Minipix TPX3 Telescope
Advacam’s MiniPIX TPX3 Telescope camera is an arrangement of the two timepix3 detectors stacked in layers equipped with either Si or CdTe sensors of various thicknesses (up to 2 mm CdTe). Each timepix3 pixel measures the energy deposited by particle and time of arrival (1.5 ns precision). The combination of Silicon and thick CdTe layer can be advantageous for the construction of Compton camera optimized for low energies of gamma rays. Modules are internally synchronized: They use the clock frequency and shutter signal derived from one common master. Both modules are connected to the DAQ computer(s) each via own USB2.0 Micro-B connector. The USB hub can be used to aggregate these two lines. The power consumption of the whole device is 2.6 W.
Description
Mijnipix TPX3 Telescope has applications in space for monitoring of cosmic rays (so called space weather). The development is performed in tight collaboration with several partners including ESA (European Space Agency) and NASA.
There are several additional application fields:
- Energetic hadron beams (e.g. for hadron therapy): Monitoring of secondary radiation (monitoring of treatment procedure).
- Fast/slow neutrons with background suppression: The neutron converter can be interlaced between layers the anti-coincidence technique is used to separate proton background from neutron signal.
- Observation of rare decay modes (detectors in face-to-face geometry).
- Double layer Compton camera for gamma rays.
The measured directional distribution can be visualized using such spherical mapping. The logarithmic intensity (flux) is shown as color.
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Sensor Material: Si or CdTe
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Sensor Thickness: 100 μm, 300 μm and 500 μm for Si; 1 mm and 2 mm CdTe
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Sensitive Area: 14 mm x 14 mm
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Time Resolution: 1.6 ns
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Readout Speed: 2.35 Million hits/s
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Frame rate: 16 fps
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Number of Pixels: 256 x 256
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Pixel Pitch: 55 μm
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Energy Resolution: 0.5-1 keV (Si) and 1.1-3.6 (CdTe)
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Min Detectable Energy: 3 keV (Si) and 5 keV (CdTe)
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Readout Chip: Timepix3
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Pixel Mode of Operation: Time-over-Threshold, Time-of -Arrival
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Connectivity: µUSB 2.0
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Weight: 30 g
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Dimensions: 80 mm x 21 mm x 14 mm
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Software: Pixet Pro
Device parameters
Operating conditions
| Symbol | Parameter | Min | Typ | Max | Units | Comment |
| TA | Temperature Range | 0 | 50 | 70 | °C | |
| Φ | Humidity | 0 | 55 | 60 | % | Not condensing |
Electrical Specification
TA = 25°C, USB voltage VCC = 4.8V| Symbol | Parameter | Min | Typ. | Max | Units | Comment |
| VCC | Supply Voltage | 4.0 | 5.0 | 5.5 | V | Comply with USB 2.0 |
| ICC | Supply Current | 300 | 500 | mA | Comply with USB 2.0, Mode dependent | |
| P1 | Power Dissipation | 2.5 | W | |||
| Bias Voltage Source for Sensor Diode | ||||||
| VBIAS | Bias Voltage (positive version) | 3 | 450 | V | Max. limited internally according to sensor type | |
| VBIAS | Bias Voltage (negative version) | -4 | -450 | V | With CdTe or CZT sensor | |
Performance characteristics
| Symbol | Parameter | Min | Typ. | Max | Units | Comment |
| ff | Frame-rate | 16 | fps | with USB 2.0 Host | ||
| TFREAD | Frame Readout Time3 | 62 | ms | |||
| fp | Pixel type hit-rate in ToT+ToA mode (pixels per second) | 2.35 x 106 | pps | with USB 2.0 Host |
Pixel mode hit-rate measurement
The whole detector is exposed to homogenous perpendicular irradiation from X-ray tube operated at 18 kVp with 2 mm Aluminum filter. The measurement type is set to “Pixels” and mode to “ToT+ToA” all other parameters are set to factory defaults (as stored in configuration file delivered with device). The exposure time is set to 0.1 s. The “Clustering” tool of PiXet-Pro is used to analyze measured data. The number of hit pixels per second is drawn as function of X-ray tube current searching for saturation.
