Small Dosimeter based on Timepix device for International Space Station

AbstraktAbstract

The radiation environment in space is different, more complex and intense than on Earth. Conventional devices and detection methods used nowadays have poor resolving power and narrow dynamic range. The reason is that most of the dose comes from energetic cosmic rays in the form of heavy ions, mainly protons, that are not present on the ground. The Timepix detector possesses suitable properties for measurements of such mixed radiation field. It is a position sensitive pixelated detector (300 μm thick silicon sensor, 256x256 square pixels with 55 μm pitch) developed at CERN in a frame of the Medipix collaboration and provides capability to visualize tracks of single particles. Measuring track of particles and their deposited energy allows us to distinguish different particles. This information can be used for sorting the particles into different categories. It is possible to distinguish light charged particles such as electrons or heavy charged particles such as ions. Moreover, the Linear Energy Transfer (LET) for charged particles can be determined. Each category is assigned a quality factor corresponding to the energy a particle would deposit in human tissue. By summing the dose of all particles an estimate of the total dose rate can be calculated. For space dosimetry purposes a miniature device with Timepix detector and custom made integrated USB based readout interface has been constructed. The entire device has dimensions of a USB flash memory stick. The whole compact device is connected to a control PC and run continuously. The PC runs a software that controls data acquisition, adjusts the acquisition time adaptively according to the particle rate, analyzes the particle tracks, evaluates the deposited energy and LET and visualizes in a simple display the estimated dose rate. The performance of the device will be tested during a mission on International Space Station planned towards the beginning of year 2012.

The radiation environment in space is different, more complex and intense than on Earth. Conventional devices and detection methods used nowadays have poor resolving power and narrow dynamic range. The reason is that most of the dose comes from energetic cosmic rays in the form of heavy ions, mainly protons, that are not present on the ground. The Timepix detector possesses suitable properties for measurements of such mixed radiation field. It is a position sensitive pixelated detector (300 μm thick silicon sensor, 256x256 square pixels with 55 μm pitch) developed at CERN in a frame of the Medipix collaboration and provides capability to visualize tracks of single particles. Measuring track of particles and their deposited energy allows us to distinguish different particles. This information can be used for sorting the particles into different categories. It is possible to distinguish light charged particles such as electrons or heavy charged particles such as ions. Moreover, the Linear Energy Transfer (LET) for charged particles can be determined. Each category is assigned a quality factor corresponding to the energy a particle would deposit in human tissue. By summing the dose of all particles an estimate of the total dose rate can be calculated. For space dosimetry purposes a miniature device with Timepix detector and custom made integrated USB based readout interface has been constructed. The entire device has dimensions of a USB flash memory stick. The whole compact device is connected to a control PC and run continuously. The PC runs a software that controls data acquisition, adjusts the acquisition time adaptively according to the particle rate, analyzes the particle tracks, evaluates the deposited energy and LET and visualizes in a simple display the estimated dose rate. The performance of the device will be tested during a mission on International Space Station planned towards the beginning of year 2012.