Space radiation detectors get personal
The personal radiation dosimeter system is made up of two parts: a phone-sized Mobile Unit, worn in a pouch on the astronaut’s body, and a Personal Storage Device, which is a docking station to recharge the Mobile Unit, download data and transmit it back to Earth.
Left, a mobile unit, and right the docking station.
Measuring 93x58x17mm, the mobile unit is specified to operate in excess of a week on one battery charge (10.5 days nominal) and can display the astronaut ID, the mission dose and the dose rate. It has recently returned from testing on the International Space Station, and in a world-first event, it actively monitored radiation during its launch into space on board the Soyuz spacecraft. The system was developed as a result of the EuCPAD (European Crew Personal Active Dosimeters) project.
A small team at Cork’s Tyndall National Institute led by Dr. Aleksandar Jaksic of Tyndall’s Devices and Systems for Radiation Dosimetry, in close co-operation with the institute’s semiconductor fabrication plant, developed, fabricated and supplied three of the four different types of radiation sensors that make up the mobile unit. Each sensor covers a different type or spectrum of radiation to give a comprehensive picture of the radiation environment in space, which is more complex and harder to measure than that on Earth.
The EuCPAD allows researchers to know at all times what the radiation level is and compare them to radiation received in different modules of the space station as well as look at the effects of a Solar Particle Events for example.
"Currently astronauts use radiation detection devices that are passive and only get analysed on their return to tell them what radiation dose they received. If a catastrophic radiation event happens, like a solar flare, they will not know about it in time to protect themselves and hide in more shielded modules of the ISS.
But this device, which can be worn in a pocket, shows the radiation levels in real time and can alarm astronauts if the dose goes above a certain threshold. In addition, it enables a time resolved personal radiation record for each astronaut", explained Dr. Jaksic.
"Designing the general concept of the instrument was the first challenge, as it needed to fully cover a complex radiation spectrum in space. For this reason, the MU comprises four sensors (thick silicon diode, thin silicon diode, Instadose, and RADFET).
Then the sensors needed to be made to stringent requirements, including very good control of design parameters (junction depth/capacitance), low noise (leakage current), and repeatability [this was Tyndall’s main responsibility]. The next challenge was comprehensive characterisation in the variety of radiation fields. Finally, system integration and tests to ESA/ISS standards were the last very demanding step", continued Jaksic by email.
On top of a RADFET wafer, the RADFET chips designed at Cork’s Tyndall National Institute.
For the research centre, the next step could be to apply the developed technologies and concepts to dosimetry in terrestrial applications, such as radiation workers’ health and safety, personal dosimetry for first responders or the general population, and possibly the design of miniaturised radiation detectors built in mobile phones, or as wearables.
“Tyndall will be actively pursuing these goals with the RADFETs and diodes developed during EuCPAD”, concluded the researcher.
Participants to this European Space Agency-sponsored collaborative project also included the German Aerospace Centre (DLR, project co-ordinator), RADOS/Mirion of Finland, Seibersdorf Laboratories of Austria, and PTB of Germany. The radiation monitor will be placed permanently on the ISS in June 2016.
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