Phosphate glasses for identification of heavy ions

Abstract

Some problems in nuclear physics and cosmic-ray astrophysics require a detector that can precisely identify one type of heavily ionizing particle against a background of other particles of higher or lower ionization rate. Films of polymers such as bisphenol acetone polycarbonate (for example, Lexan), polyethylene terephthalate (for example, Cronar) and allyl diglycol polycarbonate (for example, CR-39) are most commonly used for this purpose1. For some new applications, track detectors made of phosphate glass of suitable composition, chemically etched in an optimally chosen reagent, are proving to be much better than polymeric track detectors. One such application is the study of rare radioactive decay modes involving the occasional emission of a specific energetic nuclide such as 24Ne or 34Si in an enormous background of alpha particles or spontaneous fission fragments2,3. Another is the possibility of resolving neighbouring elements, or isotopes of a given element, in relativistic cosmic rays when the fractional difference in charge or mass is very small, as with Pb (Z = 82) and Bi (Z = 83), or 56Fe and 57Fe4. Here we present the results of a study of the relative sensitivities of a large number of phosphate glasses to relativistic ions of U, Au and La, indicating which ones are particularly useful for particle identification.