Lyoluminescence Dosimetry of L-Proline Incorporated of Sensitizer Dependence on the Temperature and pH of Solution

To increase the sensitivity of dosimeter, it has to improve the properties that are required to increase its sensitivity. It was proven that the dependence of lyoluminscence (LL) of irradiated amino acid (L-prolin) incorporated with chemiluminscence reagent (luciginine) on the pH and temperature of the solution. LL means the emission of light from dissolved material in a suitable solvent, which is previously exposed to ionizing radiation. When the incorporated phosphor irradiated to gamma rays an electronically excited species are trapped within the solid matrix, this extra energy will be emitted in the form of light ( 420-500nm), on dissolving the material in water in this test. The LL intensity increases with increasing pH of the solution. The best reproducible and optimum LL intensity is at (pH=8.5-9) of the solution, However, LL intensity will be decreased when the PH is higher than 12. In this value of pH the stability of free radicals is optimum. The same is found for solvent temperature dependence, the optimum LL intensity is at 45-48 o C. LL intensity will increase up to 70 o C,it was found that the total glow increased because of increasing the self-glow of luciginine , but LL intensity will decrease because of dissociation of phisphore structure. In addition to the self-glow of the sanitizer will increase too at temperate up to 70 o C , however, that will cause self-glow to the dosimeter material.


Introduction
From historical point review, lyoluminscence (LL) of organic solids can be considered as a special case of chemiluminscence [1]. Many years after wiedemann initial observations, Ahnstrom and Ehrestein and later Westermark and Grapengieser, have reported LL in organic solids [2]. Lyoluminescencce yield depends on many parameters such as gamma dose, particle size of the sample, amount of the solute, amount of the solvent, pH value of the solvent, temperature of the surroundings, etc. [3].
It is well-known that the phenomenon of luminescence shows the intensity depends on radiations. The intensity of LL signal is a measure of absorbed dose in the material. Repeatedly, LL has been reported from gamma irradiated and electrolytic dyed alkali halide with water containing luminal as solvent; excess color centers lead to increase LL intensity [4] The present interest in LL and its applications stems from the work initiated in Birmingham by Ettinger. The Birmingham group investigated the effect of LL in both organic and inorganic materials in more detail and first proposed the use of it for the purpose of radiation dosimetry [5]. LL has been observed in the following categories of organic compounds: mono-, poly-and oligosaccharides [6], aminoacids [7], proteins [8], as well as in some complex dry biological materials such as milk [9].
The mechanisms of LL were discussed by the aid of its spectra [10]. Strong evidence is given in favor of the involvement of peroxy radicals, formed by oxidation of radiation produced radicals in the solid [11]. While a kind of defects formed in irradiated inorganic salts, like NaCl, known as color centers, named F-centers and V-centers [12] which release energy of the ionizing radiation in the form of light when dissolved in suitable solvents. Many studies were done in order to enhance LL signal, Eriksson showed that LL signal about ten times brighter in water saturated with N 2 than with O 2 [13]. C.Bhawna etal. Study the effect of pH on LL signal by using the color centers formed in NaCl [14].
In this study , the LL of L-proline incorporated with luciginine were developed, such phosphors raises hopes that the practical range of radiation doses extends well below and its dependence on pH and the temperature of solution.

The experiment
Different concentrations of luciginine (10 -3 M up to 10 -5 M) were added to a fixed weight of Lproline (10mg), the solution left to dry at ambient temperature. Then the powder having different grain sizes were separated by using sieves of particular dimensions which represented in (Table-1). Then powder was colored for 30 seconds by exposing them to Caesium-137 (Cs 137 ) gamma source of dose rate 0.35 Gy/min. Figure-1 shows the experimental set up that is done locally in order to be used for LL measurements, solvent(water of different pH) was dropped on the powder using syringe. The intensity of LL produced was detected by an electronic integrator scalar. PMT Holder Cover LL reader Figure-3 shows the time dependence of the LL intensity for different pH of the solution for Lprolin incorporated of lucigenin. It had seen that LL intensity increases with an increasing pH value of the solvent and then it was decreased with increasing the pH value of the solvent for pH>12; so when grain size 0.1 mm, The best value for pH is 8.5.  2160 Figure-5 shows the dependence of LL signal, the total lumin. separated from self-glow where the self-glow is a lumen without radiate, on different solvent temperature. From the figure, it has seen LL intensity increases with increasing of solvent temperature, but after 45-48 o C self-glow of lucigenin become large, which makes a large uncertainty in measurements. Solvent temperature degrees more than 70 0 C cause dissociate the structure of the phosphor which causes decreasing LL signal as temperature increase.

