1. 3) First proof of concept tests 5) Results and Discussion
RADMON Reader: a portable readout system for the CERN RADMON sensors
EP-DT-DD
Irradiation Facilities
Isidre Mateu1, Maurice Glaser1, Georgi Gorine1, Michael Moll1, Giuseppe Pezzullo1, Federico Ravotti1
1 European Organization for Nuclear Research, CERN EP-DT-DD, Geneva, Switzerland
ABSTRACT
Monitoring of the Total Ionizing Dose (TID) and 1 MeV neutron equivalent fluence (Φeq) is performed at CERN Large Hadron Collider (LHC) experiments using a series of dosimeters integrated on a unique carrier printed circuit board (PCB) known as RADMON sensor [1] (Fig. 1). The sensor can be equipped with different devices: RadFETs for the TID measurement and silicon p-i-n diodes to monitor Φeq. More than 250 RADMON sensors have been installed in the LHC experiments since Besides the LHC, RADMON sensors are regularly provided to other experiments (from inside and outside CERN). In those cases, the users can set up their own readout system, or use the sensors in a passive mode, i.e. without real time readout [1]. For these applications, a compact and portable readout unit, which could be provided to the users together with the RADMON sensors is of clear interest. The development of this system is ongoing within the Irradiation Facilities team in the Experimental Physics department at CERN. The project is in an advanced phase, with already a consolidated design and a few assembled prototypes. The device is able to exploit the full range of all the above mentioned dosimeters, thus featuring a total measurement range from 0.1 Gy to 30 kGy in TID, and from 1010 n/cm2 to 5x1014 n/cm2 in Φeq. As a proof of concept, two prototypes were tested at CERN proton irradiation facility (IRRAD) and Gamma Irradiation Facility (GIF++) in In another test carried out in IRRAD in 2017, the measurements obtained with the system were directly cross-checked with the ones obtained using a commercial source measuring unit, showing less than 4% discrepancy for all dosimeters.
1) RADMON sensors
2) RADMON Reader
A DC-DC converter equipped with a feedback loop to act as a current source is used for the readout.
The converter is able to source current up to 32 mA with a voltage limit of 125V, thus allowing to fully exploit the calibrated range of all RADMON dosimeters.
A full characterization of the DC-DC converter was carried out that the requirements for the optimal readout of each dosimeter were met (e.g. maximum biasing time of the p-i-n diodes to prevent annealing)
Dosimeters are read out one at a time, with a multiplexing system allowing to address up to 8 RADMON sensors (88 dosimeters in total)
Arduino Yun microcontroller provides Ethernet and Wi-Fi connectivity.
Built-in web interface to work as stand-alone system, but can also be interfaced with other systems using HTTP requests.
Data storage can be local and/or remote.
Monitoring of Total Ionizing Dose (TID) and 1 MeV neutron equivalent fluence (φeq)
Up to 11 dosimeters per sensor: p-i-n diodes for φeq, RadFETs for TID
Readout of all devices is done by injecting a current pulse and measuring the voltage.
p-i-n diodes
RadFETs
LBSD Si-1
LBSD Si-2
BPW
REM
LAAS
Measurement range
< 1012
[neq/cm2]
<2x1011
2x1012 – 5x1014
0.1 – 3x104
[Gy]
<10
Sensitivity
1.6x108
[neq/cm2/mV]
2.7x107 [neq/cm2/mV]
9.2x109
0.1
[Gy/mV]
0.01
Readout current
25 mA
1 mA
0.16 mA
0.1 mA
Output range
1 – 10 V
0.5 – 80 V
3.5 – 40 V
3 – 10 V
3) First proof of concept tests
Two prototypes of the RADMON Reader were tested at CERN IRRAD and GIF++ facilities, aiming at:
Have a proof of concept of the design.
Identify and solve potential hardware and software problems.
Test the reliability of the system in realistic conditions
The obtained measurements were compared with the RAMSES monitors in the facilities (RAMSES), FLUKA simulations, and passive dosimeters.
A very good agreement between the RAMSES signal and all the RADMON dosimeters tested in IRRAD was observed.
