Propriedades termoluminescentes de Lif dopados com Cu e/ou Mg.

Abstract

17temwluminescence (TL) of LiF doped with different concentrations of Mg andjor Cuh as been investigated. 17te effect of the themtal treatment on the crysta/s in each cycle ( annea/ing, gamma ray exposure and readout) was studied for five successive cyc/es. 17zree different themJa/ treatments were examined: 23(fC for IO min, 40(fC for Ih and 40(fC for Ih fo//owed by IOCfC for 211. LiF doped with Mg or Mg + Cu submitted to the /ast quoted themta/ treatment a11d i"adiated witll 137 Cs gamma rays showed a reasonable sensitivity and glow curve with only one peak (W J at (242±4YC. From these data, this annealing was adopted for a// samp/es. TL sensitivity and glow peak temperatures for ali available samples exposed to 0,26mC/kg of gamma rays or 0,4 J /cm 2 of UV or to both radiations consecutively were a/so analysed. 17te glow peak due to gamma rays appears at (242±4tC and is higher than the peaks at (I02±3tC and ( I68±4tC due to UV light. It has been slwwn experimentally that UV radiation fills directly the traps, producing no phototransference of charge carriers from deep traps, filled by ionizing radiation, to the shallow mtes. Furthemwre, eaclt radiation, gamma or UV, fills different depth traps preferentially. 17tese characteristics show the potentia/ usefulness of LiF:Mg, Cu in gamma and UV radiation dosimetry simul-taneou_sly. 17te best choise amongst ali tlle analysed samples is LiF doped witlt O, I or 0,2 moi% of Mg and 0,03 moi% of Cu. Also the influence of dopallts (Mg and Cu) on the TL sensitivity of LiF to gamma rays was investigated perfonning an empírica/ analysis. An exce//ent fit between the experimental data and a mathematica/ relation was obtained. From tlzis study it was possib/e to conc/ude that if LiF !tas only Mg as impurity, its glow curve can exltibit a lzigh seltsitivity to ionizing radiation, being lwwever the maximum sensitivity extremely dependem on the Mg concentration. 17tis fact can be avoided adding small quamity of Cu, which behaves as a poisoner, decreasing the quantity of Mg responsible for TL signal. i v CAPITUI,O 4 CONPOHTAITENTO DOS LTF(S) QUAI,IDO EXPOSTOS À, RADLAçÃO cAttA ou ULTRAVTOLETA.... .. 4.7. ResposÈa TL dos LiF: llg,Cu expostos à radiação gama..,.. AnáLÍse das ÈemperaËuras dos picos Discussão e conclusões Resposta TL dos LIF: ÈIg,Cu expostos à radiação uLÈravi.oTeta (W ) 4.2.a. Curva da resposÈa TL em função da exposíção radiante O grande interesse com o LiF é evidente, haja visto que só na seção de "características dos materiais" do "9th International Conference on Solid State Dosimetry, eüê se realizou em Viena em 1989, foram apresentados 50 painéis. Desses, 14 se relacionavam diretamente com o LiF dopado com Ti, Mg e Ti, Mg, Cu e P, Mg e Cu. Outros trabalhos tratavam dos diversos materiais, entre eles: LaClr:Tr, MgO, CaCO' BeO, quartzo,vidro etc.. Na opinião do Prof. S. W. S. Mckeever(McK-84) o desenvolvimento desses novos materiais é importante, não só pelas suas inúmeras aplicaçÕes mas principalmente pelo impacto que causariam, possibilitando estudos ainda n...