- Email: [email protected]
Dedicated accelerator and microprobe line
Section I Accelerator and microprobe technology
Nuclear Instruments and Methods in Physics Research B77 (1993) 3-7 North-Holland
Dedicated
accelerator
NIMI B
Beam Interactions with Materials&Atoms
and microprobe line
K.G. Malmqvist, G. Hyltdn, M. Hult, K. Hbkansson, J.M. Knox ‘, N.P.-0. Larsson, C. Nilsson, J. Pallon, R. Schofield ‘, E. Swietlicki, U.A.S. Tapper 3 and Yang Changyi 4 Department of Nuclear Physics, Lund University and institute of Technology, Siilvegatan 14, S-223 62, Lund, Sweden
The development of a dedicated facility for nuclear microprobe analysis and the experiences from using it are discussed. The of the present Lund nuclear microprobe will be described and the advantages of using a dedicated accelerator
general properties
discussed.
1. Introduction The nuclear microprobe represents a complex analytical instrument with powerful properties for elemental analysis and imaging. A great variety of analytical methods could be used simultaneously or separately in combination with the microprobe. Many of these could be very useful in the process of solving analytical problems in a number of research fields 111.The development of the PIXE technique at our laboratory in the seventies demonstrated that for an analytical technique in order to be fully accepted, not only has it to be powerful but also to be implemented into the field in question by the analysts. Close contact between the “nuclear microprobers” and the co-operating experts thus has to be maintained throughout a project. The user-friendliness of the nuclear microprobe is normally inferior to that of normal IBA methods. It is thus even more ~portant to improve the laboratory to facilitate that collaborators participate actively in the analytical procedures. When working at a laboratory with an accelerator dedicated for a nuclear microprobe adequate techniques can be relatively easily incorporated in the analytical programmes in various fields. When choosing a dedicated machine the advantages of a single-ended accelerator, with its easier user interface and less complex ion beam optics were weighed against the higher ion energy attainable with a tandem accelerator representing about the same investment. In our case the choice was relatively easy. Since another
1 Present address: Idaho State University. Dept. of Physics, Pocatello, Idaho, USA. 2 On leave from: Univ. of Oregon, Dept. of Physics, Eugene, Oregon, USA. 3 Present address: De Beers Diamond Research Laboratory, Johannesburg, South Africa. 4 On leave from: Shanghai Inst. of Nuclear Research, Academia Sinica, Shanghai, China. Oar-SS3X/93/$06.00
accelerator, with a maximum energy of 7 MeV/u, is available at our laboratory, the beam energy was not critical for our “microbeam accelerator”. Since we have been able not only to finance a dedicated accelerator but also could take over an excellent experimental hall we are planning for at least two beam lines, initially one “high resolution” and one “routine” beam line. The present nuclear microprobe system was essentially developed and tested at the tandem accelerator and then transferred to the dedicated hall. In the following the design and characteristics of this system and some of the present and future applications will be presented.
2. Technical facilities The e~erimental hall was formerly used for an electron synchrotron accelerator. A circular structure has been formed by filling the central part of the old facility with concrete but separating it from the surrounding with an isolating elastic layer. It is now used as a very large and massive fundament for the nuclear microprobe. The nuclear microprobe from object slit to irradiation chamber (8 ml is placed entirely within this concrete fundament. Measurements of vibrations in the ~nd~ent before mounting of the beam line resulted in essentially undetectable ~plitudes even with heavy traffic on a nearby road. The accelerator is a single-ended NEC (3UH) machine that is modular with our tandem machine and thus can use a common spare part supply. They are also connected to a common insulation gas storage. The present ion source is of a standard rf-type and will mainly be used to produce beams of protons and alpha particles. The present emittance is measured to be approximately 5 pAl_~rn-~rnrad-~ for 2.5 MeV pro-
0 1993 - Elsevier Science Publishers B.V. All rights reserved
I. TECHNOLOGY
K.C. M~l~v~~t et al. / Deviated
4
Fig. 1. Schematic side view of nuclear microprobe d: diffusion
pump,
e: energy stabilising
beam line. a: turbo pump, slit, f: beam stop, g: object collimators, k: specimen chamber.
