When engineers and system integrators search for a radioactive detection sensor, the requirements go far beyond simply "detecting radiation." They need a sensor that delivers stable long-term data output, integrates cleanly into existing control systems via standard communication protocols, covers the full spectrum of ionizing radiation types, and ships pre-calibrated — ready to deploy without secondary adjustment on site.
The CESTSEN RAD-S104 Fixed Radiation Sensor Probe is engineered precisely to meet these demands. This guide covers everything procurement engineers, OEM developers, and radiation safety system designers need to evaluate the RAD-S104 for their application.

What Is a Radioactive Detection Sensor?
A radioactive detection sensor is a transducer that converts the energy of ionizing radiation — including alpha (α), beta (β), gamma (γ), and X-ray photons — into measurable electrical signals. These signals are then processed to display dose rate values, trigger alarms, or transmit data to monitoring platforms and control systems.
Radioactive detection sensors are the core sensing element in:

•Fixed radiation monitoring systems for hospitals and clinics
•Online radiation monitoring networks for nuclear facilities
•Industrial non-destructive testing (NDT) environments
•Customs and port inspection infrastructure
•Pharmaceutical cleanrooms and radiopharmacy labs
•Environmental radiation monitoring stations
•Security screening systems

Unlike portable Geiger counters designed for handheld use, fixed radiation sensor probes are built for permanent wall-mounted installation, continuous 24/7 operation, and seamless data transmission to host controllers or cloud platforms.

The Challenge of Choosing the Right Radiation Sensor for System Integration
Many engineers encounter the same pain points when specifying a radioactive detection sensor for a built system:

•Communication compatibility: Does the sensor output RS485 Modbus-RTU? Can it interface with PLCs, SCADA systems, or multi-point monitoring hosts without custom middleware?
•Calibration burden: Is factory calibration included, or does the integrator need to perform complex field calibration before commissioning?
•Ray coverage: Does the sensor detect all relevant radiation types for the application, including alpha particles from surface contamination?
•Alarm integration: Does the sensor have onboard alarm output, or does alarm logic need to be handled entirely by the host controller?
•Longevity and support: Is the sensor backed by a manufacturer with traceable calibration sources and long-term after-sales engineering support?

The RAD-S104 addresses every one of these concerns directly.

Introducing the CESTSEN RAD-S104: Professional Fixed Radioactive Detection Sensor
The RAD-S104 Series Fixed Radiation Sensor Probe is developed and manufactured by Shenzhen WanYi Technology Co., Ltd. under the CESTSEN brand. It is designed as a plug-and-play sensing node for radiation monitoring system integration, featuring a large end-window mica Geiger-Müller counter imported from the United States as its core detection element.
The RAD-S104 is the sensing front-end recommended for use with the CESTSEN GM-R200 Online Radiation Monitoring System host, but its standard RS485 Modbus protocol makes it compatible with virtually any third-party monitoring platform or PLC-based control system.

RAD-S104 Full Technical Specifications

Why a 45mm Large End-Window?
The 45mm detector diameter gives the RAD-S104 a significantly larger active detection area compared to standard pencil-type GM probes. This translates to:

•Higher sensitivity — more radiation events captured per unit time
•Lower statistical uncertainty in count rate measurements
•Faster response to changing radiation levels
•Better performance in low-level background monitoring scenarios

Typical Applications and Installation Scenarios
Hospital Radiology and Nuclear Medicine Departments
Mount the RAD-S104 in X-ray rooms, CT suites, gamma knife therapy rooms, nuclear medicine preparation areas, and radioactive waste storage rooms. The onboard alarm immediately alerts staff if radiation levels exceed safe thresholds, while RS485 output feeds real-time data to the hospital's radiation safety management system.
Pharmaceutical Factories and Radiopharmacies
Facilities handling radioactive isotopes for diagnostic or therapeutic purposes — including I-131, Tc-99m, and F-18 — require continuous area monitoring to protect production staff and meet GMP radiation safety requirements. The RAD-S104's alpha detection capability is particularly valuable for radiopharmacy environments.

Industrial Non-Destructive Testing Facilities
NDT laboratories using X-ray flaw detectors, gamma radiography sources (Ir-192, Se-75, Co-60), or linear accelerators require fixed perimeter monitoring to ensure radiation does not exceed safe levels in adjacent areas during exposure operations.
Security and Customs X-Ray Inspection Systems
Cargo X-ray inspection lanes, vehicle scanning portals, and mail screening systems can be equipped with RAD-S104 probes to continuously verify that radiation levels in operator workstations and adjacent public areas remain within regulatory limits.

System Integration Guide: Connecting the RAD-S104 to Your Platform
Wiring Overview
The RAD-S104 uses a standard 3-wire RS485 connection (A+, B-, GND) plus DC power input (12–24V). Most installations can be completed with standard shielded 4-core cable.
Modbus Register Map
ONETEST Technology provides complete Modbus register documentation, including register addresses for:

-Current dose rate value (μSv/h, mR/h, or CPS)
-Alarm status flags (Level 1 and Level 2)
-Unit selection register
-Sensor status and diagnostic registers

Optional Add-Ons:

-Extended cable lengths (custom)
-GM-R200 multi-point monitoring host
-4G wireless transmission module for cloud connectivity
-ONETEST cloud platform subscription
-External high-decibel sound and light alarm beacon
-OEM branding and custom enclosure colors

Quality Assurance:
Every RAD-S104 unit is calibrated against Co-60 and Cs-137 standard radioactive sources held under ONETEST Technology's radiation safety license, ensuring traceability to national measurement standards.