- Email: [email protected]
Beam test results of the RADEM Engineering Model
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Beam test results of the RADEM Engineering Model M. Pinto a ,∗, P. Gonçalves a , P. Socha b , W. Hajdas b , A. Marques c , J. Costa Pinto c a b c
Laboratório de Instrumentação e Física Experimental de Partículas, Av. Prof. Gama Pinto, n2, Complexo Interdisciplinar (3is), 1649-003 Lisboa, Portugal Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen, Switzerland EFACEC, S.A., Via de Francisco Sá Carneiro, 4471-907 Moreira da Maia, Portugal
ARTICLE
INFO
Keywords: RADEM Particle detector JUICE Radiation Jupiter
ABSTRACT ESAs next class-L mission to the Jovian system, the Jupiter Icy Moons Explorer (JUICE), will collect valuable data while orbiting Jupiter and three its moons for a period of three and a half years. RADEM, the Radiation Hard Electron Monitor is being developed to provide housekeeping information for the mission. It will also gather valuable scientific data on the energetic radiation environment of the Jovian system for its full duration. The Jovian radiation environment, dominated by electrons, results from Jupiter strong magnetic field and its interaction with the Galilean moons. So far, only the Galileo spacecraft performed long-term measurements of the radiation environment showing that it is extremely hazardous and complex. RADEM features four detector heads: the Proton Detector Head to measure protons energies, the Ion Detector Head to measure ion content up to oxygen; the Electron Detector head to perform electron spectral measurements; and the Directionality Detector Head to correct for electron flux angular dependences. The detectors readout are three newly custom designed ASIC IDE3466. In this work, RADEM overall properties and Engineering Model radiation tests results are presented.
1. Introduction The Jovian system is a highly rich scientific object. Its mass is greater than that of all other solar system bodies besides the Sun, contributing in a significant way to its evolution. It has 79 known moons, four of which, the Galilean moons, are unique. While Io is known for its volcanic activity, evidence shows that Europa, Callisto and Ganymede might have liquid water oceans below their surfaces and the conditions thought necessary to support life [1]. The planet also has an enormous magnetosphere extending past Saturn’s orbit which is able to trap charged particles with energies larger than those found in the Van Allen belts [1–4]. Its radiation environment is one of the major hazards to spacecrafts flying to or by the system leading to high total doses in EEE components and consequently to parametric degradation or even functional failure [5–8]. It also gives important scientific information about the magnetosphere, molecule production/destruction rates and atmosphere creation via sputtering effects in Europa [9] and Ganymede [10]. So far only the GALILEO spacecraft [11], and more recently JUNO [12], have studied the planet for a long period of time, though other missions to the outer solar system have rendezvous with the planet for gravity assisted maneuvers [8]. GALILEO is the main source of information of the radiation environment in Jupiter due to the long-term measurements made by its Energetic Particle Detector (EPD) [11,13].
JUNO on the other hand has no radiation monitor despite recent efforts to use dark current in CCDs to constrain particle fluxes [14]. ESAs next large mission — JUICE (Jupiter Icy Moons Explorer), will include a Radiation Hard Electron Monitor (RADEM) to measure both electron and proton fluxes and, to some extent, ions. The monitor will compute the total dose in-situ, acting as an alarm of high radiation levels to the spacecraft and other instruments. It will also send valuable information about the particle environment to improve existing radiation models [3,15–17]. The mission will orbit the planet for three years and Ganymede at different altitudes for 285 days before crashing into the moon [1,4]. In this paper, we present the four detector heads developed for RADEM as well as the first radiation test results of the instrument Engineering Model (EM). 2. RADEM To fulfill its housekeeping and scientific goals, four detector heads were developed for RADEM: the Electron Detector Head (EDH), the Proton Detector Head (PDH), the Heavy Ion Detector Head (HIDH) and the Directional Detector Head (DDH), each of them using 0.3 mm thick silicon PIN diodes of different sizes as radiation sensors. Fig. 1 shows RADEM EM and the position of all detector heads. The EDH structure consists of eight sensors surrounded by a copper collimator with a 15 deg aperture. Sensors are organized in a stack,
∗ Corresponding author. E-mail address: [email protected] (M. Pinto).
https://doi.org/10.1016/j.nima.2019.162795 Received 30 March 2019; Accepted 16 September 2019 Available online xxxx 0168-9002/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.
