2 Channel Digitizer with Detector Bias Supply
pulse height histograms,
FemtoDAQ instruments support particle physics experiments and measurement systems in research, education and industry. The instruments are easy to use with an excellent price / performance ratio.
An illustrative example is presented and discussed on the Cosmic Ray Net website. You will find many details there, such as FemtoDAQ data analysis and techniques of random background reduction. Please have a look!
FemtoDAQ development was supported by the Department of Energy Office of Science (Nuclear Physics) under the SBIR-STTR grant number DE-SC0013144.
The FemtoDAQ LV-2 is a compact, low cost data acquistion system. It uses a Linux based computer module for control. It provides two digitizer channels, logic I/O for connecting to external devices and a detector bias supply for use with silicon photomultiplers, PIN diodes, and other similar detectors.
Signal inputs and outputs:
Data capture, processing, and recording:
Computer interfaces and programming:
This photograph demonstrates the size and the weight of the unit. We shipped the first batch of the FemtoDAQ units to our distributor!
This photograph shows five units prior to shipping.
This photograph shows four units (A) prior to fitting the enclosures. One unit in the back (B) is powering the accessory board (C) with a 2x2 array of silicon photomultipliers.
While working on the hardware, we are also putting the final touches on the user interface. The photographs compare the GUI screens running in parallel on Windows 7 and on Ubuntu. Can you see any differences? No? That is the whole point! Our FemtoDAQ GUI is fully compatible with both Windows and Linux.
In addition to the regular graphical user interface, we also provide the scripting interface which is more convenient for long running experiments like the cosmic ray measurement shown below. This experiment hunted for the rare cosmic ray decay events for three days. The progress of the data recording was shown in the left computer window which printed a status message every hundred events. The typical mu-meson decay events are shown on the right. The "power users" will appreciate the powerful scripting capabilities which are offered by the FemtoDAQ software library.
Abstract:A simple board with four 6 mm silicon photomultipliers (SiPM) has been designed. Two such boards were attached to a piece of plastic scintillator and tested with a low-cost, two channel digital data acquisition FemtoDAQ system. The FemtoDAQ was used to bias the SiPMs, digitize the SiPM signals, and record the waveforms, histograms, and event files to disk. The test was performed in less than a day thanks to the utmost flexibility of the FemtoDAQ system.
PDF: Application Note SK001
One possible way of using FemtoDAQ is shown below. The silicon photomultiplier test board (A) is powered and biased with the ribbon cable (B) whose other end (C) is plugged into the FemtoDAQ unit. The scintillators (D, E) are mounted on the SiPMs. The SiPM signals are looped with coaxial cables (G) to the preamplifiers (H). Two cables (I) carry the pulses from the preamplifiers to the FemtoDAQ inputs. During the measurements the test board is enclosed in a cardboard box (J) painted black inside and covered with black cloth (not shown).
The photograph shows that the photosensors, the temperature sensor, and the preamplifiers are powered from the FemtoDAQ. The temperature sensor is read with the ribbon cable using the SPI protocol. We used this test setup to perform the measurements shown below.
We will now explore event recording with the FemtoDAQ. We measured the timing between two 6x6 mm silicon photomultipliers manufactured by SensL. Both SiPMs were coupled with optical grease to a single piece of the BC400 plastic scintilator (E). We put a small piece of a gas lantern mantle in front of the scintillator. The mantle contained a small amount of natural Thorium which emitted alpha particles. The particles produced flashes of light in the scintillator. Our objective was to measure the timing between two SiPM signals induced by a single flash of light.
The cathode signals from both SiPMs were amplified 10x with the opamps (H) and digitized with two FemtoDAQ channels which self-triggered on SiPM pulses. We recorded 100,000 events in a list-mode event file. Each event consisted of two correlated, ten-microsecond waveforms from both SiPMs. We processed the event file offline.
The figure shows the timing between two SiPMs extracted from the recorded event file. The timing improves when the signals grow larger, as expected from the photon counting statistics. The root-mean-square deviation ~450 picoseconds was observed at the pulse height of ~300 mV, spanning only ~15% of the available input range.
