Plastic foils as primary hydrogen standards for nuclear reaction analysis

Plastic materials like polypropylene, polyester (Mylar) and polycarbonate (Lexan or Makrofol E) contain large amounts of hydrogen and their compositions are well known. However, these materials are not stable during ion bombardment. Using the ¹H(¹⁵N,αγ)¹²C and ¹H(¹⁹F, αγ)¹⁶O nuclear resonance reaction at energies E_N = 6.50 MeV and E_F = 6.83 MeV, respectively, we have investigated the behaviour of plastic foils during ¹⁵N and ¹⁹F ion bombardment. By means of a rotating sample holder low current densities of 1–2 nA/cm² and large irradiated foil areas of up to 10 cm² were realized. Under these measuring conditions the γ-ray yields change only slightly and the initial yields, which correspond to the known compositions of the foils, can be determined with good accuracy. In this way the plastic foils can be used as primary standards for hydrogen content calibration. The method was employed to calibrate an a-Si(H) reference target.