- Email: [email protected]
Design of a single ion hit facility
Beam Interactions with Materials&Atoms
ELSEVIER
Nuclear Instruments
and Methods in Physics Research B 130 fI997) 275-279
Design of a single ion hit facility M. Cholewa ‘,l, A. Saint ‘, G.J.F. Legge a, T. Kamiya b a The University qf Melbourne, School qf Physics, Micro Anal#cal Research Centre, Parktiille. WC. 30.52, Australia b Adwnced ~ad~utj~)~Technology Center. Japan Atomic Energy Research r~.~t~fute,Takasaki, Gunma 370-12, Japan
Abstract The aim of this project is to develop a new system for single ion irradiation of ceils for genetic and cell biology studies. This charged particle focused microbeam system will provide a fuliy computer controlled irradiation facility with submicron (subcellular) resolution and will open many new avenues into studies of radiobiological mechanisms. In the first stage of this project a system for single ion detection has been developed. A thin diamond window has been tested as vacuum/atmosphere window and as a possible source of secondary electrons and/or photons for single ion detection. A detection efficiency of 91% has been achieved.
1. Introduction In recent years a number of groups in Europe, USA and Japan have started to develop, or to plan, installations for microbeam irradiation of cells to enable them to study certain radiobiological processes in ways that are inaccessible with conventional broadfield exposures. While most systems actually in operation are using collimated beams with resolution of a few microns, we are developing a facility with submicron (down to 300 nm> resolution. Ionizing radiations have been shown to induce the death of mammalian cells and initiate mutagenic or carcinogenic changes [l]. All three actions are related through chromosomal changes; the latter in particular is of profound concern to human population. It is necessary to obtain more data to understand the basic principles underlying the effects of ion i~ad~ation on living matter.
I Permanent Poland.
address:
Institute
of Nuclear
Physics,
Cracow,
The cellular effects of radiation are dependent on a number of factors, including the energy of the radiation and the intrinsic sensitivity of the cell to radiation effects. These issues are crucial in the use of non-sealed isotopes for cancer therapy, as the cellular localization of the isotope, and the energy of the isotope utilized, can have dramatic effects on the efficacy of treatment. The ability to specifically target tumors while sparing normal tissues remains one of the most attractive new forms of therapy of cancer. The recent development of monoclona1 antibodies targeting antigens has resulted in the ability to administer therapeutic reagents (such as isotopes) linked to recombinant antibodies for cancer therapy [Z]. Initial results in clinical trials are extremely promising. Single-hit studies with subcellular resolution will provide insights in a number of areas. How does radiation sensitivity vary in different regions of the cell nucleus and what information does this provide about its structure? Do any observed patterns corresponds to the dis~ibution of chromatin, or of induced
01%583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SO168-583X(97)00356-X
VI. SINGLE IONS AND EFFECTS
216
M. Cholewu
et al. /NC&.
Instr
und Meth. in Phys. Rex B I30 (1997) 275-279
DNA damage, or do they reflect long range interactions between damaged sites, or localization of repair capacity? How do the spatial sensitivities for various endpoints compare, for example inactivation, DNA damage, mutation and apoptosis? Do some cells survive the passage of high linear energy transfer (LET) ions through their nucleus because their DNA has not been traversed and damaged, or is there some other reason? What information can be found about targets for induced genomic instability and are they nuclear or cytoplasmic? Can damage transfer from hit to non-hit cells?
2. Methods 2. I. Single ion facility A schematic view of a single ion facility proposed for MARC is presented in Fig. 1. The system proposed will use an existing horizontal microbeam line
with modifications to the target chamber to accommodate a “wet cell” system. The “wet cell” system will be mounted outside the vacuum. There are already facilities at MARC for handling and controlling single ions. Several existing or proposed systems overseas are using a vertical beam line, which offers some important advantages (e.g. cell handling), but the cost of establishing such a system at MARC will exceed 1 million dollars. Construction of a vertical system will take several years to complete and will be proposed later after consolidating local and overseas collaborations and expertise in single ion irradiation and microdosimetry. The essential parameters of the proposed system can be summarized as follows; (a) a focused external beam with submicron diameter at the cell, (b) a reliable 100% efficient single ion detection system, (c) fast beam switching to prevent second hits, (d) a target holder adapted for the irradiation of cells in vitro, (e) a fully automated computer controlled system for cell recognition and positioning.
