- Email: [email protected]
Computer simulation and calibration of the charge particle spectrometer-telescope ⪡STEP-F⪢
Available
online at www.sciencedirect.com
Pergamon SCIENCE
www.elsevier.com/locate/asr
DIRECT.
doi: lO.l016/SO273-1177(03)00729-4
COMPUTER SIMULATION AND CALIBRATION OF THE CHARGE PARTICLE SPECTROMETER-TELESCOPE <
‘Kharkiv National University, Svobody square, 4, Kharkiv-77, 61077, Ukraine ‘National Space Development Agency of Japan, Tsukuba Space Center, 2-I-1, Sengen, Tsukuba, 3058.505, Japan ‘FAMScience Co., Ltd. 1-1-I 7, Ikura, Shimonoseki, 7.51-0864, Japan
ABSTRACT The spectrometer-telescope “STEP-F” is intended for detecting high-energy charged particle fluxes in near-Earth space. It has been developed to study solar cosmic rays and dynamics of the Earth’s radiation belts onboard the Russian spacecraft ctcoronas-Photon)). The results of simulations by the CERN GEANT4.2 Code under OS LINUX Red Hat 6.2 for some types of particles, which will be detected by the “STEP-F” instrument, are presented. The visualization of primary and secondary particle tracks in each detector of the telescope has allowed us to verify the energy ranges of the recorded particles and to ascertain the possibility to determine the direction of incidence of primary electrons. The detectors have been tested in a high-energy ion cyclotron accelerator at the Institute of Physical and Chemical Research (RIKEN, Japan) in order to determine the response of each of the detectors to primary a-particle and hydrogen ion H2 beams. The experimental data obtained are in good agreement with the results of Monte-Carlo simulations. The basic parameters of the “STEP-F” instrument, such as the energy range of recorded electrons, protons and a-particles, the geometric factor, the field of view and the angular resolution, are presented. 0 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.
INTRODUCTION Most space missions intended to investigate solar and magnetospheric activity include experiments for studying high-energy charged particle fluxes. For example, onboard the ESA and NASA collaborative SOHO mission the ERNE instrument measures energetic and relativistic nuclei and electrons (Valtonen et al., 1997). A Heavy Ion Telescope HIT was installed onboard the Japanese satellite ADEOS to explore charge composition of heavy ions trapped by the geomagnetic field of the Earth (Kohno et al., 1997). The Russian space project “Coronas-Photon” aimed for studying the hard electromagnetic emission of the Sun (Dudnik and Zalyubovsky, 1998) will carry two experiments for energetic charged particle measurements. The “PESCA” instrument (de1 Peral et al., 1995) will study solar energetic particles and anomalous cosmic rays. The spectrometer-telescope “STEP-F”, on the other hand, will concentrate on investigation of the pitch-angle distribution of energetic particles in the radiation belts. The detectors of particle telescopes can be tested in the laboratory by using radioactive sources and charged particle accelerators. Simultaneously, comparison of experimental data with the results of computer simulations is usually carried out (Martin et. al., 1998; Jun et al., 2002). Simulations can be easily applied to any multimodular telescope, and will give information of the gains, which have to be fixed in the amplifier channels. The electrophysical and radiometric characteristics of the position-sensitive silicon matrix detectors designed for the spectrometer-telescope “STEP-F” were studied by Frolov et al. (2001) in laboratory conditions. The main parameters, such as electrical noise and energy resolution, were found to be equal to or better than those given by well-known manufacturers for their detectors. An advantage of these matrices is a low operating voltage (optimum - 40 V) required for full charge collection. In addition, the main characteristics of the scintillation detectors Adv. Space Res. Vol. 32, No. 11, pp. 2367-2372.2003 0 2003COSPAR. Published by Elsevier Ltd. All rights Printed in Great Britain 0273-l 177/$30.00 + 0.00
reserved
2368
0. V. Dudnik
ef al.
