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Measurements of high-energy neutron and proton fluxes on-board “Mir-Spectr” orbital complex
Adv. SpaceRes. Vol. 21, No. 12, pp. 1785-1788, 1998 ©1998 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-1177/98 $19.00 + 0.00 PlI: $0273-1177(98)00067-2
Pergamon
MEASUREMENTS OF HIGH-ENERGY NEUTRON AND PROTON FLUXES ON-BOARD "MIR-SPECTR" ORBITAL COMPLEX M. I. Kudryavtsev*, A. V. Bogomolov**, V. V. Bogomolov**, Yu. I. Denisov** and S. I. Svertilov**
*Space Research Institute, Russian Academy of Science, Profsoyznaya st. 84/32, 117810 Moscow, Russia **Skobeltsyn Institute of Nuclear Physics, Moscow State University, Vorob'evy Gory, 119899 Moscow, Russia
ABSTRACT The measurements of high-energy neutron (with energies~30-300 MeV) and proton (with energies ~1-200 MeV) fluxes are being conducted on-board "Mir-Spectr" orbital complex. Neutrons are detected by the undirected (FOV ~4n sr) scintillator spectrometer, consisting of 4 identical CsI(TI) detector units (the effective area for neutrons ~30 cm2). The gamma-quanta, which can be also detected by this instrument, are separated from neutrons by the analysis of the scintillator output pulse shape. To exclude registration of charged particles an anticoincidence plastic scintillator shield is realized in each detector unit. The proton fluxes are measured by the telescope based on 3 semiconductor detectors with small geometry factor (~ 1 cm2xsr). As the first result of the experiment the upper limit of the integral flux of local and albedo neutrons in the equatorial region (L< 1. I) was estimated. The results of this measurements earl be useful for the radiation security. Also, the neutrons of solar flares can be detected in this experiment. 0 1 9 9 8 COSPAR. Published by Elsevier Science Ltd.
THE EXPERIMENT "GRIF- 1" Since October 1995, the multipurpose experiment "GRIF-1" is being carried out on-board the orbital sration "MIR" (Pankov et a1.,1990). The station has the following orbit parameters: the altitude ~400 km, the period of rotation ~90 min, the orbit inclination ~510" The complex scientific apparatus of"GRIF-I" includes the following 4 instruments: 1)The directed X-ray and soft gamma-ray spectrometer "RX-2" ( energy range AEr=10-300 keV, effective area S=300 cm2, field of view f)=l sr). The instrument is mainly intended for astrophysical observations including the monitoring of solar flare activity. 2)The omni-directional spectrometer of gamma-radiation and high energy neutrons NEGA- 1 (AE~=0.05-50 MeV, AEn=20-300 MeV, S~=250 cm-, ~ Sn=30 cm 2 ) The 1785
M. I. Kudryavtsev et al.
1786
instrument contains 4 phoswich detector modules: CsI(T1) crystal (@10cm × 10cm) is placed into the anticoincidence shield of 2 cm thick plastic scintillator. 3)The spectrometer of charged particles FON-1 with large geometrical factor-80 cm 2 sr (AEe=40-200 keV, AEp=2-100 MeV, field of view +60 ° around the instrument's axis). The instrument is intended for the measurement of the low fluxes of the charged particles below the Earth's radiation belts. It consists of 2 detector modules, based on the thin (-50 mkm) layer of CsI(TI) on the plastic scintillator. 4) The spectrometer of charged particles FON-2 with small geometric factor -0.5 cm 2 sr (AEe=40-1000 keV, AEp=I-5 MeV, field of view _+30° around the instrument's axis).The instrument is intended for measurements of high fluxes of the charged particles in the radiation belts. It is made on the basis of 2 semiconductor telescopes and 4 counters. A detailed description of"GRIF-I" is presented in Kudryavtsev el al.. (1990). RESULTS The scientific goals of the experiment include measurements of high-energy neutral radiation of solar flares and a study of the fluxes of the various types of particles in the near-Earth space. The measurements of neutrons and gamma-radiation is provided by "NEGA-I". The fluxes of electrons and protons in the zones of trapped radiation are detected by "FON-2". The detector "FON-2" serves