It has been 22 years since our company, Techno AP, was founded, and we deeply appreciate the support from the radiation measurement industry.

Now, significant advancements such as a wide array of measurement circuits and systems have been developed in the radiation measurement industry.

In particular, the substantial progress in digital measurement circuits, including remote configuration, multi-channel capabilities, and varied cost structures, has been noteworthy.

However, navigating these advancements can sometimes be complex.

As a manufacturer specializing in radiation circuit measurement, we strive to incrementally share valuable insights and information.

Fig.1

We have recently received an HPGe detector (GC1018-7500SL) from Million Technologies Canberra, which will play a crucial role in our ongoing research, development, and pre-shipment inspections.

The previous detector I used, manufactured by PGT (Princeton Gamma Tech), finally became unusable after 15 years of service. Despite multiple repairs that temporarily revived it each time, the latest increase in the leakage current proved irreversible. Even after attempting vacuuming, it failed to regain functionality.

Its longevity surpasses that of other HPGe units, likely due to consistent replenishment with liquid nitrogen since it was purchased.

The HPGe detector visible in the background, an elbow type, operates on a transistor reset mechanism primarily suited for high counting rates.

Typically used for performance evaluations under normal conditions, it contrasts with the more common resistive feedback type, which serves as the mainstream choice.

Fig.2

The GC1018-7500SL detector delivered features a P-type coaxial design with a detection efficiency of 10%. Although its 10% detection efficiency is the lowest in its category, historically it was priced around 1 million yen, but current prices are believed to have risen further. Low detection efficiency indicates a small crystal size and low capacitance, which often results in minimal noise and excellent resolution.

In our applications for research and development as well as shipping inspections, superior resolution holds greater significance than detection efficiency. Efficiency primarily depends on the measuremtent of the detector, whereas resolution is influenced by both the detector and its associated circuitry.

Thus, the radiation measurement circuit's paramount role is to measure signals without compromising the detector's fundamental performance.

The HPGe detector exhibited a resolution of 1.64 keV for 1.33 MeV and 0.708 keV for 122 keV, demonstrating outstanding performance. Previously, the best resolution achieved with a PGT detector was 1.7 keV, which was also considered excellent.

Fig. 3 Amplifier 6μs spectrum

Initially, I assessed the resolution using an analog module. Given the high resolution, the 8k-channel MCA does not provide sufficient resolution. As a result, we have decided to conduct tests using a 16k-channel MCA.

The setup involved the following sequence
HPGe → Amplifier ST6μs (ORTEC 572) → MCA (TechnoAP APG7300D).

The radiation sources used were Am-241, Eu-152, Cs-137, and Co-60. Measurements were conducted over a period of one hour at an approximate counting rate of 1.5 kcps.

Subsequently, I applied the GaussFIT in the MCA(TechnoAP APG7300D) to measure resolution. The results showed a resolution of 0.707 keV at 122 keV and 1.6 keV at 1.33 MeV, demonstrating excellent performance.
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Fig. 4 Comparison of DSP and amplifier pulse shaping

Next, I proceeded to introduce our flagship model APU101 DSP.

This Digital Signal Processor is meticulously crafted with carefully chosen operational amplifiers, A/D converters, and power supplies. Despite my extensive experience, encountering a resolution as precise as 1.6 keV was unprecedented and a significant departure from the precision typically seen with analog methods.

Initially, I began by configuring the risetime. In the oscilloscope display, the top blue waveform represents the preamplifier output, the yellow-green waveform depicts the semi-Gaussian shape from the 572 amplifier, and the purple waveform illustrates the trapezoidal shape from the DSP.

The ORTEC 572 amplifier was configured with a Shaping Time (ST) of 6 μs, but the time from the preamplifier output to the peak of the semi-Gaussian waveform measured approximately 14.1 μs. Consequently, the Risetime for the DSP's trapezoidal shaping was also set to 14.1 μs, with a flat-top duration of 0.6 μs, which is recommended for coaxial-type HPGe detectors, where risetime typically ranges from 0.6 to 0.8 μs.

Fig. 5 DSP15μs spectrum

HPGe to DSP RT15μs（TechnoAP APU101）

Similarly, the measurement utilized Am-241, Eu-152, Cs-137, and Co-60 sources over a period of one hour, achieving a counting rate of approximately 1.5 thousand counts per second (kcps).

Upon measuring the resolution using function fitting (GaussFIT), the results showed 0.672 keV at 122 keV and 1.595 keV at 1.33 MeV. This performance is comparable to analog methods. It's remarkable to see the resolution fall below 1.6 keV. A notable distinction from analog methods is that the DSP exhibits superior resolution particularly at lower energy levels.

Fig. 6 Comparison of DSP and amplifier energy resolution

In the next phase, I plan to explore different scenarios, including high counting rates, shorter ST (risetime), and broader energy ranges. The receipt of the exceptional HPGe detector has significantly boosted my enthusiasm.

Our entire team is committed to enhancing our product offerings. We deeply appreciate your ongoing support.