employed in “STEP-F” have been determined in laboratory measurements at low energies by using y-sources. The purpose of this work is to study the physical characteristics of silicon matrix and scintillation detectors of the “STEP-F” instrument by comparing the experimental data, obtained in the RIKEN heavy ion cyclotron, with Monte-Carlo computer simulations. Special emphasis is put on the study of the possible effects of secondary particles on the signals from different elements of a single matrix, as well as on estimating the number of albedo secondary particles generated in the first scintillation detector. THE MAIN CHARACTERISTICS
OF THE SPECTROMETER
- TELESCOPE “STEP-F”
“STEP-F”, a satellite spectrometer-telescope of high-energy charged particles, is aimed to determine pitchangle, spatial and temporal distributions of trapped and precipitated particles in the Earth’s radiation belts. It consists of a detector unit installed on the external surface of the spacecraft, and of a digital data processing unit located in a hermetic module. The detector unit (see Figure 1) contains two identical silicon position-sensitive matrix detectors Dl and D2 (see Figure 2) and two CsI(T1) scintillator crystals D3 and D4 viewed by large-area photodiodes and a photomultiplier tube. The telescope technique with position-sensitive detectors provides a wide operational energy range and a possibility to determine the species and arrival directions of incident particles. Each element of the silicon matrix is a separate autonomous semiconductor detector and has its own analogue signal shaping amplifier. The digital signal processing unit of “STEP-F” is based on a 16-bit microcontroller with a flexible structure. It is a multichannel device receiving and processing pulse signals from the detector unit. The species of particles, their energies and directions of incidence are determined in real time. The control and test functions of the unit provide information of the status of the spectrometer-telescope and enables detection of possible faults and errors during adjustments and autonomous tests, as well as during satellite system-level tests. The instrument identifies the incident particles and determines their kinetic energies by means of the dE/dx-E method, and simultaneously determines the trajectories of the particles by using the coordinates obtained from the position-sensitive matrix detectors. The field of view of the telescope is 97’ x 97’, and the angular resolution in the field of view is -8’. The active areas of the detectors are: Dl and D2 - 19 cm2, D3 - 28 cm2, and D4 - 38 cm2. Some operational characteristics of the instrument are presented in Table 1.
Si matrix Si matrix CsI(TI) CsI(TI)
LA-J --Photo
Fig. 1. A scheme of the detector “STEP-F”instrument.
head for the
tube
Fig. 2. Position-sensitive detectors.
silicon matrix
ComputerSimulationandResults
2369
Table 1. Operational characteristics of the instrument. Event Logic’
Energy Range (MeV)
DlD2D3D4
Electrons: 0.2 - 0.45 Protons: 3.53 - 7.3 Alphas: 13.7 - 29.45 Electrons: 0.45 - 0.55 1 Protons: 7.3 - 9.95 Alphas: 29.45 - 40.05 Electrons: 1.2 - 16 Protons: 14.5 - 61 Alphas: 62 - 248.5 Electrons: > 16.8 Protons: > 64 Alphas: > 262
DlD2D3D4
DlD2D3D4
DlD2D3D4
* The feature like 0102
Typical Geometry Factor (cm’+r)
Measurements
’
70
Intensities of particles in the full field of view
56
Energy and angular distribution of particles Energy and angular distribution of particles in 10 differential energy channels Angular distributions and integral intensities of particles
66 - 54
78
means logical coincidence, the feature like 0102
APPLICATION OF THE GEANT4.2 CODE FOR SIMULATING THE DETECTORS
means logical anti-coincidence.
PARTICLE
PASSAGE THROUGH
Preliminary simulations of the instrument response to energetic charged particles and comparison of the results with laboratory measurements were carried out at an early phase of the instrument development. The CERN Geant4.2 code was used in the simulations. The deposited energies and stopping ranges of electrons, protons and cl-narticles in each of the telescope detectors were calculated as a function of primary particle energy. The , S-ray processes, including production, ionisation bremsstrahlung and multiple Coulomb scattering, were taken into account in the simulation of electron passage. The ionisation energy losses and inelastic scattering of nucleons were taken into consideration in the passage of cl-particles and protons (GEANT4 Collaboration, 2000). The low energy (LE) extension package for electromagnetic interactions, based on the exploitation of evaluated data libraries and applicable in the energy range 250 eV - 100 GeV, was used. 0.04’ :.. .' ~ ,.j jj : The LE extension model provides a more accurate simulation 0.1 1 10 of the detector response than the “standard” package (Apostolakis et al., 1999; Ivanchenko et al., 1999). E (MeV) It is known that electrons are strongly affected by multiple scattering. Therefore, each value of the calculated deposited energy and the stopping range differs from the previous one. In order to determine the most probable deposited energy in each detector, the number of events for each value of primary energy was chosen to be N=lOO,OOOin the simulation of electron passage through the spectrometer. The results of simulations of the deposited energies are shown in Figure 3. Due to the strong multiple scattering, some electrons stop in the Dl detector, while others pass directly through leaving only a small amount of energy in Dl 1 10 20 Therefore, the energy losses AE presented in Figure 3a have E (MeV) two values in the narrow range of primary energies starting from -0.3 MeV. Figure 3 illustrates the energy ranges of Fig. 3. Most probable deposited energies AE vs. electrons detected by the instrument. primary electron energies E: a) in Dl; b) in D3 The trajectories of low-energy electrons passing through and D4 detectors of the “STEP-F” instrument. _
._
2370
0. V. Dudnik
et al.