M. Pinto, P. Gonçalves, P. Socha et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
connected to either a LG or HG channel of an IDE3466 ASIC. Tests were separated into three categories: energy response of LG and HG channels; flux scaling and coincidence logic functionality. 3.1. Energy response In the particle test campaign at PSI, RADEM EM was exposed to various radiation types to verify its responses and energy levels. First radiation source used for the calibration was a flat 137 Cs source that emits 662 keV gamma particles. Gammas of this energy interact with the detector material via Compton scattering depositing a maximum of 480 keV in the detector. Particles coming from the source located at top of the EDH collimator were penetrating through the hole detector stack depositing energy in every detector bin. The second source was 90 Sr emitting 𝛽 − radiation with a continuous spectrum up to 2.3 MeV. The source was also placed on top of the EDH collimator to verify detector responses in the first three bins corresponding to this energy. The last tests were done using the proton beam at PIF. Calibrations were done using 100 and 200 MeV proton beam centered on a EDH and HIDH with a flux up to 4.56E4 particles/cm2 /s.
Fig. 1. RADEM Engineering Model. The four detector heads: EDH; PDH; HIDH and DDH are indicated in the picture.
3.2. Flux scaling response The proton beam at PIF was also used to verify the response of detectors to increasingly higher fluxes. A 200 MeV proton beam centered on the DDH central pixel was used and the count rate on all pixels registered. LT in all diodes was set to 10 fC in all diodes and HT was disabled. Fluxes were set to 2.28E4, 4.56E4 and 22.8E4 particles/cm2 /s. 3.3. Coincidence To test the coincidence logic, a point-like 90 Sr source was placed directly above the EDH. The purpose of this test was to verify if the count rate registered in the second diode counting from the top of the detector head (D2), was the same as the one registered by the coincidence logic counting (D1+D2) particles depositing energy in both the top diode (D1) and the second diode. All channels LT were set to 6 fC and no HT was enabled. Results were obtained for several Mono-stable trigger Coincidence Times (MCT) [19].
Fig. 2. Schematic of the EDH and DDH. The PDH and HIDH follow the design principle as the former.
separated by aluminum and tantalum absorbers in a way that provides quasi-logarithmic coverage of the electron spectrum from 0.3 to 40 MeV. The PDH is built in a similar way: eight sensors separated by absorbers covering proton energies from 5 to 250 MeV with a 20 deg aperture angle. The HIDH will allow to discriminate ions from Helium to Oxygen with energies from 8 to 670 MeV. It consists of two silicon sensors surrounded by a copper collimator with an opening angle of 45 deg. The DDH is a single pixelated silicon diode sensor placed below a copper collimator, with 28 apertures, each corresponding to an individual sensitive pixel pointing to different polar and azimuth angle. It also has three pixels outside of the collimator Field-Of-View (FOV) to measure the background radiation. The RADEM instrument concept, including its response to the Jovian environment and the proof-of-concept tests, are discussed in [18]. A mission dedicated ASIC IDE3466 [19] developed by IDEAS, with four Low-Gain (LG) channels and 32 HighGain (HG) channels and coincidence logic is responsible for the readout of all detector heads. Each HG channel has two discriminators to set Low and a High Thresholds (LT and HT respectively) while the LG channels only have one discriminator. Both the EDH and the DDH are connected to the HG channels of two independent IDE3466 ASICs while the PDH and the HIDH are connected to the HG and LG channels of a third ASIC respectively. Fig. 2 displays a schematic of the EDH and the DDH.
4. Results and discussion 4.1. Radiation response Results of the RADEM threshold scan using a 137 Cs source are shown in Fig. 3. Since 137 Cs gammas are highly penetrative, this measurement allowed us to test the responses of every sensitive diode in the EDH. The tests showed that all diodes were responding to the gamma radiation. Differences in the geometry and the location of the radiation source contributed to the observed differences in the count rates. Fig. 4 presents the results of the measurements done with a 90 Sr electron source. As expected, the count rate decreases for diodes located deeper in the stack due to energy loss in the previous diodes and absorbers. Count rate in subsequent diodes drops due to the particle energy loss inside the detector stack. No counts in diodes 4 to 8 were registered as expected for electrons of these energies. The response of the EDH to 100 MeV protons was also tested at PIF. Results of the measurement are shown in Fig. 5. All sensors of the detector stack responded to the proton irradiation. The peak shows that the full deposited energy spectrum was measured, shifting to higher values, as expected, for successive diodes in the stack. This is because the Linear Energy Transfer (LET) of the protons increases as they lose energy. Proton irradiation at PIF with the beam centered on HIDH was done in order to verify the functionality of LG channels of the ASIC. D2 of HIDH response to the 200 MeV proton beam is shown on Fig. 6. The measurement has shown the functionality of the HIDH and LG channels.
