Thermoluminescence solid-state nanodosimetry--the peak 5A/5 dosemeter

Abstract

The shape of composite peak 5 in the glow curve of LiF:Mg,Ti (TLD-100) following (90)Sr/(90)Y beta irradiation, previously demonstrated to be dependent on the cooling rate used in the 400°C pre-irradiation anneal, is shown to be dependent on ionisation density in both naturally cooled and slow-cooled samples. Following heavy-charged particle high-ionisation density (HID) irradiation, the temperature of composite peak 5 decreases by ∼5°C and the peak becomes broader. This behaviour is attributed to an increase in the relative intensity of peak 5a (a low-temperature satellite of peak 5). The relative intensity of peak 5a is estimated using a computerised glow curve deconvolution code based on first-order kinetics. The analysis uses kinetic parameters for peaks 4 and 5 determined from ancillary measurements resulting in nearly 'single-glow peak' curves for both the peaks. In the slow-cooled samples, owing to the increased relative intensity of peak 5a compared with the naturally cooled samples, the precision of the measurement of the 5a/5 intensity ratio is found to be ∼15% (1 SD) compared with ∼25% for the naturally cooled samples. The ratio of peak 5a/5 in the slow-cooled samples is found to increase systematically and gradually through a variety of radiation fields from a minimum value of 0.13±0.02 for (90)Sr/(90)Y low-ionisation density irradiations to a maximum value of ∼0.8 for 20 MeV Cu and I ion HID irradiations. Irradiation by low-energy electrons of energy 0.1-1.5 keV results in values between 1.27 and 0.95, respectively. The increasing values of the ratio of peak 5a/5 with increasing ionisation density demonstrate the viability of the concept of the peak 5a/5 nanodosemeter and its potential in the measurement of average ionisation density in a 'nanoscopic' mass containing the trapping centre/luminescent centre spatially correlated molecule giving rise to composite peak 5.

Figure 1.

Deconvoluted glow curve of LiF:Mg,Ti (TLD-100) into component glow peaks following irradiation by ⁹⁰Sr/⁹⁰Y beta (top) and alpha particles (bottom) in ‘naturally cooled’ samples. Note the enhanced intensity of peak 5a following the alpha particle irradiation.

Figure 2.

Schematic representation of the molecular TC/LC complex giving rise to peak 4 and composite peak 5. Following irradiation, the complex can capture an e-h (giving rise to peak 5a)—an electron-only (peak 5), a hole-only (peak 4) or be un-occupied. The linear dose response is due to e-h recombination in the e-h-occupied complex. Reproduced from Horowitz and Olko ⁽¹⁾.

Figure 3.

Comparison of glow curves following 6 MeV photon irradiation in ‘naturally cooled’ and ‘slow-cooled’ samples. Note the shift of T_max to lower temperatures in the slow-cooled samples and the disappearance of the shoulder arising from peak 4. This is attributed to an increased intensity of peak 5a in the slow-cooled samples.

Figure 4.

Intensity ratios of 5a/5 as a function of ionisation density/LET for different charged particle species.

Figure 5.

Deconvoluted glow curves following ⁹⁰Sr/⁹⁰Y irradiation: naturally cooled material (right); slow-cooled material (left).

Figure 6.

Deconvoluted glow curve following 4.5 MeV proton irradiation in a slow-cooled sample.

Figure 7.

Deconvoluted glow curve following 7.5 MeV alpha particle irradiation in a slow-cooled sample.

Figure 8.

Deconvoluted glow curve following 1.7 MeV deuteron irradiation in a slow-cooled sample.

Figure 9.

Deconvoluted glow curve following 2.0 MeV alpha particle irradiation in a slow-cooled sample.

Figure 10.

Deconvoluted glow curve following 20.6 MeV copper ion irradiation in a slow-cooled sample.

Figure 11.

Deconvoluted glow curve following 1.5 keV electron irradiation in a slow-cooled sample.