Introduction

In the SiPM-3000 we combine the successful eMorpho design with the ability to directly operate a SiPM-based radiation detector. The SiPM-3000 retains all the powerful capabilities of the eMorpho, including direct waveform sampling at 40MHz for on-the-fly pulse shape discrimination.

While the FPGA is acquiring data the ARM processor controls the SiPM, executes gain and performance stabilization. On top of that it has the resources to provide data processing and exposes a USB interface.

The SiPM-3000 is ideal for high-precision spectroscopy and loss-less histogram acquisition combined with pulse shape discrimination (PSD). Applications are traditional Phoswich detectors and, of course, the newer multipurpose scintillators NAIL, CLLB, and CLYC. In these materials PSD can be used to separate gamma-rays from neutrons.

Construction principle

The detector assemblies have been designed to accommodate crystals from different manufacturers and to allow a replacement of the crystal, either for an upgrade or for a repair. Replacing a crystal is simple enough to be performed in the field, with minimal requirements for tools and training.

The scintillator-crystal itself is hermetically sealed in a thin aluminum housing with a glass window. The encapsulated crystal is mounted inside a removable aluminum cup, which also includes padding to provide a spring load pushing the scintillator against the SiPM and the optical coupling component.

Replacing the crystal only requires to undo 4 screws and remove the cup. Swap out the crystal and screw the cup back into place. Done.

SiPM-3000 Assembly

A user can easily replace the encapsulated scintillator crystal with another of their own choice.

Brief Specifications

• Hardware is suitable for all scintillators
• Energy histogram (on board) 4096 x 32
• Accurate count rate measurements
• Efficient pile up rejection
• On the fly pulse shape discrimination
• List mode: 340 events buffer
• Trace capture: 1024 ADC samples
• Non-volatile memory 4 kByte
• Power: 4.3V to 5.5V, 60mA
• SiPM supply: 39V/1mA DC/10mA surge
• Uses 2N3904 as external temperature sensor.
• USB 1.2 interface compatible with USB 2.0
• On-board ARM software is secure against reverse engineering.
• Open source application programmer's interface; Python API; Data Server >
• wxPython-based graphics user interface for Windows and Linux; Software

Capabilities

SiPM-3000 Standard and Optional Capabilities
Capability	Description
Analog	Operate SiPM-arrays at up to 37V. Direct anode to amplifier coupling for highest signal fidelity and best pulse shape discrimination.
Gain stabilization	The SiPM-3000 can adjust the operating voltage and the digital gain independently as a function of temperature to ensure that both gain and trigger threshold remain constant over temperature. Such a look up table necessarily depends on the scintillator, and developers can program their own tables. A third lookup table can be used in conjunction with LED-based gain stabilization or for custom purposes.
Two-bank counter and histogram	The SiPM-3000 can count pulses in either of two active banks, one for samples to be measured and one for storing a background measurement. In dynamic environments, the two banks can be used to implement loss-less counting: One bank acquires data while the other bank can be read at leisure.
Net counts and histograms	Custom SiPM-3000 embedded software can report background-subtracted histograms and count rates.
High-speed DSP	In the SiPM-3000 the MCA is implemented in an FPGA and its input data stream is the digitized scintillator pulse waveform. As a result, the FPGA can apply pulse shape discrimination in real time. This supports various specialty applications at the highest possible speed and throughput. Examples are phoswiches and neutron/gamma detectors.
Analysis	Custom SiPM-3000 embedded software can report the probability that the measured sample count rate is compatible with the background count rate. Users can set an alarm threshold in terms of probability: Alarm if there is little chance (<ε) that the sample count rate is caused by the measured background.
Dynamic alarming	Custom SiPM-3000 embedded software and FPGA firmware can analyse and report count rates in time slices of 100ms, ie at a rate of 10/s. The device automatically tracks slowly changing backgrounds and will alarm on a passing source. Its digital output can be used to drive an audio or visual alarm.
Communication	The SiPM-3000 implements a USB-2.0 compatible USB 1.2 interface.