“Wet-cell”
E@m “on” “off
Fig. 1.Schematic diagram of the single ion hit facility at MARC.
M. Cholewa et al. /Nucl.
Instr. and Meth. in Phys. Res. B I30 (1997) 275-279
2.2. Single ion detection Development of the most efficient detection system for single ion hit will be an important factor in the success of this project. Several different designs have been proposed over recent years. One of these systems developed at Legnaro, Italy [3] uses secondary electrons for detecting single charged particles with efficiency of 98%. In this case a detection system can only be located in front of the irradiated target in the vacuum as it uses a microchannel plate (MCP) detector. In our design we decided not to go this way, as high electric fields and the necessity of using a thin carbon foil in the detector will interfere with the focused beam and reduce beam resolution. This effect has been observed when a similar system was tested at JAERI, Takasaki [4]. A different approach, with the use of a thin scintilator and photomultiplier detector, at the CRC Gray Laboratory [5] achieved an efficiency of 100%. In this case the photomultiplier tube (Hamamatsu model R56OOU) is detecting photons generated by ions passing through a 3 micron thick scintilator (NE 105A) which is sandwiched between a 3 micron thick vacuum window and the bottom of a Petri dish. The photomultiplier detector is located in the atmosphere. This system is very sensitive to electronic noise as it not using a coincidence circuit. In our system we would like to take advantage of the fact that a thin window is required at the exit of the vacuum chamber. The window (between vacuum and atmosphere) will be used (as shown in Fig. 1) to detect single ions passing into the “wet cell”, by detecting either secondary electrons or photons or both. We had been investigating the possibility of using a thin (about 2 micron thick) diamond window. The advantage of using thin diamond is that its efficiency for photon or secondary electron production can be modified easily by implantation of different ions. For example an implantation with boron ions will produce a window with an enhanced secondary electron production [6] and implantation with nitrogen will produce a window with enhanced secondary photon production. 2.3. Cell recognition and positioning A fully automated (computer controlled) cell recognition and positioning system will become an
217
essential part of many present and future experiments performed in the School of Physics with either SPM, laser Raman microprobe, X-ray microprobe or single ion hit facility. Such systems are not commercially available at the moment and the only possibility is to develop it ourselves in collaboration with industry. So far such a system has been successfully developed at CRC Gray La~ratory ES] for fast cell recognition and positioning during single cell irradiation with individual ions experiments. A similar software package (AUTOSCOPE) has been developed by a local commercial company (Austoscan Systems Pty. Ltd., Melbourne, Australia). However, the AUTOSCOPE package requires a major redevelopment to suit the needs of our experiments at MARC. It is essential for the system of cell recognition and positioning to use as little light as possible to locate the position of cells which could be achieved by the use of high sensitivity CCD camera. The whole system while integrated with single ion hit should be able to process (cell recognition, cell positioning, single cell hit, single ion detection and beam switching) more than 3000 cells per hour. This way cells can be irradiated at a particular part of the cell cycle and a large number of cells processed is required because of the statistical nature of these experiments.
3. Results and discussion It was decided to investigate the possibility of using a 2 micron thick diamond as vacuum window which could provide also a source for secondary electrons or photons to detect single ions. Several groups have investigated a single ion detection system with a geometry similar to that shown in Fig. 1; but achieved efficiency was never greater than 30%. In these experiments a thin (5 to 10 micron thick) plastic scintilator was used in combination with photomultiplier detectors working in coincidence. The experimental setup for measuring detection efficiency using secondary electrons or photons generated by ions is shown in Fig. 2. A 226Ra alpha source was used to obtain 4.4 to 7.7 MeV alpha particles. A collimator of 3 mm diameter in front of VI. SINGLE IONS AND EFFECTS
278
r
v
ECHO-t-lC
0
ELECTRONS a? h
IONS
Fig. 2. Schematic representation of the system used for measurement of detection efficiency of single ions. SED: secondary electron detector; PD: photomultiplier tube; SBD: surface barrier detector; SF: special filter; PA: preamplifier; A: amplifier; CFD: constant fraction discriminator; TAC: time-to-analog converter; C: counter; D: delay; OR: switch between PD or SED circuit.