FemtoDAQ can accumulate pulse height histograms in real time. The measurement was performed with a 1x1x1 cm CsI(Tl) crystal (D) optically coupled to a single 6 mm SiPM device from SensL. The geometrical light collection efficiency was limited to ~36% by the size of the SiPM. The SiPM cathode signal was amplified 10x with the opamp (H) and digitized with one FemtoDAQ channel. A weak 22Na source was used to irradiate the crystal. The pulse height was used to increment a histogram in real time without recording the events to a file. The pulse processing was performed by the instrument at 2335 counts per second. The count rate was limited by the low source activity and the small size of the crystal.
The figure shows the pulse height histogram with the horizontal axis scaled in energy units. The positron annihilation peak is clearly visible at 511 keV. Its resolution is limited by the poor light collection efficiency due to the mismatch between the crystal and the light sensor. The 1,274 keV peak is clearly discernible despite the small size of the scintillator.
These measurements are now extensively presented and discussed on the Cosmic Ray Net website. You will find many details there, such as data analysis and techniques of random background reduction. Please have a look!
FemtoDAQ can process any signals, including those from classic vacuum photomultipliers (PMT) which are often employed with NaI(Tl) crystals to detect ionizing radiation. In order to demonstrate this application we performed a "classic" cosmic ray experiment. At sea level the cosmic rays consist of mu-mesons arriving at the rate of about one mu-meson per square cm, per minute. Most mu-mesons penetrate and then leave the detector. Such "punch-through" mesons produce single pulses during their passage. Once in a while a mu-meson will come to rest within the detector volume. The stopped meson will decay into an electron and a neutrino after spending a few microseconds within the detector. Such events produce two pulses in sequence. The first pulse is induced when the mu-meson hits the detector. The subsequent pulse is produced when the mu-meson decays.
We used a 3 by 4 inch NaI(Tl) crystal as an active volume for the mu-meson capture. The detector consisted of the crystal coupled to a vacuum phototube (PMT) enclosed in the metal pipe behind the NaI(Tl) crystal. We biased the tube with +1,200 volts from the HV supply and connected its output to one FemtoDAQ channel. FemtoDAQ was programmed to select double pulses in the ADC data stream. FemtoDAQ recorded 849 mu-meson decay events in its internal solid state storage during three days of running. Two such events are shown below. In both recorded waveforms the first pulse was generated when the mu-meson dissipated its kinetic energy in the crystal before it stopped. The second pulse was created by the electron emitted from the decay of the mu-meson. The "time interval" between the pulses reflects the life time of the mu-meson within the detector volume.
We processed the waveforms from the file and histogrammed the time intervals between the leading edges. The histogram clearly shows the expected decay pattern of the cosmic mu-meson. The exponential fit to the decay curve yielded a time constant tau = 1.9 microseconds, consistent with the literature value of 2.2 microseconds. The drop of the histogram towards zero below 0.6 microseconds was due to the difficulty of identifying the second pulse edge when it partly overlapped with the first one. Such superimposed pulses could not be identified by the real time edge detection algorithm.
After completing the NaI(Tl) measurement we started a similar measurement with a detector composed of fast plastic BC412 coupled to Hamamatsu R6233. Both the detector and the HV / signal splitter box were supplied by iRad Inc (email@example.com). The legend: A. HV / signal splitter box. B. HV supply. C. FemtoDAQ. D. Plastic detector. E. FemtoDAQ control.
The first double-pulse waveform collected with this detector is shown below. Next to it we are showing the same waveform expanded around the baseline. The RMS noise is about a single LSB, which is close to the hardware limit of the ADC chip. The pulse shape is excellent, without any indication of the overshoot following the trailing edge.
The measurement with BC412 was started on Friday Feb/05/2016. After five days of running we reached the following result.
We collected the following statistics of events.
Total processed events= 3,512,000, waveforms written to disk= 8551, waveforms with multiple pulses= 1531.
After fitting the time histogram shown above, we found 554 muon decays (the integrated exponential part of the histogram).
The fraction of "true decay" / "all double" = 554 / 1531 = 36%.
The fraction "true decay" / "all events" = 554 / 3512000 = 1.577e-4.
These measurements are further discussed on the Cosmic Ray Net website. You will find many details there, such as data analysis and techniques of random background reduction. Please have a look!
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