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A radiation effects facility using a 1.7 MV tandem accelerator
cm __
Nuclear Instruments
and Methods in Physics Research B 99 (1995) 780-783
__
lifiiil
NOMB
Beam InteractIons with Materials A Atoms
ELSEVIER
A radiation effects facility using a 1.7 MV tandem accelerator D.L. Damcott, J.M. Cookson, V.H. Rotberg Department
of Nuclear Engineering,
*
*,G.S. Was
University of Michigan, Ann Arbor, MI 48109, USA
Abstract A facility has been established at the Michigan Ion Beam Laboratory for the study of radiation effects on materials. The capabilities include a broad range of materials (metals, ceramics and polymers), radiation damage rates (10-s to 10e3 dpa/s) and irradiation temperatures (- 196°C to 600°C). The key to the utility of this facility is the control of irradiation dose, dose uniformity, and sample temperature during irradiation. Temperature stability is maintained by simultaneous heating and cooling of the sample stage, and use of a liquid metal interface (for metal samples). The temperature of individual samples in the irradiated area is measured via an infrared pyrometer and thermocouples. Temperature uniformity is confirmed by the pyrometer, while dose uniformity is provided by a split aperture. A total of eight input channels transmit temperature and beam current signals to a 486DX computer to provide feedback to the operator and to record the irradiation history at a frequency of 1 point per second. Continuous irradiations lasting up to 120 hours have been successfully conducted.
1. Introduction The need for basic information regarding the microstructural effects of ionizing particles has become increasingly important, particularly in the case of neutron exposure of components in aging light water reactors (LWRs). Although it may seem preferable in this latter case to study samples exposed to neutrons in-core, the time, expense, and accessibility make alternatives worth examining closely. If ion irradiation can generate microstructures comparable to those of interest, the radiation damage by neutrons can be studied more prudently. Temperature, dose rate, and accumulated dose are the critical parameters which determine the microstructural changes resulting from irradiation; control of these parameters is necessary in order to reproducibly generate the desired microstructure. Careful selection of irradiation conditions allows for the production of samples in which the microstructure of interest is generated. A facility which can closely control these parameters has been developed at the University of Michigan using the 1.7 MV tandetron accelerator.
* Work supported in part by United States Department of Energy under grant DE-FGO7-88ER-12825, the Office of Basic Energy Sciences grant DE-FG02-93ER-12130, and the Associated Western Universities, Inc., Northwest Division under grant DEFG06-89ER-75522. * Corresponding author. Tel. + 1 313 936 0166, fax + 1 313 936 8820.
The facility has primarily been used for irradiating stainless steels with 3.2 MeV protons [l-3]. The facility has also been used for proton irradiations for the examination of flux pinning in high temperature superconductors [4]; low dose proton irradiation for examination of diffusion length damage coefficients in InP for space applications [s]; phase transformations in Ni,Al [6], and coating-substrate interface modification [7].
2. Facility description The ion beams used for these radiation effects studies are produced by the General Ionex Tandetron accelerator in the Michigan Ion Beam Laboratory [8]. The samples are mounted on a stage within a specially designed, electrically isolated chamber attached to the existing target chamber on the 1.5” beam line (Figs. la and lb). For the cases which employ a high power density input when the ion beam is present (3.2 MeV protons, 10 p,A/cm’), a thermally conductive path must be maintained between the samples and the stage throughout the irradiation to control sample surface temperature. This is achieved by mounting the samples on a copper block with a liquid metal coupling between the samples and the stage. Round bars across the top and bottom of the samples hold the samples in position. A schematic of the stage arrangement is shown in Fig. lc. The nominal temperature of the sample surface during irradiation can be controlled to within k 10°C of the desired goal temperature, which can range between 200°C and 500°C. Higher
0168-583X/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0168-583X(94)00618-0
D.L. Damcott et al. /Nucl. Instr. and Meth. in Phys. Res. B 99 (1995) 780-783
effects
radtatian dedicated
chamber
UHV chamber
a
__ El
Cl
Ceramic isdator
ApWtUR design
I
;
Liquid metal between samptes and stage
Samples secured
to stage
d)
Fig. 1. (a) Schematic of beamline, showing position of dedicated radiation effects chamber. (b) The controlled temperature stage used for the proton irradiations (electrically isolated from the rest of the beamline). (c) Detail of the controlled temperature irradiation stage in (b). As heat can be both added and removed, the temperature could be controlled precisely. The inset shows the “L7” aperture design. (d) A typical temperature map using the pyrometer to determine individual sample temperatures in the irradiated region.