the telescope can vary considerably due to the total effect of small deflections by multiple scattering or by deflections into large angles caused by a single close-range collision (Radiation Dosimetry, 1984). In addition to the particle species, it is also important to determine their directions of incidence. “STEP-F” allows us to determine the directions of incident primary electrons above a threshold energy Et,. Simulations of 500,000 electrons for each primary energy between 0.325 MeV and 5.25 MeV were carried out by using the GEANT4.2 Code in order to study the most probable scattering angle of electrons passing through the silicon matrix Dl and the thin aluminum shield above it. The simulations showed that the most probable scattering angle at energies up to 4.5 MeV is not larger than 7.8’. With increasing primary energy, the effect of scattering in electron trajectories decreases. The results of these simulations indicate that it is possible to determine the initial directions of electrons with energies above -4.5 MeV. This is achieved by using the information provided by the matrix detectors. At lower energies (from 0.325 MeV to 4.5 MeV), directional measurements become difficult due to the scattering in the shielding foil and the Dl layer. THE RESULTS OF CALIBRATION
ON THE RIKEN ION CYCLOTRON
ACCELERATOR
Application of lOO-MeVhucleon a-particle Beam to Determine the Thickness of Passive Layers in the Detectors Calibration measurements of each type of detectors, preamplifiers and shaping amplifiers by using u-particle beams of energy E=lOO MeVlnucleon and H2 ion beams of energy 70 MeVlnucleon were carried out in the cyclotron accelerator at the Institute of Physical and Chemical Research (RIKEN, Japan). Aluminium absorbers of different thickness were used to obtain various values of energies of the incident a-particles. The thickness was 21, 25, 30, 35 and 36 mm in the experiment series. Measurements without an absorber were also carried out. The pulse amplitudes from detectors D2 and D3 corresponding to the incident u-particle energies 62.5 MeV, 84 MeV, 164 MeV, 214 MeV, 254 MeV, and 400 MeV were obtained as a result of the experiment data processing. Simultaneously, computer simulations of energy losses in the detectors by a-particless in the energy range 10 MeVt 410 MeV were carried out for a small number of particles (N=lO) with variable steps of input energy, Figure 4 shows the results of the simulations together with experimental data (in Voltage) for detector D3, used as the E-detector in Fig. 4. The simulation results of deposited energies the dE/dx-E method. as compared to the experimental data of pulse The comparison of simulation results with the amplitudes from a-particle signals. The experimental experimental data allowed us to verify the energy values relating to detector D3 are marked by squares. ranges of the a-particles recorded by the detectors. Alpha particles with energies up to 13.7 MeV are stopped by the shielding aluminium foil placed just above the first silicon matrix Dl, while a-particles with energies in the ranges 40.5 MeV+ 62 MeV, and 248.5 MeVc-262 MeV are stopped in the coating materials of the scintillation detectors D3 and D4. Excluding these energy gaps, particles with energies from 13.7 MeV to 262 MeV are stopped in the active detector materials and give contributions to the pulse amplitudes of the analogue signals. Effects of secondary particles on detector signals In order to study the effects of secondary particles on detector signals, the energy spectra from most of the Dl and D2 matrix elements were obtained by using a 140-MeV H2 ion beam. The axis of the beam was directed in parallel to the telescope axis and was displaced to the peripheral elements 7, 8, 9, and 11 of the matrices as shown in Figure 5 (the beam is indicated by the circle). These elements registered 58, 36, 3 and 2.5 percent of particles,
Computer
Simulation
and Results
2371
121,
cl
-
35 6
25 cl
15 cl
23 cl
cl
cl
13
cl
”
I
tRIKEN
”
,‘,.I
‘.
”
”
I’,
”
#A Ep=70 MeV / c=209307 MATRIX 1 ELEMENT N7
21
-20
40cfi\N8NoE;O0
1 1
120 140
19 cl
Fig. 5. Beam projection on the elements of the silicon matrix. Spatial scale is preserved.
