- Email: [email protected]
A solid-state spectrometer for cooled beams with high acceptance and resolution in space and energy
NUCLEAR PHYSICS A ELSEVIER
Nuclear Physics A626 (1997) 447c~450c
A s o l i d - s t a t e s p e c t r o m e t e r for c o o l e d b e a m s w i t h h i g h a c c e p t a n c e a n d r e s o l u t i o n in s p a c e a n d e n e r g y * S. Igel a, A. Budzanowski u, M. Drochner c, D. Frekers d, W. Garske d, K. Grewer d. A. Hamacher ~, G. Kemmerling c, K. Kilian ~, S. Kliczewski b H. Machner ta, H. Plendl a, D. Proti~ a B. Razen ~, R. V. Srikantiah *~, K. Zwoll c qnstitut fiir Kernphysik, Forsehungszentrum Jiilich, D 52425 Jfilich, Germany bInstitute of Nuclear Physics, 31342 Cracow, Poland CZentrallabor f/ir Elektronik, Forschungszentrum J/ilich, D 52425 J/ilich, Germany dInstitut fiir Kernphysik, Universit/it Miinster, D-48149 Miinster, Germany The GEM detector, a hybrid system consisting of the Germanium Wall and the magnetic spectrometer BIG KARL, was developed to investigate meson production and meson-nucleus interaction with cooled external proton beams from the COSY accelerator at J/ilieh. The Germanium Wall is a stack of up to four annular position-sensitive semiconductor detectors made from high-purity germanium. Its special structure allows experiments with high counting rates. Design features and results from first test runs with the uncooled COSY beam are presented. 1. D E S I G N
FEATURES
Tlle magnetic spectrometer BIG KARL enables momentum measurements as well as ray tracing in x- and y-direction with a resolution better than 10 -a. However, BIG KARL is limited in angular acceptance to 4-25 mrad in x- and +100 mrad in y-direction [1]. The Germanium Wall was added close behind the target in order to increase the acceptance of the total system to :t:287.5 mrad in each direction. An energy and position resolution similar to the magnetic spectrometer was anticipated (see Figure 1). The central holes in the diodes serve as an exit for the primary COSY beam. Reaction particles scattered into this region will be detected by BIG KARL. Therefore the diameters of the holes were optimized with respect to the expected beam dimensions and the acceptance of the magnetic spectrometer. The first detector is 1.8 mm thick and has a position-sensitive structure of 200 archimedic spirals with opposite orientation on each side, defining about 40000 pixels. Due to *This work was supported in part by SCSR Poland 2P302 025 05, INT Karlsruhe X081.24, INT Jfilich 6BOA2A, BMBF 06 MS 568 I TP4, and FZ Jfilich. Two of us (H. M. and H. S. P.) are grateful for support by a NATO grant (scientific affairs). tcorresponding author, e-mail [email protected] *on leave of absence from Bhaba Atomic Research Centre, Bombay, India. 0375-9474/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0375-9474(97)00568-X
448c
S. Igel et al./Nuclear Physics A626 (1997) 447c-450c
LH2-Target
\
"Quirl"-detector mth~O spirals~,~j~
"/
i~
~~ ~'~ ~.~\
V
70SY-BEAM~
\. /
.
d: " ~
~'-~
~ ~
-target point
E-detec t ors with 32 pies
!-?