also as a background monitor for "NEGA-I" in order to estimate the role of the charged particles in producing the additional gamma-rays and neutrons in the anomaly. Neutrons and gamma-quanta are measuring in "NEGA-1" separately. The principle of their separation is based on the dependence of the pulse shape in CsI(TI) on the ionization density of the detecting particle. Neutrons are detected by the products of their nuclear interactions: protons, alpha-particles etc. All these particles posess higher ionization density then electrons, produced in the interactions of gamma-quanta. The electronic separation circuit compares the signals proportional to the total light yield during the first -1.2 ~sec and during the next -7 ~tsec and generates the master pulse "neutron" only when the first signal has higher amplitude. The example of counting rates, measured by "NEGA-I" is presented in Figure 1. The time period shown in this figure corresponds to -2 hours of observations. Two parameters of neutrons (energy releases equivalent to the energies of gamma quanta 5-15 MeV and >15 MeV) and the corresponding parameters of gamma-quanta are presented. It is seen from the figure, that the count rates of neutrons on the equator are 20 times lower, due to the circuit of the separation. The decrease of the background level allows high sensitivity to the neutrons of solar flares to be achieved (if any of them will occur). The value of the minimal detectable flux with the duration -30 min in the experiment "GRIF1" is equal to -0.015 cm2s ~, that is -2 times smaller than in the experiment on SMM (Chupp et al., 1982).
High Energy Neutron and Proton Fluxes on MIR
1787
1.6 1,1 1.1 , I.,40, 21 . I..7 . I..07. 1,2, I.,95. 1,7. I.!5 .I.07 . 1,85 1.05 1,25 1.75 2,1 1,8 1,0S 1,55 2,0 1.85 1,05 1,25 I
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10:30 1"0:45 11:00 11:15 11:30 11:4.5 12:00 12:15 UT Fig. I. The counting rates of neutrons and gamma-quanta, measured by "NEGA-1" during ~2 hours of observations 20.02.1996. The scale of the parameter L is also presented.
The analysis of the behavior of the count rates in neutron channels in comparison with other parameters allowed, to show that the main part of events in the neutron channels is caused by gamma-quanta. Figure 2 shows the two-dimensional diagram of the count rates in neutron channel (AE=5-15 MeV) versus the count rates of the corlespondent gammaray channel (5-15 MeV) multiplied by one of the neighbouring energetic channels (1.5-5 MeV).The straight line confirms the hypothesis that most of the events in neutron channels are caused by the statistical coincidences of gamma-quanta events. An attempt was made to take into account various background factors and to estimate the neutron fluxes in the station. The preliminary results give the value of the upper limit of the integral flux of local and albedo neutrons in the equatorial region (L
1788
M.I. Kudryavtsev et al.
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Fig. 2. The diagram illustrating the nature of the events in neutron parameters (see the text).
The measurement of other sorts of particles by the background patrol detectors allow us to conclude that protons and electrons could not be the source of the background in the neutron channels. The fluxes of protons with energies E>50 MeV, measured by FON-2 during the period shown in Figure 1, were less than 100 m "2 s"] sr -i
REFERENCES Chupp, E.L., D.J. Forrest, J.M. Ryan, J. Heslin, C. Reppin, K. Pinkau, G. Kanbach, E. Rieger, and G.H. Share, A Direct Observation of Solar Neutrons Following the 0118 UT Flare on 1980, June 21, Astrophys. J., 263, L95 (1982). Kudryavtsev, M.I., V.M. Pankov, Ju.G. Shkurkin, A.V. Bogomolov, V.V. Bogomolov, Yu.I. Denisov, G.Ya. Kolesov, Yu.I. Logachev, S.I. Svertilov, and Yu.I. Vydai, Instrumentation for Background Monitoring in Astrophysical and Ecological Programs, Papers of the IVth International Seminar "Space Science Engineering", Moscow, Vol. 3, P. 42, (1990).