Fig. 6. Spectrum of ions H2 and decay from element 7 of matrix I,
products
correspondingly, because the diameter of the beam was equal to -5 mm. Figure 6 shows a typical spectrum measured from the element 7 of matrix 1. Protons of energy E=70 MeV compose the major part of the beam as is shown in Figure 6. In counting the number of particles detected by each element of the matrix, either protons (crosshatched region in Figure 6) or secondary particles with energies less than 70 MeV were taken into account. The number of particles recorded during the calibration process by element #7 of each matrix is taken as a relative unit. The total quantities of particles recorded in most of the elements in both matrices are presented in Figure 7. Both primary beam particles and secondaries produced in the aluminium foil above Dl and in detectors Dl, D2 and D3 (albedo particles), are taken into account. To mark the differencies in the number of particles detected by various elements, a logarithmic scale is used in the vertical axis. Figure 7 shows that particles were mainly recorded by elements 7, 8, 9 and 11 (crosshatched columns) and in a negligible number - (~1%) - by the closely located elements. Computer simulations were also performed for the same configuration of the elements of the silicon matrices and direction of the beam axis. 150000 primary protons at the energy of 70 MeV were simulated. The number of recorded particles in each element of the matrices was calculated by the technique used in the experiment, and was normalised to the number of particles in element 7, as in the experiment. Figure 7 presents the simulation results, giving the MATRIX 2 MATRIX 1 number of primary protons and secondary particles NUMBER OF ELEMENT recorded in the elements of the two matrices (light columns). Figure 7 shows a fairly good agreement between Fig.7. The number of particles in each element of the experimental data and simulation. It is necessary to both matrices after passage of H2 beam (experimental data and results of simulation). emphasize the importance of computer simulations of
2312
0. V. Dudnik
et al.
the instrument response before constructing it. A conclusion may also be drawn that the effects of secondary particles in detector signals are almost negligible when operatimg at high primary particle energies. In particular, the number of secondary albedo particles produced in the scintillation detector D3 is negligible. Therefore, the error in the counting rate of the D2 detector due to secondary species produced in the D3 scintillator at high energies of charged primary particles will be small. CONCLUSION The software we have developed and the Monte Carlo simulation together with the application of the CERN GEANT 4.2 Code give good agreement with the experimental results obtained at the RIKEN high energy ion cyclotron. By this technique, we have determined the operational energy ranges of the “STEP-F” instrument for electrons, protons and a-particles. It has been found, both experimentally and by simulations, that the signals from neighboring elements of the position-sensitive silicon matrix are not affected by secondary particles. In particular, the number of albedo secondary particles generated in the scintillator is rather small as compared to the primary particles, so that secondaries do not significantly contribute to the total intensity of recorded primary particles. ACKNOWLEDGMENTS This work is supported by the Science and Technology Center in Ukraine (STCU Grant N 1578). The authors gratefully acknowledge the assistance of the RIKEN cyclotron staff in calibrating the “STEP-F” instrument. REFERENCES Apostolakis, J., S. Giani, M. Maire et al., GEANT4 low energy electromagnetic models for electrons and photons, CERN-OPEN-99-034,1999. de1 Peral, L., J. Medina, S. Sanchez et al., Detector system for low-energy cosmic ions study, Nucl. Ins@. and Meth., A 354,539-546, 1995. Dudnik, 0. V. and I. I. Zalyubovsky, The Ukrainian instruments set for the ground accompaniment of the joint Ukrainian-Russian satellite project “PHOTON” to study the hard radiation of the Sun and solar-Earth’s magnetosphere connections, Adv. Space Rex, 21, (l/2), 343-345, 1998. Frolov, 0. S., A. V. Dudnik, A. A. Sadovnichiy et al., Development of silicon matrixes and channels of amplification of signals for a telescope - spectrometer of charged particles, Proc. of 27’h Intern. Cosmic Ray Conf, Hamburg, Germany, Copernicus Gesellschaft, 2305-2308,200l. GEANT4 Collaboration, in GEANT4 Physics Reference Manual, Application Software Group, CERN, Geneva, 2000. Jun, I., J. M. Ratliff, H. B. Garrett and R. W. McEntire, Monte Carlo simulation of the Galileo energetic particle detector, Nucl. Instr. and Meth., A 490,465-475, 2002: International Commission on Radiation Units and Measurements, in Radiation Dosimetry: Electron beams with energies between I and 50 MeV, ICRU Report 35, Bethesda, Maryland, USA, 1984. Ivanchenko, V. N., S. Giani, M. G. Pia, L. Urban, P. Nieminen, GEANT4 simulation of energy losses of slow hadrons, CERN-OPEN-99-121, 1999. Kohno, T., I. Yamagiwa, H. Miyasaka, T. Goka and H. Matsumoto, Observation of heavy ions with ADEOS satellite, Proc. 251hIntern. Cosmic Ray Co& Durban, South Afiicu, 2, 3 17-320, 1997. Martin, C., E. Bronchalo, J. Medina et al., A new multi-detector telescope calibration method, Proc. 2Th Intern. Cosmic Ray Conf, Hamburg, Germany, Copernicus Gesellschaft, 2431-2434,200l. Valtonen, E., J. Peltonen, P. Peltonen et al., Energetic and relativistic nuclei and electron experiment of the SOHO mission. Nucl. Instr. andMeth., A 391,249-268, 1997.