; Veto
ulr '
E3
Figure 1. Left side: schematical drawing of the Ge-Wall. Right side: detectors mounted in the eryostat, veto in front of the target, Quirl and E-detectors E1 and E3 behind. this structure the detector is called 'Quirl-deteetor'. It will be used for position determination and for energyloss measurements (AE). This kind of spiral structure is already used in several plastic scintillator hodoscopes [2] and is now applied for the first time to semiconductor detectors. The size of the spirals increases from 68/zm near the hole to 170 #m at the outer radius, thus the pixel size varies by a factor of ten, covering always approximately the same solid angle. This leads to similar counting rates on every segment in experiments with a symmetric O-distribution of events. The single read-out of every channel makes experiments with high counting rates possible. Furthermore, the spiral structure allows easy connection of each channel on the outer circumference of the detector. The Quirl-detector is followed by up to three Ge diodes of about 17mm thickness each with a pie-chart structure of 32 segments on the front side. They will enable precise energy measurements for recoiling nuclei. Due to the segmentation these detectors are again well suited for experiments with high counting rates. In addition the structure helps to solve ambiguities in position determination of particles detected in coincidence. The total thickness of the Ge-Wall is about 8 0 m m which is sufficient to stop e.g. I50 MeV protons. All detectors are manufactured in house [3]. At this stage the Quirl-detector as well as the first and the third E-detector have been tested during experiment, while the second E-detector is still under construction. Tile detectors are mounted in a modular cryostat as shown in Figure 1. In the currently used setup it also houses a liquid hydrogen/deuterium target and a set of annular scintillators acting as veto counters [4, 5]. In order to minimize the material surrounding the detectors we constructed the feedthroughs for the signal read-out of 500 Ge-Wall channels using Kapton ribbons with printed leads. Dimensions of the detectors are given in Table 1 and a more detailed description of the setup can be found in [6].
449c
S. Igel et al./Nuclear Physics A626 (1997) 447c -450c
Table 1 Geometrical dimensions of the Ge-Wall detectors. detector thickness diameters whole diode structure central hole AE 1.8mm 63mm 35.6mm 4.3ram E1 !7.0mm 65.7mm 52.7mm 4 . 6 - 5 . 6 n , m E3 15.5mm 102mm 77.0mm 7.5 8.5mm
2. T E S T S W I T H R A D I O A C T I V E
pitch
grooves
68 170pm 452-51741~m 736 7560pm
21 inn 40pro 45pm
SOURCES
In order to determine the energy resolution, the detectors were tested with several radioactive sources. An example of a 6°Co-spectrum obtained with the third E-detector is given in Figure 2. In terms of energy loss it should be possible to detect charged particles with the desired relative resolution in the order of 10 .3 . The small pitch of the Quirl detector causes a crosstatk due to the splitting of charge carriers collected in adjacent spirals [7]. To obtain a good energy resolution one has to sum up the signals from neighbouring spirals. For the spectrum shown in Figure 2 this is done by connecting several spirals to the same amplifier chain. In the experiment the channels are read out separately. Entries in the ADC channels of adjacent elements are summed up in the data analysis. By calculating the eentroid of these clusters one can improve the position resolution with respect to the pitch.
Gamma spectrumwith E-detectorsegment
300~
6000~
2500"
5000"
200C
4000" C0-60:1332.48ke1 FWHM=4.65keV ]lI
150(
I"
v
2000"
200
600 channelNo
400
800
J
1000
I spiral 3 adjacentspirals
~ 3000"
100C
0
Gamma spectra with Quid spirals
FwH.=5ke,
,, !I
1000" .....
I1 . . . . . . . . . . . . . .
10 20 30 40 50 60 70 80 90 100110120 channelNo,
Figure 2. Left: 6°Co-7-spectra obtained with one element of the third E-detector. Right: -~41Am-7-spectrum obtained with the Quirl detector. If signals from adjacent elements are summed up the photopeak becomes visible.
450c
S. lgel et al./Nuclear Physics A626 (1997) 447c 450c
3. P R E L I M I N A R Y
RESULTS
OF A FIRST BEAMTIME
Tile Ge-Wall was recently tested with an uncooled proton beam of 8 2 5 M e V / c at COSY. The Quirl-detector with its precise position information was used as a monitor during focusing the beam. In first test runs deuterons from the reaction p p -+ dzr + were measured• The very preliminary results shown in Figure 3 indicate, that deuterons and protons can be separated. The position of the deuteron candidates can be reconstructed with the Quirl. The events lie within the errorbars on the kinematic ellipse as expected from phase space.
