Living beings constantly absorb 14C in tissues; Although 14C disintegrates, in living tissues it it constantly renews itself by keeping itself in balance while they are alive. After the death of the organism, it ceases the absorption of 14C and therefore its concentration begins to decrease according to the equation dx dt = x, > 0

(1) where x (t) represents the number of 14C atoms present in the tissue at time t. It is also known that when taking a sample of fossil tissue the disintegration rate N (t) is proportional to the quantity of 14C atoms present in the sample at time t and is expressed in disintegrations per minute per gram, dpmg, of 14C. The reference decay is 13.56 dpmg at death, that is, N (0) = 13.56.

In 1964 at the archaeological site of Teotihuacan, excavations were carried out in several basements located along from the Avenue of the Dead. Charred remains of beams that belonged to roofs and jambs were found. A of the beams belonging to the palace of Quetzalpapalotl gave 10.86 disintegrations per minute per gram of 14C. Determine the date this beam was used.