3. Test methods A large battery of tests were designed to verify RADEM EM overall functionality and response to radiation. For these tests we leveraged on all sensors having the same working principle: a silicon PIN diode 2
Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.
M. Pinto, P. Gonçalves, P. Socha et al.
Fig. 3. RADEM EDH response of the eight diodes to the
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
137
Cs gamma source.
Fig. 6. RADEM HIDH response to the 200 MeV proton beam.
Fig. 4. RADEM EDH response of the three top diodes to the
90 Sr
electron source.
Fig. 7. Flux scaling response of several DDH pixels. Count rate in all channels increased linearly with flux as required.
4.3. Coincidence The count rate for the three channels D1, D2 and D1+D2 of the EDH, obtained in a MCT scan is shown in Fig. 8. D1 and D2 counts do not change much above MCT 200 ns. In the D1+D2 channel count rate increases with MCT up to 300 ns, and remains stable for higher value. The total count difference between D1 and D2 is expected because 90 Sr emits electrons with energies up to 2.28 MeV. While a large number of the electrons emitted in the direction of D1 deposit sufficient energy in the diode to be counted, a significant fraction of them does not reach D2 or does not deposit enough energy to trigger it. In the case of the coincidence channel, D1+D2, this effect is enhanced since it requires both D1 and D2 to trigger. This means that threshold for detection should be kept as low as possible.
Fig. 5. RADEM EDH LT scan with a 100 MeV proton beam. D1 counts are multiplied by four, the ratio between D1 and D2–D8 diodes for visualization purposes only.
4.2. Flux scaling 5. Conclusions The proton beam was also centered with the DDH to test response as a function of the incoming flux. Results obtained are shown in Fig. 7 for several DDH pixels. As it can be seen, the count rate increases linearly with flux as required. Differences between pixel count rates are due to the different sizes of the pixels. Previous breadboard tests had shown already that the ASIC can handle the maximum count rate expected for the mission without saturating [13].
In this paper we have presented functional and radiation tests of RADEM EM. The instrument has three detector heads all of which were exposed to gammas, electrons and/or protons. Low threshold scans with a 137 Cs source on top of the EDH showed a clear response on all silicon sensors. The count rate on the sensors decreased for larger thresholds as expected. Differences between sensor count rates can be explained by the position of the sensors in relation to the source (solid angle). 3
Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.
M. Pinto, P. Gonçalves, P. Socha et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Acknowledgment This work was supported by the European Space Agency (ESA/ ESTEC Contract 1-7560/13/NL/HB). References [1] O. Grasset, et al., Jupiter ICY moons explorer (JUICE): An ESA mission to orbit Ganymede and to characterize the Jupiter system, Planet. Space Sci. 78 (2013) 1–21. [2] J.I. Vette, The AE8 trapped electron model environment, NSSDC/WDCAR & S 9124, 1991. [3] A. Sicard-Piet, S. Bourdarie, N. Krupp, JOSE: A new Jovian specification environment model, IEEE Trans. Nucl. Sci. 53 (3) (2011) 923–931. [4] JUICE –Jupiter Icy moons ExplorerEnvironmental Specification, JS-14-09, Issue 5, Revision 5. [5] T.R. Oldham, F.B. McLean, Total ionizing dose effects in MOS oxides and devices, IEEE Trans. Nucl. Sci. 50 (3) (2003) 483–499. [6] D.M. Fleetwood, Total ionizing dose effects in MOS and low-dose-rate sensitive linear-bipolar devices, IEEE Trans. Nucl. Sci. 60 (3) (2013) 1706–1730. [7] J.R. Srour, C.J. Marshall, P.W. Marshall, Review of displacement