Pressure quenching of positronium in solid biphenyl Original Research Article

In solid crystalline biphenyl, ortho-positronium (o-Ps), abundant at normal pressure, can be eliminated by application of a pressure of about 100 MPa. The lifetime of o-Ps shortens with the rise of pressure, as a result of diminishing of the free spaces in which it is trapped. However, the lifetime of para-Ps seems to increase, and at 80 MPa, it cannot be distinguished from that of free positrons. Another new effect is the reappearance of the long-lived component in the positron lifetime spectrum at high pressures. The same effect of positronium reappearance, although not so well pronounced, was found in biphenyl at low temperatures.