the source limited the divergence angle for alpha particles hitting a thin (about 2 micron thick) boron doped diamond window. The distance between the collimator and the target was 100 mm. In this configuration the photons and/or secondary electrons generated in a thin diamond window or a 5 micron thick plastic scintilator were detected by a photomultiplier (Hamamatsu model R647) or a secondary electron detector (Amptek model MD502) respectively. The secondary electron detector and photomultiplier tube were placed at the distance of 20 mm and 40 mm respectively at roughly 45” in relation to the beam. A charged particle detector was placed at the distance of 5 mm behind the thin window. Photons or secondary electrons were detected in coincidence with a signal from the charged particle detector. The START detector (charged particle detector, ORTEC model BA 20 200 100) was connected through preamplifier (ORTEC model 1421, amplifier (ORTEC model 454) and constant fraction discrimi-
nator (ORTEC model 4631 to the START input of a time-to-analg converter (ORTEC model 567). As a STOP detector either the photomultiplier tube or secondary electron detector was being used. The signal from the photomultiplier detector was first amplified by a fast preamplifier (Philips model 6954). This signal was fed into the CFD (ORTEC model 463). The signal from the CFD was used as a STOP for the TAC. Similar circuitry was used for the secondary electron detector (Amptek model MD.5021 with a preamplifier (Phifips model 6954) and the CFD (ORTEC model 463). The number of coincidence counts was measured and compared with the number of counts from the charged particle detector. 3.1. Photon detection The efficiency of photon detection in this geometry was about 2% with the Hamamatsu photomultiplier detector and boron doped diamond window. This efficiency was increased to 40% when the
M. cholera
ef ai. / Nucl. instr. and Meth. in Phys. Res. B 130 119971 275-279
diamond window was replaced with a 5 micron thick scintilator from Bicron (Bicron model BC400). 3.2. Secondary
electron
detection
A 88% transmission thin molybdenum position in front of the Amptek secondary detector. The grid was biased to + 1200 V secondary electrons generated from a thin window. Secondary detection efficiency was about boron doped diamond window.
grid was electron to attract diamond 97% for
4. Conclusions We have shown that a 2 micron thick diamond window doped with boron can be successfully used as a vacuum window and at the same time as a secondary electron generator. In these initial experiments the detection efficiency for secondary electrons and photons was 97% and 2% respectively for the geometry of Fig. 2. With the same geometry an efficiency of 40% for photons has been observed when 5 micron thick plastic (Bicron BC400) was being used. The high efficiency of 97% for single ion hit using a secondary electron detector from Amptek was achieved after applying a special filter to the
279
detector. This enabled reduction of the noise from about 160 mV to less than 10 mV. This small modification enabled us to achieve an excellent detection efficiency. By further modifications to the geometry and bias arrangements it should be possible to obtain a detection efficiency very close to 100% for MeV alpha particles. In the near future we are planning to perform experiments with MeV protons and heavy ions. It is planned to investigate other materials as a vacuum window (e.g. Si3N4) and at the same time as a possible source of either secondary electrons or photons. The advantage of such a geometry as presented in Fig. 1 for single ion detection is that the noise level of the detection system can be eliminated by the use of a coincidence circuit.
References Ill C. Geard, Nucl. Instr. and Meth. B 54 (1991) 411. [2] X.Y. Larson et al., Acta Oncologica 32 (1993) 709. [3] P. Boccaccio, L. Vannucci, R.A. Ricci, I. Massa, G. Vannini and A. Sarti, Nucle. Instr. and Meth. A 243 (1986) 599. [4] T. Sakai, T. Hamano, T. Suda. T. Hirao and T. Kamiya, these proceedings (ICNMTA-961, Nucl. Instr. and Meth. B 130 (19971498. I51 M. Folkard, K.M. Prise, B. Vojnovic, H.C. Newman, M.J. Roper and B. Michael, lnt. J. Radiat. Biol. 69 (1996) 729. [61 A. Shih, J. Yater, P. Pehrsson. J. Butler and R. Abrams, Mater. Res. Sot. Symp. Proc. 416 (1995) 461.