The 3 LAAS RadFET installed in GIF++ proceeded from a defective batch with unknown calibration curve Nevertheless, a clear correlation between the RADMON and RAMSES signals was observed. A new test is currently ongoing
5) Results and Discussion
The comparison of the raw voltage measured by the EP-RADMON Reader (VRU) and the SMU (VSM) for a Si-1 p-i-n diode and a LAAS RadFET over more than 80 days of acquisition shows very good agreement
A similar overlap was observed for the readout of a BPW p-i-n and a REM RadFET,
No data loss due to a malfunctioning of the EP-RADMON Reader during the whole data taking period.
Voltage error
𝜀 𝑉 (%)= 𝑉 𝑅𝑈 − 𝑉 𝑉𝑀 𝑉 𝑉𝑀 ×100
With the RADMON Reader acting as current source, comparison of the voltage measurement given by the RADMON Reader (VRU) with the voltage measured by the SMU acting as voltmeter (VVM)
With the SMU Reader acting as current source, comparison of the dose/fluence measurement given by the RADMON Reader (SRU) with the independent measurement of the SMU (SSM).
TID/φeq error
𝜀 𝑆 (%)= 𝑆𝑅𝑈− 𝑆 𝑆𝑀 𝑆 𝑆𝑀 ×100
4) System validation in IRRAD
New test in IRRAD using a test-bench in which the same RADMON sensor is measured alternatively by the RADMON reader and a commercial Source Meter Unit (SMU).
SMU used as a benchmark system to quantify the accuracy and precision of the RADMON Reader readout
A LabVIEW interface was used to synchronize all the hardware.
The test-bench was also used before the test to construct calibration curves for the current sourced and the voltage measured by the DC-DC converter. Resistor values covering the impedance range of all RADMON dosimeters were used
Calibration plot
In all cases these errors are well below the uncertainty of the RADMON dosimeters themselves
The system could already be used as dosimetry reference in a real experiment without significant loss of performance
Device
Voltage
με, σε (%)
TID/φeq
Si-1 (1011<φeq[n/cm2]<1012)
0.98, 0.6
0.17,0.49
REM (10<TID[Gy]<3x104)
0.01, 0.04
1.3, 0.72
LAAS (1<TID[Gy]<10)
-0.03, 0.03
1.56, 0.62
6) Future Work
All the data presented in this article was obtained during still a development phase of the readout system
The final consolidated architecture has been implemented in a unique printed circuit board (PCB). The first units have been produced and will be tested in the inmediate future
The test-bench used for the last tests in IRRAD will be further improved adding a direct measurement of the readout current with an ammeter for better calibration.
In addition, the assessment of the system performance at different temperatures, with tests in climate chamber, is foreseen..
References
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[3] S. Tavernier, ”Experimental Techniques in Nuclear and Particle Physics” ,pp , Springer-Verlag Berlin Heidelberg 2010.
[4] F. Ravotti, “Development and Characterisation of Radiation Monitoring Sensors for the High Energy Physics Experiments of the CERN LHC,” PhD thesis, Geneva, 2006.
[5] R. Chaplin, “Defects and Transmutations in Reactor-Irradiated Copper” ,pp , Journal of Nuclear Materials,vol.108, 1982.
[6] J.W. Martin, “The electrical resistivity of some lattice defects in FCC metals observed in radiation damage experiments”, Journal of Physics F, vol.2, 1972
[7] R.B. Ross, “Metallic Materials Specification Handbook”, 4th edition, London Chapman & Hall, 1992
[8] L. Meimei et al., “Low temperature neutron irradiation effects on microstructure and tensile properties of molybdenum”, Journal of Nuclear Materials, vol. 376, pp , 2008.
Special thanks to the colleagues from JSI that helped a lot with the irradiation test: Anže Jazbec , Igor Mandic, Vladimir Cindro, and Luka Snoj. Thanks also to the the EP-DT Irradiation Facility team at CERN, Maurice Glaser, Blerina Gkotse and Isidre Mateu; and to the team in EPFL-EDLAB, Chiara Rossi and Jacopo Bronuzzi.
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