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Bragg-curve spectroscopy at high rates
Nuclear Instruments and Methods in Physics Research A243 (1986) 601-602 North-Holland, Amsterdam
601
Letter to the Editor
BRAGG-CURVE S P E C T R O S C O P Y AT HIGH RATES Fabiana G R A M E G N A , Gianfranco PRETE and Giuseppe VIESTI 1) INFN LN Legnaro and/~Department of Physics, UnilJersity of Padoua, ltalv
Ileana [ORI, Arialdo M O R O N I and Fabio G H I N E L L I INFN and Department of J'~vsics, Unil,,ersityof Milan, Italy Received 23 September 1985
The performance of a Bragg ionization chamber has been investigated as a function of the counting rate with = 5 MeV/amu 32S beams: up to = 20 kHz the energy resolution is below 0.9% and the Z resolving power is more than 50.
The axial ionization c h a m b e r has become a detector of fairly large use, especially in connection with the Bragg-curve spectroscopy technique, in experimental nuclear physics with heavy ion beams. In this field there is nowadays an increasing interest, at b e a m energies below 10 M e V / a m u , in exclusive experiments using high resolution detectors, while in the high energy region large solid angle detection systems are needed to explore complex p h e n o m e n a having many fragments in the outgoing reaction channel. The Bragg c h a m b e r could be a good candidate for these applications which, however, d e m a n d a high c o u n t i n g rate capability. Only few indications have been
reported so far a b o u t a d e p e n d e n c e of the Bragg chamber performance on the counting rate [1]. We report in this letter on an experimental investigation of the energy resolution and the Z resolving power of an axial ionization c h a m b e r as a function of the c o u n t i n g rate up to = 20 kHz. The technical details of the detector, r o u t i n e l j used at the L N L T a n d e m facility, have been previously reported together with the perform a n c e at low c o u n t i n g rates [1,2]. The c h a m b e r was operated at 180 T o r t of P10, with an entrance window of 1.5 /Lm thick mylar foil. It was connected to a sliding seal scattering c h a m b e r a n d the observation angle was in the range 0~ h = 10 ° - 30 °. 80
a) z
70 •
© L~
O
O
N
60
Si
50 40 I
AI
I
f
I
CI
b)
.9 Na
LU
K LU
.7
~3
O pO
,
i 20
,
t
,
= 40
,
i
i 6O
BP
r
O
D
I
i 80
100
120
(au)
Fig. 1. Bragg-peak spectrum at a counting rate of 17 kHz. 0 1 6 8 - 9 0 0 2 / 8 6 / $ 0 3 . 5 0 © Elsevier Science Publishers B.V. ( N o r t h - H o l l a n d Physics Publishing Division)
1~5
I
25
Rate (kHz) Fig. 2. (a) Z resolving power and (b) energy resolution (fwhm) as a function of the counting rate (see text).
602
F. Gramegna et al. / Bragg- curt~e ~7~ectroscopv at high rates
The energy pulse height and pulse height resolution were measured using the elastic scattering of 140 MeV 32S ions on a 150 # g / c m 2 Au target. For these measurements the c h a m b e r angular opening was limited to A0 -- 1 ° by a Ta collimator. The Z resolving power was evaluated by b o m b a r d ing a thick (0.5 m g / c m 2) 5SNi target with the same beam. The detector opening angle was set to J 0 = 4 ° to increase the counting rate. The element identification was performed by means of the Bragg-peak amplitude, o b t a i n e d using a main amplifier with 0.5 ~s shaping time. As an example the Bragg-peak spectrum at 17 kHz counting rate and corresponding to the energy window 75 < E < 115 MeV is shown in fig. 1. For both sets of measurements the counting rate was varied by changing the observation angle a n d / o r the beam intensity. The obtained Z resolving power, evaluated in a 5 MeV wide energy window in the quasi-elastic region for Z = 16, and the energy resolution are shown in fig. 2 as a function of the counting rate. The increase in the
c o u n t i n g rate does not substantially deteriorate the good resolution characterizing the Bragg-curve spectroscopy at low rates: up to 20 kHz the energy resolution is below 0.9% and Z / A Z is more than 50. Moreover, at a fixed observation angle, no shift in the energy peak position was observed up to the highest measured rate. The present study indicates the realistic possibility of building large solid angle axial ionization chambers having a satisfactory performance. Further improvements in the counting rate capability of this detector, related to the use of faster counting gas, will be pursued in the near future.
References [1] A. Moroni, I. Iori, Li Zu Yu, G. Prete, G. Viesti, F. Gramegna and A. Dainelli, Nucl. Instr. and Meth. 225 (1984) 57 and references therein. [2] A. Moroni, I. Iori, G. Prete, F. Gramegna and G. Viesti, Lett. Nuovo Cim. 40 (1984) 321.