A E I [MeV} 80 70
• %•
60
•
. .
•
50 40 30 20
. i"~. i ' .-:.:?:%/.-::. " : .) ": ~:5:~,i,.. -- i " '~:";~":: d
•
" .
.
-..,
~.
"
..
:
z;
=.
;'~:Ft-..
.~ • ,...~ ii~" :i "~.-- ,". " ~"~, -',,~7~'"'"":P .- ..~..:;~,..z •
.
.
•
'
•
10 00
10
20
30 40 50 AE3 [MeV]
60
70
80
Figure 3. Preliminary A E - A E plot fi'om first test runs of the Ge-Wall at the COSY beam.
4. D I S C U S S I O N We have shown that the Germanium Wall is appropriate to complete the BIG K A R L magnetic spectrometer in order to build up a detector system with a high acceptance and a wide dynamic range. A satisfactory energy resolution in all channels of the E-detectors is obtained with radioactive sources. Preliminary results from a first b e a m t i m e allow particle identification with A E - A E - s p e c t r a . It is possible to reconstruct the position of the incoming ejectiles. We may state that the Germanimn Wall is now ready for use in the experiments of the GEM collaboration [8]. REFERENCES
1. B. Razen et al., Nuclear Physics A, contribution to this conference. 2. M. Dahmen et al., Nuel. Instr. and Meth. in Physics Research A348 (1994) 97. 3. A. Hamacher et al., Nucl. Instr. and Meth. in Physics Research A295 (1990) 128. 4. V. Jaeckle et al., Nucl. Instr. and Meth. in Physics Research A 349 (1994) 15. 5. A. Hassan et al., Nuclear Physics A, contribution to this conference. 6. S. Igel et al., A c t a Physica Polonica Vol. B26(1995) 627. 7. S. Igel, Berichte des Forschungszentrums Jiilich Jiil-2860 (1993). 8. H. Machner, A c t a Physica Polonica Vol. B26(1995) 571.
Nuclear Physics A626 (1997) 447c~450c
A s o l i d - s t a t e s p e c t r o m e t e r for c o o l e d b e a m s w i t h h i g h a c c e p t a n c e a n d r e s o l u t i o n in s p a c e a n d e n e r g y * S. Igel a, A. Budzanowski u, M. Drochner c, D. Frekers d, W. Garske d, K. Grewer d. A. Hamacher ~, G. Kemmerling c, K. Kilian ~, S. Kliczewski b H. Machner ta, H. Plendl a, D. Proti~ a B. Razen ~, R. V. Srikantiah *~, K. Zwoll c qnstitut fiir Kernphysik, Forsehungszentrum Jiilich, D 52425 Jfilich, Germany bInstitute of Nuclear Physics, 31342 Cracow, Poland CZentrallabor f/ir Elektronik, Forschungszentrum J/ilich, D 52425 J/ilich, Germany dInstitut fiir Kernphysik, Universit/it Miinster, D-48149 Miinster, Germany The GEM detector, a hybrid system consisting of the Germanium Wall and the magnetic spectrometer BIG KARL, was developed to investigate meson production and meson-nucleus interaction with cooled external proton beams from the COSY accelerator at J/ilieh. The Germanium Wall is a stack of up to four annular position-sensitive semiconductor detectors made from high-purity germanium. Its special structure allows experiments with high counting rates. Design features and results from first test runs with the uncooled COSY beam are presented. 1. D E S I G N
FEATURES
Tlle magnetic spectrometer BIG KARL enables momentum measurements as well as ray tracing in x- and y-direction with a resolution better than 10 -a. However, BIG KARL is limited in angular acceptance to 4-25 mrad in x- and +100 mrad in y-direction [1]. The Germanium Wall was added close behind the target in order to increase the acceptance of the total system to :t:287.5 mrad in each direction. An energy and position resolution similar to the magnetic spectrometer was anticipated (see Figure 1). The central holes in the diodes serve as an exit for the primary COSY beam. Reaction particles scattered into this region will be detected by BIG KARL. Therefore the diameters of the holes were optimized with respect to the expected beam dimensions and the acceptance of the magnetic spectrometer. The first detector is 1.8 mm thick and has a position-sensitive structure of 200 archimedic spirals with opposite orientation on each side, defining about 40000 pixels. Due to *This work was supported in part by SCSR Poland 2P302 025 05, INT Karlsruhe X081.24, INT Jfilich 6BOA2A, BMBF 06 MS 568 I TP4, and FZ Jfilich. Two of us (H. M. and H. S. P.) are grateful for support by a NATO grant (scientific affairs). tcorresponding author, e-mail [email protected] *on leave of absence from Bhaba Atomic Research Centre, Bombay, India. 0375-9474/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0375-9474(97)00568-X
