General Characteristics of B3 Film Dosimeters

Dosimeter conditioning and packaging

Conditioning for optimum/stable response

GEX manufactures the B3 product in a controlled environment. Dosimeters are conditioned and packaged in a controlled environment at the manufacturing facility. The B3 film is hydrophilic, and the paper overlay or card traps moisture and oxygen, which are necessary elements for the B3 film chemical reaction that occurs in the presence of ionizing radiation.

Follow GEX B3 dosimeter product storage instructions.

Dosimeter conditioning and packaging

Protection provided by packaging

The pouch protects B3 dosimeters from fingerprints, oils and dirt.  ·        

Keep B3 dosimeter in the original factory pouch/package until removal is necessary.

If dosimeter is removed from original factory pouch prior to irradiation, handle with care. Follow GEX B3 dosimeter handling instructions.

Time since manufacture

Change in dosimeter response over prolonged time intervals

B3 film is shelf stable under normal storage conditions until the expiration date printed on the product box.

Use the B3 product within the expiration date of the manufactured lot.

After the expiration date, the response of B3 film is suspected to slowly decrease over time due to natural degradation of the chemistry and polymer. No definitive study has been performed; GEX recommends measuring the film background Absorbance value (Ao) prior to irradiation, and use Ai-Ao/t = R calculation of response.

Temperature

Long-term & short-term effects at extremes of temperature

B3 film products may be sensitive to high temperature before irradiation, and the dosimeter’s response may be impacted. No impact of cold storage has been observed. Stable storage temperatures will minimize any effect on the moisture content changes of the film that is known to impact the dosimeter response.

Follow GEX B3 dosimeter product storage instructions.

Relative humidity (RH)

Long-term & short-term effects at extremes of humidity

Packaged dosimeters: The effect of frequent, large variations in moisture content of the film during storage has not been studied. Stable storage temperatures may likely minimize any changes to the moisture content of the film that affects the chemistry or polymer during pre-irradiation storage.

Un-packaged dosimeters: see Relative Humidity (RH) conditions during irradiation

Follow GEX B3 dosimeter product storage instructions.

Keep B3 dosimeter in the original factory pouch/package until removal is necessary.

If dosimeter is removed from original factory pouch prior to irradiation, see Relative Humidity (RH) conditions during irradiation

Exposure to light

Long-term & short-term effects on dosimeters from light

B3 film dosimeters are not sensitive to visible light. B3 film products are sensitive to UV light, but the packaging protects the B3 film from exposure. Exposure to UV light will permanently increase the pre-irradiation absorbance (darken the color of the film) with the rate of change depending on UV intensity.

Direct sunlight effects can occur very rapidly. Effects from fluorescent lighting are generally quite slow.

Sometimes UV exposure is not avoidable such as placing unpackaged dosimeters in a factory setting where UV light sources are used for ambient lighting. It is possible that effects are negligible, but the user must verify any such condition.

Follow GEX B3 dosimeter product storage instructions.

Keep B3 dosimeter in the original factory pouch/package until removal is necessary.

Control UV light. See Evaluation, control and monitoring of UV-light in B3 dosimetry environments. If the effect is characterized as being minimal, exposure for a few minutes might be acceptable and justified with data.

Irradiation temperature

Variation of response with temperature

The influence of temperature on B3 response is not significant at the lower end of the B3 dose range (nominally 15 kGy or less). The effects of temperature on dosimeter response are increasingly significant with higher doses.

Seasonal effects - Irradiation facilities located in temperate climates may experience a “seasonal” effect on the response and thus the dose measurements coinciding with the change in the temperature inside the irradiation facility with the seasons. 

B3 film performs exceptionally well at lower temperatures (< 35.0°C).

B3 film can be calibrated and used at temperatures well below 0°C; the response function is somewhat depressed at freezing temperatures or lower. For example, in an environment with an average temperature of -24.0°C, the B3 response is approximately 90% of the response at room temperature over the entire dose range.

Temperatures above 60°C can cause a reduction of the response function of B3 film. Use of B3 Film products in irradiation temperatures above 60°C is at the user’s discretion (per ASTM 51275)

In-plant calibration, under normal process and environmental conditions for all applications and processes and done in accordance with ISO/ASTM 51261 Method 2.

Maintain lower temperatures during irradiation (< 35.0°C).

Account for the impact of the ‘seasonal effects’ on B3 dosimeter response; calibrate during average temperature conditions and account for variation in measurement uncertainty.

Avoid irradiation temperatures above 60°C or study the effects and use appropriate methods of accounting for the effects.

Design calibration plans that use techniques to prevent temperatures in excess of 60̊   Celsius. See Dosimetry System Calibration - Technical Report

Exposure to light

Effect of light on response

Same influence as in the Pre-irradiation category.

Users should cover unpackaged dosimeters with material to block UV immediately after the dosimeter is irradiated until the dosimeters are returned to a UV-controlled environment.

Radiation energy

Variation of response with radiation energy

The response of the chemistry of B3 films is independent of radiation energy, but the user must consider any dose gradients in the film when using electron energies < 150 keV.

Calibrate under the conditions of use. See Calibration of Dosimetry Systems Used in Low Energy Electron Irradiation.

Packaging Type

Response variation due to number of dosimeters in a pouch

There may be measurable variance between different B3 Dosimeter Product packaging configurations such as 1 or 2 dosimeters in a pouch due to differences in the amount moisture and oxygen inside the package caused by the different volume of materials comprising the dosimeters (overlays and adhesives) used to manufacture the different product types.

See oxygen and relative humidity effects during irradiation.

