Instrumentation & Measurement Magazine 23-9 - 39

Fig. 3. Implemented sensor nodes for radiation monitoring. (a) Sensor node based on a Geiger sensor; (b) Air pumping system realized for sensor nodes based on
a silicon detector; (c) Sensor node based on a silicon detector; (d) Sensor node based on a scintillation detector.

that are able to carry out energy-resolved measurements of
gamma ray and alpha particles. In particular, the authors
have investigated the possibility of realizing cost-effective
handheld spectrometer for in-field measurements, whose
performance are close to those granted by traditional laboratory instrumentation. The nodes, currently in the stage of
laboratory prototypes, mostly share the same hardware and
software architecture of the Geiger node; the main difference
consists in the specific sensor exploited to detect the desired
radiations.
A cost-effective windowless silicon (Si) diode (namely,
S3590 Si PIN photodiode by Hamamatsu) was used to develop
the alpha particles spectrometer, while a NaI(Tl) scintillation
radiation detector (namely, 905-3 by Ortec, 2 by 2 inches Crystal) was exploited for gamma ray spectrometry.
With specific regard to the case of alpha particles, the node
exploiting the silicon sensor is equipped with a flushing system able to concentrate atmospheric particulate on a millipore
filter positioned at 1 cm in front of the detector, as shown in
Fig. 3b. This way, the energy loss by the particles along the
path through the air is minimized, thus enhancing the node
sensitivity. One critical issue is the light sensitivity of the silicon photodiode; the drawback has been overcome thanks to
the geometry of the air pumping system implemented in 3D
print technology.
December 2020	

The sensor interface is mandated to carry out the radiation
measurements; in particular, spectrometric measurements
are provided as energy levels histogram of particles or rays
impinging on the detector surface. The sensor interface comprises a sensor conditioning section, mandated to convert the
current pulses provided by the sensors into voltage signals
compliant with the successive microcontroller ADC module;
Fig. 3c shows the actual prototype currently realized, while
Fig. 4 reports the functional block diagram of the conditioning section.
The preamplifier is a low-noise hybrid charge amplifier
that carries out the very first conversion of current into a voltage pulse. It is worth noting that ORTEC 905-3 is equipped
with its own preamplifier section and a voltage divider network for external adjustment of photomultiplier grid potential
to increase performance of scintillation detector (Fig. 3d). The

Fig. 4. Block diagram of the conditioning section for spectrometer nodes.

IEEE Instrumentation & Measurement Magazine	39



Instrumentation & Measurement Magazine 23-9

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