tons. The intention is to improve this by development of the ion source. This work will be carried out in an off-line ion source test bench facility The lack of an electron stripping stage justifies the planned development of a brighter ion source. The choice of a singleended accelerator has the drawback of an in-tank ion source, which is not practical, in particular in the development of ion sources. By equipping the tank with a quick opening flange system operated by hydraulics this disa~antage is min~ised and the ion source easily maintained and also the overall operation of the accelerator facilitated. The beam line (fig. 1) is equipped with one turbo molecular pump, three oil diffusion pumps along the line and a fourth directly underneath the specimen chamber. As object collimator two different types can
Fig. 2. Copper
K,
X-ray
accelerator and ~icro~ro~
map from a two-dimensional
line
b: prefocusing magnetic doublet, c: analysing h: limiting aperture, i: achromatic quadrupole
magnet, triplet,
be selected, one with a l-100 km opening slit and one STIM slit which can be set very accurately to small openings as well as being completely removed as to facilitate ion-beam alignment (both types commercially available [2]). For accurate control of the beam position a magnetic steerer is mounted inside the accelerator and an electrostatic steerer on the beam line just before the object coflimator. The startup procedure is thus facilitated and for routine use of the nuclear microprobe limited to normally well below one hour. The focusing system has been described earlier and is designed in order to suppress chromatic aberrations. A magnetic quadrupole triplet with an inner coaxial electrostatic quadrupole triplet acts as an achromatic lens. The property of the lens system has been characterised using the grid shadow technique [3] and the
scan of a 2.5 MeV proton 50-100 PA.
microbeam
over a copper
grid. Beam
current
5
ICC;.MalmqGstet al. / Dedicated acceleratorand microprobeline
results are presented elsewhere [4]. So far, in application studies the lens has only been used with the magnetic elements active. The deflection system is a postlens ferrite-cored magnetic system f.51.The deflection patterns are controkd by a computer and can be set to form irregular scans or to repeatedly dwell on a number of preselected spots. During the testing of the optical properties of the microprobe after the transfer to the new dedicated accelerator several problems related 10 the ac power supply systems (50 Hz, 220/380 V> and vibrations have been identified. Because of temporary sharing of a
detector
single data acquisition system with other multi-parameter experiments at the tandem accelerator, problems of mixing ground systems with resulting ground Loops have been obtained. In addition to this a problem with zero and ground in a three-phase ac current supply has severely distorted the beam quality. In fig. 2 the present beam resolution after correcting this problem is demorrstrated by using a SO-100 pA beam on a Cu grid. Another related problem is the installment of an ultrahigh puwer laser facility fTW laser) at the physics department. The ac power feed uses 500 A in a separate line that is passing in the vicinity of our experi-
Sample Objective::
Si detector
Annular
wheel
Faraday cup ~ST’IMdetector Bellows Microscope ISOW
Optional tube k&err& beam, @-Id shadow) Fig. 3. ‘Fop view of experimental arrangement. Specimen chamber is in open position. Sample holder position when indicated by dotted lines. I. TECI3Ci”OLOGY
6
KG. Malmqvtit et al. / Dedicated accelerator and microprobe line
mental hall. Several tests are presently being carried out to verify that this will not affect the microbeam quality in an unacceptable manner. The movement from the tandem to the new accelerator means that the present lens support is not adequately designed to avoid vibrations from different parts as motors, pumps, etc. The beam will thus oscillate relative to the sample. In order to improve this temporarily the irradiation chamber and the lens have been firmly connected together and the setup been loaded with lead bricks. The vibrations as measured by piezoelectric sensors were thereby significantly reduced. This is also demonstrated in tests of STIM when a 0.4 X 0.6 km2 beam size has been measured. The irradiation chamber (fig. 3) has been modified significantly since it was first reported at the last microprobe conference [6]. From the first experiences some redesign of mechanical construction has been made. A valve that allows separating the beam tube and magnets from the chamber has been installed to reduce pumping down time. An annular surface barrier detector has been mounted at the entrance to the chamber to allow detection of backscattered particles using a large solid angle. A secondary electron detector (channeltron) is mounted for fast imaging of specimen surfaces. A stereo microscope (maximum 300 x ) is viewing the sample from the front via a mirror with a hole for the beam to pass. A second microscope (maximum 600 X > allows viewing from the rear the beam spot through transparent specimens. Close behind the sample wheel a sliding holder with a selection of two objectives for the second microscope, one STIM detector, a hole and a Faraday cup for charge integration is positioned. The latter is connected via a preamplifier to a digitizer allowing integration at picocoulomb level (FAST ComTec 7803-l + Canberra 7803 Digitizer). The position with a hole is used to let the ion beam through for external microprobe analysis or for grid shadow measurements. An optical lens close to the irradiated specimen is followed by a second one together focusing the light produced either on an entrance slit of a monochromator followed by a photomultiplier tube or directly into the PM tube. Both spot and scanned image analysis of the luminescence light can be performed. The development of this facility seems very promising for imaging, in particular in geoscience and materials science.