E-mail address of O.V.Dudnik dudnik(nnord.vostok.net Manuscript received October 14,2002; revised January 18,2003; accepted February 3,2003.
online at www.sciencedirect.com
Pergamon SCIENCE
www.elsevier.com/locate/asr
DIRECT.
doi: lO.l016/SO273-1177(03)00729-4
COMPUTER SIMULATION AND CALIBRATION OF THE CHARGE PARTICLE SPECTROMETER-TELESCOPE <
‘Kharkiv National University, Svobody square, 4, Kharkiv-77, 61077, Ukraine ‘National Space Development Agency of Japan, Tsukuba Space Center, 2-I-1, Sengen, Tsukuba, 3058.505, Japan ‘FAMScience Co., Ltd. 1-1-I 7, Ikura, Shimonoseki, 7.51-0864, Japan
ABSTRACT The spectrometer-telescope “STEP-F” is intended for detecting high-energy charged particle fluxes in near-Earth space. It has been developed to study solar cosmic rays and dynamics of the Earth’s radiation belts onboard the Russian spacecraft ctcoronas-Photon)). The results of simulations by the CERN GEANT4.2 Code under OS LINUX Red Hat 6.2 for some types of particles, which will be detected by the “STEP-F” instrument, are presented. The visualization of primary and secondary particle tracks in each detector of the telescope has allowed us to verify the energy ranges of the recorded particles and to ascertain the possibility to determine the direction of incidence of primary electrons. The detectors have been tested in a high-energy ion cyclotron accelerator at the Institute of Physical and Chemical Research (RIKEN, Japan) in order to determine the response of each of the detectors to primary a-particle and hydrogen ion H2 beams. The experimental data obtained are in good agreement with the results of Monte-Carlo simulations. The basic parameters of the “STEP-F” instrument, such as the energy range of recorded electrons, protons and a-particles, the geometric factor, the field of view and the angular resolution, are presented. 0 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.
INTRODUCTION Most space missions intended to investigate solar and magnetospheric activity include experiments for studying high-energy charged particle fluxes. For example, onboard the ESA and NASA collaborative SOHO mission the ERNE instrument measures energetic and relativistic nuclei and electrons (Valtonen et al., 1997). A Heavy Ion Telescope HIT was installed onboard the Japanese satellite ADEOS to explore charge composition of heavy ions trapped by the geomagnetic field of the Earth (Kohno et al., 1997). The Russian space project “Coronas-Photon” aimed for studying the hard electromagnetic emission of the Sun (Dudnik and Zalyubovsky, 1998) will carry two experiments for energetic charged particle measurements. The “PESCA” instrument (de1 Peral et al., 1995) will study solar energetic particles and anomalous cosmic rays. The spectrometer-telescope “STEP-F”, on the other hand, will concentrate on investigation of the pitch-angle distribution of energetic particles in the radiation belts. The detectors of particle telescopes can be tested in the laboratory by using radioactive sources and charged particle accelerators. Simultaneously, comparison of experimental data with the results of computer simulations is usually carried out (Martin et. al., 1998; Jun et al., 2002). Simulations can be easily applied to any multimodular telescope, and will give information of the gains, which have to be fixed in the amplifier channels. The electrophysical and radiometric characteristics of the position-sensitive silicon matrix detectors designed for the spectrometer-telescope “STEP-F” were studied by Frolov et al. (2001) in laboratory conditions. The main parameters, such as electrical noise and energy resolution, were found to be equal to or better than those given by well-known manufacturers for their detectors. An advantage of these matrices is a low operating voltage (optimum - 40 V) required for full charge collection. In addition, the main characteristics of the scintillation detectors Adv. Space Res. Vol. 32, No. 11, pp. 2367-2372.2003 0 2003COSPAR. Published by Elsevier Ltd. All rights Printed in Great Britain 0273-l 177/$30.00 + 0.00
reserved
2368
0. V. Dudnik
ef al.
