Positron annihilation methods are unique and strong tools to investigate materials. However, positrons are usually injected from outside of the samples. Therefore, the samples should be in a vacuum or radioisotopes should be attached. Recently, Selim et al. applied high-energy gamma-rays (2 MeV) produced by a 6 MeV electron linac to create positrons in thick materials. We have also been trying a similar technique. In our case, high-energy gamma-rays (similar to20 MeV) produced in laser-induced Compton-backscattering are applied to positron creation in samples. The gamma-rays do not spread and are not absorbed in air. When you place a sample in the path of the gamma-rays, positrons are created in the sample and conventional positron annihilation methods can be applied. Moreover, it is not necessary to place the samples in vacuum and radioisotopes are not required. This means that the measurements of materials such as metals at very high temperature, near or over melting points, will be possible. The details of this method and some examples of experimental results will be introduced.