Gain stabilization

The SiPM-3000 can use a 20-point lookup table that describes the desired operating voltage and digital gain vs temperature behavior. The embedded processor applies this to counteract the SiPM vs temperature gain drift. Typically, the lookup table starts at lut_tmin=-30°C and increments in lut_dt=5°C steps up to 65°C. However, the developer can configure that to meet their requirements. And the developer can program a lookup table of their own choice into the non-volatile memory of the SiPM-3000.

The developer programming the lookup tables into the SiPM-3000 can set the lut_mode lock-bit to 1. That prevents a user from reading back a proprietary gain-stabilization lookup table.

Time-slice operation

There are dynamic situations, where a radioactive source can be measured only for a brief moment. Examples are a vehicle passing through a radiation portal monitor, or a person with a backpack detector walking past a stationary source.

The time-slice operation supports these cases. When equipped with the appropriate software and FPGA firmware, the SiPM tracks slow changes in the environmental background. An alarm is created when during a summation time (L) of typically 4 seconds, the accumulated counts are significantly more than what is expected from the background. The alarm threshold is defined as the probability that the measured counts (N) during a period L, could have been caused by the established background rate over the same period (B).A threshold of 1.0e-4 means that we alarm when P(Counts ≥ N|BCK) < 1.0e-4.

For example, assume a summation time of 4 seconds and a background rate of 500cps for BCK=2000. Now assume that we count 2500cps in a particular 4s-period. The probability of the established background to cause 2224 counts or more in 4s is P(Counts ≥ 2224|BCK=2000) = 2.86e-7. This smaller than the alarm threshold of 1.0e-4, and the embedded program will generate an alarm.

If the alarm condition is permanent, the software resets all the logic after a period of H time slices and starts counting again. It now will accept the suddenly higher level of radioactivity as the new normal background.

Performance

The SiPM-3000 provides high-quality spectra with a very low energy trigger threshold.

Here we show energy spectra for certain MCA + detector combination.

We emphasize the low-energy behavior by showing a zoom-in on the lower 100keV.

SiPM: 3.24cm²; NaI(Tl): 50×50mm; Premium; Energy Range: 1.6MeV

Typical energy resolution @ 12kcps.

The lower 100keV part of the Cs-137 spectrum, showing the effective trigger threshold of around 8keV.

SiPM: 5.76cm²; NaI(Tl): 50×50mm; Premium; Energy Range: 1.6MeV

Typical energy resolution @ 12kcps.

The lower 100keV part of the Cs-137 spectrum, showing the effective trigger threshold of around 8keV.

Pulse Shape Discrimination (PSD)

The SiPM-3000 has a general purpose built-in method for PSD.

Using summation weights, users can select two classes of pulses.

When PSD is ON, there will be two 2K×32 energy spectra, one for each class of pulse.

When PSD_Select is ON, user can see the internal PSD Value spectrum used to classify the events. Events with a PSD Value < 0 fall in one class, those with PSD Value >0 fall into the second class. Ideally the two classes are well-separated by a gap in the PSD Value histogram.

See the user's manual for details.

SiPM β/γ Phoswich with 50mm NaI and a 3mm plastic scintilator (PVT)

Average pulse shapes for βs (blue) and γs (orange). The number bar shows the values of the summation weights.

β/γ Separation for a weak Sr-90 source and background γ-radiation

PSD value spectrum showing the separation into two classes. We allowed a 5% spill-over of βs into the γ-class, so that the fraction of false βs would be below 0.005%.

Downloads and Pricing

Prices may change without prior notice.

• Flyer: English, 简体中文
• User's manual
• Connector pin outs
• MCA Selection Guide
• Self-extracting Windows driver installer: Version 3.0
• Software and documentation for all MCA wxMCA.zip
• On-line software documentation

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