employed in “STEP-F” have been determined in laboratory measurements at low energies by using y-sources. The purpose of this work is to study the physical characteristics of silicon matrix and scintillation detectors of the “STEP-F” instrument by comparing the experimental data, obtained in the RIKEN heavy ion cyclotron, with Monte-Carlo computer simulations. Special emphasis is put on the study of the possible effects of secondary particles on the signals from different elements of a single matrix, as well as on estimating the number of albedo secondary particles generated in the first scintillation detector. THE MAIN CHARACTERISTICS
OF THE SPECTROMETER
- TELESCOPE “STEP-F”
“STEP-F”, a satellite spectrometer-telescope of high-energy charged particles, is aimed to determine pitchangle, spatial and temporal distributions of trapped and precipitated particles in the Earth’s radiation belts. It consists of a detector unit installed on the external surface of the spacecraft, and of a digital data processing unit located in a hermetic module. The detector unit (see Figure 1) contains two identical silicon position-sensitive matrix detectors Dl and D2 (see Figure 2) and two CsI(T1) scintillator crystals D3 and D4 viewed by large-area photodiodes and a photomultiplier tube. The telescope technique with position-sensitive detectors provides a wide operational energy range and a possibility to determine the species and arrival directions of incident particles. Each element of the silicon matrix is a separate autonomous semiconductor detector and has its own analogue signal shaping amplifier. The digital signal processing unit of “STEP-F” is based on a 16-bit microcontroller with a flexible structure. It is a multichannel device receiving and processing pulse signals from the detector unit. The species of particles, their energies and directions of incidence are determined in real time. The control and test functions of the unit provide information of the status of the spectrometer-telescope and enables detection of possible faults and errors during adjustments and autonomous tests, as well as during satellite system-level tests. The instrument identifies the incident particles and determines their kinetic energies by means of the dE/dx-E method, and simultaneously determines the trajectories of the particles by using the coordinates obtained from the position-sensitive matrix detectors. The field of view of the telescope is 97’ x 97’, and the angular resolution in the field of view is -8’. The active areas of the detectors are: Dl and D2 - 19 cm2, D3 - 28 cm2, and D4 - 38 cm2. Some operational characteristics of the instrument are presented in Table 1.
Si matrix Si matrix CsI(TI) CsI(TI)
LA-J --Photo
Fig. 1. A scheme of the detector “STEP-F”instrument.
head for the
tube
Fig. 2. Position-sensitive detectors.
silicon matrix
ComputerSimulationandResults
2369
Table 1. Operational characteristics of the instrument. Event Logic’
Energy Range (MeV)
DlD2D3D4
Electrons: 0.2 - 0.45 Protons: 3.53 - 7.3 Alphas: 13.7 - 29.45 Electrons: 0.45 - 0.55 1 Protons: 7.3 - 9.95 Alphas: 29.45 - 40.05 Electrons: 1.2 - 16 Protons: 14.5 - 61 Alphas: 62 - 248.5 Electrons: > 16.8 Protons: > 64 Alphas: > 262
DlD2D3D4
DlD2D3D4
DlD2D3D4
* The feature like 0102
Typical Geometry Factor (cm’+r)
Measurements
’
70
Intensities of particles in the full field of view
56
Energy and angular distribution of particles Energy and angular distribution of particles in 10 differential energy channels Angular distributions and integral intensities of particles
66 - 54
78
means logical coincidence, the feature like 0102
APPLICATION OF THE GEANT4.2 CODE FOR SIMULATING THE DETECTORS
means logical anti-coincidence.
PARTICLE
PASSAGE THROUGH
Preliminary simulations of the instrument response to energetic charged particles and comparison of the results with laboratory measurements were carried out at an early phase of the instrument development. The CERN Geant4.2 code was used in the simulations. The deposited energies and stopping ranges of electrons, protons and cl-narticles in each of the telescope detectors were calculated as a function of primary particle energy. The , S-ray processes, including production, ionisation bremsstrahlung and multiple Coulomb scattering, were taken into account in the simulation of electron passage. The ionisation energy losses and inelastic scattering of nucleons were taken into consideration in the passage of cl-particles and protons (GEANT4 Collaboration, 2000). The low energy (LE) extension package for electromagnetic interactions, based on the exploitation of evaluated data libraries and applicable in the energy range 250 eV - 100 GeV, was used. 0.04’ :.. .' ~ ,.j jj : The LE extension model provides a more accurate simulation 0.1 1 10 of the detector response than the “standard” package (Apostolakis et al., 1999; Ivanchenko et al., 1999). E (MeV) It is known that electrons are strongly affected by multiple scattering. Therefore, each value of the calculated deposited energy and the stopping range differs from the previous one. In order to determine the most probable deposited energy in each detector, the number of events for each value of primary energy was chosen to be N=lOO,OOOin the simulation of electron passage through the spectrometer. The results of simulations of the deposited energies are shown in Figure 3. Due to the strong multiple scattering, some electrons stop in the Dl detector, while others pass directly through leaving only a small amount of energy in Dl 1 10 20 Therefore, the energy losses AE presented in Figure 3a have E (MeV) two values in the narrow range of primary energies starting from -0.3 MeV. Figure 3 illustrates the energy ranges of Fig. 3. Most probable deposited energies AE vs. electrons detected by the instrument. primary electron energies E: a) in Dl; b) in D3 The trajectories of low-energy electrons passing through and D4 detectors of the “STEP-F” instrument. _
._
2370
0. V. Dudnik
et al.
