Radioactivity of the water in the ground shield of accelerators

We consider in the present work the activation of the subsurface water taken from the premises of the Mezonnaya Fabr[ka in Krasnaya Pakhra, Moscow District; we studied the absorption of the isotopes formed in the water by the soil. The water had been irradiated for 35 days by secondary particles (with energies of up to 70 GeV) generated by the proton synchrotron of the Institute of High-Energy Physics (city of Serpukhov). The flux of particles with energies in excess of 20 MeV amounted to (4.5  0.7) �9 107 particles/era 2 �9 sec at the point of irradiation; the flux of thermal neutrons was (2.0 :~ 0.3) �9 107 neutrons/cm 2 �9 The water was stored for one month after its irradiation. The short-lived isotopes (T1/2 < 1 week) had practically decayed after that time. The induced ~, radioactivity was measured with a semiconductor spectrometer. The induced fl radioactivity was determined with a UMF-1500 device with small background and with a Protok 4n-fl-counter (for measuring the tritium). A ring counter was the radiation detector of the UMF equipment. The specific activities of the isotopes were determined with the method of measuring the fl radiation of thick-layer sources [9]. The isotope composition of the source and the contribution of each isotope to the measured activity were determined by constructing the absorption curve of the fi radiation in aluminum. The tritium concentration was measured in distilled water which had been irradiated along with the subsurface water. One month after the irradiation, only the fl emitter, the tritium, remains in the distilled water (the tritium is formed only from oxygen, as in the case of the subsurface water); the tritium need not be separated from the other isotopes. The results are listed in Table 1. The subsurface water which had been contaminated inthe region of the accelerator comes into contactwith the rocks of the water-bearing level which can cause purification of the water mainIy by absorption of the isotopes by the soil. The absorbing capability of the ground for the radioactive isotopes is characterized by the distribution coefficient, which was determined as follows: 5 g of soil were placed into a receptacle to which 50 g of radioactive solution were added; the contents were mixed; thenthe solutiou was divided with a centrifuge and the residualradioact ivity of the solution was determined. The distribution coefficient was calculated with the formula K d =As/Af, where A s denotes the specific activity of the solid phase (soil), and Af denotes the specific activity of the fluid phase (solution removed by centrifuging). In order to determine the distribution coefficient of beryUium, irradiated subsurface water was the initial solution. When the absorption of the remaining isotopes was investigated, radioactive standard samples of NaCI, (NI-I4)2HPOa, SO a ions, and CaC12 dissolved in nonirradiated subsurface water were employed. The results are listed in Table 2. It follows from Table 2 that the absorption depends upon both the isotope and the type of the soil (samples from the premises of the Mezonnaya Fabrika).