VI. SINGLE IONS AND EFFECTS
ELSEVIER
Nuclear Instruments
and Methods in Physics Research B 130 fI997) 275-279
Design of a single ion hit facility M. Cholewa ‘,l, A. Saint ‘, G.J.F. Legge a, T. Kamiya b a The University qf Melbourne, School qf Physics, Micro Anal#cal Research Centre, Parktiille. WC. 30.52, Australia b Adwnced ~ad~utj~)~Technology Center. Japan Atomic Energy Research r~.~t~fute,Takasaki, Gunma 370-12, Japan
Abstract The aim of this project is to develop a new system for single ion irradiation of ceils for genetic and cell biology studies. This charged particle focused microbeam system will provide a fuliy computer controlled irradiation facility with submicron (subcellular) resolution and will open many new avenues into studies of radiobiological mechanisms. In the first stage of this project a system for single ion detection has been developed. A thin diamond window has been tested as vacuum/atmosphere window and as a possible source of secondary electrons and/or photons for single ion detection. A detection efficiency of 91% has been achieved.
1. Introduction In recent years a number of groups in Europe, USA and Japan have started to develop, or to plan, installations for microbeam irradiation of cells to enable them to study certain radiobiological processes in ways that are inaccessible with conventional broadfield exposures. While most systems actually in operation are using collimated beams with resolution of a few microns, we are developing a facility with submicron (down to 300 nm> resolution. Ionizing radiations have been shown to induce the death of mammalian cells and initiate mutagenic or carcinogenic changes [l]. All three actions are related through chromosomal changes; the latter in particular is of profound concern to human population. It is necessary to obtain more data to understand the basic principles underlying the effects of ion i~ad~ation on living matter.
I Permanent Poland.
address:
Institute
of Nuclear
Physics,
Cracow,
The cellular effects of radiation are dependent on a number of factors, including the energy of the radiation and the intrinsic sensitivity of the cell to radiation effects. These issues are crucial in the use of non-sealed isotopes for cancer therapy, as the cellular localization of the isotope, and the energy of the isotope utilized, can have dramatic effects on the efficacy of treatment. The ability to specifically target tumors while sparing normal tissues remains one of the most attractive new forms of therapy of cancer. The recent development of monoclona1 antibodies targeting antigens has resulted in the ability to administer therapeutic reagents (such as isotopes) linked to recombinant antibodies for cancer therapy [Z]. Initial results in clinical trials are extremely promising. Single-hit studies with subcellular resolution will provide insights in a number of areas. How does radiation sensitivity vary in different regions of the cell nucleus and what information does this provide about its structure? Do any observed patterns corresponds to the dis~ibution of chromatin, or of induced
01%583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SO168-583X(97)00356-X
VI. SINGLE IONS AND EFFECTS
216
M. Cholewu
et al. /NC&.
Instr
und Meth. in Phys. Rex B I30 (1997) 275-279
DNA damage, or do they reflect long range interactions between damaged sites, or localization of repair capacity? How do the spatial sensitivities for various endpoints compare, for example inactivation, DNA damage, mutation and apoptosis? Do some cells survive the passage of high linear energy transfer (LET) ions through their nucleus because their DNA has not been traversed and damaged, or is there some other reason? What information can be found about targets for induced genomic instability and are they nuclear or cytoplasmic? Can damage transfer from hit to non-hit cells?
2. Methods 2. I. Single ion facility A schematic view of a single ion facility proposed for MARC is presented in Fig. 1. The system proposed will use an existing horizontal microbeam line
with modifications to the target chamber to accommodate a “wet cell” system. The “wet cell” system will be mounted outside the vacuum. There are already facilities at MARC for handling and controlling single ions. Several existing or proposed systems overseas are using a vertical beam line, which offers some important advantages (e.g. cell handling), but the cost of establishing such a system at MARC will exceed 1 million dollars. Construction of a vertical system will take several years to complete and will be proposed later after consolidating local and overseas collaborations and expertise in single ion irradiation and microdosimetry. The essential parameters of the proposed system can be summarized as follows; (a) a focused external beam with submicron diameter at the cell, (b) a reliable 100% efficient single ion detection system, (c) fast beam switching to prevent second hits, (d) a target holder adapted for the irradiation of cells in vitro, (e) a fully automated computer controlled system for cell recognition and positioning.