Pergamon
MEASUREMENTS OF HIGH-ENERGY NEUTRON AND PROTON FLUXES ON-BOARD "MIR-SPECTR" ORBITAL COMPLEX M. I. Kudryavtsev*, A. V. Bogomolov**, V. V. Bogomolov**, Yu. I. Denisov** and S. I. Svertilov**
*Space Research Institute, Russian Academy of Science, Profsoyznaya st. 84/32, 117810 Moscow, Russia **Skobeltsyn Institute of Nuclear Physics, Moscow State University, Vorob'evy Gory, 119899 Moscow, Russia
ABSTRACT The measurements of high-energy neutron (with energies~30-300 MeV) and proton (with energies ~1-200 MeV) fluxes are being conducted on-board "Mir-Spectr" orbital complex. Neutrons are detected by the undirected (FOV ~4n sr) scintillator spectrometer, consisting of 4 identical CsI(TI) detector units (the effective area for neutrons ~30 cm2). The gamma-quanta, which can be also detected by this instrument, are separated from neutrons by the analysis of the scintillator output pulse shape. To exclude registration of charged particles an anticoincidence plastic scintillator shield is realized in each detector unit. The proton fluxes are measured by the telescope based on 3 semiconductor detectors with small geometry factor (~ 1 cm2xsr). As the first result of the experiment the upper limit of the integral flux of local and albedo neutrons in the equatorial region (L< 1. I) was estimated. The results of this measurements earl be useful for the radiation security. Also, the neutrons of solar flares can be detected in this experiment. 0 1 9 9 8 COSPAR. Published by Elsevier Science Ltd.
THE EXPERIMENT "GRIF- 1" Since October 1995, the multipurpose experiment "GRIF-1" is being carried out on-board the orbital sration "MIR" (Pankov et a1.,1990). The station has the following orbit parameters: the altitude ~400 km, the period of rotation ~90 min, the orbit inclination ~510" The complex scientific apparatus of"GRIF-I" includes the following 4 instruments: 1)The directed X-ray and soft gamma-ray spectrometer "RX-2" ( energy range AEr=10-300 keV, effective area S=300 cm2, field of view f)=l sr). The instrument is mainly intended for astrophysical observations including the monitoring of solar flare activity. 2)The omni-directional spectrometer of gamma-radiation and high energy neutrons NEGA- 1 (AE~=0.05-50 MeV, AEn=20-300 MeV, S~=250 cm-, ~ Sn=30 cm 2 ) The 1785
M. I. Kudryavtsev et al.
1786
instrument contains 4 phoswich detector modules: CsI(T1) crystal (@10cm × 10cm) is placed into the anticoincidence shield of 2 cm thick plastic scintillator. 3)The spectrometer of charged particles FON-1 with large geometrical factor-80 cm 2 sr (AEe=40-200 keV, AEp=2-100 MeV, field of view +60 ° around the instrument's axis). The instrument is intended for the measurement of the low fluxes of the charged particles below the Earth's radiation belts. It consists of 2 detector modules, based on the thin (-50 mkm) layer of CsI(TI) on the plastic scintillator. 4) The spectrometer of charged particles FON-2 with small geometric factor -0.5 cm 2 sr (AEe=40-1000 keV, AEp=I-5 MeV, field of view _+30° around the instrument's axis).The instrument is intended for measurements of high fluxes of the charged particles in the radiation belts. It is made on the basis of 2 semiconductor telescopes and 4 counters. A detailed description of"GRIF-I" is presented in Kudryavtsev el al.. (1990). RESULTS The scientific goals of the experiment include measurements of high-energy neutral radiation of solar flares and a study of the fluxes of the various types of particles in the near-Earth space. The measurements of neutrons and gamma-radiation is provided by "NEGA-I". The fluxes of electrons and protons in the zones of trapped radiation are detected by "FON-2". The detector "FON-2" serves also as a background monitor for "NEGA-I" in order to estimate the role of the charged particles in producing the additional gamma-rays and neutrons in the anomaly. Neutrons and gamma-quanta are measuring in "NEGA-1" separately. The principle of their separation is based on the dependence of the pulse shape in CsI(TI) on the ionization density of the detecting particle. Neutrons are detected by the products of their nuclear interactions: protons, alpha-particles etc. All these particles posess higher ionization density then electrons, produced in the interactions of gamma-quanta. The electronic separation circuit compares the signals proportional to the total light yield during the first -1.2 ~sec and during the next -7 ~tsec and generates the master pulse "neutron" only when the first signal has higher amplitude. The example of counting rates, measured by "NEGA-I" is presented in Figure 1. The time period shown in this figure corresponds to -2 hours of observations. Two parameters of neutrons (energy releases equivalent to the energies of gamma quanta 5-15 MeV and >15 MeV) and the corresponding parameters of gamma-quanta are presented. It is seen from the figure, that the count rates of neutrons on the equator are 20 times lower, due to the circuit of the separation. The decrease of the background level allows high sensitivity to the neutrons of solar flares to be achieved (if any of them will occur). The value of the minimal detectable flux with the duration -30 min in the experiment "GRIF1" is equal to -0.015 cm2s ~, that is -2 times smaller than in the experiment on SMM (Chupp et al., 1982).