601
Letter to the Editor
BRAGG-CURVE S P E C T R O S C O P Y AT HIGH RATES Fabiana G R A M E G N A , Gianfranco PRETE and Giuseppe VIESTI 1) INFN LN Legnaro and/~Department of Physics, UnilJersity of Padoua, ltalv
Ileana [ORI, Arialdo M O R O N I and Fabio G H I N E L L I INFN and Department of J'~vsics, Unil,,ersityof Milan, Italy Received 23 September 1985
The performance of a Bragg ionization chamber has been investigated as a function of the counting rate with = 5 MeV/amu 32S beams: up to = 20 kHz the energy resolution is below 0.9% and the Z resolving power is more than 50.
The axial ionization c h a m b e r has become a detector of fairly large use, especially in connection with the Bragg-curve spectroscopy technique, in experimental nuclear physics with heavy ion beams. In this field there is nowadays an increasing interest, at b e a m energies below 10 M e V / a m u , in exclusive experiments using high resolution detectors, while in the high energy region large solid angle detection systems are needed to explore complex p h e n o m e n a having many fragments in the outgoing reaction channel. The Bragg c h a m b e r could be a good candidate for these applications which, however, d e m a n d a high c o u n t i n g rate capability. Only few indications have been
reported so far a b o u t a d e p e n d e n c e of the Bragg chamber performance on the counting rate [1]. We report in this letter on an experimental investigation of the energy resolution and the Z resolving power of an axial ionization c h a m b e r as a function of the c o u n t i n g rate up to = 20 kHz. The technical details of the detector, r o u t i n e l j used at the L N L T a n d e m facility, have been previously reported together with the perform a n c e at low c o u n t i n g rates [1,2]. The c h a m b e r was operated at 180 T o r t of P10, with an entrance window of 1.5 /Lm thick mylar foil. It was connected to a sliding seal scattering c h a m b e r a n d the observation angle was in the range 0~ h = 10 ° - 30 °. 80
a) z
70 •
© L~
O
O
N
60
Si
50 40 I
AI
I
f
I
CI
b)
.9 Na
LU
K LU
.7
~3
O pO
,
i 20
,
t
,
= 40
,
i
i 6O
BP
r
O
D
I
i 80
100
120
(au)
Fig. 1. Bragg-peak spectrum at a counting rate of 17 kHz. 0 1 6 8 - 9 0 0 2 / 8 6 / $ 0 3 . 5 0 © Elsevier Science Publishers B.V. ( N o r t h - H o l l a n d Physics Publishing Division)
1~5
I
25
Rate (kHz) Fig. 2. (a) Z resolving power and (b) energy resolution (fwhm) as a function of the counting rate (see text).
602
F. Gramegna et al. / Bragg- curt~e ~7~ectroscopv at high rates
The energy pulse height and pulse height resolution were measured using the elastic scattering of 140 MeV 32S ions on a 150 # g / c m 2 Au target. For these measurements the c h a m b e r angular opening was limited to A0 -- 1 ° by a Ta collimator. The Z resolving power was evaluated by b o m b a r d ing a thick (0.5 m g / c m 2) 5SNi target with the same beam. The detector opening angle was set to J 0 = 4 ° to increase the counting rate. The element identification was performed by means of the Bragg-peak amplitude, o b t a i n e d using a main amplifier with 0.5 ~s shaping time. As an example the Bragg-peak spectrum at 17 kHz counting rate and corresponding to the energy window 75 < E < 115 MeV is shown in fig. 1. For both sets of measurements the counting rate was varied by changing the observation angle a n d / o r the beam intensity. The obtained Z resolving power, evaluated in a 5 MeV wide energy window in the quasi-elastic region for Z = 16, and the energy resolution are shown in fig. 2 as a function of the counting rate. The increase in the
c o u n t i n g rate does not substantially deteriorate the good resolution characterizing the Bragg-curve spectroscopy at low rates: up to 20 kHz the energy resolution is below 0.9% and Z / A Z is more than 50. Moreover, at a fixed observation angle, no shift in the energy peak position was observed up to the highest measured rate. The present study indicates the realistic possibility of building large solid angle axial ionization chambers having a satisfactory performance. Further improvements in the counting rate capability of this detector, related to the use of faster counting gas, will be pursued in the near future.
References [1] A. Moroni, I. Iori, Li Zu Yu, G. Prete, G. Viesti, F. Gramegna and A. Dainelli, Nucl. Instr. and Meth. 225 (1984) 57 and references therein. [2] A. Moroni, I. Iori, G. Prete, F. Gramegna and G. Viesti, Lett. Nuovo Cim. 40 (1984) 321.