A STUDY OF THE IRRADIATION TEMPERATURE COEFFICIENT

FOR L-ALANINE AND DL-ALANINE DOSEMETERS

Marc F. Desrosiers1,, Min Lin2, Sarene ́e L. Cooper1, Ying Cui2 and Kesheng Chen2

1

Ionizing Radiation Division, Physics Laboratory, National Institute of Standards and Technology,

Gaithersburg, MD 20899, USA

2

Radiometrology Center, China Institute of Atomic Energy, 102413 Beijing, China

Alanine dosimetry is now well established both as a reference and routine dosemeter for industrial irradiation processing.

Accurate dosimetry under the relatively harsh conditions of industrial processing requires a characterisation of the parameters

that influence the dosemeter response. The temperature of the dosemeter during irradiation is a difficult quantity to measure

so that the accuracy of the temperature coefficient that governs the dosemeter response becomes a critical factor. Numerous

publications have reported temperature coefficients for several types of alanine dosemeters. The observed differences in the

measured values were commonly attributed to the differences in the polymer binder or the experimental design of the

measurement. However, the data demonstrated a consistent difference in the temperature coefficients between L-alanine

and DL-alanine. Since there were no commonalities in the dosemeter composition or the measurement methods applied, a clear

conclusion is not possible. To resolve this issue, the two isomeric forms of alanine dosemeters were prepared and irradiated in

an identical manner. The results indicated that the DL-alanine temperature coefficient is more than 50% higher than the

L-alanine temperature coefficient.

INTRODUCTION

A correction for the average temperature experienced by a dosemeter during irradiation with electrons and photons improves the accuracy of the dose

measurement. The relationship between the dosemeter’s radiation response to the absorbed dose and its

temperature during irradiation is termed the irradiation temperature coefficient. This temperature coefficient is typically expressed in percentage change per

degree. The temperature rise in dosemeters irradiated with high-intensity ionising radiation sources

can be appreciable; however, the temperature during

irradiation is often difficult or impractical to be measured directly. In the absence of a direct measurement, an estimation of the irradiation temperature

is often employed to make this correction for the

computation of the absorbed dose. Since this estimate includes unavoidable significant errors, the

magnitude of the temperature coefficient is the next

consideration in any efforts to minimise the measurement uncertainty.

In 2000, a compilation of all the published temperature coefficients was tabulated.(1) The observed

differences were attributed to several factors that

include the polymer binder type and concentration;

manufacturing parameters; experimental design of

the temperature-controlled irradiations; and computations from limited data. One influence not

explored was the isomeric composition of alanine.

NIST’s high-precision temperature-controlled irradiation apparatus and the dosemeter manufacturing

technology of the China Institute of Atomic Energy

(CIAE) was joined in a collaborative effort to examine dosemeters prepared with L-a-alanine, composed

solely of the L isomer, and DL-a-alanine, a mixture of

the L and D isomers.

MATERIALS AND METHODS

The preparation of alanine dosemeters was carried

out at CIAE. (The mention of commercial products

throughout this paper does not imply recommendation or endorsement by the National Institute of

Standards and Technology, nor does it imply that

products identified are necessarily the best available

for this purpose.) Two different dosemeter types

were prepared identically from uniform mixtures of

either L-alanine (Beijing Chemical Reagent Company, BR) or DL-alanine (Beijing Chemical Reagent

Company, BR) with pure paraffin (melting point

range from 54 to 56C; Shanghai Huashen, BR).

Each dosemeter had a mass of 60 mg with 95%

alanine and 5% paraffin by weight. The protocol

for manufacturing alanine dosemeters can be summarised as follows:

 Grinding the polycrystalline alanine.

 Sieving the ground alanine to select a particle size

range from 50 to 125 mm.

 Cutting the paraffin to small diameter granules.

 Uniform mixing of the alanine and the paraffin

through a two-step procedure of grinding and

heating (61C) several times.

 Pressing the mixture into a mold to form cylindrical pellets of 4.8 mm in diameter and 3 mm in

height. 

Corresponding author: marcd@nist.gov

Radiation Protection Dosimetry (2006), Vol. 120, No. 1–4, pp. 235–237

doi:10.1093/rpd/nci543 Advance Access published on April 27, 2006

Published by Oxford University Press (2006).
Irradiations were conducted in a Gammacell 220

(Nordion, Canada) 60Co gamma source (dose

rate  15 kGy h1

). The dosemeters were placed in

a custom-designed aluminium holder surrounded by

a controlled-temperature airflow that was capable of

achieving thermal equilibrium from 80 to þ100C

during irradiation(1). The holder accommodated six

dosemeters, in which three dosemeters of each type

were spaced equally in the holder and irradiated

simultaneously to 10 kGy. The dosemeters in the

holder assembly were pre-equilibrated to the target

temperature prior to each irradiation. The irradiation temperature was held at the target temperature

(within 1C) throughout the irradiation period.

