Scattering of Hardγ-Rays

Abstract

Measurements have been made on the scattering of 7-rays from Th C" by Al and Pb. For Al the scattering is, within experimental error, that predicted by the Klein Nishina formula. For Pb additional scattered rays were observed. The wavelength and space distribution of these are inconsistent with an extranuclear scatterer, and hence they must have their origin in the nuclei.

A brief review of antimatter production

“…In 1930, C. Y. Chao performed a few γ-ray scattering experiments on different elements [3,4]. γ-rays from Th C after being filtered through 2.7cm of Pb were used as the primary beam.…”

“…The STAR collaboration also reported its observation of 4 He nucleus [18,20] in April 2011, with 10 billion goldgold collisions taken in the year 2007 and 2010. In addi-tional to the particle identification method by combining energy loss ( dE/dx ) and rigidity provided by TPC, the observation of 4 He nucleus relies on the measured traveling time of tracks given by the barrel TOF [39], which is composed of 120 trays, surrounding the TPC. With the barrel TOF, the mass value of particles can be calculated via m 2 = p 2 (t 2 /L 2 − 1) (where t and L are the time of flight and path length of tracks, respectively) for particle identification.…”

“…Together with 2 4 He candidates detected by TPC alone in the year 2007 which is presented in the figure, 18 4 He can-didates are observed by the STAR experiment. So far, 4 He is the heaviest antimatter nucleus observed in the world. Right after the public report of 4 He from the STAR collaboration, the LHC-ALICE collaboration also claimed the observation of 4 4 He particles [40].…”

“…However, the modern concept of antimatter is originated from the negative energy state solution of a quantum-mechanical equation, which was proposed by Dirac in 1928 [2]. Two years later, Chao found that the absorption coefficient of hard γ-rays in heavy elements was much larger than that was to expected from the Klein-Nishima formula or any other [3,4]. This "abnormal" absorption is in fact due to the production of the pair of electron and its anti-partner, so-called positron.…”

“…Furthermore, as we learned from heavy ion collisions, the production rate for 4 He produced by colliding the high energy cosmic rays with interstellar materials is too low to be observed. Even one 4 He or heavier antinucleus observed in the cosmic rays should be a great hint of the existence of massive antimatter in the Universe. Finally, the successful trap of antihydrogen atoms leads to a precise test of the CPT symmetry law, as well as a measurement of the gravitational effects between antimatter and matter in the future.…”