Whole-body dosimetry

The perfect dosimeter for mixed radiation fields

Our thermoluminescent Albedo dosimeters are the perfect whole-body dosimeters for the surveillance of mixed radiation fields (neutrons, photons), in which the proportion of the neutron dose equivalent may exceed 20% of the photon dose equivalent.

The thermoluminescence (TL) dosimetry is an established method for measuring the personal dose equivalent caused by photon or neutron radiation. Our Albedo dosimeters are ideally suited for the official surveillance of the personal dose in mixed radiation fields. Due to measurement methods developed according to the state-of-the-art in science and technology, our Albedo dosimeters can cover a large energy range.

A detector card equipped with four TL detectors is located in a plastic cassette.  Two of the detectors are disposed behind an "Albedo neutron window".

If ionizing radiation hits the detectors, energy is stored in the detector crystal.  Upon heating, a part of this energy is released again in the form of light. The light intensity is a measure unit for the absorbed radiation.

We use Harshaw 6600 type TL readers for dose calculation.

Our Albedo dosimeter is as an official personal dosimeter approved for photon radiation by virtue of its construction by the Physikalisch-Technische Bundesanstalt (PTB). 

Short description

Albedo is a dosimeter designed for measuring the equivalent dose by X-ray, gamma and neutron radiation within the personal and on-site dosimetry.

The dosimeter probe contains in an Albedo capsule a numbered, reusable detector card that supports four thermoluminescence detectors, of which two are disposed behind an "Albedo neutron window", respectively. For fixing the dosimeter, a protective wrapper with belt clip is recommended.

The measurement system is intended for use in mixed radiation fields (neutrons, photons). For photon radiation, it is type-approved for the quantity Hp(10).

A personal dose monitoring with the Albedo dosimeter in mixed radiation fields is recommended, if the proportion of the neutron dose equivalent reaches more than 20% of the photon dose equivalent. 

Assembling of the Albedo dosimeter

Source: Helmholtz Zentrum München, Michael Haggenmüller

Assembling of the Albedo dosimeter

Source: Helmholtz Zentrum München, Michael Haggenmüller

Functioning and dose determination

When exposed to ionizing radiation, mobile pairs of charge carriers (electrons and electron holes) are generated in a crystal, which are trapped in crystalline voids. Upon heating, they are freed from these higher level energy and long-lived states and recombine to emit light (thermoluminescence, shortly, TL). The light intensity is a direct measurement unit for the emitted dose. Upon enrichment with neutron sensitive isotopes (eg, Li-6), the crystal can also be sensitized to thermal neutrons.

The two-component Albedo dosimeter contains two TL-detector pairs, of which the first measures the neutrons scattered back from the body (albedo neutrons), while the second measures the thermal neutrons incident on the body (field neutrons). The indication of the neutron dose equivalent is generated from the display of the Albedo detector pairs and from the corresponding calibration factor for the particular scope of application.

Each detector pair comprises a photon-sensitive detector as well as a photon/neutron-sensitive detector. The solely photon-sensitive detector is used to determine the respective photon dose. The relative proportion of neutrons is determined from the difference between the two detectors. The ratio between the field neutrons and the Albedo neutrons provides an additional energy correction factor (DIN 6802-4).

The Albedo dosimeter can also be used in high energy accelerators, as the neutron radiation field at these workplaces always shows a proportion of scattered neutrons with low energy, and thus a sufficient signal for the dose determination is generated in the detector. This has been verified by measurements at various high-energy accelerators. 

Wearing options

The dosimeter is worn on a part of the body representative for the radiation field (usually on the upper part of the trunk), the backside of the probe should be closely attached to the body of the exposed person, the backside labeled "Back" should face towards the dosimeter user.

Wearing option of the dosimeter

Source: Helmholtz Zentrum München, Michael Haggenmüller

Wearing option of the dosimeter

Source: Helmholtz Zentrum München, Michael Haggenmüller

Operating instructions

The Albedo dosimeter is the property of the monitoring service and it is provided to the customer on a loan basis. When used, it has to be firmly assigned to a person and, after expiration of the monitoring period (usually one month), It has to be returned to the monitoring service for evaluation along with the name of the wearer and the exposure conditions. Unused dosimeters should be sent back to the monitoring service at the end of a quarter, in order for them to be baked out ("zeroed") for reutilization, because the dosimeters continuously measure the ambient radiation.

With the Albedo dosimeter, the energy field for neutrons occurring in the routine monitoring is sufficiently covered. Because of the energy dependence of the neutron responsivity, it is distinguished among four typical application areas (N1 to N4), in which the radiation protection officer must classify the occupationally exposed persons (see DIN 6802-4).

N1Nuclear reactors (strong shielding)
N2Nuclear fuel cycle
N3Radionuclide sources, e. g. 252Cf, 241Am(Be)
N4High-energy accelerators 

 

It shall be ensured that the dosimeter is used only in the intended application area. In individual cases, a calibration in each scatter radiation field may be required. Calibrations in the scatter radiation field are carried out in consultation with the monitoring service.

The dosimeter is suitable for use at ambient temperatures of +10 ° C to +40 ° C and a relative humidity of 10% to 90%. The Albedo dosimeter should not be exposed to direct sunlight radiation over 1000 W / m² or mechanical shocks over 4900 m / s ². If necessary, the dosimeter capsule can be cleaned with a damp cloth. Albedo dosimeters must be protected during storage against moisture and temperatures above +60 ° C. It is important to ensure that at the storage place only low ambient radiation and, in particular, no thermal neutrons occur. The dosimeters must not be opened or damaged mechanically, so that the very sensitive detectors are not destroyed or lost.

Energy range and measuring range

Energy rangeLimits of detectionNominal operating range
in accordance with PTB requirements
Photons25 keV - 7 MeV25 keV - 7 MeV
Neutronsthermic - 10 MeV-
Dose measuring rangeLimits of detection Nominal operating range
in accordance with PTB requirements
Photons0,1 mSv - 2 Sv0,1 mSv - 2 Sv
Neutrons0,1 mSv - 2 Sv-

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