Beta-neutrino recoil broadening in?-delayed proton emission of32Ar and33Ar

Abstract

Abstract. In high-resolution measurements of delayed protons following the/?-decays of 32Ar and 33At we have observed significant line broadening caused by the/?-v recoil motion of the daughter nuclei. The measured line shapes agree well with the calculation for both Fermi and Gamow-Teller decays and yield new spectroscopic information on the transitions and excited states involved. For the Gamow-Teller strength in the/?+-decay of 33Ar to the isobaric analogue state in 33C1 an upper limit of B~T < 0.029 was determined.

Detailedβ-decay study ofAr33

“…To ensure correct identification due to the different decay branches, the γ-gated proton spectrum for the 2230 keV γ line was normalized to the β-gated spectrum by means of the proton peak at 1317 keV which is assumed to be only due to emission to the first excited state [9]. As this line is seen in the β-gated spectrum and, of course, in the spectrum gated with the 2230 keV γ line, both spectra can be normalized with respect to each other and a common relative normalization can be established.…”

“…The matrix element for nuclei with an isospin quantum number T = 3/2 is √ 3. This allows the Fermi f t value to be calculated to be 2048 s. [9] are neither resolved in the present work nor in the work of Borge et al [8]. The absolute intensities have been determined by normalizing all proton group with respect to the 3173 keV line for which the absolute branching ratio was established as described in the text.…”

“…This contribution can either be determined experimentally (see e.g. [9,11]), be neglected assuming its contribution to be small, or taken from theoretical predictions. We will calculate the Fermi part neglecting the corrections mentioned above and take the GT contribution from Ref.…”

“…Schardt et al [9] and Garcia et al [11] also determined limits of possible scalar contributions to β decay and the Fermi-to-Gamow-Teller ratio of the decay of 33 Ar. We will in particular use this ratio in our analysis and comparison to theory.…”

“…The decay of 33 Ar, the subject of the present work, was studied several times in the past (see [4][5][6][7][8][9][10][11]). Our experimental data are compared to the most recent work from these authors and experimental averages are confronted to theoretical shell-model calculations using different effective interactions optimized for the 2s1d nuclear shell-model space.…”