3. Applications In the new nuclear microprobe facility only a few projects of application have been started so far. In geoscience the geochemical studies of minerals which were started already at the tandem accelerator are
continued. This will most certainly be a major field of application for several years to come in co-operation with both international and local geologists. Within the large program of environmental studies at our department one project deals with the combined use of various microprobe techniques applied to the characterisation of individual aerosol particles. The LAMMA technique [7] and the electron microprobe are combined with the nuclear microprobe [S]. This approach promises to produce results for a new understanding of formation and transformation of air pollution particles that is not attainable with, for instance, macro PIXE studies. In biology several projects have been started. One project of environmental relevance is related to the enhanced soil acidification due to sulphur precipitation in Scandinavia. The sulphur is originating from firing of fossile fuels in central and western Europe. The lower pH leads to an accelerated mobility and availability of aluminium in soil. The nuclear microprobe is used to investigate the uptake and the distribution of Al in fine roots of trees and plants that have been cultured under laboratory conditions with varying pH and Al concentrations. Preliminary results are very promising 191. The earlier large-scale medical studies related to central nervous system are to be continued soon. They have been awaiting the upgraded facility. At present several studies of arteriosclerosis and of pathological skin [lo] are being performed. In materials science we have started work within a Swedish researcher consortium on nanometer structures in materials science. This is a long-term multidisciplinary program, aimed at developing new structures mainly within nanoelectronics but also to find new ways of integrating materials with living organisms. The nuclear microprobe is used to characterise the structures produced. Another material-related project is carried out in co-operation with CERN in order to improve radiation hardness in particle physics detectors. In experiments planned for the Large Hadron Collider radiation deterioration of detectors is foreseen as a severe problem due to the large luminosity in planned experiments [ll]. The fine structures in detectors will be tested in simulated radiation situations in a systematic study at CERN. The nuclear microprobe will be one of the most important methods to characterise deposited matter.
4. Dedicated vs parasitic mode In ion beam analysis the central part is formed by the accelerator. All users of various IBA techniques would prefer to have full access to it to be able to set the conditions for experiments. For several reasons, such as economy and staff, this may not always be
I
K.G. Malrrqvist et al. / Dedicated accelerator and microprobe line
feasible. However, when using a nuclear microprobe there is indeed a pertinent question to pose: Should you invest in a dedicated accelerator? If at all possible the answer should definitely be yes! The special characteristics of the instrument and methods applied justify this in more than one way. The demands made by the beam optical system of the nuclear microprobe are normally so high that it is a tedious and time-consuming procedure before each microprobe run to re-adjust the accelerator to fully suit the nuclear microprobe. The preparation time before each run shift will often be too long and hence severely affect the efficiency and scientific production. Although one may improve this by going to longer running periods this is not always possible. It is not possible to do this preparation off-line since access to the accelerator is normally required. The application projects normally involve many samples that have to be analysed within a reasonable time. This is particularly the case in life sciences where the natural biological variability requires analysis of many samples to obtain statistically significant results. If imaging of the specimens should be utilised it is of utmost importance that an experiment has much beam time available. Imaging of normal substrates takes very long times, often many hours per specimen. This is difficult without full access to an accelerator. The special requirements within an application could much easier be met if enough time is available to make necessary alterations to the experimental facility. High priority can then be devoted to both development and normal sample processing. In a nondedicated facility there is always a risk that any one of them will dominate thus in the end leading to less good science being produced. From our own experience and from discussion with several other users of dedicated facilities [12,13] the advantages are so important that they cannot be neglected. Productivity and quality will increase and, equally important, the postgraduate studies and postdoc programmes are much better handled. The latter is a fact that is very important for the future of the field. Bearing the above discussion in mind it is a natural recommendation to try to, if at all possible, implement nuclear microprobes at dedicated accelerators.
