The present invention relates to a synthetic resin composition containing a lanthanoid and a process for producing the same.
Synthetic resins such as methacrylic resin have been used widely in various fields, since they have excellent transparency, weather resistance and mechanical properties. However, they could not be used for shielding radiation because they have no such properties.
Recently, radiation-shielding materials comprising a methacrylic resin containing lead have been developed (see Japanese Patent Publication No. 2360/1960 and Japanese Patent Laid-Open Nos. 9994/1978, 9995/1978, 9996/1978 and 63310/1978).
However, these radiation-shielding materials containing lead have only an insufficient capacity of shielding neutron rays, though they shield effectively electromagnetic waves such as X-rays and .gamma.-rays and charged particles such as .alpha.-rays and .beta.-rays.
It has been known to add a boron compound to a polyethylene or methacrylic resin to obtain a high-molecular material capable of shielding neutron rays (Japanese Patent Laid-Open No. 144597/1980). According to this process, a high neutron rays-absorbing capacity can be obtained. However, the capacity is gradually reduced as the neutron absorption proceeds, since helium and lithium formed by the neutron absorption have no appreciable neutron-absorbing capacity. Further, the optical and mechanical properties of the resin are yet unsatisfactory.
It has also been known that a rare earth element has a thermal neutron-absorbing capacity higher than that of boron. However, this element has only a poor compatibility with the synthetic resin, since it is a solid metal. Thus, synthetic resins having excellent optical and mechanical properties have not been obtained yet.