The electron paramagnetic resonance (EPR) signal measurement protocol for the Bruker ECS106

spectrometer measurements was described in detail

previously(1). Essentially, each dosemeter was measured at two angles and these measurements were

normalised to the dosemeter mass and the EPR signal amplitude of the spectrometer’s internal reference material (ruby crystal). The average of the

normalised signal amplitudes for both angles was

used as the dosemeter response.

The response for the dosemeters irradiated from

10 to þ50C underwent linear regression and the

resultant function was used to compute the predicted

EPR response at 25C. This value served as the

reference point from which the relative response

for each measurement was calculated. The value

for the slope of the relative response plotted versus

the irradiation temperature is the temperature

coefficient.

RESULTS AND DISCUSSION

A graphical display of the published temperature

coefficients plotted against the absorbed dose at

which they were measured is shown in Figure 1.

The data were taken from Nagy(1) and references

therein, with the exception of one data point

(0.11% per K at 50 kGy)(2). The temperature coefficients selected for this graph were limited to the data

that identified the isomeric form of the alanine and

to the measurements made in a temperature range

that approximated the range used in this study (10

to þ50C). The L-alanine response with temperature

was shown to be nonlinear below 10C(2).

There is a distinct difference between the DLalanine and the L-alanine temperature coefficients.

The mean DL-alanine temperature coefficient, 0.24%

per K is 57% higher than the mean L-alanine temperature coefficient, 0.15% per K. Despite this obvious difference, it has never been conclusively

determined if this difference can be attributable to

the isomeric form of the alanine. Potential influences

from dosemeter composition and/or dimensions

along with the experimental design of the measurements were too dissimilar among the studies.

Qualitatively, the data in Figure 1 suggest that the

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

0.3

0 1 2

Log of Absorbed Dose (kGy)

Temperature Coefficient (%/K)

L-Alanine

DL-Alanine

Figure 1. A graph of published temperature coefficients for DL-alanine and L-alanine dosemeters vs. the absorbed

dose in kGy.

M. F. DESROSIERS ET AL.

236
magnitude of these effects is relatively small. The

standard deviation of the DL-alanine temperature

coefficients is 4%. These measurements were made

on dosemeters of similar composition and dimensions from three different research groups. The

standard deviation of the L-alanine temperature

coefficients is 16%; these data were compiled from

five dosemeter types, four different research groups,

and a broad range of dosemeter dimensions (from

films to 1 cm pellets).

As described above in Materials and Methods

section, the two dosemeter types were collocated

and irradiated simultaneously from 10 to þ50C.

The percentage difference in response at a specific

temperature relative to the predicted response at

25C is plotted in Figure 2. The slope of these data

for each dosemeter type is the temperature coefficient. From these data, the DL-alanine temperature

coefficient was determined to be 0.19% per K while

that of the L-alanine was determined to be 0.12% per

K. Both these coefficients are 20% lower than the

mean coefficients for the respective isomeric alanine

dosemeter forms extracted from Figure 1. This

difference may be attributable to the experimental

design of the measurement system. Interestingly, the

DL-alanine temperature coefficient is once again 57%

higher than the L-alanine temperature coefficient.

As mentioned above, the L-alanine response with

temperature was shown to be nonlinear below

10C(2). To determine if this effect can be observed

in DL-alanine, two temperatures below 10C were

selected (30 and 77C). It was found that the

DL-alanine dosemeter response deviated from linearity below 10C in a manner analogous to the

L-alanine dosemeters. The magnitude of the deviation was consistent with the previous study on

low-temperature effects on the alanine dosemeter

response.

CONCLUSION

These data present conclusive evidence that the

temperature coefficient for the dosemeters prepared

with DL-alanine is more than 50% higher than those

prepared with L-alanine. Therefore, L-alanine dosemeters are preferred for measurement applications

where the irradiation temperatures differ greatly

from the calibration irradiation temperature, especially if minimising the measurement uncertainty is a

concern.

REFERENCES

1. Nagy, V., Puhl, J. M. and Desrosiers, M. F. Advancements in accuracy of the alanine dosimetry system. Part

2. The influence of the irradiation temperature. Radiat.

Phys. Chem. 57(1), 1–9 (2000).

2. Desrosiers, M. F., Cooper, S. L., Puhl, J. M., McBain,

A. L. and Calvert, G. W. A study of the alanine dosemeter irradiation temperature coefficient in the 77C

to þ50C range. Radiat. Phys. Chem. 71(1), 365–370

(2004).

-10%

-8%

-6%

-4%

-2%

0%

2%

4%

6%

-20.0 -10.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0

Irradiation Temperature ( ̊C)

EPR Amplitude relative to 25  ̊C (%)

DL

L

Linear (DL)

Linear (L)

Figure 2. The percentage difference in EPR response, relative to the predicted response at 25C, for DL- alanine and

L-alanine dosemeters vs. the irradiation temperature in C.

IRRADIATION TEMPERATURE COEFFICIENT FOR L-ALANINE AND DL-ALANINE DOSEMETERS

237