Welcome to Gamma Spectroscopy’s documentation!¶
Introduction¶
This is a data acquisition app for gamma spectroscopy. The Qt app requires a 5000-series PicoScope (e.g. the 5242D) for data acquisition.
A GUI for gamma spectroscopy using a PicoScope¶
Introduction¶
This is a data acquisition app for gamma spectroscopy. The Qt app requires a 5000-series PicoScope (e.g. the 5242D) for data acquisition.
Gamma spectroscopy of nuclear sources is commonly performed using either custom hardware (somewhat cheaper, easier to use, but less versatile) or modular hardware like NIM-crates (more expensive, harder to use, but more versatile). For the undergraduate physics lab at the Vrije Universiteit Amsterdam and the University of Amsterdam we require the versatility of modular hardware, but would like the ease-of-use of custom solutions. This way, students can focus on their research instead of working through a bunch of manuals.
Typically, a gamma detector (e.g. a NaI-scintillator/PMT or HPGe-detector) is connected to an amplifier which is connected to a multi-channel analyzer (MCA). Proprietary software must be used to read out the MCA. For more elaborate setups, a single-channel analyzer or pulse shaper is added to the mix. This can easily result in a time-consuming quest to find the cause of a very common situation: “it doesn’t work.”
We’ve decided to replace all NIM modules with a single PicoScope device. This is a digital oscilloscope which is connected over USB to a PC or laptop. Using the SDK it is easy to interface with the device and to write custom software for use by our students.
Screenshot of the GUI showing a plot of the gamma spectrum of a nuclear source (sodium-22, black line). Another detector at the opposite side of the source picks up coincident annihilation radiation gammas.
Installation¶
In this section we will cover the installation of the gamma-spectroscopy package as well as the prerequisites (see below). On Windows, first make sure that the Anaconda distribution is installed and run all command-line commands from the Anaconda Prompt application.
Prerequisites¶
- PicoSDK
- Python wrappers for PicoSDK
- NumPy
- PyQt5
- PyQtGraph
To install the PicoSDK C libraries, follow the instructions at https://github.com/picotech/picosdk-python-wrappers. To install the wrapper itself, you can follow the instructions at that page or simply install from GitHub (you need to have Git installed):
$ pip install git+https://github.com/picotech/picosdk-python-wrappers
To install NumPy and the Qt5 packages you can use e.g. pip or conda, depending on your current Python setup. For example, using conda:
$ conda install numpy pyqt pyqtgraph
Gamma-spectroscopy¶
You can install the latest release of this package directly from PyPI:
$ pip install gamma-spectroscopy
or, alternatively, you can install the latest development version from GitHub:
$ pip install git+https://github.com/davidfokkema/gamma-spectroscopy
Running the application¶
You can start the application GUI directly from the command-line (On Windows, first start the Anaconda Prompt application to get to the command-line):
$ gamma-spectroscopy
We will look into ways to include gamma-spectroscopy in Anaconda Navigator or as a stand-alone application so you don’t first have to start a console.
User Guide¶
This is, for now, a very short overview of the software.
Connecting the hardware¶
Set up your detector. You can connect your detector to channel A on the PicoScope. Connect the PicoScope to a USB 3.0 port on your computer. That’s it!
Using the software¶
Screenshot of the GUI showing a plot of a gamma detection from a nuclear source (sodium-22). The green guides show the instant of triggering (vertically) as well as the trigger level (horizontally). The purple guides show the measured pulse height and the blue guide shows the measured baseline.
Screenshot of the GUI showing a plot of the gamma spectrum of a nuclear source (sodium-22, black line). Another detector at the opposite side of the source picks up coincident annihilation radiation gammas. The green guide on the left shows the trigger level and the purple guide shows the minimum pulse height which can be reliably detected (due to baseline shifts). On the right, the red line shows the maximum pulse height which can be detected due to clipping at the upper range of the PicoScope. If you want to adjust the clipping level, change range and offset values accordingly.
Taking data¶
The data acquisition process is controlled using the three buttons in the lower left corner of the window.
- Clear
- Clear all events from memory and start over.
- Single
- Take a single measurement from the detector. You can use this to step through a few detections to get a feel for the shape of the signal.
- Start/Stop
- Start or stop a data acquisition run. Data acquisition will run for the amount of time specified on the right under Run duration and then stop automatically.
Settings¶
The Event plot window shows the range of the signal that can be accurately sampled. Try to fit your signals of interest just inside the window for maximum accuracy.
- Range
- Specify the voltage range for the events of interest. If you a value which is too large, you can hardly see any events and they will not be accurately sampled. If you choose a value which is too low, many events will overflow.
- Offset
- You can shift the baseline of the signal in either direction to make more room for the signals you’re interested in.
- Enable trigger
- When enabled, the hardware will only detect events above a certain threshold.
- Trigger threshold
- Signals must cross this threshold to be detected. In other words, the pulse height must be greater than this value.
- Trigger on
- Specify the hardware channel of the PicoScope which will be used for the trigger.
- Pulse polarity
- If the detector outputs negative pulses, specify negative polarity to correctly trigger on the signals and analyze their pulse height.
- Timebase
- A low value means taking a very short time between samples. Thus, the signal is more accurately sampled in time. Keep in mind, however, that taking a large number of samples per event in the case of a high event rate will result in application freezes. Adjust this value in steps to avoid a freeze.
- Pre-trigger window / post-trigger window
- When taking data, the PicoScope will process events internally in a buffer. For each event, a small amount of data will be transferred to the computer. The amount of data is controlled in terms of the duration of the event. The pre-trigger window is the time window before the trigger that will be included. The post-trigger window specifies the amount of time after the trigger occurred. If you want to use a very short sampling time you can keep these values low to restrict the number of samples.
- Number of captures
- When this value is larger than 1, the PicoScope will lock up until this number of events is detected and only then send data to the computer. This will generally result in a bit shorter dead time and in some cases lower CPU usage. Shorter dead time means that after detecting an event the hardware is quickly ready to detect another. If the dead time is too large, you will lose events.
- Baseline correction
- For each event, the value of the pulse height is adjusted for the baseline level, which may shift a bit during the data run. This generally results in more accurate measurements.
- Show Channel A / Show Channel B
- Enable or disable the PicoScope channels.
- Upper threshold (SW)
- If signals cross this level on the trigger channel, the entire event is discarded. In other words, the signal must stay below this threshold. It works almost exactly as an upper trigger threshold. The difference is that this `trigger’ is implemented in software, and that the baseline correction is performed on the data before applying this trigger. This makes it easy to select the upper threshold based on data in the spectrum plot since baseline fluctuations are eliminated.
- Enable upper threshold
- When enabled, the software will only detect events below a certain threshold.
- Lower level discriminator / Upper level discriminator
- In the Spectrum plot window, hide data outside the discriminator levels. Note that the data is not actually discarded. If you change the levels, hidden data can become visible again. This is in contrast to the threshold levels.
- Histogram bins
- The number of bins in the histogram. This value can be adjusted during and after taking data, without loss of the original pulse height values.
Exporting data¶
The spectrum shown onscreen can be exported using File -> Export spectrum.