D. Wayne Cooke

Thermoluminescence and emission spectra studies of 6‐methylmercaptopurine and 6‐methylmercaptopurine riboside x irradiated at 10 K

In this work we report the first thermoluminescence (TL) and emission spectra studies of the sulphur‐containing DNA base analog 6‐methylmercaptopurine (6MeMP), and its riboside, 6‐methylmercaptopurine riboside (6MeMPR),x irradiated at 10 K. The 6MeMP glow curve exhibits TL peaks at 28, 40, 68, 78, 112, and 140 K with typical emission from each peak consisting of a band possessing maxima at 500 and 530 nm. Only three prominent peaks were found in the 6MeMPR glow curve: 42, 52, and 140 K. Typical emission from each of these TL peaks consisted of a band with maxima at 455 and 485 nm. Thermal activation energies and frequency factors associated with each glow peak were extracted from the experimental data and used in formulating a model to explain the observed emission. Ultraviolet (UV)‐induced glow curves, emission spectra, and photobleaching studies were also conducted in efforts to deduce the mechanisms of charge recombination in 6MeMP and 6MeMPR. The results indicate that metastable states exist in both 6...

Low‐temperature thermoluminescence studies of Al203

Thermoluminescence (TL) and emission spectra studies of single‐crystal A1203 have been conducted in the temperature interval 10‐300 K. Glow curves resulting from either x or UV radiation at 10 K were recorded and analyzed to yield thermal activation energies (E) and frequency factors (s) associated with each glow peak. A typical glow curve exhibits maxima at 60 K (E = 0.17 eV, s = 5×1012 s−1), 100 K (E = 0.22 eV, s = 8×109 s−1), 220 K (E = 0.56 eV, s = 7×1010 s−1), 260 K (E = 0.72 eV, s = 3×1012 s−1), and 290 K (E and s could not be deduced). Spectral emission from these peaks are characterized by predominant bands centered near either 330 or 410 nm. Specifically, the TL peaks at 60, 100, 220 K exhibit the band near 330 nm, whereas the 260‐ and 290‐K peaks display the 410‐nm band. Thermal annealing, optical excitation, and photobleaching experiments were also conducted in efforts to deduce the recombination mechanisms responsible for the glow peaks. Experimental results suggest that the 60‐, 100‐, and 220...

Thermoluminescence studies of LiF (TLD‐100) in the temperature interval 10–300 K

LiF (TLD‐100) has been investigated by thermoluminescence (TL) techniques in the temperature interval 10–300 K. Emission spectra data, in conjunction with thermal annealing, photobleaching, and optical repopulation studies, support the model previously proposed by Cooke to explain the TL mechanism in TLD‐100 over the temperature range of 90–500 K. By extending the studies to 10 K, six new glow peaks have been observed; maxima occur at 20, 44, 60, 66, 84, and 124 K. The latter peak represents a shoulder on the intense glow peak occurring near 138 K (previously reported) and is attributed to the thermal release of trapped electrons. The remaining peaks are associated with the thermal detrapping of shallow trapped holes which produce 400‐nm band emission. By incorporating the existence of shallow trapped holes into the existing model we present a band‐gap model which depicts the TL mechanism in TLD‐100 valid in the temperature interval 10–500 K.

Radiation damage in single crystal L-Histidine as studied by low-temperature thermoluminescence techniques

Abstract X-irradiation of single crystal L-Histidine at 10 K produces TL glow peaks at 38, 72, 84, 122, 162, 204, and 245 K. The 84 K peak is the most intense one and is characterized by a thermal activation energy of 0.073 eV and frequency factor of 1.1×10 3 s -1 . Moreover, it is readily photobleachable, whereas the other glow peaks are not, and is tentatively correlated with the thermal decay of a carboxyl anion radical. Computer simulation of the Randall-Wilkins first-order TL expression provided a check on the experimentally derived parameters characterizing the 38 and 84 K peaks. The initial-rise method did not produce accurate parameters for the 38 K peak; however, computer simulation yielded an activation energy of 0.022 eV and a frequency factor of 20 s -1 which were in agreement with the experimental shape of the glow curve. This TL peak is attributed to the thermal destruction of an imidazole cation radical. Emission spectra measurements of the 84 K luminescence (other peaks were of insufficient intensity) indicated that TL results from thermal release of electrons and their subsequent de-excitation to the ground state via the singlet and triplet manifolds. At sufficiently high temperatures (∼78 K) one only observes singlet state emission due to intersystem crossing.

Low‐temperature thermoluminescent behavior of 5′dCMP single crystals

Thermoluminescence (TL) and emission spectra studies of x‐irradiated single crystals of deoxycytidine‐5′‐phosphate monohydrate (5′ dCMP) were conducted in the interval 10–300 K. Two intense glow peaks were observed at 42 and 74 K with additional weaker peaks at 112, 140, and 200 K. By applying the Randall–Wilkins theory of glow curves to our data we obtained thermal activation energies (E) and frequency factors (s) characterizing each of the glow peaks, except the one at 200 K—it was of insufficient intensity. The parameters are: 42 K (E = 0.032±0.009 eV, s = 316 s−1); 74 K (E = 0.095±0.035 eV, s = 105 s−1); 112 K (E = 0.080±0.02 eV, s = 20 s−1); and 140 K (E = 0.12±0.04 eV, s = 56 s−1). As a check on the validity of the Randall–Wilkins theory we generated theoretical glow curves using the experimental parameters of the 42 K peak. Excellent agreement between the two glow curves was found. Typical spectral emission from each glow peak consists of band emission exhibiting maxima at 428 and 463 nm. We attrib...