5. Conclusions
A versatile nuclear microprobe has been implemented in combination with a dedicated electrostatic accelerator. The technical details and experiences of using this system and the present status have been
discussed. A user-friendly combination has been the result of using a dedicated accelerator. The experimental work in various fields of application is much facilitated as compared to the earlier situation when sharing the accelerator with many different experiments. For serious scientific achievements in many fields of application the dedicated accelerator approach is very important.
Acknowledgements
In this project the donators of the dedicated accelerator, i.e., the Knut&Alice Wallenberg and the Crafoord foundations are particularly thanked. In the funding of this work during several years the Carl Trygger foundation and the Swedish research councils NFR, FRN and MFR have supplied substantial support in addition to the funds from our university.
References [ll U.A.S. Tapper and K.G. Malmqvist, Anal. Chem. 63 (1991) 715A. PI Technisches Biiro S. Fischer, Am Berg 9, D-6105 OberRamstadt, Germany. [31 D.N. Jamieson and G.J.F. Legge, Nucl. Instr. and Meth. B29 (1987) 544. [41 U.A.S. Tapper and D.N. Jamieson, Nucl. Instr. and Meth. B44 (1989) 227. l51 U.A.S. Tapper, N.E.G. Liivestam, E. Karlsson and K.G. Malmqvist, Nucl. Instr. and Meth. B22 (1987) 317. 161 K. Themner, M.B. Hub, K. HLkansson, N.P.-0. Larsson, N.E.G. Lovestam, L.-B. Nilsson, J. Pallon, U.A.S. Tapper and K.G. Malmqvist, Nucl. Instr. and Meth. B54 (1991) 36. [71 L.A. Currie, R.A. Fletcher and G.A. KIouda, Aerosol Sci. and Tech. 10 (1989) 370. Bl P. Artaxo, M.L. Rabelo, F. Watt, G.W. Grime and E. Swietlicki, presented at this Conference (3rd Int. Conf. on Nuclear Microprobes, Uppsala, Sweden, 1992). PI M. Hult, B. Bengtsson, N.P.-0. Larsson and C. Yang, Scanning Microsc. 6 (1992) 581. ml J. Pallon, J. Knox, T. Pinheiro, B. Forslind and Y. Werner-Linde, these Proceedings (3rd Int. Conf. on Nuclear Microprobes, Uppsala, Sweden, 1992) Nucl. Instr. and Meth. B77 (1993) 287. D11 R.D. Heyer, R. Mackenzie, T.C. Meyer, F. Sauli, K.W.D. Ledingham, R. Jennings, R.P. Singhal, KG. MaImqvist and H.J. Whitlow, A study to improve the radiation hardness of gaseous detectors for use at very high luminosities, RADHARD, RD-10 (CERN, 1991). 1121 S.H. Sie, W.L. Griffin, C.C. Ryan, C.F. Suter and D.R. Cousens, Nucl. Instr. and Meth. B54 (1991) 284. [131 G.W. Grime, M. Dawson, M. Marsh, I.C. McArthur and F. Watt, Nucl. Instr. and Meth. B54 (1991) 52.
I. TECHNOLOGY
Nuclear Instruments and Methods in Physics Research B77 (1993) 3-7 North-Holland
Dedicated
accelerator
NIMI B
Beam Interactions with Materials&Atoms
and microprobe line
K.G. Malmqvist, G. Hyltdn, M. Hult, K. Hbkansson, J.M. Knox ‘, N.P.-0. Larsson, C. Nilsson, J. Pallon, R. Schofield ‘, E. Swietlicki, U.A.S. Tapper 3 and Yang Changyi 4 Department of Nuclear Physics, Lund University and institute of Technology, Siilvegatan 14, S-223 62, Lund, Sweden
The development of a dedicated facility for nuclear microprobe analysis and the experiences from using it are discussed. The of the present Lund nuclear microprobe will be described and the advantages of using a dedicated accelerator
general properties
discussed.