the telescope can vary considerably due to the total effect of small deflections by multiple scattering or by deflections into large angles caused by a single close-range collision (Radiation Dosimetry, 1984). In addition to the particle species, it is also important to determine their directions of incidence. “STEP-F” allows us to determine the directions of incident primary electrons above a threshold energy Et,. Simulations of 500,000 electrons for each primary energy between 0.325 MeV and 5.25 MeV were carried out by using the GEANT4.2 Code in order to study the most probable scattering angle of electrons passing through the silicon matrix Dl and the thin aluminum shield above it. The simulations showed that the most probable scattering angle at energies up to 4.5 MeV is not larger than 7.8’. With increasing primary energy, the effect of scattering in electron trajectories decreases. The results of these simulations indicate that it is possible to determine the initial directions of electrons with energies above -4.5 MeV. This is achieved by using the information provided by the matrix detectors. At lower energies (from 0.325 MeV to 4.5 MeV), directional measurements become difficult due to the scattering in the shielding foil and the Dl layer. THE RESULTS OF CALIBRATION
ON THE RIKEN ION CYCLOTRON
ACCELERATOR
Application of lOO-MeVhucleon a-particle Beam to Determine the Thickness of Passive Layers in the Detectors Calibration measurements of each type of detectors, preamplifiers and shaping amplifiers by using u-particle beams of energy E=lOO MeVlnucleon and H2 ion beams of energy 70 MeVlnucleon were carried out in the cyclotron accelerator at the Institute of Physical and Chemical Research (RIKEN, Japan). Aluminium absorbers of different thickness were used to obtain various values of energies of the incident a-particles. The thickness was 21, 25, 30, 35 and 36 mm in the experiment series. Measurements without an absorber were also carried out. The pulse amplitudes from detectors D2 and D3 corresponding to the incident u-particle energies 62.5 MeV, 84 MeV, 164 MeV, 214 MeV, 254 MeV, and 400 MeV were obtained as a result of the experiment data processing. Simultaneously, computer simulations of energy losses in the detectors by a-particless in the energy range 10 MeVt 410 MeV were carried out for a small number of particles (N=lO) with variable steps of input energy, Figure 4 shows the results of the simulations together with experimental data (in Voltage) for detector D3, used as the E-detector in Fig. 4. The simulation results of deposited energies the dE/dx-E method. as compared to the experimental data of pulse The comparison of simulation results with the amplitudes from a-particle signals. The experimental experimental data allowed us to verify the energy values relating to detector D3 are marked by squares. ranges of the a-particles recorded by the detectors. Alpha particles with energies up to 13.7 MeV are stopped by the shielding aluminium foil placed just above the first silicon matrix Dl, while a-particles with energies in the ranges 40.5 MeV+ 62 MeV, and 248.5 MeVc-262 MeV are stopped in the coating materials of the scintillation detectors D3 and D4. Excluding these energy gaps, particles with energies from 13.7 MeV to 262 MeV are stopped in the active detector materials and give contributions to the pulse amplitudes of the analogue signals. Effects of secondary particles on detector signals In order to study the effects of secondary particles on detector signals, the energy spectra from most of the Dl and D2 matrix elements were obtained by using a 140-MeV H2 ion beam. The axis of the beam was directed in parallel to the telescope axis and was displaced to the peripheral elements 7, 8, 9, and 11 of the matrices as shown in Figure 5 (the beam is indicated by the circle). These elements registered 58, 36, 3 and 2.5 percent of particles,
Computer
Simulation
and Results
2371
121,
cl
-
35 6
25 cl
15 cl
23 cl
cl
cl
13
cl
”
I
tRIKEN
”
,‘,.I
‘.
”
”
I’,
”
#A Ep=70 MeV / c=209307 MATRIX 1 ELEMENT N7
21
-20
40cfi\N8NoE;O0
1 1
120 140
19 cl
Fig. 5. Beam projection on the elements of the silicon matrix. Spatial scale is preserved.