Sensor parameters
TA = 25°C| Symbol | Parameter | Si | CdTe | Units | Comment | ||||
| Thickness | 100 | 300 | 500 | 1000 | 1000 | 2000 | µm | ||
| Minimum energy threshold | 2.0 – 2.7 | 2.0 – 2.7 | 2.0 – 3.0 | 2.0 – 3.0 | 2.5 – 4.5 | 3.0 – 5.0 | keV | ||
| σ Thl@60 | Energy resolution in ToT mode (σ @ 60 keV) | 1.2 – 2.6 | 1.3 – 2.7 | 1.4 – 3.5 | 1.7 – 3.6 | 2.8 – 5.4 | 2.9 – 8.3 | keV | |
| σThl@122 | Energy resolution in ToT mode (σ @ 122 keV) | 3.4 – 6.0 | 4.5 – 9.9 | keV | |||||
| Typical detectable energy range for X-rays | 2.0 – 60 | 2.5 – 500 | keV | See chart below | |||||
| Pixel size | 55 | µm | |||||||
Basic principles, measurement types and modes
The ionizing radiation particle interacts with the sensor material creating an electric charge. This charge is collected by electric field and brought to pixel preamplifier where it is amplified and shaped forming triangular voltage pulse. The amplitude and duration of this pulse is proportional to energy deposited by particle within the pixel. The situation when the voltage pulse amplitude in particular pixel exceeds preselected threshold value is called “event” or “hit”. Each pixel contains three digital counters (10, 14 and 4 bits). These counters are used differently according to measurement type and mode. There are four basic values which can be measured and stored in counters of each pixel:Measurement modes:
| Number of Events | number of events (hits) in the pixel during exposure time (this mode is suitable mainly for frame type readout) |
| Time-over-Threshold (ToT) | measured as number of periods of 40 MHz clock signal (25 ns step) when amplifier output signal stays over the energy threshold. The ToT can be transformed to energy in keV using per-pixel-calibration function. The coefficients for per-pixel-calibration are unique for each detector pixel and they are stored in configuration file delivered with device. The energy calibration is valid only for given values of other detector parameters as delivered in configuration file (especially threshold) |
| Time-of-Arrival (ToA) | number of periods of 40 MHz clock signal (25 ns step) from start of exposure till the event is registered by pixel (i.e. pulse in pixel crosses the threshold). The range is 409.6 µs. Additional 16 bits are added in FPGA in readout electronics so that the total range is 26.8 seconds. The additional bits are usable only if the pixel hit rate is below maximal value (see fp in table of Performance characteristics) |
| Fast-Time-of-Arrival (FToA) | time difference between event detection and next clock signal measured with step of 1.5625 ns. Range is 4 bits. The combination of ToA and FToA gives precise time of event detection in nanoseconds using following formula: Time [ns] = ToA*25 – FToA*1.5625 ToA and FTOA are combined together by software. If saved then ToA and FToA are stored as separate items |
Measurement types:
| Frame type measurement | No data is sent out of device during the exposure time. All measured events are accumulated in counters of pixels. Event counter is incremented and ToT is integrated for all events. The measured data is read-out after end of exposure time for all pixels with nonzero content. No measurement can be performed during readout process. |
| Pixel type measurement | Information about all hit pixels is read-out immediately and continuously during exposure time. If hit rate is below maximal value (see fp in table of Performance characteristics) then there is virtually no deadtime. |
Major modes and types of operation (rarely used combinations are shown with gray background):
| Type | Mode | Range | Description |
| Frame (reading all pixels after end of exposure) | Event+iToT | 10 bit + 14 bit | 2 output frames per exposure: 1st Events = Number of events in pixel, 2nd iToT = total time over threshold for all events in pixel. |
| iToT | 14 bit | 1 output frame: iToT = total time over threshold for all events in pixel. | |
| ToA | 18 bit | 1 output frame: ToA+FToA1 = Time of Arrival of first event in pixel. | |
| Pixel (reading only hit pixels continuously during exposure) | ToT+ToA | 10 bit + 18 bit | 4 numbers per pixel per event: Position, ToT, ToA and FToA. |
| ToA | 18 bit | 3 numbers per pixel per event: Position, ToA and FToA1 defined.. | |
| Only ToT | 10 bit | 2 number per pixel per event: Position and ToT. |
Device description
| The device is supplied with USB flash disk containing installer of PiXet-Pro software, unique device configuration and calibration file and protocol on quality tests. The device casing is made of aluminum with sliding cover made of stainless steel protecting sensor window. The communication and powering is provided by USB Micro-B connector and cable. |
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USB connector
USB type Micro-B, Standard USB 2.0 High-Speed.
1 ToA and FToA are combined together by software automatically. If saved, ToA and FToA are stored as separate items (for Pixel type measurement).
