Propagation speed of y-radiation in brass

The propagation speed (PS) of visible light -represented by a short frequency range in the large frame of electromagnetic radiations (ER) frequencies- in air was measurecL during the last centuryl li, using a great deal of different methods, with high precision results being achieved. Presently, a well accepted value, with very small uncertainty, is c= 299,792.458 Km/siCJ (c reporting to the Latin word celeritas: "speed swiftness·'). \Vhen propagating in denser material media (MM), such value is always lower when compared to the air value, with the propagating MM density playing an important role. Until present, such studies focusing propagation speeds, refractive indexes, dicspersions were specially related to visible light, or to ER in wavelengths ranges dose to it, and with a transparent MM. A first incursion in this subject dealing \\~th y-rays was performed using an electronic coincidence c01.mting system, when the vaIue of it's PS was measured in air, Cf(air)= 298,300.15 Km/s(3l ; a method that went on with later electronic improvements. always in air. To perfonn such measurements the avaiIability of a y-radiation source in which two y-rays are emitted simultaneousIy in opposite directions -as already used(4.5) as welI as applied in the present case- turns out to be essential to the feasibility of the experiment, as far as no reflection techniques could be used. Such a suitable source was the positron emitter cCNa placed in a thin walI metal container in which the positrons are stopped and annihilated when reacting \\1th the medium electrons, in such way originating -as it is very welI established from momentlill1/energy conservation laws(6J- 1:\\70 y-rays, energy 511 KeV each. both emitted simultaneously in opposite directions. In alI the previous experiments were used photomultiplier detectors coupled to NaI(Tl) crystal scintillators, which have a good energy resolution but a deficient time resolution for such purposes. Presently, as an innovative improvement, were used BaF2 and CsF crystal scintilIators which display a much better time resolution. IncidentalIy, the use of y-rays would a110w a detennination of ER propagation values in non-transparent MM, nontransparent for visible light; and in such a way better sketching their structural -or of other nature- properties that may interfere \\'Ith this propagation.