Finger-Type Ionization Chamber
| Brand | N/A |
|---|---|
| Origin | Beijing, China |
| Manufacturer Type | Authorized Distributor |
| Origin Category | Domestic |
| Model | Finger-Type Ionization Chamber |
| Pricing | Upon Request |
| Energy Range (Photons) | 7.5 keV – 420 keV |
| Maximum Measurement Volume | 17.6 cm³ |
| Nominal Operating Voltage | 400 V |
| Leakage Current | ≤1 pA |
| Chamber Wall Material | Triple-layer polyimide (0.5 mm per layer, density 1.42 g/cm³ |
| Electrode Material | Polyimide |
| Maximum Continuous Dose Rate (99% saturation) | 17 Gy/s |
| Maximum Continuous Dose Rate (99.5% saturation) | 8.5 Gy/s |
| Maximum Pulsed Dose Rate (99% saturation) | 1.18 mGy/pulse |
| Maximum Pulsed Dose Rate (99.5% saturation) | 0.59 mGy/pulse |
Overview
The Finger-Type Ionization Chamber is a precision radiation detection instrument engineered for high-fidelity, real-time measurement of photon beam fluence and dose rate in diagnostic and therapeutic radiology applications. Based on the fundamental principle of gas ionization—where incident photons interact with the fill gas (typically air or nitrogen) to produce electron–ion pairs—the chamber converts charge collection into a quantifiable electrical signal proportional to absorbed dose. Its compact, cylindrical “finger” geometry enables insertion into narrow beam paths, phantoms, or collimator apertures, making it especially suitable for reference dosimetry in linear accelerator (LINAC) output calibration, kV imaging system QA, and small-field beam characterization. Designed for operation at a nominal bias voltage of 400 V, the chamber maintains stable charge collection efficiency across its specified photon energy range (7.5 keV to 420 keV), covering diagnostic X-ray, mammography, and superficial therapy beams.
Key Features
- Optimized wall construction using triple-layer polyimide (0.5 mm per layer, total areal density 21.3 mg/cm²) ensures near-tissue equivalence for photon energies below 100 keV while minimizing energy-dependent over-response.
- 17.6 cm³ sensitive volume provides sufficient signal-to-noise ratio for low-dose-rate measurements without compromising spatial resolution in confined geometries.
- Leakage current ≤1 pA guarantees minimal baseline drift and high measurement stability during extended acquisitions—critical for compliance with IEC 60731 and AAPM TG-51 protocols.
- Robust saturation performance: achieves 99% charge collection efficiency up to 17 Gy/s under continuous irradiation and tolerates pulsed beams up to 1.18 mGy per pulse—enabling use in both conventional radiotherapy and emerging ultra-high-dose-rate (FLASH) beam characterization studies.
- Polyimide electrodes eliminate metallic components from the sensitive region, reducing perturbation effects and improving long-term calibration stability under repeated irradiation.
Sample Compatibility & Compliance
This ionization chamber is intended for use with standard electrometers compliant with IEC 61674 (medical X-ray systems) and IEC 60731 (radiation therapy dosimetry equipment). It meets dimensional and electrical interface requirements for integration into water phantoms, solid phantoms, and beam-line fixtures used in routine QA and commissioning. While not intrinsically certified to ISO/IEC 17025, the chamber is supplied with a traceable calibration certificate (NIM or equivalent national metrology institute) valid for one year from date of issue. Its design supports adherence to key regulatory frameworks including AAPM Task Group reports (TG-51, TG-61, TG-191), IAEA TRS-398, and EN 61267 for diagnostic reference dosimetry.
Software & Data Management
The chamber operates as a passive transducer and requires connection to a compatible, calibrated electrometer (e.g., PTW Unidos, IBA Dosimetry Razor, or Standard Imaging MAX). No proprietary software is bundled; however, raw charge output (in pC or nC) is fully compatible with industry-standard dosimetry platforms—including OmniPro-I’mRT, SNC Patient, and MATLAB-based analysis pipelines—that support manual or automated correction for temperature, pressure, polarity, recombination, and beam quality. Electrometer firmware must support pulsed-mode recombination correction algorithms (e.g., two-voltage analysis per IAEA TRS-398 Annex III) to ensure accuracy under non-continuous irradiation conditions. Audit trails and calibration metadata can be maintained in accordance with GLP/GMP documentation practices when integrated into validated QA workflows.
Applications
- Reference dosimetry for kV X-ray units (diagnostic radiography, fluoroscopy, CBCT).
- Output factor and profile measurements in small-field stereotactic radiosurgery (SRS/SBRT) beamlines.
- Beam quality verification (HVL determination) per IEC 61267.
- Commissioning and periodic QA of orthovoltage and superficial therapy units.
- Characterization of pulsed and modulated beams where recombination effects must be rigorously quantified.
- Research applications involving mixed-field environments when combined with appropriate filtration and correction methodologies.
FAQ
What is the recommended electrometer for this chamber?
A Class A or Class B electrometer compliant with IEC 60731 and capable of measuring currents down to 1 pA is required. Common models include PTW Unidos E, IBA Dosimetry Razor, or Standard Imaging ISOMED 2000.
Is the chamber waterproof or suitable for immersion in water phantoms?
Yes—it is hermetically sealed and rated for full immersion in temperature-controlled water phantoms per IEC 60731 Clause 7.3.2.
Does it require temperature and pressure correction during use?
Yes. All ionization chamber measurements must be corrected using standard PTP factors as defined in IAEA TRS-398 and AAPM TG-51.
Can it be used for electron beam dosimetry?
No. This chamber is optimized for photon beams only. Electron beam measurements require a different wall composition and cavity theory correction framework.
What is the recalibration interval?
Annual recalibration is recommended per ISO/IEC 17025 guidelines and clinical QA standards such as AAPM TG-142.