1. Introduction The nuclear microprobe represents a complex analytical instrument with powerful properties for elemental analysis and imaging. A great variety of analytical methods could be used simultaneously or separately in combination with the microprobe. Many of these could be very useful in the process of solving analytical problems in a number of research fields 111.The development of the PIXE technique at our laboratory in the seventies demonstrated that for an analytical technique in order to be fully accepted, not only has it to be powerful but also to be implemented into the field in question by the analysts. Close contact between the “nuclear microprobers” and the co-operating experts thus has to be maintained throughout a project. The user-friendliness of the nuclear microprobe is normally inferior to that of normal IBA methods. It is thus even more ~portant to improve the laboratory to facilitate that collaborators participate actively in the analytical procedures. When working at a laboratory with an accelerator dedicated for a nuclear microprobe adequate techniques can be relatively easily incorporated in the analytical programmes in various fields. When choosing a dedicated machine the advantages of a single-ended accelerator, with its easier user interface and less complex ion beam optics were weighed against the higher ion energy attainable with a tandem accelerator representing about the same investment. In our case the choice was relatively easy. Since another
1 Present address: Idaho State University. Dept. of Physics, Pocatello, Idaho, USA. 2 On leave from: Univ. of Oregon, Dept. of Physics, Eugene, Oregon, USA. 3 Present address: De Beers Diamond Research Laboratory, Johannesburg, South Africa. 4 On leave from: Shanghai Inst. of Nuclear Research, Academia Sinica, Shanghai, China. Oar-SS3X/93/$06.00
accelerator, with a maximum energy of 7 MeV/u, is available at our laboratory, the beam energy was not critical for our “microbeam accelerator”. Since we have been able not only to finance a dedicated accelerator but also could take over an excellent experimental hall we are planning for at least two beam lines, initially one “high resolution” and one “routine” beam line. The present nuclear microprobe system was essentially developed and tested at the tandem accelerator and then transferred to the dedicated hall. In the following the design and characteristics of this system and some of the present and future applications will be presented.
2. Technical facilities The e~erimental hall was formerly used for an electron synchrotron accelerator. A circular structure has been formed by filling the central part of the old facility with concrete but separating it from the surrounding with an isolating elastic layer. It is now used as a very large and massive fundament for the nuclear microprobe. The nuclear microprobe from object slit to irradiation chamber (8 ml is placed entirely within this concrete fundament. Measurements of vibrations in the ~nd~ent before mounting of the beam line resulted in essentially undetectable ~plitudes even with heavy traffic on a nearby road. The accelerator is a single-ended NEC (3UH) machine that is modular with our tandem machine and thus can use a common spare part supply. They are also connected to a common insulation gas storage. The present ion source is of a standard rf-type and will mainly be used to produce beams of protons and alpha particles. The present emittance is measured to be approximately 5 pAl_~rn-~rnrad-~ for 2.5 MeV pro-
0 1993 - Elsevier Science Publishers B.V. All rights reserved
I. TECHNOLOGY
K.C. M~l~v~~t et al. / Deviated
4
Fig. 1. Schematic side view of nuclear microprobe d: diffusion
pump,
e: energy stabilising
beam line. a: turbo pump, slit, f: beam stop, g: object collimators, k: specimen chamber.
tons. The intention is to improve this by development of the ion source. This work will be carried out in an off-line ion source test bench facility The lack of an electron stripping stage justifies the planned development of a brighter ion source. The choice of a singleended accelerator has the drawback of an in-tank ion source, which is not practical, in particular in the development of ion sources. By equipping the tank with a quick opening flange system operated by hydraulics this disa~antage is min~ised and the ion source easily maintained and also the overall operation of the accelerator facilitated. The beam line (fig. 1) is equipped with one turbo molecular pump, three oil diffusion pumps along the line and a fourth directly underneath the specimen chamber. As object collimator two different types can
Fig. 2. Copper
K,
X-ray
accelerator and ~icro~ro~
map from a two-dimensional
line
b: prefocusing magnetic doublet, c: analysing h: limiting aperture, i: achromatic quadrupole
magnet, triplet,
be selected, one with a l-100 km opening slit and one STIM slit which can be set very accurately to small openings as well as being completely removed as to facilitate ion-beam alignment (both types commercially available [2]). For accurate control of the beam position a magnetic steerer is mounted inside the accelerator and an electrostatic steerer on the beam line just before the object coflimator. The startup procedure is thus facilitated and for routine use of the nuclear microprobe limited to normally well below one hour. The focusing system has been described earlier and is designed in order to suppress chromatic aberrations. A magnetic quadrupole triplet with an inner coaxial electrostatic quadrupole triplet acts as an achromatic lens. The property of the lens system has been characterised using the grid shadow technique [3] and the
scan of a 2.5 MeV proton 50-100 PA.