sample temperatures (600°C) are achieved by using a nickel stage identical in design to the copper stage and the same mounting procedures. For a desired temperature of 2OO”C, gallium is used as the bonding metal; indium or tin are used for higher temperature irradiations. The temperature during irradiation is controlled by simultaneously heating the stage from the rear with an electric cartridge heater inserted into a cavity in the back of the stage and cooling the stage with flowing air, or recirculating ethylene glycol for low temperature irradiations (200°C). With a power density of 40 W/cm2, a temperature difference of up to 100°C between the front of
781
the samples and the back of the stage is typical during irradiation at any temperature. Modification of the mounting procedure to melt and resolidify the metal for bonding prior to irradiation allows for low temperature irradiations using a continuous flow of liquid nitrogen in the cooling loop. The sample temperature is monitored using an infrared pyrometer which can be remotely controlled to scan the irradiated region, thus confirming sample temperature uniformity. The pyrometer is calibrated to the desired temperature range prior to irradiation by heating the sample stage and adjusting the emissivity setting of the pyrometer such that the temperature reading closely matches the temperatures given by up to nine thermocouples spot-welded to the sample surfaces. An example temperature map using the calibrated pyrometer which indicates the uniformity of sample temperatures is shown in Fig. Id. The incident ion beam is focused down to a spot approximately 6 mm in diameter and then rastered across the samples. Half of the beam is overscanned onto a 2-piece “L7” shaped aperture (see the inset of Fig. lc). This aperture arrangement results in a 10 mm by 16 mm uniformly irradiated region on the samples. This aperture is also useful in the alignment of the scanned beam. By balancing the measured current on the two isolated halves of the aperture by adjustment of the X- and y-steering, correct positioning of the scanned beam is assured. Computer monitoring of the proton irradiations was developed over the course of the experimental program, mainly motivated by the need to gather accurate temperature and dose rate information for each irradiation. It is a versatile program which has been successfully applied to irradiations with other ions and ion energies. An added advantage of the computer monitoring is that on-line information becomes available to the operator, which greatly assists in controlling the temperature accurately, as well as keeping track of long term trends in the accelerator conditions. An IBM compatible PC-486AT computer is interfaced to the analog and digital signals available for temperature and current via an A/D board, which is installed in the computer. Eight analog differential input channels and two digital counter input channels are available as well as two analog and two digital counter output channels. The eight analog inputs are divided up in the following way: five are for thermocouples, one is for the pyrometer analog output, and the two remaining input channels are for the two sides of the split aperture. One of the two digital counter inputs is attached to the digitized output of the current integrator, while the other digital input is linked to one of the digital outputs of the board, which acts as a counting gate. Only one analog output is used in this setup, attached to the emitter side of a transistor used for an audible alarm. The software is written in the LabWindowsTM environment (available from National Instruments, Inc.), in the C programming language. The main data acquisition screen
XVII. RADIATION
PROCESSING
D.L. Damcott et al. /Nuct. fnstr. and Meth. in Phys. Res. B 99 (1995) 780-783
300.0 200.0
100.0 0.0
T1 me(seconds) 25 a 20 0 15.0 10.0 5.0 00
Time(r=na4,
Fig. 2. A portion of the main data acquisition page showing the two real time graphs for temperature and stage current. There are also sliders for aperture currents. The data are updated continuously.
colored sliders, and the difference between these currents is calculated, giving an indication of any beam drifting. The desired conditions can be readily programmed into the computer, and deviations beyond acceptable limits can trigger the audible alarm to alert the operator. Those deviations are written to a special “out of bounds” data file. The temperature and current history of the entire irradiation, as well as the out of bounds conditions, are summarized in the “end run graphs” page, shown in Fig. 3. Samples irradiated with high energy protons become slightly activated; post-irradiation beta particle counting using a Tennelec LB 5100 automated alpha/beta counter is used to check the uniformity of the irradiation across these samples. The specific activity of these samples typically varies by less than 8% for a seven-sample irradiation. Any of the coupling metal remaining on the unirradiated side of the samples is removed mechanically and by electropolishing, if necessary, prior to sample analysis.
