²³⁹Pu alpha spectrum analysis based on PIPS detector response function and variations with vacuum and distance

Effect factors of the absorption of the source, air, entrance window, and dead layer of a detector must be considered in the measurement of monoenergetic alpha particles, along with statistical noise and other factors that collectively cause the alpha spectrum to exhibit a well-known low-energy tail. Therefore, the establishment of an alpha spectrum detector response function from the perspective of a signaling system must consider the various factors mentioned above. The detector response function is the convolution of an alpha-particle pulse function, two exponential functions, and a Gaussian function, followed by calculation of the parameters of the detector response function using the weighted least-squares fitting method as proposed in this paper. In our experiment, ²³⁹Pu alpha spectra were measured by a high-resolution, passivated implanted planar silicon (PIPS) detector at 10 levels of vacuum and 10 source-detector distances. The spectrum-fitting results were excellent as evaluated by reduced Chi-square (χ²) and correlation coefficients. Finally, the variation of parameters with vacuum level and source-detector distance was studied. Results demonstrate that σ, τ₁, and τ₂ exhibit no obvious trend of variation with vacuum in the range 2000-20,000 mTorr, and at a confidence level of 95%, the values of τ₁ and τ₂ decline in a similar fashion with source-detector distance by the power exponential function, while the value of σ declines linearly. (authors)