THE EFFECT OF GADOLINIUM ON THE ESR RESPONSE OF ALANINE AND AMMONIUM TARTRATE EXPOSED TO THERMAL NEUTRONS

Many efforts have been made to develop neutron capture therapy (NCT) for cancer treatment. Among the challenges in using NCT is the characterization of the features of the mixed radiation field and of its components. In this study, we examined the enhancement of the ESR response of pellets of alanine and ammonium tartrate with gadolinium oxide exposed to a thermal neutron beam. In particular, the ESR response of these dosimeters as a function of the gadolinium content inside the dosimeter was analyzed. We found that the addition of gadolinium improves the sensitivity of both alanine and ammonium tartrate. However, the use of gadolinium involves a reduces in or abolishes tissue equivalence because of its high atomic number (ZGd 64). Therefore, it is necessary to find the optimum compromise between the sensitivity to thermal neutrons and the reduction of tissue equivalence. Our analysis showed that a low concentration of gadolinium oxide (of the order of 5% of the total mass of the dosimeter) can enhance the thermal neutron sensitivity more than 13 times with an insignificant reduction of tissue equivalence

ESR RESPONSE TO 60 CO-RAYS OF AMMONIUM TARTRATE PELLETS USING GD2O3 AS ADDITIVE.

This work presents experimental results regarding a new ammonium tartrate blend for ESR dosimetry, with a higher sensitivity and a lower lowest detectable dose (LDD) to 60 Co -rays than the recently used pure ammonium tartrate. The blend composed by ammonium tartrate and gadolinium-oxide (Gd2 O3 ) shows a greater sensitivity (∼2 times) and a smaller LDD than ammonium tartrate. The increased sensitivity was mainly attributed to the great atomic number (Z = 64) of gadolinium, that increases the effective atomic number of the blend; the interaction probability with photons and consequently the radical yield is therefore enhanced. Moreover ammonium tartrate with Gd2 O3 has a linear dose response in the investigated dose range (1–50 Gy). We find this blend suitable for use in ESR dosimetry

EPR dosimetry in a mixed neutron and gamma radiation field

Suitability of Electron Paramagnetic Resonance (EPR) spectroscopy for criticality dosimetry was evaluated for tooth enamel, mannose and alanine pellets during the ‘international intercomparison of criticality dosimetry techniques’ at the SILENE reactor held in Valduc in June 2002, France. These three materials were irradiated in neutron and gamma-ray fields of various relative intensities and spectral distributions in order to evaluate their neutron sensitivity. The neutron response was found to be around 10% for tooth enamel, 45% for mannose and between 40 and 90% for alanine pellets according their type. According to the IAEA recommendations on the early estimate of criticality accident absorbed dose, analyzed results show the EPR potentiality and complementarity with regular criticality techniques

Improvement of neutron sensitivity for lithium formate ESR dosimeters: A Monte Carlo analysis

This work presents the computational analysis of the sensitivity improvements that could be achieved in lithium formate monohydrate (LFM) electron paramagnetic resonance (EPR) dosemeters exposed to neutron beams. Monte Carlo (MC) simulations were performed on LFM pellets exposed to neutron beams with different energy spectra at various depths inside a water phantom. Various computations were carried out by considering different enrichments of 6Li inside the LFM matrix as well as addition of different amounts of gadolinium oxide inside the pellet blend. The energy released per unit mass was calculated with the aim of redicting the increase in dose achievable by the addition of sensitizers inside the pellets. As expected, a larger amount of 6Li induces an increase of energy released because of the charged secondary particles (i.e. 3H ions and α particles) produced after neutron capture. For small depths in water phantom and low-energy neutron spectra the dose increase due to 6Li enrichment is high (more than three orders of magnitude with respect to the case of with 7Li). In case of epithermal neutron beams the energy released in 6Li-enriched LFM compound is smaller but larger than in the case of fast neutron beams. On the other hand, the computational analysis evidenced that gadolinium is less effective than 6Li in improving neutron sensitivity of the LFM pellets. Discussion based on the features of MC transport code is provided. This result suggests that 6Li enrichment of LFM dosemeters would be more effective for neutron sensitivity improvement and these EPR dosemeters could be tested for dosimetric applications in Neutron Capture Therapy

Application of the ESR spectroscopy to estimate the original dose in irradiated chicken bone

The paper discusses the results of an investigation aimed to use the ESR spectroscopy as a quantitative procedure to estimate the original dose in irradiated chicken. The time stability of the ESR signal was at first carried out, to obtain a correction factor to be applied to the dose estimated with the added dose method. Our results show that this procedure gives an estimation of the original dose within ±25%