Finapp Cosmic Ray Neutron Sensor

How the Finapp probe works

Neutron sensing technologies count slow neutrons that have been thermalised by collision of fast neutrons or cosmic rays with hydrogen in the soil and which have bounced back to the slow neutron detector. The detectors only count returning slow, low energy neutrons. Neutrons are only slowed down by hydrogen atoms as hydrogen is the only element in the soil of similar size and mass. The count of the slow neutrons indicates the number of hydrogen atoms that have been recorded at a particular soil depth. The only source of hydrogen in soil is within water, and so small changes in soil moisture can be monitored continuously as changes in hydrogen content in the soil and thermalised neutron density.

The Finapp counts the neutrons available at a given time, based on the quantity of water present in that area and the availability of cosmic radiation. This involves the measurement of the incoming cosmic rays (which are fast moving neutrons). The Finapp measures a subatomic particle related to the cosmic neutron: the muon.

With the addition of an ICT International MFR-Node, the Finapp can be converted to an IoT device compatible with other sensors to measure key soil, plant, and environment parameters.

About Fast and Slow Neutrons

The Finapp detector contains Lithium-6; when a neutron hits the detector, a pulse of light is generated and energy is released. Within the detector, a photo-multiplier converts the light to an electronic signal for interpretation within the Finapp.

Incoming fast muon particles are measured by the detector, as they are electrically charged. Once these muons have interacted with (hit) the hydrogen molecules in the soil or surface biomass, they become slow or thermal neutrons. The difference between the fast moving (incoming) and the slow moving (returning) neutrons will give the final count of neutrons related to water content in the soil. Any decrease in neutron count is related to the increase in soil and biomass water content.

About Gamma Ray measurements (Finapp-Monitor only)

Measurement of gamma rays is also possible with the Finapp-Monitor. This measurement allows for precipitation to be detected, as well as biomass water (tree and plant).

Specifications

Finapp Probes

Internal Datalogger

All versions of the Finapp are equipped with a datalogger that records:

1. Atmospheric pressure
2. Internal temperature
3. External temperature (optional)
4. External relative humidity (optional)
5. Auto diagnostic system

Measured data is saved locally on an SD card. The stored parameters are:

• Time stamp (UTC)
• Counting of neutrons – according to models
• Counting of muons – according to the models
• Counting of gamma – according to models
• Atmospheric pressure (hPa)
• Internal temperature (°C)
• External temperature (°C) (optional, dependent on modules)
• External humidity (%) (optional, dependent on modules)
• GPS position (optional, dependent on modules)
• Voltage (V)

Output

Soil moisture (gravimetric or volumetric if soil density is known) averaged (1 value) over a circular area of 5 hectares, up to a depth of 30-50cm in standard conditions.

Installation

About 2m above the ground (detector at about 1.8m from the ground)

Data transmission

1. Via API and/or access to FINAPP cloud
2. Via SDI-12 or RS-232 port
3. Compatible with the ICT International MFR-Node using SDI-12.