Fig. 6. Spectrum of ions H2 and decay from element 7 of matrix I,
products
correspondingly, because the diameter of the beam was equal to -5 mm. Figure 6 shows a typical spectrum measured from the element 7 of matrix 1. Protons of energy E=70 MeV compose the major part of the beam as is shown in Figure 6. In counting the number of particles detected by each element of the matrix, either protons (crosshatched region in Figure 6) or secondary particles with energies less than 70 MeV were taken into account. The number of particles recorded during the calibration process by element #7 of each matrix is taken as a relative unit. The total quantities of particles recorded in most of the elements in both matrices are presented in Figure 7. Both primary beam particles and secondaries produced in the aluminium foil above Dl and in detectors Dl, D2 and D3 (albedo particles), are taken into account. To mark the differencies in the number of particles detected by various elements, a logarithmic scale is used in the vertical axis. Figure 7 shows that particles were mainly recorded by elements 7, 8, 9 and 11 (crosshatched columns) and in a negligible number - (~1%) - by the closely located elements. Computer simulations were also performed for the same configuration of the elements of the silicon matrices and direction of the beam axis. 150000 primary protons at the energy of 70 MeV were simulated. The number of recorded particles in each element of the matrices was calculated by the technique used in the experiment, and was normalised to the number of particles in element 7, as in the experiment. Figure 7 presents the simulation results, giving the MATRIX 2 MATRIX 1 number of primary protons and secondary particles NUMBER OF ELEMENT recorded in the elements of the two matrices (light columns). Figure 7 shows a fairly good agreement between Fig.7. The number of particles in each element of the experimental data and simulation. It is necessary to both matrices after passage of H2 beam (experimental data and results of simulation). emphasize the importance of computer simulations of
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the instrument response before constructing it. A conclusion may also be drawn that the effects of secondary particles in detector signals are almost negligible when operatimg at high primary particle energies. In particular, the number of secondary albedo particles produced in the scintillation detector D3 is negligible. Therefore, the error in the counting rate of the D2 detector due to secondary species produced in the D3 scintillator at high energies of charged primary particles will be small. CONCLUSION The software we have developed and the Monte Carlo simulation together with the application of the CERN GEANT 4.2 Code give good agreement with the experimental results obtained at the RIKEN high energy ion cyclotron. By this technique, we have determined the operational energy ranges of the “STEP-F” instrument for electrons, protons and a-particles. It has been found, both experimentally and by simulations, that the signals from neighboring elements of the position-sensitive silicon matrix are not affected by secondary particles. In particular, the number of albedo secondary particles generated in the scintillator is rather small as compared to the primary particles, so that secondaries do not significantly contribute to the total intensity of recorded primary particles. ACKNOWLEDGMENTS This work is supported by the Science and Technology Center in Ukraine (STCU Grant N 1578). The authors gratefully acknowledge the assistance of the RIKEN cyclotron staff in calibrating the “STEP-F” instrument. REFERENCES Apostolakis, J., S. Giani, M. Maire et al., GEANT4 low energy electromagnetic models for electrons and photons, CERN-OPEN-99-034,1999. de1 Peral, L., J. Medina, S. Sanchez et al., Detector system for low-energy cosmic ions study, Nucl. Ins@. and Meth., A 354,539-546, 1995. Dudnik, 0. V. and I. I. Zalyubovsky, The Ukrainian instruments set for the ground accompaniment of the joint Ukrainian-Russian satellite project “PHOTON” to study the hard radiation of the Sun and solar-Earth’s magnetosphere connections, Adv. Space Rex, 21, (l/2), 343-345, 1998. Frolov, 0. S., A. V. Dudnik, A. A. Sadovnichiy et al., Development of silicon matrixes and channels of amplification of signals for a telescope - spectrometer of charged particles, Proc. of 27’h Intern. Cosmic Ray Conf, Hamburg, Germany, Copernicus Gesellschaft, 2305-2308,200l. GEANT4 Collaboration, in GEANT4 Physics Reference Manual, Application Software Group, CERN, Geneva, 2000. Jun, I., J. M. Ratliff, H. B. Garrett and R. W. McEntire, Monte Carlo simulation of the Galileo energetic particle detector, Nucl. Instr. and Meth., A 490,465-475, 2002: International Commission on Radiation Units and Measurements, in Radiation Dosimetry: Electron beams with energies between I and 50 MeV, ICRU Report 35, Bethesda, Maryland, USA, 1984. Ivanchenko, V. N., S. Giani, M. G. Pia, L. Urban, P. Nieminen, GEANT4 simulation of energy losses of slow hadrons, CERN-OPEN-99-121, 1999. Kohno, T., I. Yamagiwa, H. Miyasaka, T. Goka and H. Matsumoto, Observation of heavy ions with ADEOS satellite, Proc. 251hIntern. Cosmic Ray Co& Durban, South Afiicu, 2, 3 17-320, 1997. Martin, C., E. Bronchalo, J. Medina et al., A new multi-detector telescope calibration method, Proc. 2Th Intern. Cosmic Ray Conf, Hamburg, Germany, Copernicus Gesellschaft, 2431-2434,200l. Valtonen, E., J. Peltonen, P. Peltonen et al., Energetic and relativistic nuclei and electron experiment of the SOHO mission. Nucl. Instr. andMeth., A 391,249-268, 1997.
E-mail address of O.V.Dudnik dudnik(nnord.vostok.net Manuscript received October 14,2002; revised January 18,2003; accepted February 3,2003.