“Wet-cell”
E@m “on” “off
Fig. 1.Schematic diagram of the single ion hit facility at MARC.
M. Cholewa et al. /Nucl.
Instr. and Meth. in Phys. Res. B I30 (1997) 275-279
2.2. Single ion detection Development of the most efficient detection system for single ion hit will be an important factor in the success of this project. Several different designs have been proposed over recent years. One of these systems developed at Legnaro, Italy [3] uses secondary electrons for detecting single charged particles with efficiency of 98%. In this case a detection system can only be located in front of the irradiated target in the vacuum as it uses a microchannel plate (MCP) detector. In our design we decided not to go this way, as high electric fields and the necessity of using a thin carbon foil in the detector will interfere with the focused beam and reduce beam resolution. This effect has been observed when a similar system was tested at JAERI, Takasaki [4]. A different approach, with the use of a thin scintilator and photomultiplier detector, at the CRC Gray Laboratory [5] achieved an efficiency of 100%. In this case the photomultiplier tube (Hamamatsu model R56OOU) is detecting photons generated by ions passing through a 3 micron thick scintilator (NE 105A) which is sandwiched between a 3 micron thick vacuum window and the bottom of a Petri dish. The photomultiplier detector is located in the atmosphere. This system is very sensitive to electronic noise as it not using a coincidence circuit. In our system we would like to take advantage of the fact that a thin window is required at the exit of the vacuum chamber. The window (between vacuum and atmosphere) will be used (as shown in Fig. 1) to detect single ions passing into the “wet cell”, by detecting either secondary electrons or photons or both. We had been investigating the possibility of using a thin (about 2 micron thick) diamond window. The advantage of using thin diamond is that its efficiency for photon or secondary electron production can be modified easily by implantation of different ions. For example an implantation with boron ions will produce a window with an enhanced secondary electron production [6] and implantation with nitrogen will produce a window with enhanced secondary photon production. 2.3. Cell recognition and positioning A fully automated (computer controlled) cell recognition and positioning system will become an
217
essential part of many present and future experiments performed in the School of Physics with either SPM, laser Raman microprobe, X-ray microprobe or single ion hit facility. Such systems are not commercially available at the moment and the only possibility is to develop it ourselves in collaboration with industry. So far such a system has been successfully developed at CRC Gray La~ratory ES] for fast cell recognition and positioning during single cell irradiation with individual ions experiments. A similar software package (AUTOSCOPE) has been developed by a local commercial company (Austoscan Systems Pty. Ltd., Melbourne, Australia). However, the AUTOSCOPE package requires a major redevelopment to suit the needs of our experiments at MARC. It is essential for the system of cell recognition and positioning to use as little light as possible to locate the position of cells which could be achieved by the use of high sensitivity CCD camera. The whole system while integrated with single ion hit should be able to process (cell recognition, cell positioning, single cell hit, single ion detection and beam switching) more than 3000 cells per hour. This way cells can be irradiated at a particular part of the cell cycle and a large number of cells processed is required because of the statistical nature of these experiments.
3. Results and discussion It was decided to investigate the possibility of using a 2 micron thick diamond as vacuum window which could provide also a source for secondary electrons or photons to detect single ions. Several groups have investigated a single ion detection system with a geometry similar to that shown in Fig. 1; but achieved efficiency was never greater than 30%. In these experiments a thin (5 to 10 micron thick) plastic scintilator was used in combination with photomultiplier detectors working in coincidence. The experimental setup for measuring detection efficiency using secondary electrons or photons generated by ions is shown in Fig. 2. A 226Ra alpha source was used to obtain 4.4 to 7.7 MeV alpha particles. A collimator of 3 mm diameter in front of VI. SINGLE IONS AND EFFECTS
278
r
v
ECHO-t-lC
0
ELECTRONS a? h
IONS
Fig. 2. Schematic representation of the system used for measurement of detection efficiency of single ions. SED: secondary electron detector; PD: photomultiplier tube; SBD: surface barrier detector; SF: special filter; PA: preamplifier; A: amplifier; CFD: constant fraction discriminator; TAC: time-to-analog converter; C: counter; D: delay; OR: switch between PD or SED circuit.