Test the different packaging configurations and account for any significant difference of response in the measurement uncertainty budget or calibrate each packaging configuration separately (per ASTM 51275),

Product Type

Response variation due to dosimeter Product Type

There may be measurable difference between different product types (different forms of B3 film dosimeter) such as GEX B3, B3 WINdose and B3 DoseStix due to differences in the amount moisture and oxygen inside the package caused by the different overlays and adhesives used to manufacture the different product types.

See oxygen and relative humidity effects during irradiation.

Test the different dosimeter product types and account for any significant difference of response in the measurement uncertainty budget or calibrate each product type separately.

Packaging

Response variation due to the irradiation outside versus inside of a sealed package.

There is often a measurable variance between pouched and un-pouched dosimeters.

Calibrate using packaged dosimeters or controlled conditions at the time of irradiation, otherwise use packaged dosimeters during calibration where possible.

Storage time

Variation of response with time between irradiation & measurement

Unless conditioned after irradiation using heat treatment, the B3 film response will continue to increase for a period of time after irradiation and the magnitude of the increase is dependent on the amount of dose and temperature during irradiation.

Use post irradiation heat treatment. See Heat Treatment of B3 Film after irradiation - GEX guidance.

Storage temperature

Variation of response with temperature following irradiation

The B3 film response is effected by storage temperature as described in the above Categories – Temperature.

Move irradiated dosimeters to controlled storage conditions before heat treatment in accordance with a documented procedure. Calibrate dosimeters adhering to the same procedure (i.e. under the conditions of use).

Use post irradiation heat treatment. See Heat Treatment of B3 Film after irradiation - GEX guidance.

Conditioning treatment

Deliberate exposure to a conditioning treatment to obtain stable response

Post-irradiation heat treatment of B3 film is necessary in most applications. Heat treatment after irradiation render the dosimeters very stable for long periods sufficient for most user applications.

Without heat treatment, there may be significant variation in time between irradiation and heat treatment may result in variation of the response.

The irradiation temperature impacts the temperature necessary to heat-treat B3 film. Higher temperatures during irradiation means the irradiated B3 film will have a lower glass transition temperature, and you will need to lower the temperature of the heat-treatment process. See References - Glass transition temperature of Risø B3 radiochromic film dosimeter and its importance on the post-irradiation heating procedure

Use a heat treatment process (condition treatment) to stabilize the response B3 dosimeters after irradiation; this will eliminate the effect of storage time, storage temperature and storage relative humidity (RH) on dosimeter response.  See GEX B3 dosimeter product Storage Post-Irradiation Storage.

Post irradiation heat treatment is the recommended and standard practice for B3 dosimetry - see References

Heat Treatment of B3 Film after irradiation - GEX guidance.

Use a controlled method for heat treatment. Account for any effects of allowed procedural variation on the magnitude of the influence in the measurement uncertainty budget (i.e. if variation is allowed in the procedure such as time between irradiation and measurement this must be accounted for in the uncertainty budget).

Test the heat treatment process before routine use of B3 dosimeters to ensure the irradiation temperature does not cause damage to the B3 film during heat treatment.

Storage relative humidity*

Variation of response with relative humidity

The dosimeters may be affected if the conditions of storage before measurement of the irradiated dosimeters are significantly variable.

See Conditioning Treatment above.

Exposure to light

Effect of light on response

Same influence as in the Pre-irradiation category.

Control exposure of film dosimeters to UV-light sources after irradiation.

Light

Effect of light during measurement

Same influence on dosimeter as in the Pre-irradiation category. Stray light in the optical system of the reader may impact the accuracy of the dosimeter measurement in a spectrophotometer.

Control UV light. See Evaluation, control and monitoring of UV-light in B3 dosimetry environments. If the effect is characterized as being minimal, exposure for a few minutes might be acceptable and justified with data.

Eliminate stray light during dosimeter measurement - Always use readers and dosimetry holders that are designed to eliminate stray light during dosimeter measurements, such as the GEX dosimetry system. Alternatively, always close the lid of the spectrophotometer during dosimeter measurements and test for Stray Light during spectrophotometer performance verification testing.

Temperature

Effect of temperature during measurement

Measurement time is short enough that there is no effect on the response of the dosimeter, heat treated or not.

Large fluctuation in temperature may cause small variation in reader performance.

Operate readers and all electronic equipment within the manufacturers stated temperature range.

Relative humidity (RH)

Effect of relative humidity during measurement

Measurement time is short enough that there is no effect on the response of the dosimeter, heat treated or not.

Large fluctuation in relative humidity may cause small variation in reader performance.

Operate readers and all electronic equipment within the manufacturers stated temperature range.

Instrument Settings

Effect of instrument parameters during measurement

Optical measurements of thin films using highly isolated wavelengths of visible light (e.g. 552nm as is the recommendation for B3 dosimeters) are subject to variability due to the degree of isolation of the wavelengths selected. Spectrophotometers all have a fixed or variable spectral bandwidth (SBW) and measurement variation is directly proportional to SBW value used.

The variation in response measurement of B3 film dosimeters is caused by a phenomenon known as optical interference fringing. The impacts of optical interference fringing are much greater at the low range of dose for the B3 dosimeters.

Optical interference fringing is minimized or eliminated by widening the spectral bandwidth used. However, spectrophotometer SBW settings may not be available at widths that are optimal for all product use cases.

Use a SBW of 4nm or greater. Otherwise plan variability of measurement outside of published variation expectations for the B3 dosimeter.

Consider the use of higher SBW for doses 10 kGy or lower.

No additional uncertainty is required to be budgeted for this effect. All variation is included in an assessment of measurement reproducibility.