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In the radiation shielding of thermonuclear reactors inhomogeneities are usually present in the form of voids or inclusions of a different material which make provision for dismantling the installations for reactor plasma heating and vacuum pumping, diagnostics of its operation, the supply of coolants, and other purposes. As a rule, the presence of inhomogeneities is accompanied by a significant degradation of the radiation shielding characteristics, and this requires additional measures to be adopted for reducing the radiation beyond the shielding to acceptable values. Under the conditions of tight geometry which characterize thermonuclear reactors the scope is usually limited for making provision for an excess thickness of shielding in the region of local inhomogeneities in order to compensate for possible inaccuracies in the calculations. Stringent requirements are therefore imposed on the accuracy of calculating the dose rate beyond the radiation shielding in the regions of local inhomogeneities.It is well known that it will not be possible to verify directly the characteristics of projected shielding with a 14 MeV neutron source, under reactor conditions, until the first thermonuclear test reactor is constructed and put into operation. Therefore when designing such a reactor the neutron transport and neutron data must be substantiated in specially organized benchmark experiments with a generator as a 14-MeV neutron source and radiation shielding mocknps which model the transport of the neutrons and ~/photons characteristic of specific configurations.One of the key radiation shielding configurations [1, 2] is a model having a slit which is longitudinal with respect to the direction of propagation of the 14-MeV neutrons and corresponds to a 5-20-mm wide gap in the reactor vessel and radiation shielding. One can consider typical models in the form of pure structural material (the vessel construction) and structural material with 20% of water (radiation shielding). In the present work we investigated both models of slit compositions utilizing iron with an overall mockup thickness of 400 mm. Different mockup geometries are considered for the poss~ility of performing a relative analysis of the effect of a slit gap (Fig. 1), namely solid shielding (without a slit); shielding with straight slits of various widths through the entire thickness or half the thickness of the shielding; shielding with a slit displaced at half the thickness of the shielding (the slit axis being displaced by 20 or 60 mm); iron--water shielding with a 20-mm wide straight central slit. EXPERIMENTAL ASSEMBLYThe shielding mockups were assembled from rectangular 25 x 200 x 500-mm blocks manufactured from steel with an iron content of 98.7%. The chemical composition of the impurities, with a 30% error in the content of the elements, was as follows: Na, Mg, S, C1, V, Cr, Mn, Ni, Cu, Zn, 7.2.10-3%; O, <10-3%; C, 1.7.10-1%; N, <10-3%; Co, 1.46.10-2%.A general view of the shielding models is shown in Fig. 2. The shielding was assembled with blocks ov...

The cross section of Celd2 has been determined by the activation method and found to be 0.954X0.05 barns relative to a value of uc,5B = 36.3 barns. Disintegration rates were determined by a 47r counter. The value obtained agrees with that of Icatcoff el al.