A fully analytical description of the allowed β spectrum shape is given in view of ongoing and planned measurements. Its study forms an invaluable tool in the search for physics beyond the standard electroweak model and the weak magnetism recoil term. Contributions stemming from finite size corrections, mass effects, and radiative corrections are reviewed. Particular focus is placed on atomic and chemical effects, where the existing description is extended and analytically provided. The effects of QCD-induced recoil terms are discussed, and cross-checks were performed for different theoretical formalisms. Special attention was given to a comparison of the treatment of nuclear structure effects in different formalisms. Corrections were derived for both Fermi and Gamow-Teller transitions, and methods of analytical evaluation thoroughly discussed. In its integrated form, calculated f values were in agreement with the most precise numerical results within the aimed for precision. The need for an accurate evaluation of weak magnetism contributions was stressed, and the possible significance of the oft-neglected induced pseudoscalar interaction was noted. Together with improved atomic corrections, an analytical description was presented of the allowed β spectrum shape accurate to a few parts in 10-4 down to 1 keV for low to medium Z nuclei, thereby extending the work by previous authors by nearly an order of magnitude.

High precision analytical description of the allowed β spectrum shape

Nuclear Data Sheets for A = 210

Nuclear data sheets for A = 210

Internal bremsstrahlung from P32, Sr89, Y90, Y91 and Bi210

Auto-ionization in β-decay: A model calculation

Internal bremsstrahlung spectra from S35 and Pm147 have been investigated with the NaI scintillation spectrometer. Both the absolute cross section of production and the energy distribution agree with theoretical predictions. The theoretical internal bremsstrahlung spectrum of RaE was calculated by using both the observed forbidden beta spectrum and an allowed beta distribution. No significant differences in shape were found in these two cases except in the absolute cross section of production. 

The ionization accompanying beta decay was studied in the case of RaE and also in Pm147 by measuring the characteristic x-rays in an NaI scintillation counter as well as in a proportional counter spectrometer. Both K and L radiations were observed, and their absolute cross sections were compared with the theoretical calculations of Migdal, Feinberg, and Levinger. Because of the approximate nature of the theoretical calculations, the agreement between the theoretical and experimental results is considered satisfactory.

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F. Boehm

Papers

Internal Bremsstrahlung and Ionization Accompanying Beta Decay