Response curves for the thermoluminescence induced by alpha particles: interpretation using track structure theory

Abstract

A three dimensional model is developed to describe the linear-sublinear behaviour of the thermoluminescence JTL) dose response curve induced by heavy charged particles specifically 'low energy' (-1 MeV U-') alpha particles. Supralinearity induced by alpha particles is shown to be suppressed or non-existent owing to the very low probability \<2%) of overlapping tracks in the dose region 10-5000 Gy where electron induced supralinearity is normally observed. Description of the sublinear behaviour is based on calculations using the Monte Carlo as well as analytical methods in which the alpha particle track is described as a cylindrical volume whose height corresponds to the range of the alpha particle and whose effective radius, refir is a single free parameter, determined by fitting the theoretical dose response to experimental results. The calculations are based on the approximation that the sublinear behaviour is a result of overlapping tracks in which the overlapping regions are completely saturated, i.e., the increase in dose in the overlapping volume does not result in an increase in the TL signal. Using this assumption a theoretical dose response curve is obtained which is sublinear at high dose and in excellent agreement with experimental results as shown by X 2 / n values. The values for re* determined from other workers' data (for 5 MeV alpha particles stopping in LiF:Mg, Ti) for the glow peaks appearing at 130, 190, 255 and 390°C are 100 8, i X 2 / n = 1.3), 150 8, i ~* / n = 0.8), 85 8, i(X2/n = 1.07) and 70 8, (,y2/n = 2) respectively. The value of r e * = 150 8, for peak 5 is in excellent agreement with radial dose distribution data for alpha particles stopping in LiF. t The dose-TL response, f k ( D ) , of a uniformly irradiated mass of TL material is the ratio of the TL efficiency, Cik(D) at dose D to q(&) at 'low dose'&: thusfk(D) = a k ( D ) / C i k ( & ) . The thermoluminescent efficiency, Cxk, is the ratio of the mean energy emitted as TL light, Z+, to the mean energy, E, imparted to the TL material by the radiation field, cxk = Z+/E.

Selectivity and Efficiency of Pyrene Attachment to Polyethylene Films by Bombardment with MeV-Range Protons

“…Greater selectivity of attachment at lower doses is not unexpected. The probability of overlap of radiation fields from randomly deposited proton tracks ( P 0+1 ) can be calculated using eq 16, where R is the radius of the radiation field of a proton track in cm, n is the number of proton tracks, and A 0 is the total area bombarded (1 cm 2 ). For 1.0 MeV protons with 1.5 nm radii for entering tracks, almost no track overlap is expected when fluences are ≤10 12 H + /cm 2 .…”

Comparison of Energy Deposition Modes in Polyethylene Films by Megaelectronvolt Range Neutrons, Electrons, Protons, and α Particles as Monitored by Covalent Attachment of Doped Pyrene Molecules

“…At higher doses, the probability of track overlap increases and, with it, the probability for secondary reactions . For instance, the probability of overlap of radiation fields from randomly deposited 1.0 MeV proton tracks with 1.5 nm radii at the point of entry into a film is calculated to be almost zero at ≤10 12 H + /cm 2 and 16% at 10 13 H + /cm 2 fluences 5b. Thus, higher doses lead to the sequential generation of radicals and ions in a unit volume within a film.…”

“…A progressive decrease in attachment selectivity (note loss of the characteristic 377 nm band) is observed as the depth of the protons increases. The emission spectrum of film 7 (located at the end of the penetration range predicted for 4.5 MeV protons, where secondary chemical events are more probable 40 ) lacks some of the vibronic structure and the sharp band at 377 nm that are characteristic of 1-alkylated pyrene moieties. However, a significant amount of radiation of sufficient energy to effect pyrenyl attachments penetrates the polyethylene beyond the Bragg region, and the emission from film 9 is again like that of a 1-pyrenyl moiety.…”

TL response of LiF : Mg,Ti exposed to intermediate energy1H,3He,12C,16O and20Ne ions

“…From the standpoint of basic research, understanding the TL response of LiF : Mg,Ti exposed to ions is considered important for a better comprehension of the basic phenomena in the interaction of ions with this material and the subsequent processes leading to the light emission (glow curve) from the heated irradiated crystal. For these reasons, many studies have been performed over the last few years concerning the investigation of the ion-induced effect in this material [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], most of them exposing the TL material to low-energy heavy charged particles. Studies of TL properties induced by intermediate or high-energy ions are relatively scarce and in these the analysis of the glow curve has been based on the total light signal or the 'dosimetric' peak 5, without a detailed analysis of the rest of the glow curve.…”