Dosimeter FAQ

HARWELL Dosimeters are the dosimeter specialists - and our experienced team has produced this FAQ document to answer queries regarding dosimeters and dosimetry. If you have a question you believe should be answered in the FAQ, please submit it here or complete our feedback form.

What is a Dosimeter?

Dosimeters are devices which register doses of radiation. Dosimeters are typically made of small pieces of radiation-sensitive material which change when irradiated. By measuring the property which changes, for example colour, using a spectrophotometer, the exposure to radiation dose can be calculated.

What are Dosimeters used for?

Dosimeters are mainly used to measure radiation exposure in areas such as the nuclear industry, medicine and the sterilisation of medical devices

Who are Harwell Dosimeters?

HARWELL Dosimeters is one of a number of companies which evolved from UKAEA. We are located on the Harwell Science and Innovation Campus, which we share with technical companies old and new, large and small.

What Products and Services do Harwell Dosimeters make?

HARWELL Dosimeters produces high-quality dosimeters mainly for use in the sterilisation of medical devices. Three types, Red 4034, Amber 3042, and Gammachrome YR are made from radiation-sensitive poly-methylmethacrylate (pmma) in the form of optically transparent pieces individually sealed in laminate sachets. They darken when irradiated, and the radiation-induced darkening, accurately measurable by means of a spectrophotometer, is a function of the radiation dose absorbed. We maintain a page providing technical specifications for each product.

What Equipment is required to read the Dosimeters?

A spectrophotometer.

What specification is required for the spectrophotometer?

The minimum requirements are:

• Spectral slit width maximum 2nm

• Wavelength

  Required range: The full uv / visible range is normal but at least 400 to 700 nm
  Accuracy ± 1 nm
  Precision ± 0.5 nm

• Photometric

  Absorbance range 3A
  Accuracy ± 2% max ± 1% over as much of the range as possible

What is the Shelf-Life of Harwell Perspex Dosimeters?

The shelf-life of Harwell Perspex^® Red 4034, Amber 3042 and Gammachrome YR^® dosimeters stored in appropriate conditions is at least 10 years.

All three types of Harwell Perspex^® (dyed polymethylmethacrylate) dosimeter, Red 4034, Amber 3042 and Gammachrome YR^® may be satisfactorily calibrated after being stored in appropriate conditions for ten years.

In a detailed assessment, the original calibration of all Red 4034 dosimeters studied was shown to be still valid after five years, and for two of the batches selected for study it remained valid after ten years.

What conditions are required for the storage of Perspex dosimeters?

We recommend that the dosimeters are stored in the temperature range 20±5°C, because we have long-term experience of that range in our own facilities.  Humidity is of no concern, as the Perspex is protected by an aluminium foil laminate sachet.

The temperature recommendation does not imply that the dosimeters are necessarily unsatisfactory if they are stored in conditions outside that temperature range.  As many customers cannot readily comply under all circumstances, for example for dosimeters attached to products in a warehouse before irradiation, we also provide the following additional guidance, in order to provide flexibility, and to avoid being unnecessarily restrictive:-

• Long-term storage at 20±5°C is probably ideal;
  
  
• the evidence is very strong that repeated exposure to temperatures up to 27°C for considerable periods produces no significant effect;
  
  
• brief exposure to a much higher temperature, such as 35°C, probably has no significant effect

Do you make the Dosimeters yourselves?

We buy in carefully specified raw materials. Subsequent processes and quality control are all in-house with the exception of the blister packaging required for the alanine dosimeter 'Radspin^®'.

Do you sell electronic dosimeters?

No. We were once in the same organisation as Harwell Instruments, who made devices which carry the name 'Harwell'. They currently operate as 'Canberra'.

Do you sell personal dosimeters?

No. A company which evolved from UKAEA, as we did, and which provides personal dosimetry services currently operate as 'Nuvia'.