3. Summary is shown in Fig. 2. This is a highly versatile way of combining the information from the various signals into an easily understandable format. The temperature and target current have real time graphs, which provide the data from the last five minutes, while the other inputs are continuously updated. The aperture currents are indicated by
Fig. 3. The “end run graphs” page. The temperature be plotted upon its completion.
The facility described has been used for a wide variety of radiation damage studies, involving different ions and materials. While the most extensive use of the facility to date has been motivated by radiation effects in nuclear reactors, the equipment and techniques we have developed
and current histories, as well as out of bounds deviations,
for an entire irradiation
can
D.L. Damcott et al. /Nucl. Instr. and Meth. in Phys. Res. B 99 (1995) 780-783
for that work are highly versatile, and can be readily modified for other applications. The value of this approach to study radiation damage has been demonstrated, yielding results in a fraction of the time and at a fraction of the cost of using in-situ irradiation.
References
[3] [4] [5]
[6] [7]
[ll J.M. Cookson, D.L. Damcott, R.D. Carter, G.S. Was and M. Atzmon, J. Nucl. Mater., 202 (1993) 104. [2] D.L. Damcott, R.D. Carter, J.R. Cookson, J.R. Martin, G.S.
[8]
783
Was and M. Atzmon, Radiat. Eff. Defects in Solids 118 (1991) 383. D.L. Damcott, T.R. Allen and G.S. Was. J. Nucl. Mater., in press. M.L. Griffith and J.W. Halloran, Phys. Rev. B 46 (1992) 104. R. Hakimzadeh, C. Vargas-Aburto, S.G. Bailey and W. Williams, 5th Int. Conf. on Indium Phosphide and Related Materials, IEEE Electron Devices Society, Paris, France, April 18-22, 1993. D. Cavasin and G.S. Was, Nucl. Ins&. and Meth., B 59/60 (1991) 875. M. McIntyre and G.S. Was, TMS Materials Week, Oct. 2-7. 1994. V.H. Rotberg and G.S. Was. Nucl. Instr. and Meth. B 40/41 (1989) 722.
XVII. RADIATION PROCESSING
Nuclear Instruments
and Methods in Physics Research B 99 (1995) 780-783
__
lifiiil
NOMB
Beam InteractIons with Materials A Atoms
ELSEVIER
A radiation effects facility using a 1.7 MV tandem accelerator D.L. Damcott, J.M. Cookson, V.H. Rotberg Department
of Nuclear Engineering,
*
*,G.S. Was
University of Michigan, Ann Arbor, MI 48109, USA
Abstract A facility has been established at the Michigan Ion Beam Laboratory for the study of radiation effects on materials. The capabilities include a broad range of materials (metals, ceramics and polymers), radiation damage rates (10-s to 10e3 dpa/s) and irradiation temperatures (- 196°C to 600°C). The key to the utility of this facility is the control of irradiation dose, dose uniformity, and sample temperature during irradiation. Temperature stability is maintained by simultaneous heating and cooling of the sample stage, and use of a liquid metal interface (for metal samples). The temperature of individual samples in the irradiated area is measured via an infrared pyrometer and thermocouples. Temperature uniformity is confirmed by the pyrometer, while dose uniformity is provided by a split aperture. A total of eight input channels transmit temperature and beam current signals to a 486DX computer to provide feedback to the operator and to record the irradiation history at a frequency of 1 point per second. Continuous irradiations lasting up to 120 hours have been successfully conducted.
1. Introduction The need for basic information regarding the microstructural effects of ionizing particles has become increasingly important, particularly in the case of neutron exposure of components in aging light water reactors (LWRs). Although it may seem preferable in this latter case to study samples exposed to neutrons in-core, the time, expense, and accessibility make alternatives worth examining closely. If ion irradiation can generate microstructures comparable to those of interest, the radiation damage by neutrons can be studied more prudently. Temperature, dose rate, and accumulated dose are the critical parameters which determine the microstructural changes resulting from irradiation; control of these parameters is necessary in order to reproducibly generate the desired microstructure. Careful selection of irradiation conditions allows for the production of samples in which the microstructure of interest is generated. A facility which can closely control these parameters has been developed at the University of Michigan using the 1.7 MV tandetron accelerator.