High Energy Neutron and Proton Fluxes on MIR
1787
1.6 1,1 1.1 , I.,40, 21 . I..7 . I..07. 1,2, I.,95. 1,7. I.!5 .I.07 . 1,85 1.05 1,25 1.75 2,1 1,8 1,0S 1,55 2,0 1.85 1,05 1,25 I
I
I
I
I
1o
~..~
__
/~'~.
//"~,
",~~
1o
Photons .,¢/5"15 MaV
.~.
"~,~.~"
:4
O~ r_
Q
\ 'q"~
I
I
1
I
I
]
~-~,
I
J MeV .4
. . . .
I
I
10:30 1"0:45 11:00 11:15 11:30 11:4.5 12:00 12:15 UT Fig. I. The counting rates of neutrons and gamma-quanta, measured by "NEGA-1" during ~2 hours of observations 20.02.1996. The scale of the parameter L is also presented.
The analysis of the behavior of the count rates in neutron channels in comparison with other parameters allowed, to show that the main part of events in the neutron channels is caused by gamma-quanta. Figure 2 shows the two-dimensional diagram of the count rates in neutron channel (AE=5-15 MeV) versus the count rates of the corlespondent gammaray channel (5-15 MeV) multiplied by one of the neighbouring energetic channels (1.5-5 MeV).The straight line confirms the hypothesis that most of the events in neutron channels are caused by the statistical coincidences of gamma-quanta events. An attempt was made to take into account various background factors and to estimate the neutron fluxes in the station. The preliminary results give the value of the upper limit of the integral flux of local and albedo neutrons in the equatorial region (L
1788
M.I. Kudryavtsev et al.
150.00
,?, t~
,,-,: 100.00 ,,?,,
i
. :,,...'
C :;=
,.F" "'
.~ "
50.00
. ,.-~:"~~
./... 0,00
.
. . . . . . . . .
0
'
. . . . . .
. . . .
. . . . .
4000000
N Ir5-1 51. N ir1.~-51,
s2
Fig. 2. The diagram illustrating the nature of the events in neutron parameters (see the text).
The measurement of other sorts of particles by the background patrol detectors allow us to conclude that protons and electrons could not be the source of the background in the neutron channels. The fluxes of protons with energies E>50 MeV, measured by FON-2 during the period shown in Figure 1, were less than 100 m "2 s"] sr -i
REFERENCES Chupp, E.L., D.J. Forrest, J.M. Ryan, J. Heslin, C. Reppin, K. Pinkau, G. Kanbach, E. Rieger, and G.H. Share, A Direct Observation of Solar Neutrons Following the 0118 UT Flare on 1980, June 21, Astrophys. J., 263, L95 (1982). Kudryavtsev, M.I., V.M. Pankov, Ju.G. Shkurkin, A.V. Bogomolov, V.V. Bogomolov, Yu.I. Denisov, G.Ya. Kolesov, Yu.I. Logachev, S.I. Svertilov, and Yu.I. Vydai, Instrumentation for Background Monitoring in Astrophysical and Ecological Programs, Papers of the IVth International Seminar "Space Science Engineering", Moscow, Vol. 3, P. 42, (1990).