Two-dimensional angular correlation of annihilation radiation ͑2D-ACAR͒ spectra have been taken for 10 19 cm Ϫ3 phosphorus-doped Si in the as-grown state after having been subjected to 1.8 MeV electron fluences of 1ϫ10 18 and 2ϫ10 18 cm Ϫ2. Positron annihilation lifetime spectroscopy confirms, in accordance with previous works, that positrons are saturation trapping into (V Si :P) pair defect ͑E-center͒ monovacancy sites in the electron irradiated samples. In the as-grown case, the positron-electron autocorrelation functions along the ͓111͔ and ͓1-10͔ directions, obtained through Fourier transformation of the 2D-ACAR data, reveal zero-crossings that deviate only slightly from the lattice points, in a manner consistent with positron-electron correlation effects. Conversely, in the spectra of the irradiated samples, the zero-crossing points are observed to move outward further by between 0.15 and 0.50 Å. This displacement is associated with positron annihilation with electrons in localized orbitals at the defect site. An attempt is made to extract just the component of the defect's positron-electron autocorrelation function that relates to the localized defect orbitals. In doing this features are found that correspond to the expected atomic positions at the vacancy defect site suggesting that this real-space function may provide a convenient means for obtaining a mapping of localized orbitals. The observed approximate separability of positron and electron wave-function autocorrelates leads to an estimate of 0.22 eV for the positron binding energy to the E-center.

In the last few years a number of excellent deconvolution algorithms have been developed for use in "de-blurring" 2D images. Here we report briefly on one such algorithm we have studied which uses the non-negativity constraint to optimize the regularization and which is applied to the 2D image like data produced in Coincidence Doppler Broadening Spectroscopy (CDBS). The system instrumental resolution functions are obtained using the 514keV line from 85 Sr. The technique when applied to a series of well annealed polycrystalline metals gives two photon momentum data on a quality comparable to that obtainable using 1D Angular Correlation of Annihilation Radiation (ACAR).

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