* Work supported in part by United States Department of Energy under grant DE-FGO7-88ER-12825, the Office of Basic Energy Sciences grant DE-FG02-93ER-12130, and the Associated Western Universities, Inc., Northwest Division under grant DEFG06-89ER-75522. * Corresponding author. Tel. + 1 313 936 0166, fax + 1 313 936 8820.
The facility has primarily been used for irradiating stainless steels with 3.2 MeV protons [l-3]. The facility has also been used for proton irradiations for the examination of flux pinning in high temperature superconductors [4]; low dose proton irradiation for examination of diffusion length damage coefficients in InP for space applications [s]; phase transformations in Ni,Al [6], and coating-substrate interface modification [7].
2. Facility description The ion beams used for these radiation effects studies are produced by the General Ionex Tandetron accelerator in the Michigan Ion Beam Laboratory [8]. The samples are mounted on a stage within a specially designed, electrically isolated chamber attached to the existing target chamber on the 1.5” beam line (Figs. la and lb). For the cases which employ a high power density input when the ion beam is present (3.2 MeV protons, 10 p,A/cm’), a thermally conductive path must be maintained between the samples and the stage throughout the irradiation to control sample surface temperature. This is achieved by mounting the samples on a copper block with a liquid metal coupling between the samples and the stage. Round bars across the top and bottom of the samples hold the samples in position. A schematic of the stage arrangement is shown in Fig. lc. The nominal temperature of the sample surface during irradiation can be controlled to within k 10°C of the desired goal temperature, which can range between 200°C and 500°C. Higher
0168-583X/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0168-583X(94)00618-0
D.L. Damcott et al. /Nucl. Instr. and Meth. in Phys. Res. B 99 (1995) 780-783
effects
radtatian dedicated
chamber
UHV chamber
a
__ El
Cl
Ceramic isdator
ApWtUR design
I
;
Liquid metal between samptes and stage
Samples secured
to stage
d)
Fig. 1. (a) Schematic of beamline, showing position of dedicated radiation effects chamber. (b) The controlled temperature stage used for the proton irradiations (electrically isolated from the rest of the beamline). (c) Detail of the controlled temperature irradiation stage in (b). As heat can be both added and removed, the temperature could be controlled precisely. The inset shows the “L7” aperture design. (d) A typical temperature map using the pyrometer to determine individual sample temperatures in the irradiated region.
sample temperatures (600°C) are achieved by using a nickel stage identical in design to the copper stage and the same mounting procedures. For a desired temperature of 2OO”C, gallium is used as the bonding metal; indium or tin are used for higher temperature irradiations. The temperature during irradiation is controlled by simultaneously heating the stage from the rear with an electric cartridge heater inserted into a cavity in the back of the stage and cooling the stage with flowing air, or recirculating ethylene glycol for low temperature irradiations (200°C). With a power density of 40 W/cm2, a temperature difference of up to 100°C between the front of
781
the samples and the back of the stage is typical during irradiation at any temperature. Modification of the mounting procedure to melt and resolidify the metal for bonding prior to irradiation allows for low temperature irradiations using a continuous flow of liquid nitrogen in the cooling loop. The sample temperature is monitored using an infrared pyrometer which can be remotely controlled to scan the irradiated region, thus confirming sample temperature uniformity. The pyrometer is calibrated to the desired temperature range prior to irradiation by heating the sample stage and adjusting the emissivity setting of the pyrometer such that the temperature reading closely matches the temperatures given by up to nine thermocouples spot-welded to the sample surfaces. An example temperature map using the calibrated pyrometer which indicates the uniformity of sample temperatures is shown in Fig. Id. The incident ion beam is focused down to a spot approximately 6 mm in diameter and then rastered across the samples. Half of the beam is overscanned onto a 2-piece “L7” shaped aperture (see the inset of Fig. lc). This aperture arrangement results in a 10 mm by 16 mm uniformly irradiated region on the samples. This aperture is also useful in the alignment of the scanned beam. By balancing the measured current on the two isolated halves of the aperture by adjustment of the X- and y-steering, correct positioning of the scanned beam is assured. Computer monitoring of the proton irradiations was developed over the course of the experimental