microbeam
over a copper
grid. Beam
current
5
ICC;.MalmqGstet al. / Dedicated acceleratorand microprobeline
results are presented elsewhere [4]. So far, in application studies the lens has only been used with the magnetic elements active. The deflection system is a postlens ferrite-cored magnetic system f.51.The deflection patterns are controkd by a computer and can be set to form irregular scans or to repeatedly dwell on a number of preselected spots. During the testing of the optical properties of the microprobe after the transfer to the new dedicated accelerator several problems related 10 the ac power supply systems (50 Hz, 220/380 V> and vibrations have been identified. Because of temporary sharing of a
detector
single data acquisition system with other multi-parameter experiments at the tandem accelerator, problems of mixing ground systems with resulting ground Loops have been obtained. In addition to this a problem with zero and ground in a three-phase ac current supply has severely distorted the beam quality. In fig. 2 the present beam resolution after correcting this problem is demorrstrated by using a SO-100 pA beam on a Cu grid. Another related problem is the installment of an ultrahigh puwer laser facility fTW laser) at the physics department. The ac power feed uses 500 A in a separate line that is passing in the vicinity of our experi-
Sample Objective::
Si detector
Annular
wheel
Faraday cup ~ST’IMdetector Bellows Microscope ISOW
Optional tube k&err& beam, @-Id shadow) Fig. 3. ‘Fop view of experimental arrangement. Specimen chamber is in open position. Sample holder position when indicated by dotted lines. I. TECI3Ci”OLOGY
6
KG. Malmqvtit et al. / Dedicated accelerator and microprobe line
mental hall. Several tests are presently being carried out to verify that this will not affect the microbeam quality in an unacceptable manner. The movement from the tandem to the new accelerator means that the present lens support is not adequately designed to avoid vibrations from different parts as motors, pumps, etc. The beam will thus oscillate relative to the sample. In order to improve this temporarily the irradiation chamber and the lens have been firmly connected together and the setup been loaded with lead bricks. The vibrations as measured by piezoelectric sensors were thereby significantly reduced. This is also demonstrated in tests of STIM when a 0.4 X 0.6 km2 beam size has been measured. The irradiation chamber (fig. 3) has been modified significantly since it was first reported at the last microprobe conference [6]. From the first experiences some redesign of mechanical construction has been made. A valve that allows separating the beam tube and magnets from the chamber has been installed to reduce pumping down time. An annular surface barrier detector has been mounted at the entrance to the chamber to allow detection of backscattered particles using a large solid angle. A secondary electron detector (channeltron) is mounted for fast imaging of specimen surfaces. A stereo microscope (maximum 300 x ) is viewing the sample from the front via a mirror with a hole for the beam to pass. A second microscope (maximum 600 X > allows viewing from the rear the beam spot through transparent specimens. Close behind the sample wheel a sliding holder with a selection of two objectives for the second microscope, one STIM detector, a hole and a Faraday cup for charge integration is positioned. The latter is connected via a preamplifier to a digitizer allowing integration at picocoulomb level (FAST ComTec 7803-l + Canberra 7803 Digitizer). The position with a hole is used to let the ion beam through for external microprobe analysis or for grid shadow measurements. An optical lens close to the irradiated specimen is followed by a second one together focusing the light produced either on an entrance slit of a monochromator followed by a photomultiplier tube or directly into the PM tube. Both spot and scanned image analysis of the luminescence light can be performed. The development of this facility seems very promising for imaging, in particular in geoscience and materials science.
