Alpha and gamma spectroscopy methods for thoron progeny implanted in glasses and other materials

Many retrospective studies regarding the long time exposure to radon (222Rn) are based on theaccumulation of 210Pb (T1/2=22.3y) on the surface of glass objects or other materials and measuring thespecific alpha activity of 210Po (T1/2=138 d, E?=5.3 MeV) resulted by implanting of radon daughters,due to the alpha recoil. In the case of thoron (22oRn) this method is not applicable because there is nota long life time isotope to allow a signifficant accumulation of any descendant. The longest life timeof the thoron descendants is 212Pb with a live time of T1/2= 10.6 hours. But a study involving thorondaughters implanted at the surface of glasses or other materials (plastic, wood, paper, polyethylene,Plexiglas, Cu or Al foils) can be useful in the simulation of radon progeny implantation. Thissimulation is possible due to the equilibrium of implantation, which is obtained in a short time (about50 h) compared to about 100 y in the case of 222Rn. An alpha spectrometry method was recentlyapplied to measure the thoron contribution in the case of integrating track-etch detectors used forthoron monitoring or in the studies regarding radon and thoron progeny deposition. The purpose ofthis work is to obtain the alpha and gamma spectra (especially alpha) for thoron daughters implanted atthe surface of different materials and to show the possibility of this method to simulate the radonprogeny implantation and thus to find some parameters used in the Jacobi model. For measurementswe used a PIPS detector of Canberra type (900 mm2) with 25 keV energy resolution and a NaI(Tl)scintillator for gamma counting. The samples were obtained by exposure of our materials in a thoronvessel ( 0.3 L) containing 200 g Th(NO3)25H2O. The first results shoved that these alpha spectra canbe obtained and that the width of alpha peaks depends on the materials. The constant of implantationestimated for all used samples varies between 10 mBq/m2:Bq/m3 and 62 mBq/m2:Bq/m3 for the case ofequilibrium.