448c
S. Igel et al./Nuclear Physics A626 (1997) 447c-450c
LH2-Target
\
"Quirl"-detector mth~O spirals~,~j~
"/
i~
~~ ~'~ ~.~\
V
70SY-BEAM~
\. /
.
d: " ~
~'-~
~ ~
-target point
E-detec t ors with 32 pies
!-?
; Veto
ulr '
E3
Figure 1. Left side: schematical drawing of the Ge-Wall. Right side: detectors mounted in the eryostat, veto in front of the target, Quirl and E-detectors E1 and E3 behind. this structure the detector is called 'Quirl-deteetor'. It will be used for position determination and for energyloss measurements (AE). This kind of spiral structure is already used in several plastic scintillator hodoscopes [2] and is now applied for the first time to semiconductor detectors. The size of the spirals increases from 68/zm near the hole to 170 #m at the outer radius, thus the pixel size varies by a factor of ten, covering always approximately the same solid angle. This leads to similar counting rates on every segment in experiments with a symmetric O-distribution of events. The single read-out of every channel makes experiments with high counting rates possible. Furthermore, the spiral structure allows easy connection of each channel on the outer circumference of the detector. The Quirl-detector is followed by up to three Ge diodes of about 17mm thickness each with a pie-chart structure of 32 segments on the front side. They will enable precise energy measurements for recoiling nuclei. Due to the segmentation these detectors are again well suited for experiments with high counting rates. In addition the structure helps to solve ambiguities in position determination of particles detected in coincidence. The total thickness of the Ge-Wall is about 8 0 m m which is sufficient to stop e.g. I50 MeV protons. All detectors are manufactured in house [3]. At this stage the Quirl-detector as well as the first and the third E-detector have been tested during experiment, while the second E-detector is still under construction. Tile detectors are mounted in a modular cryostat as shown in Figure 1. In the currently used setup it also houses a liquid hydrogen/deuterium target and a set of annular scintillators acting as veto counters [4, 5]. In order to minimize the material surrounding the detectors we constructed the feedthroughs for the signal read-out of 500 Ge-Wall channels using Kapton ribbons with printed leads. Dimensions of the detectors are given in Table 1 and a more detailed description of the setup can be found in [6].
449c
S. Igel et al./Nuclear Physics A626 (1997) 447c -450c
Table 1 Geometrical dimensions of the Ge-Wall detectors. detector thickness diameters whole diode structure central hole AE 1.8mm 63mm 35.6mm 4.3ram E1 !7.0mm 65.7mm 52.7mm 4 . 6 - 5 . 6 n , m E3 15.5mm 102mm 77.0mm 7.5 8.5mm
2. T E S T S W I T H R A D I O A C T I V E
pitch
grooves
68 170pm 452-51741~m 736 7560pm
21 inn 40pro 45pm
SOURCES
In order to determine the energy resolution, the detectors were tested with several radioactive sources. An example of a 6°Co-spectrum obtained with the third E-detector is given in Figure 2. In terms of energy loss it should be possible to detect charged particles with the desired relative resolution in the order of 10 .3 . The small pitch of the Quirl detector causes a crosstatk due to the splitting of charge carriers collected in adjacent spirals [7]. To obtain a good energy resolution one has to sum up the signals from neighbouring spirals. For the spectrum shown in Figure 2 this is done by connecting several spirals to the same amplifier chain. In the experiment the channels are read out separately. Entries in the ADC channels of adjacent elements are summed up in the data analysis. By calculating the eentroid of these clusters one can improve the position resolution with respect to the pitch.