3. Applications In the new nuclear microprobe facility only a few projects of application have been started so far. In geoscience the geochemical studies of minerals which were started already at the tandem accelerator are
continued. This will most certainly be a major field of application for several years to come in co-operation with both international and local geologists. Within the large program of environmental studies at our department one project deals with the combined use of various microprobe techniques applied to the characterisation of individual aerosol particles. The LAMMA technique [7] and the electron microprobe are combined with the nuclear microprobe [S]. This approach promises to produce results for a new understanding of formation and transformation of air pollution particles that is not attainable with, for instance, macro PIXE studies. In biology several projects have been started. One project of environmental relevance is related to the enhanced soil acidification due to sulphur precipitation in Scandinavia. The sulphur is originating from firing of fossile fuels in central and western Europe. The lower pH leads to an accelerated mobility and availability of aluminium in soil. The nuclear microprobe is used to investigate the uptake and the distribution of Al in fine roots of trees and plants that have been cultured under laboratory conditions with varying pH and Al concentrations. Preliminary results are very promising 191. The earlier large-scale medical studies related to central nervous system are to be continued soon. They have been awaiting the upgraded facility. At present several studies of arteriosclerosis and of pathological skin [lo] are being performed. In materials science we have started work within a Swedish researcher consortium on nanometer structures in materials science. This is a long-term multidisciplinary program, aimed at developing new structures mainly within nanoelectronics but also to find new ways of integrating materials with living organisms. The nuclear microprobe is used to characterise the structures produced. Another material-related project is carried out in co-operation with CERN in order to improve radiation hardness in particle physics detectors. In experiments planned for the Large Hadron Collider radiation deterioration of detectors is foreseen as a severe problem due to the large luminosity in planned experiments [ll]. The fine structures in detectors will be tested in simulated radiation situations in a systematic study at CERN. The nuclear microprobe will be one of the most important methods to characterise deposited matter.
4. Dedicated vs parasitic mode In ion beam analysis the central part is formed by the accelerator. All users of various IBA techniques would prefer to have full access to it to be able to set the conditions for experiments. For several reasons, such as economy and staff, this may not always be
I
K.G. Malrrqvist et al. / Dedicated accelerator and microprobe line
feasible. However, when using a nuclear microprobe there is indeed a pertinent question to pose: Should you invest in a dedicated accelerator? If at all possible the answer should definitely be yes! The special characteristics of the instrument and methods applied justify this in more than one way. The demands made by the beam optical system of the nuclear microprobe are normally so high that it is a tedious and time-consuming procedure before each microprobe run to re-adjust the accelerator to fully suit the nuclear microprobe. The preparation time before each run shift will often be too long and hence severely affect the efficiency and scientific production. Although one may improve this by going to longer running periods this is not always possible. It is not possible to do this preparation off-line since access to the accelerator is normally required. The application projects normally involve many samples that have to be analysed within a reasonable time. This is particularly the case in life sciences where the natural biological variability requires analysis of many samples to obtain statistically significant results. If imaging of the specimens should be utilised it is of utmost importance that an experiment has much beam time available. Imaging of normal substrates takes very long times, often many hours per specimen. This is difficult without full access to an accelerator. The special requirements within an application could much easier be met if enough time is available to make necessary alterations to the experimental facility. High priority can then be devoted to both development and normal sample processing. In a nondedicated facility there is always a risk that any one of them will dominate thus in the end leading to less good science being produced. From our own experience and from discussion with several other users of dedicated facilities [12,13] the advantages are so important that they cannot be neglected. Productivity and quality will increase and, equally important, the postgraduate studies and postdoc programmes are much better handled. The latter is a fact that is very important for the future of the field. Bearing the above discussion in mind it is a natural recommendation to try to, if at all possible, implement nuclear microprobes at dedicated accelerators.
5. Conclusions
A versatile nuclear microprobe has been implemented in combination with a dedicated electrostatic accelerator. The technical details and experiences of using this system and the present status have been
discussed. A user-friendly combination has been the result of using a dedicated accelerator. The experimental work in various fields of application is much facilitated as compared to the earlier situation when sharing the accelerator with many different experiments. For serious scientific achievements in many fields of application the dedicated accelerator approach is very important.
Acknowledgements
In this project the donators of the dedicated accelerator, i.e., the Knut&Alice Wallenberg and the Crafoord foundations are particularly thanked. In the funding of this work during several years the Carl Trygger foundation and the Swedish research councils NFR, FRN and MFR have supplied substantial support in addition to the funds from our university.
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I. TECHNOLOGY