damage effects in silicon devices, IEEE Trans. Nucl. Sci. 50 (3) (2003) 653–670. [8] J.R. Srour, J.W. Palko, Displacement damage effects in irradiated semiconductor devices, IEEE Trans. Nucl. Sci. 60 (3) (2013) 1740–1766. [9] D. Hal, et al., Detection of an oxygen atmosphere on Jupiter’s moon Europa, Nature 373 (1995) 677–679. [10] M. McGrath, E. Lellouch, D.F. Strobel, P. Johnson, Satellite atmospheres, in: F. Bagenal, T.E. Dowling, W. McKinnon (Eds.), Jupiter-the Planet, Satellites and Magnetosphere, Cambridge Univ. Press, Oxford, 2004, pp. 457–483. [11] D.J. Williams, The galileo energetic particle detector, Space Sci. Rev. 60 (1–4) (1992) 385–412. [12] S.J. Bolton, et al., The JUNO mission, Space Sci. Rev. 213 (2017) 5–37. [13] I. Jun, J.M. Ratliff, H.B. Garrett, R.W. McEntire, Monte CaRlo simulations of the galileo energetic particle detector, Nucl. Instrum. Methods Phys. Res. A 480 (3) (2002) 465–475. [14] A. Carlton, M. de Soria-Santacruz Pich, W. Kim, I. Jun, K. Cahoy, Using the Galileo solid-state imaging instrument as a sensor of Jovian energetic electrons, IEEE Trans. Nucl. Sci. 66 (1) (2019). [15] N. Divine, H.B. Garret, Charged particle distribution in Jupiter’s magnetosphere, J. Geophys. Res. 88 (1983) 6889–6903. [16] J.E.P. Connerney, et al., New models of Jupiter’s magnetic field constrained by the Io flux tube footprint, J. Geophys. Res. 103 (1998) 11929–11939. [17] S. Bourdarie, A. Sicard, Physical electron belts model from Jupiter’s surface to the orbit of europa, J. Geophys. Res. 109 (2004) 1–13. [18] M. Pinto, et al., Development of a directionality detector for RADEM, the radiation hard electron monitor aboard the JUICE mission, IEEE Trans. Nucl. Sci. 13 (52) (2019). [19] T.A. Stein, et al., Front-end readout ASIC for charged particle counting with the RADEM instrument on the ESA JUICE mission, in: Proceedings of SPIE 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, vol. 990546, 2016.
Fig. 8. Total counts in D1 (red), D2 (green) and D1+D2 (blue) with to a 90 Sr source placed on top of the collimator for different MCT. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
A 90 Sr source was used to test EDH response to low energy electrons (up to 2.3 MeV). Only the response of the three top sensors was successfully tested, since 2.3 MeV electrons do not reach the remaining stack sensors. The two top diodes were also subject to coincidence tests. Count rates in the second sensor were compared to count rates of a coincidence channel between the first and the second sensors for different Mono-stable Coincidence Times. Both channels were tested with a low threshold of 6 fC. Differences observed between the two channels were attributed to the threshold. The distribution of deposited energy in the EDH and IDH were studied also with proton beams at PIF. The EDH was irradiated with a 100 MeV proton uniform beam inside its FOV. A LT scan shows the distribution peak in all of the sensors. A 200 MeV proton beam sent towards the side of the HIDH in order to increase the deposited energy in the sensors. In this case, the peak was not observed because the particles LET was insufficient considering that the HIDH sensors are connected to the LG channels of the ASIC. However it was shown that these channels respond to radiation as expected. Linear response to increasingly larger fluxes was also observed with the DDH for a 200 MeV proton beam irradiation. To summarize, all detector heads sensors were responsive to different types of radiation. Both LG and HG channels of the ASIC, as well as its coincidence logic, were tested and successfully validated. The Engineering Qualification and Flight Models are now under construction and are expected to be calibrated in 2019 and 2020 respectively.
