This work de scribes the pre lim i nary anal y sis of Fricke gels do sim e ters char ac ter ized by a new for mu la tion mak ing use of a ma trix of poly vi nyl al co hol cross-linked by add ing glutaraldehyde and an a lyzed by means of nu clear mag netic res o nance relaxometry. In pre vi ous op ti cal stud ies, these gels have shown prom is ing dosimetric fea tures in terms of pho ton sen si tiv ity and low diffu sion of fer ric ions pro duced af ter ir ra di a tion. In this work, we used a por ta ble nu clear mag netic res o nance relaxometer to mea sure the re laxation times (which are im por tant for dosimetric ap pli ca tions) of these gel ma te ri als. For this pur pose, we per formed a study for op ti miz ing the ac qui si tion pa ram e ters with a nu clear magnetic res o nance relaxometer. Gel sam ples were ex posed to clin i cal 6 MV pho tons in the dose range be tween 0 and 20 Gy. Nu clear mag netic res o nance relaxometry mea sure ments were performed and the sen si tiv ity to pho ton beams was mea sured for var i ous val ues of the Fe 2+ ion con cen tra tion. The anal y ses pointed out that the MR sig nal in creases as the Fe 2+ con tent increases and the in crease is about 75 % when the con cen tra tion of Fe 2+ ions is in creased from 0.5 mM to 2.5 mM. Fur ther more, the sen si tiv ity im prove ment achieved with in creas ing the Fe 2+ con cen tra tion is about 60 %. This pa per shows that the por ta ble nu clear mag netic res onance relaxometer used for anal y sis of po rous ma te ri als can be used for char ac ter iza tion of these dosimetric gels and this study can be con sid ered as the first step for the char ac ter iza tion of these do sim e ters which in fu ture could be used for 3-D dose map ping in clin i cal ap pli ca tions.