Discussion
When irradiated organic solids are dissolved in water, then the free radicals (reactive oxygen species), that trapped within the solid matrix, releases from F-centres and the formation of hydrate electrons ( eaq ) take place. The subsequent recombination of hydrated electrons with its counterpart (V-centers) at water solid interface gives rise to luminescence. Schematically the mechanism of LL may be described by the following equations: Hydration → F-centre + eaq eaq + V 2 -centre → h υ (Recombination :water-solid interface). Chandra et al. [12] have shown that the LL intensity (I) exponentially depends on different parameters and it can be expressed as: I α {exp(-αt)-exp(-βt)} ……………………….………….. (1) Where: β is the rate constant for the recombination of free radicals, α, rate of dissolution of a solute in the solvent, t is time dissolution. The above equation shows that when water will be dropped into the solute, initially the LL intensity should increase linearly with time, attain maximum value and then it should decrease exponentially with time. This fact is supported by the result illustrated in Figure-4. It is evident from Figure-2 that I max initially increases and then decreases with increasing grain size of the crystals.
Equation .1 indicates I decrease with increasing grain size of the phosphorus, firstly due to the formation of less density of free radicals in larger grain as compared to that in the phosphorus of smaller grains, and secondly due to the decreases of (α) rate of dissolution with increasing grain size of the phosphorus. For smaller grain size, I may decrease with decreasing grain size because of the less stability of the free radicals in the phosphorus of smaller dimensions, where the significant bleaching of the free radicals which agree with [13]. Figure-3 shows the dependence of LL intensity on the pH of the solution. It is seen that LL intensity is optimum for the particular pH of the solvent. It has been shown that the maximum intensity in LL is observed the pH range in which the stability of the hydrated electron is optimum which agree with [10][11]. Equation (1) shows that the LL intensity depends on different parameters. These factors β,N o ( relation constant of equation 1) t and α are independent of the pH value of the solution.
It's known that pH is the negative logarithm of hydrogen ion concentration: pH = -log [H + ], pure water is essentially a covalent compound. It ionizes very slightly and the following equilibrium is established.
H 2 O → H + + OH -Where H + is a hydrogen ion and OHis a hydroxyl ion. The removal of one orbital electron from a hydrogen atom yields the positive hydrogen ion or hydrogen cation, which is, in fact, a bare proton. The bare protons have no separate existence in solution and own its stability to salvation by a water molecule to give a hydronium ion (H 2 O + ). The ionization equilibrium of water is thus represented more accurately as: It has been found for the low value of pH, the LL intensity decreases with decreasing pH of the solution. The decreasing pH means the increase in the hydrogen ion concentration or [H 3 O + ] concentration. For lower pH the existence of more hydrogen ions may cause decreases in the number of hydrogen ions. Because the electron of the hydrated electron may combine with the hydrogen ions. Thus the probability of non-radioactive recombination of the hydrated electron may combine with hydrogen ions. Thus the probability of non-radiative combination of hydrate electron may decrease with decreasing pH of the solution and consequently the LL intensity may decrease with decreasing pH of the solution and consequently the LL intensity may decrease with decreasing pH of the solution. It has been found that for higher pH, the LL intensity decreases with increasing pH of the solution. As the pH increasing means the increasing concentration of [OH -] ions. Consequently, the number of holes responsible for luminescence may decrease with increasing pH of the solution. As a matter of the fact, for higher pH value, the LL intensity may decrease with increasing pH of the solution. In this way, the LL intensity should be optimum for a particular pH of solution.

Conclusion
It was concluded that amino acid (L-prolin) incorporated with chemiluminscence reagent (luciginine)is the best dosimeter for LL technique. It was proven that LL intensity is related to the construction of free radicals that are generated by the radiation. In our procture it was dealing with omino acid which is the smallest building unite of protein that is the main component of human muscles, therefore, the mentioned Phosphor can be used as a tissue equivalent for dosimetry purposes in case of invitro studies. The optimum conditions of LL signal were obtained at considered phosphorus of size 0.1 mm, pH= (8.5-9) and solvent temperature 45-48 o C. These conditions was the best approach of the LL signal.