program, mainly motivated by the need to gather accurate temperature and dose rate information for each irradiation. It is a versatile program which has been successfully applied to irradiations with other ions and ion energies. An added advantage of the computer monitoring is that on-line information becomes available to the operator, which greatly assists in controlling the temperature accurately, as well as keeping track of long term trends in the accelerator conditions. An IBM compatible PC-486AT computer is interfaced to the analog and digital signals available for temperature and current via an A/D board, which is installed in the computer. Eight analog differential input channels and two digital counter input channels are available as well as two analog and two digital counter output channels. The eight analog inputs are divided up in the following way: five are for thermocouples, one is for the pyrometer analog output, and the two remaining input channels are for the two sides of the split aperture. One of the two digital counter inputs is attached to the digitized output of the current integrator, while the other digital input is linked to one of the digital outputs of the board, which acts as a counting gate. Only one analog output is used in this setup, attached to the emitter side of a transistor used for an audible alarm. The software is written in the LabWindowsTM environment (available from National Instruments, Inc.), in the C programming language. The main data acquisition screen
XVII. RADIATION
PROCESSING
D.L. Damcott et al. /Nuct. fnstr. and Meth. in Phys. Res. B 99 (1995) 780-783
300.0 200.0
100.0 0.0
T1 me(seconds) 25 a 20 0 15.0 10.0 5.0 00
Time(r=na4,
Fig. 2. A portion of the main data acquisition page showing the two real time graphs for temperature and stage current. There are also sliders for aperture currents. The data are updated continuously.
colored sliders, and the difference between these currents is calculated, giving an indication of any beam drifting. The desired conditions can be readily programmed into the computer, and deviations beyond acceptable limits can trigger the audible alarm to alert the operator. Those deviations are written to a special “out of bounds” data file. The temperature and current history of the entire irradiation, as well as the out of bounds conditions, are summarized in the “end run graphs” page, shown in Fig. 3. Samples irradiated with high energy protons become slightly activated; post-irradiation beta particle counting using a Tennelec LB 5100 automated alpha/beta counter is used to check the uniformity of the irradiation across these samples. The specific activity of these samples typically varies by less than 8% for a seven-sample irradiation. Any of the coupling metal remaining on the unirradiated side of the samples is removed mechanically and by electropolishing, if necessary, prior to sample analysis.
3. Summary is shown in Fig. 2. This is a highly versatile way of combining the information from the various signals into an easily understandable format. The temperature and target current have real time graphs, which provide the data from the last five minutes, while the other inputs are continuously updated. The aperture currents are indicated by
Fig. 3. The “end run graphs” page. The temperature be plotted upon its completion.
The facility described has been used for a wide variety of radiation damage studies, involving different ions and materials. While the most extensive use of the facility to date has been motivated by radiation effects in nuclear reactors, the equipment and techniques we have developed
and current histories, as well as out of bounds deviations,
for an entire irradiation
can
D.L. Damcott et al. /Nucl. Instr. and Meth. in Phys. Res. B 99 (1995) 780-783
for that work are highly versatile, and can be readily modified for other applications. The value of this approach to study radiation damage has been demonstrated, yielding results in a fraction of the time and at a fraction of the cost of using in-situ irradiation.
References
[3] [4] [5]
[6] [7]
[ll J.M. Cookson, D.L. Damcott, R.D. Carter, G.S. Was and M. Atzmon, J. Nucl. Mater., 202 (1993) 104. [2] D.L. Damcott, R.D. Carter, J.R. Cookson, J.R. Martin, G.S.
[8]
783
Was and M. Atzmon, Radiat. Eff. Defects in Solids 118 (1991) 383. D.L. Damcott, T.R. Allen and G.S. Was. J. Nucl. Mater., in press. M.L. Griffith and J.W. Halloran, Phys. Rev. B 46 (1992) 104. R. Hakimzadeh, C. Vargas-Aburto, S.G. Bailey and W. Williams, 5th Int. Conf. on Indium Phosphide and Related Materials, IEEE Electron Devices Society, Paris, France, April 18-22, 1993. D. Cavasin and G.S. Was, Nucl. Ins&. and Meth., B 59/60 (1991) 875. M. McIntyre and G.S. Was, TMS Materials Week, Oct. 2-7. 1994. V.H. Rotberg and G.S. Was. Nucl. Instr. and Meth. B 40/41 (1989) 722.
XVII. RADIATION PROCESSING