Advanced methods of active neutron dosimetry for individual monitoring and radiation field analysis

• Research unit: EU RFP
• Project number: 95.0560

Key words (English)

Direction storage; neutron dosimeter; ion chamber

Alternative project number (English)

EU project number: FI4P-CT95-0024

Research programs (English)

EU-programme: 4. Frame Research Programme - 5.2 Nuclear fission safety

Short description (English)

See abstract

Partners and International Organizations (English)

Coordinator: BRD, Physikalisch-Technische Bundesanstalt (D)

Abstract (English)

A novel detector type developed by RADOS is based on an ionization chamber with so called Direct Ion Storage (DIS). The ionization chamber is sensitive both to neutrons and photons. Chambers with highest possible neutron sensitivities (A-150 and Polythylen with BN or LiNO3) as well as chambers with lowest possible neutron sensitivities (Graphite and Teflon) are being developed to allow for differential readings. To realize a neutron dosemeter a double-chamber system combined in one detector is built.
The responses for neutron sources, monoenegetic neutrons and field spectra were determined for the following combined detector types:
- Type 1: A Polyethylen (PE) chamber containing 4% LiNO3 with a Graphite chamber.
- Type 2: An A-150 chamber containing 10% BN with a Graphite chamber.
- Type 3: An A-150 chamber containing 0.1% BN with a Teflon/Graphite chamber.
Type 1 has the flattest overall neutron response, except for a factor 8 higher response for thermalised field spectra, therefore the content of LiNO3 must be further optimised. Type 2 shows a strong increasing response with increasing thermalisation of spectra and is not suitable for single use, but could be used as a flag detector for thermal neutrons accompanying a less sensitive properly responding detector. Type 3 shows low response for thermalised neutron spectra.
Tests were performed for long time stability , photon discrimination and angle dependence.
To sum up, the feasibility of neutron dosimetry with ion chambers and DIS electronics has been proved. The results obtained with prototype detectors indicate the system's promising potential for future legal dosimeters. The system has basic limitations, however, and further development is needed to produce industrial prototypes for future routine use. A remaining limitation of the system is that, at present, the detectors provide reliable results only if the photon dose is not greater than twice the neutron dose. Apart from dosimetric properties, the advantages of the system are its small size and weight, easy readout and relatively low production cost.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 95.0560