the source limited the divergence angle for alpha particles hitting a thin (about 2 micron thick) boron doped diamond window. The distance between the collimator and the target was 100 mm. In this configuration the photons and/or secondary electrons generated in a thin diamond window or a 5 micron thick plastic scintilator were detected by a photomultiplier (Hamamatsu model R647) or a secondary electron detector (Amptek model MD502) respectively. The secondary electron detector and photomultiplier tube were placed at the distance of 20 mm and 40 mm respectively at roughly 45” in relation to the beam. A charged particle detector was placed at the distance of 5 mm behind the thin window. Photons or secondary electrons were detected in coincidence with a signal from the charged particle detector. The START detector (charged particle detector, ORTEC model BA 20 200 100) was connected through preamplifier (ORTEC model 1421, amplifier (ORTEC model 454) and constant fraction discrimi-
nator (ORTEC model 4631 to the START input of a time-to-analg converter (ORTEC model 567). As a STOP detector either the photomultiplier tube or secondary electron detector was being used. The signal from the photomultiplier detector was first amplified by a fast preamplifier (Philips model 6954). This signal was fed into the CFD (ORTEC model 463). The signal from the CFD was used as a STOP for the TAC. Similar circuitry was used for the secondary electron detector (Amptek model MD.5021 with a preamplifier (Phifips model 6954) and the CFD (ORTEC model 463). The number of coincidence counts was measured and compared with the number of counts from the charged particle detector. 3.1. Photon detection The efficiency of photon detection in this geometry was about 2% with the Hamamatsu photomultiplier detector and boron doped diamond window. This efficiency was increased to 40% when the
M. cholera
ef ai. / Nucl. instr. and Meth. in Phys. Res. B 130 119971 275-279
diamond window was replaced with a 5 micron thick scintilator from Bicron (Bicron model BC400). 3.2. Secondary
electron
detection
A 88% transmission thin molybdenum position in front of the Amptek secondary detector. The grid was biased to + 1200 V secondary electrons generated from a thin window. Secondary detection efficiency was about boron doped diamond window.
grid was electron to attract diamond 97% for
4. Conclusions We have shown that a 2 micron thick diamond window doped with boron can be successfully used as a vacuum window and at the same time as a secondary electron generator. In these initial experiments the detection efficiency for secondary electrons and photons was 97% and 2% respectively for the geometry of Fig. 2. With the same geometry an efficiency of 40% for photons has been observed when 5 micron thick plastic (Bicron BC400) was being used. The high efficiency of 97% for single ion hit using a secondary electron detector from Amptek was achieved after applying a special filter to the
279
detector. This enabled reduction of the noise from about 160 mV to less than 10 mV. This small modification enabled us to achieve an excellent detection efficiency. By further modifications to the geometry and bias arrangements it should be possible to obtain a detection efficiency very close to 100% for MeV alpha particles. In the near future we are planning to perform experiments with MeV protons and heavy ions. It is planned to investigate other materials as a vacuum window (e.g. Si3N4) and at the same time as a possible source of either secondary electrons or photons. The advantage of such a geometry as presented in Fig. 1 for single ion detection is that the noise level of the detection system can be eliminated by the use of a coincidence circuit.
References Ill C. Geard, Nucl. Instr. and Meth. B 54 (1991) 411. [2] X.Y. Larson et al., Acta Oncologica 32 (1993) 709. [3] P. Boccaccio, L. Vannucci, R.A. Ricci, I. Massa, G. Vannini and A. Sarti, Nucle. Instr. and Meth. A 243 (1986) 599. [4] T. Sakai, T. Hamano, T. Suda. T. Hirao and T. Kamiya, these proceedings (ICNMTA-961, Nucl. Instr. and Meth. B 130 (19971498. I51 M. Folkard, K.M. Prise, B. Vojnovic, H.C. Newman, M.J. Roper and B. Michael, lnt. J. Radiat. Biol. 69 (1996) 729. [61 A. Shih, J. Yater, P. Pehrsson. J. Butler and R. Abrams, Mater. Res. Sot. Symp. Proc. 416 (1995) 461.
VI. SINGLE IONS AND EFFECTS