Sponsored by Vitrek, LLCReviewed by Maria OsipovaJan 27 2025
PC-based digitizers and digital signal processing software work together to perform multichannel analyzer (MCA) and modular instrumentation functions at a reduced cost.
Introduction
Nuclear and particle physics, almost synonymous with high-energy physics, is an important subfield of experimental physics. A wide range of studies in this domain are classified as scattering experiments, in which an incident particle strikes a target, and the resulting scattered particles are investigated.
Scattering processes may involve the formation or destruction of particles. The modern way to examine scattered particles is to use particle detectors, which detect individual particles that collide with them.
This article overviews the typical devices used to collect data in particle counting applications. It then explains how the GaGe RazorMax Express CompuScope digitizer/oscilloscope can generate and save the data.
The instrument's high-speed data collection and signal processing combination provides an efficient and cost-effective method for conducting particle investigations.
Figure 1. Examples of photo-multiplier tubes, or PMTs. Image Credit: Photo courtesy of Hamamatsu
Gathering Data
Photomultiplier tubes (PMTs) and semiconductor detectors are widely used in modern particle-counting applications. This is an important first stage in particle studies for acquiring data to be examined.
As shown in Figure 1, PMTs are sensitive detectors of light photons that impinge upon their photocathode. When detecting photons, a scintillator material is commonly placed before a PMT.
The scintillator turns subatomic particles into light photons, which the PMT detects. Therefore, the PMT can be used as a detector for a wide range of particles. Many applications use semiconductor detectors (Figure 3) instead of PMTs.
When a particle strikes one of these detectors, an electrical pulse, like that of PMTs, is produced. Pulses can last a few nanoseconds to a few microseconds, and their amplitude is proportional to the particle's incident energy.
Figure 2. The graph depicts a typical negative-polarity sub-microsecond pulse that is output by a PMT. Image Credit: Vitrek, LLC
Analyzing Data
The multichannel analyzer, or MCA, is the primary instrument for PMTs and semiconductor detectors that generate energy proportionate output pulses.
In pulse height analysis (PHA) mode, the MCA presents a histogram (Figure 4) showing the number of particles identified versus pulse amplitude, which is proportional to particle energy.
Figure 4 displays a histogram of the number of pulses (counts) detected at a given amplitude, like those in Figure 2, and is represented as "Channel Number." The image shows a peak slightly below Channel 1500 and an increasing count at lower channels, indicating background noise.
Particle investigations require more flexible and adaptable apparatus than other applications, in addition to complicated processing, such as coincidence detection.
This requirement from nuclear and particle physics sparked the development of modular equipment, which refers to instruments that fit into a platform that provides common electrical power, compactness, and easy connections.
The nuclear instrumentation module (NIM) chassis was an early standardized modular platform, providing common AC and DC power to NIM instrument modules.
Later platform standards, like CAMAC and VXI, introduced digital connection between instrument modules and a host computer, enabling instrument configuration, control, and data recovery. Today's PC, which has PCI Express (PCIe) slots for modular device cards, is derived from modular platforms such as CAMAC.
Figure 3. Example of a semiconductor detector. Image Credit: Leybold
GaGe RazorMax Express Compuscope Advantages
The GaGe RazorMax Express CompuScope digitizer/oscilloscope (Figure 5) performs the same functions as an MCA and standard modular instrumentation but at a reduced cost.
Any possible particle processing method can be run as digital signal processing (DSP) on digital waveform data collected by the instrument's CompuScope.
Figure 4. Diagram of a typical display output from a multichannel analyzer. Image Credit: Vitrek, LLC
Figure 5. Vitrek’s GaGe RazorMax Express Compuscope 161G4. Image Credit: Vitrek, LLC
One significant advantage of the GaGe RazorMax Express CompuScope digitizer/oscilloscope over an MCA or typical instrument module is that it can store all raw particle pulse waveforms. For example, these results could be used to detect and remove multi-pulse events.
The RazorMax Express also offers a distinct benefit for particle experiments: the ability to do "Complex Triggering." In this mode, trigger events from all channels are Boolean "OR"ed to produce the final trigger event.
This way, if a particle enters any of CompuScope’s detectors, it triggers. This method can be extended to include numerous CompuScope boards by linking their Trigger Out and Trigger In connections.
The RazorMax Express may be used with the flagship GaGeScope software. It provides an oscilloscope-like interface where users can control their CompuScope without writing a single line of computer code.
GaGeScope does not provide particle counting display or analysis or control the other devices required for a comprehensive particle counting system.
Instead, GaGeScope offers robust Software Development Kits (SDKs) that let users create their software programs in C, LabVIEW, MATLAB, Python, or almost any other language from the Windows or Linux environment.
Application Example: Digitizer Operation in a Nuclear and Particle System
Consider a user with four PMTs and associated conditioning electronics. The PMTs generate broad pulses roughly 1 microsecond wide, but require the system to be equipped with faster detectors.
The system will be utilized in several trials with various configurations and count rates. The user chose the GaGe RazorMax Express CompuScope 161G4. It has four input channels that will digitize the four PMT signals. More RazorMax Express cards can be added to increase channel numbers.
When an incident particle hits a target, particles enter four detectors positioned at specific angles. These pulses are acquired by the four channels of a RazorMax Express card installed on the host PC.
Data from the four channels is sent to a GPU card for fast processing and reduction. It is then transferred to a custom software application using a Gage Software Development Kit sample program.
At 1000 MS/s, the RazorMax Express captures one sample every nanosecond and can handle pulse widths as small as 10 nanoseconds. The RazorMax's 16-bit vertical ADC resolution enables "Multiple Record Mode," which captures brief records of around 1 microsecond.
Re-arming the RazorMax Express takes less than 1 microsecond and allows count rates of up to 500 kHz. In "Streaming Mode," data is sent directly to the PCIe bus and then streamed into PC RAM.
When sampling continuously on all four channels, the RazorMax Express generates a data stream of 8 GB/s, which is equal to the theoretical maximum Gen 3 X8 PCIe bus. In practice, the user will only acquire half the time, resulting in a maximum data rate of 4 GB/s.
Waveform data can be streamed to a hard drive for later analysis or to a DSP algorithm on the host PC or GPU card. Algorithms can process raw waveform data in real-time to produce the required output. The DSP can be monitored and modified until the desired results are achieved.
In many applications, triggers are created at predetermined times. "Time Stamp" values are used in particle physics studies to calculate inter-particle detection intervals or average count rates.
Time Stamps determine the arrival time of each particle pulse to the nanosecond level. They are added to the end of every Multiple Record waveform in the data stream. The counter frequency can be set to an external 10 MHz reference frequency if absolute timing is necessary.
Figure 6. Atomic particle counting system uses a GaGe RazorMax Express to acquire the detector pulses. Image Credit: Vitrek, LLC
Conclusion
The Gage RazorMax Express CompuScope digitizer/oscilloscope, combined with its sophisticated streaming software and triggering capabilities, enables the user to create a low-cost measuring system for various nuclear and particle studies.
This information has been sourced, reviewed and adapted from materials provided by Vitrek, LLC.
For more information on this source, please visit Vitrek, LLC.