4
Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Beam test results of the RADEM Engineering Model M. Pinto a ,∗, P. Gonçalves a , P. Socha b , W. Hajdas b , A. Marques c , J. Costa Pinto c a b c
Laboratório de Instrumentação e Física Experimental de Partículas, Av. Prof. Gama Pinto, n2, Complexo Interdisciplinar (3is), 1649-003 Lisboa, Portugal Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen, Switzerland EFACEC, S.A., Via de Francisco Sá Carneiro, 4471-907 Moreira da Maia, Portugal
ARTICLE
INFO
Keywords: RADEM Particle detector JUICE Radiation Jupiter
ABSTRACT ESAs next class-L mission to the Jovian system, the Jupiter Icy Moons Explorer (JUICE), will collect valuable data while orbiting Jupiter and three its moons for a period of three and a half years. RADEM, the Radiation Hard Electron Monitor is being developed to provide housekeeping information for the mission. It will also gather valuable scientific data on the energetic radiation environment of the Jovian system for its full duration. The Jovian radiation environment, dominated by electrons, results from Jupiter strong magnetic field and its interaction with the Galilean moons. So far, only the Galileo spacecraft performed long-term measurements of the radiation environment showing that it is extremely hazardous and complex. RADEM features four detector heads: the Proton Detector Head to measure protons energies, the Ion Detector Head to measure ion content up to oxygen; the Electron Detector head to perform electron spectral measurements; and the Directionality Detector Head to correct for electron flux angular dependences. The detectors readout are three newly custom designed ASIC IDE3466. In this work, RADEM overall properties and Engineering Model radiation tests results are presented.
1. Introduction The Jovian system is a highly rich scientific object. Its mass is greater than that of all other solar system bodies besides the Sun, contributing in a significant way to its evolution. It has 79 known moons, four of which, the Galilean moons, are unique. While Io is known for its volcanic activity, evidence shows that Europa, Callisto and Ganymede might have liquid water oceans below their surfaces and the conditions thought necessary to support life [1]. The planet also has an enormous magnetosphere extending past Saturn’s orbit which is able to trap charged particles with energies larger than those found in the Van Allen belts [1–4]. Its radiation environment is one of the major hazards to spacecrafts flying to or by the system leading to high total doses in EEE components and consequently to parametric degradation or even functional failure [5–8]. It also gives important scientific information about the magnetosphere, molecule production/destruction rates and atmosphere creation via sputtering effects in Europa [9] and Ganymede [10]. So far only the GALILEO spacecraft [11], and more recently JUNO [12], have studied the planet for a long period of time, though other missions to the outer solar system have rendezvous with the planet for gravity assisted maneuvers [8]. GALILEO is the main source of information of the radiation environment in Jupiter due to the long-term measurements made by its Energetic Particle Detector (EPD) [11,13].
JUNO on the other hand has no radiation monitor despite recent efforts to use dark current in CCDs to constrain particle fluxes [14]. ESAs next large mission — JUICE (Jupiter Icy Moons Explorer), will include a Radiation Hard Electron Monitor (RADEM) to measure both electron and proton fluxes and, to some extent, ions. The monitor will compute the total dose in-situ, acting as an alarm of high radiation levels to the spacecraft and other instruments. It will also send valuable information about the particle environment to improve existing radiation models [3,15–17]. The mission will orbit the planet for three years and Ganymede at different altitudes for 285 days before crashing into the moon [1,4]. In this paper, we present the four detector heads developed for RADEM as well as the first radiation test results of the instrument Engineering Model (EM). 2. RADEM To fulfill its housekeeping and scientific goals, four detector heads were developed for RADEM: the Electron Detector Head (EDH), the Proton Detector Head (PDH), the Heavy Ion Detector Head (HIDH) and the Directional Detector Head (DDH), each of them using 0.3 mm thick silicon PIN diodes of different sizes as radiation sensors. Fig. 1 shows RADEM EM and the position of all detector heads. The EDH structure consists of eight sensors surrounded by a copper collimator with a 15 deg aperture. Sensors are organized in a stack,
∗ Corresponding author. E-mail address: [email protected] (M. Pinto).
https://doi.org/10.1016/j.nima.2019.162795 Received 30 March 2019; Accepted 16 September 2019 Available online xxxx 0168-9002/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.
