Study of positron lifetime in scintillation materials

The possi­bi­lity of appli­ca­tion of posi­tron anni­hi­la­tion life­time spec­tro­scopy for defect cha­rac­te­ri­za­tion in scin­til­la­tors is inve­sti­ga­ted. The method is suc­cess­fully used for metal and semi­con­duc­tor mate­rial eva­lu­ation. A posi­tron cre­ated during radio­ac­tive decay is used as a probe while it anni­hi­la­tes in the exa­mi­ned mate­rial.

The method is sen­si­tive eno­ugh to iden­tify even small con­cen­tra­tions of vacancy defects. The posi­trons implan­ted in the sam­ple quic­kly lose their energy and anni­hi­late with dif­fe­rent times and pro­ba­bi­li­ties depen­ding on the den­sity of the local elec­tric field. In the case of a per­fect cry­stal lat­tice the phe­no­me­non is delo­ca­li­zed, but when there are vacancy defects, the distur­bed poten­tial ori­gi­na­ting from the lack of atoms in the lat­tice traps the posi­trons expan­ding their life­time in com­pa­ri­son to a case of the per­fect lat­tice. By fit­ting mul­ti­ple expo­nen­tial com­po­nents to the measu­red posi­tron life­times it is possi­ble to cal­cu­late the trap­ping rates which are pro­por­tio­nal to defect con­cen­tra­tions.

Leader:

Kamil Bry­lew, PhD