Gamma spectrumwith E-detectorsegment
300~
6000~
2500"
5000"
200C
4000" C0-60:1332.48ke1 FWHM=4.65keV ]lI
150(
I"
v
2000"
200
600 channelNo
400
800
J
1000
I spiral 3 adjacentspirals
~ 3000"
100C
0
Gamma spectra with Quid spirals
FwH.=5ke,
,, !I
1000" .....
I1 . . . . . . . . . . . . . .
10 20 30 40 50 60 70 80 90 100110120 channelNo,
Figure 2. Left: 6°Co-7-spectra obtained with one element of the third E-detector. Right: -~41Am-7-spectrum obtained with the Quirl detector. If signals from adjacent elements are summed up the photopeak becomes visible.
450c
S. lgel et al./Nuclear Physics A626 (1997) 447c 450c
3. P R E L I M I N A R Y
RESULTS
OF A FIRST BEAMTIME
Tile Ge-Wall was recently tested with an uncooled proton beam of 8 2 5 M e V / c at COSY. The Quirl-detector with its precise position information was used as a monitor during focusing the beam. In first test runs deuterons from the reaction p p -+ dzr + were measured• The very preliminary results shown in Figure 3 indicate, that deuterons and protons can be separated. The position of the deuteron candidates can be reconstructed with the Quirl. The events lie within the errorbars on the kinematic ellipse as expected from phase space.
A E I [MeV} 80 70
• %•
60
•
. .
•
50 40 30 20
. i"~. i ' .-:.:?:%/.-::. " : .) ": ~:5:~,i,.. -- i " '~:";~":: d
•
" .
.
-..,
~.
"
..
:
z;
=.
;'~:Ft-..
.~ • ,...~ ii~" :i "~.-- ,". " ~"~, -',,~7~'"'"":P .- ..~..:;~,..z •
.
.
•
'
•
10 00
10
20
30 40 50 AE3 [MeV]
60
70
80
Figure 3. Preliminary A E - A E plot fi'om first test runs of the Ge-Wall at the COSY beam.
4. D I S C U S S I O N We have shown that the Germanium Wall is appropriate to complete the BIG K A R L magnetic spectrometer in order to build up a detector system with a high acceptance and a wide dynamic range. A satisfactory energy resolution in all channels of the E-detectors is obtained with radioactive sources. Preliminary results from a first b e a m t i m e allow particle identification with A E - A E - s p e c t r a . It is possible to reconstruct the position of the incoming ejectiles. We may state that the Germanimn Wall is now ready for use in the experiments of the GEM collaboration [8]. REFERENCES
1. B. Razen et al., Nuclear Physics A, contribution to this conference. 2. M. Dahmen et al., Nuel. Instr. and Meth. in Physics Research A348 (1994) 97. 3. A. Hamacher et al., Nucl. Instr. and Meth. in Physics Research A295 (1990) 128. 4. V. Jaeckle et al., Nucl. Instr. and Meth. in Physics Research A 349 (1994) 15. 5. A. Hassan et al., Nuclear Physics A, contribution to this conference. 6. S. Igel et al., A c t a Physica Polonica Vol. B26(1995) 627. 7. S. Igel, Berichte des Forschungszentrums Jiilich Jiil-2860 (1993). 8. H. Machner, A c t a Physica Polonica Vol. B26(1995) 571.