M. Pinto, P. Gonçalves, P. Socha et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
connected to either a LG or HG channel of an IDE3466 ASIC. Tests were separated into three categories: energy response of LG and HG channels; flux scaling and coincidence logic functionality. 3.1. Energy response In the particle test campaign at PSI, RADEM EM was exposed to various radiation types to verify its responses and energy levels. First radiation source used for the calibration was a flat 137 Cs source that emits 662 keV gamma particles. Gammas of this energy interact with the detector material via Compton scattering depositing a maximum of 480 keV in the detector. Particles coming from the source located at top of the EDH collimator were penetrating through the hole detector stack depositing energy in every detector bin. The second source was 90 Sr emitting 𝛽 − radiation with a continuous spectrum up to 2.3 MeV. The source was also placed on top of the EDH collimator to verify detector responses in the first three bins corresponding to this energy. The last tests were done using the proton beam at PIF. Calibrations were done using 100 and 200 MeV proton beam centered on a EDH and HIDH with a flux up to 4.56E4 particles/cm2 /s.
Fig. 1. RADEM Engineering Model. The four detector heads: EDH; PDH; HIDH and DDH are indicated in the picture.
3.2. Flux scaling response The proton beam at PIF was also used to verify the response of detectors to increasingly higher fluxes. A 200 MeV proton beam centered on the DDH central pixel was used and the count rate on all pixels registered. LT in all diodes was set to 10 fC in all diodes and HT was disabled. Fluxes were set to 2.28E4, 4.56E4 and 22.8E4 particles/cm2 /s. 3.3. Coincidence To test the coincidence logic, a point-like 90 Sr source was placed directly above the EDH. The purpose of this test was to verify if the count rate registered in the second diode counting from the top of the detector head (D2), was the same as the one registered by the coincidence logic counting (D1+D2) particles depositing energy in both the top diode (D1) and the second diode. All channels LT were set to 6 fC and no HT was enabled. Results were obtained for several Mono-stable trigger Coincidence Times (MCT) [19].
Fig. 2. Schematic of the EDH and DDH. The PDH and HIDH follow the design principle as the former.
separated by aluminum and tantalum absorbers in a way that provides quasi-logarithmic coverage of the electron spectrum from 0.3 to 40 MeV. The PDH is built in a similar way: eight sensors separated by absorbers covering proton energies from 5 to 250 MeV with a 20 deg aperture angle. The HIDH will allow to discriminate ions from Helium to Oxygen with energies from 8 to 670 MeV. It consists of two silicon sensors surrounded by a copper collimator with an opening angle of 45 deg. The DDH is a single pixelated silicon diode sensor placed below a copper collimator, with 28 apertures, each corresponding to an individual sensitive pixel pointing to different polar and azimuth angle. It also has three pixels outside of the collimator Field-Of-View (FOV) to measure the background radiation. The RADEM instrument concept, including its response to the Jovian environment and the proof-of-concept tests, are discussed in [18]. A mission dedicated ASIC IDE3466 [19] developed by IDEAS, with four Low-Gain (LG) channels and 32 HighGain (HG) channels and coincidence logic is responsible for the readout of all detector heads. Each HG channel has two discriminators to set Low and a High Thresholds (LT and HT respectively) while the LG channels only have one discriminator. Both the EDH and the DDH are connected to the HG channels of two independent IDE3466 ASICs while the PDH and the HIDH are connected to the HG and LG channels of a third ASIC respectively. Fig. 2 displays a schematic of the EDH and the DDH.
4. Results and discussion 4.1. Radiation response Results of the RADEM threshold scan using a 137 Cs source are shown in Fig. 3. Since 137 Cs gammas are highly penetrative, this measurement allowed us to test the responses of every sensitive diode in the EDH. The tests showed that all diodes were responding to the gamma radiation. Differences in the geometry and the location of the radiation source contributed to the observed differences in the count rates. Fig. 4 presents the results of the measurements done with a 90 Sr electron source. As expected, the count rate decreases for diodes located deeper in the stack due to energy loss in the previous diodes and absorbers. Count rate in subsequent diodes drops due to the particle energy loss inside the detector stack. No counts in diodes 4 to 8 were registered as expected for electrons of these energies. The response of the EDH to 100 MeV protons was also tested at PIF. Results of the measurement are shown in Fig. 5. All sensors of the detector stack responded to the proton irradiation. The peak shows that the full deposited energy spectrum was measured, shifting to higher values, as expected, for successive diodes in the stack. This is because the Linear Energy Transfer (LET) of the protons increases as they lose energy. Proton irradiation at PIF with the beam centered on HIDH was done in order to verify the functionality of LG channels of the ASIC. D2 of HIDH response to the 200 MeV proton beam is shown on Fig. 6. The measurement has shown the functionality of the HIDH and LG channels.
