Supralinearity of peak 5 and peak 6 in TLD-700

Abstract

Theories attempting to explain supralinearity observed in thermoluminescent dosimeters (TLDs) are typically concerned with trap creation [1], track interaction [2], and pre-existing c-hit trap structures [3]. The present work extends the last concept and explores its implications for heavy-ion response.We describe the response of a c-hit detector to gamma-rays by two parameters-the hittedness, c, and the characteristic dose, E 0 , of gamma-rays at which there is an average of one hit per sensitive element. To calculate the response of such a detector to heavy charged particles we also need to know a third parameter-the radius of the sensitive element, a 0 . We take a 0 to be related to the size of the sensitive region around a trapping site. The radial distribution of local dose around the path of a heavy ion is then used as a transfer function, relating the low-LET response of a detector to its high-LET response [4].In earlier work [3] it was suggested that the supralinear response of TL materials for gamma irradiations can be represented by a sum of c-hit components, implying the existence of corresponding (but otherwise undefined) trap structures in this detector. In support of this concept, we note the near-quadratic (2-hit) X-ray response found by Crittenden et al. [5] for peaks 5 and 6 in BDH LiF doped with 80 ppm Mg and Ti, measured at a ramp speed of 20°C min -1 . Peak 6 in the material doped with 3 ppm Ti and measured at 420 nm wavelength appears to have a near 2-hit response saturating at about 800 krad.Decomposition of experimentally measured responses of TLDs to gamma-or X-rays can yield the values of hittedness, characteristic dose, and relative contribution of each component, but cannot provide us with any information on the size of the sensitive element. The value of a 0 must be inferred from the response to high-LET radiations.The response of LiF to fast charged particles has been measured for protons, alpha-particles, and some heavier ions (C, O, and Ne) for TLD-100 [6,7] and TLD-700 [8]. The efficiency of LiF, if plotted as a function of the stopping power of the charged particle, appears to be of the order of that for 60 Co at lower values of LET and then to decrease with increasing LET [6][7][8][9][10].Enhancement of the ratio of heights of peak 6 to peak 5 is observed for LiF irradiated with alpha-particles [9,10] and fast neutrons [II], compared with the ratio for gamma-irradiation. A decrease of supralinearity and loss of sensitivity, relative to gamma-irradiation, are seen for LiF (TLD-700) exposed to 3.7 MeV alpha-particles and 13.3 MeV protons stopping in the material [10]. AbstractTrack theory has been applied to an earlier suggestion, that the supralinearity of TLDs at high gamma-ray doses is due to pre-existing 1-hit and 2-hit trap structures, to calculate high-LET response. Measured 60 Co dose responses for peaks 5 and 6 in LiF (TLD-700) were decomposed to yield parameters characterizing each peak as a two-component c-hit mixture. One value of "trap radius" was assigned to each two...

The radial distribution of dose around the path of a heavy ion in liquid water

“…In practice, however, the electron energy spectrum varies from shell to shell with radial distance from the ion's path, making it impossible to perform a suitably matched exact calibration. Ultimately, neglecting the difference between the radially varying electron energy spectrum from delta-rays and the energy spectrum of the secondary electrons following gamma-ray irradiation can be justified by the considerable success of this first-order model in describing the response of physical detectors, such as the appearance of tracks in nuclear emulsions (Katz and Kobetich, 1969), the light output of scintillators , or thermoluminescent dosimeters (Waligórski and Katz, 1980), and the response of biological systems: inactivation of enzymes and viruses (Butts and Katz, 1967), survival of mammalian cells (Roth et al, 1976;Katz et al, 1985), or generation of neoplastic transformations in such cells , after high-LET irradiations.…”

Thermoluminescence and photoluminescence analyses of MEH-PPV, MDMO-PPV and RU(bpy) 3 gamma-irradiated polymer thin films

“…The M (D) function used to fit the experimental TL dose curves originated from the track structure theory of Katz (Larsson and Katz 1976;Waligórski and Katz 1980a;Waligórski and Katz 1980b;Waligórski et al, 1993). The analytical expression of the M(D) function is given by the following equation, which, in fact, is the sum of two saturating exponentials.…”

Characteristics of Mg2SiO4:Tb (TLD-MSO-S) relevant for space radiation dosimetry

“…Although TLDs are highly sensitive to low-LET radiation, the ThermoLuminescence (TL) yield per unit irradiation dose decreases for high LET radiation (Berger and Hajek, 2008;Hajek et al, 2008aHajek et al, , 2008bBilski et al, 2004;Olko, 2004;Horowitz et al, 2001;Benton et al, 2000;Geib et al, 1998aGeib et al, , 1998bDoke et al, 1995;Waligórski and Katz, 1980). Therefore, TLDs are likely to underestimate the absorbed dose in LEO radiation fields that include high LET components.…”