. The nuclear reaction 11B(p,α)2α, which has an especially high cross-section (300 mb) for 660 keV protons, has been used to analyse brain tissue from BPA-injected rats. Previous studies on other boron compounds have shown significant background problems when the alpha particles are detected in the backward direction. By a specially designed set-up, alpha particles in the forward and backward direction are detected simultaneously, and only the coincidences between the two directions are considered to be true boron events. In this way we could achieve excellent background suppression. The analysis shows that BPA indeed is tumour selective. Quantifications show a boron abundance of 150 ± 20 ng/cm 2 in normal tissue and 567 ± 70 ng/cm 2 in tumour tissue. If the rat is fed with l-dopa before the injection of BPA the uptake increases 3–4 times. The boron is homogeneously distributed in the cellular structure and no specific intracellular accumulation has been shown.

Characterization of a new large area HPGe X-ray detector for low beam current application

In the new sub-micron beamline at the Lund Nuclear Microprobe facility a special large area HPGe X-ray detector has been installed. It consists of eight 100-mm 2-size detector elements arranged in an annular formation around the beam entrance hole. Different parameters like FWHM, FWTM, peak-to-background ratio and peak-to-valley ratio for each individual detector element as well as their sum spectra have been investigated. The data handling, i.e. how eight parallel signals are individually stored and summed together, has been discussed. The possibility to use the detector for simultaneous measurement of high and low energy photons, i.e. PIXE combined with PIGE has been demonstrated.

Calibration of a new chamber using GUPIX software package for PIXE analysis

A new chamber has been designed and constructed for the second beam line at the Lund Nuclear Microprobe facility, Sweden. The aim with the chamber is to perform standardized analyses with most of the nuclear analytical techniques (proton induced X-ray emission, particle elastic scattering analysis, proton induced gamma emission, nuclear reaction analysis, etc.) with a millimetre size beam. The beam line and chamber constructions are described in this paper. The possibility to run samples in batch, and the special arrangement developed for this is described. A mass calibration of the PIXE set-up has been done with MicroMatter thin film standards and other thick standards. The spectra were acquired with CAMAC based data acquisition system with Kmax interfacing software. The GUPIX software package recently installed in our laboratory has been used to process the PIXE spectra and the results are compared with the certified values. For standardization the instrumental constant H (solid angle and correction factor) is determined relying completely on the GUPIX data base (cross-sections, fluorescence and Coster–Kronig probabilities, stopping powers and attenuation coefficients) for a large set of elements. These H values are saved inside the GUPIX library, to be used in future analysis.

The layout and performance of the Lund nuclear microprobe trigger and data acquisition system

Recently a new data acquisition system has been installed at the Lund nuclear microprobe facility. The trigger layout for this beam scanning and data acquisition system that support a great variety of simultaneously techniques (PIXE, STIM, RBS, and NRA) is presented in detail. The technical status, total trigger throughput and data flow is described. Examples of typical system performance for PIXE, STIM and RBS obtained during routine runs are discussed. Details on hardware and software specifications are given.

Elemental analysis of single phytoplankton cells using the Lund nuclear microprobe

The occurrence of annual marine phytoplankton blooms is becoming a global problem. In Europe, the NUTOX project supported by the EC investigates if unbalanced nutrient compositions in the water promote the dominance of harmful phytoplankton species. One of the tasks is the determination of the elemental composition of single phytoplankton cells. This is carried out using the Lund Nuclear Microprobe with a special focus on C, N, P and K. The overall aim is to understand the mechanism leading to toxin production, model it and eventually propose a counteracting method. The preparative method, used to isolate single living cells while reducing their salt environment, is an important part of the analytical procedure. A comparison of light element detection using backscattering from protons and nuclear reaction analysis using deuterons is made.

Characterisation of ferromagnetic magnetic storage media surfaces by complementary particle induced X-ray analysis and time of flight-energy dispersive elastic recoil detection analysis

Thin (10 nm–1 μm) films of ferromagnetic material constitute an important class of materials that are difficult to analyse by conventional ion beam analytical (IBA) techniques because they are based on the ferromagnetic elements (Co, Fe, Mn, Ni, and Cr). The similar or overlapping isotope masses makes it difficult to separate the elemental signals using time of flight and energy dispersive elastic recoil detection (ToF-E ERD). In this exploratory study we have investigated the use of Particle Induced X-ray Emission (PIXE) measurements to refine the mass dispersive depth profile information from ToF-E ERD. The surfaces of two commercial magnetic media were investigated. One sample was a 312′′ double density diskette with a coating of ferrite particles in an organic binder. The other sample was a complex C/Co/Cr/Ni–P/Al multilayer structure taken from a standard hard disc. The Lund nuclear microprobe with a 2.55 MeV proton beam was used for PIXE analysis. ToF-ERD measurements were carried out using a 55 MeV 127I10+ ion beam incident at 67.5° to the surface normal. The time of flight and kinetic energy of recoils ejected at 45° to the ion beam direction was measured in a detector telescope. The findings demonstrate that by detailed analysis of the PIXE spectra it is possible to remove the ambiguities in mass assignment of the ToF-ERD data associated with the ferromagnetic elements.

Application of micro-PIXE to fish life history analyses: trace element analysis of otoliths

Otoliths are biogenic, carbonate concretions which form part of the hearing/balance system in fishes. The radial growth of otoliths and the variation of trace elements along the radius appear to capture important aspects of fishes' environmental history. At the Lund Nuclear Microprobe Laboratory, we have begun to use Proton-Induced X-ray Emission spectroscopy (PIXE) for micro-elemental analysis of otoliths. The experimental procedure is discussed and a number of examples of what can be investigated are presented. In particular, movement of diadromous species (eel, menhaden, and anadromous brown trout) can be detected between fresh and brackish water by Sr/Ca ratio. This technique has also been used to identify fish that were raised in freshwater hatcheries and then released to brackish water (pike-perch example).

New CAMAC based data acquisition and beam control system for Lund nuclear microprobe

A new CAMAC based data acquisition system has been installed at the Lund Nuclear Microprobe facility. This paper reports on the development and present status of the data acquisition system. The system is a true multiparameter CAMAC based system with fast Fera bus readout and in crate memory buffer. The user interface is based on Sparrow Kmax software for a Power Macintosh platform. The system read out and tag the event data with position on-line, which make fast on-line monitoring of spectra or element maps possible.Simultaneously, all data can be saved event by event for off-line analysis. The beam scanning part is software controlled through a timed D/A converter, this allows fast scanning of the beam. With a CCD-camera and video card the area to be analysed could be defined directly from the image, and the sample position can be moved. Any kind of irregular scan patterns could be defined.