3. Test methods A large battery of tests were designed to verify RADEM EM overall functionality and response to radiation. For these tests we leveraged on all sensors having the same working principle: a silicon PIN diode 2
Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.
M. Pinto, P. Gonçalves, P. Socha et al.
Fig. 3. RADEM EDH response of the eight diodes to the
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
137
Cs gamma source.
Fig. 6. RADEM HIDH response to the 200 MeV proton beam.
Fig. 4. RADEM EDH response of the three top diodes to the
90 Sr
electron source.
Fig. 7. Flux scaling response of several DDH pixels. Count rate in all channels increased linearly with flux as required.
4.3. Coincidence The count rate for the three channels D1, D2 and D1+D2 of the EDH, obtained in a MCT scan is shown in Fig. 8. D1 and D2 counts do not change much above MCT 200 ns. In the D1+D2 channel count rate increases with MCT up to 300 ns, and remains stable for higher value. The total count difference between D1 and D2 is expected because 90 Sr emits electrons with energies up to 2.28 MeV. While a large number of the electrons emitted in the direction of D1 deposit sufficient energy in the diode to be counted, a significant fraction of them does not reach D2 or does not deposit enough energy to trigger it. In the case of the coincidence channel, D1+D2, this effect is enhanced since it requires both D1 and D2 to trigger. This means that threshold for detection should be kept as low as possible.
Fig. 5. RADEM EDH LT scan with a 100 MeV proton beam. D1 counts are multiplied by four, the ratio between D1 and D2–D8 diodes for visualization purposes only.
4.2. Flux scaling 5. Conclusions The proton beam was also centered with the DDH to test response as a function of the incoming flux. Results obtained are shown in Fig. 7 for several DDH pixels. As it can be seen, the count rate increases linearly with flux as required. Differences between pixel count rates are due to the different sizes of the pixels. Previous breadboard tests had shown already that the ASIC can handle the maximum count rate expected for the mission without saturating [13].
In this paper we have presented functional and radiation tests of RADEM EM. The instrument has three detector heads all of which were exposed to gammas, electrons and/or protons. Low threshold scans with a 137 Cs source on top of the EDH showed a clear response on all silicon sensors. The count rate on the sensors decreased for larger thresholds as expected. Differences between sensor count rates can be explained by the position of the sensors in relation to the source (solid angle). 3
Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.
M. Pinto, P. Gonçalves, P. Socha et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
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Fig. 8. Total counts in D1 (red), D2 (green) and D1+D2 (blue) with to a 90 Sr source placed on top of the collimator for different MCT. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
A 90 Sr source was used to test EDH response to low energy electrons (up to 2.3 MeV). Only the response of the three top sensors was successfully tested, since 2.3 MeV electrons do not reach the remaining stack sensors. The two top diodes were also subject to coincidence tests. Count rates in the second sensor were compared to count rates of a coincidence channel between the first and the second sensors for different Mono-stable Coincidence Times. Both channels were tested with a low threshold of 6 fC. Differences observed between the two channels were attributed to the threshold. The distribution of deposited energy in the EDH and IDH were studied also with proton beams at PIF. The EDH was irradiated with a 100 MeV proton uniform beam inside its FOV. A LT scan shows the distribution peak in all of the sensors. A 200 MeV proton beam sent towards the side of the HIDH in order to increase the deposited energy in the sensors. In this case, the peak was not observed because the particles LET was insufficient considering that the HIDH sensors are connected to the LG channels of the ASIC. However it was shown that these channels respond to radiation as expected. Linear response to increasingly larger fluxes was also observed with the DDH for a 200 MeV proton beam irradiation. To summarize, all detector heads sensors were responsive to different types of radiation. Both LG and HG channels of the ASIC, as well as its coincidence logic, were tested and successfully validated. The Engineering Qualification and Flight Models are now under construction and are expected to be calibrated in 2019 and 2020 respectively.
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Please cite this article as: M. Pinto, P. Gonçalves, P. Socha et al., Beam test results of the RADEM Engineering Model, Nuclear Inst. and Methods in Physics Research, A (2019) 162795, https://doi.org/10.1016/j.nima.2019.162795.