Isospin mixing in theT=5/2ground state ofAs71

Abstract

The presence of isospin mixing in the T = 5/2 ground state of 71 As was studied via anisotropic positron emission from oriented nuclei. A small isospin-forbidden Fermi component in the predominantly Gamow-Teller β decay was established, corresponding to an isospin mixing probability of (13 ± 4) × 10 −6 . The sign of the magnetic moment of 71 As was determined to be positive.

Half-life ofFr221in Si and Au at 4 K and at millikelvin temperatures

“…Note that electron capture decay rates may depend on the material hosting the radioactive isotope via small modifications of the electron density around the EC-decaying nucleus (see, e.g., [8] and references therein). In contrast to the above results, several experiments carried out at a later stage on the β-decaying isotopes 198 Au [9][10][11][12], 22 Na [11,12], 64 Cu [13], and 74 As [14], and on the EC-decaying 7 Be [10], did not observe any changes of the half-lives up to the permille level when these isotopes were embedded in a metallic environment and cooled down to 10-20 K.…”

“…Substitutional fractions of about 70% to 95% are generally observed for 60-keV implantations into a cold (i.e., 4 K or lower) Fe foil (e.g., Refs. [21][22][23][24]). In LTNO experiments on α-decaying isotopes implanted in Fe, no half-life changes at the percent level were observed between room temperature and 1 K [17], and between 4 K and 50 mK [16].…”

“…The half-life of α-decaying 210 Po implanted in copper was reported to shorten by 6.3(14)% when cooled down to 12 K [4], the half-life of β + -decaying 22 Na embedded in Pd was observed to be 1.2(2)% shorter at 12 K [5], the half-life of β − -decaying 198 Au embedded in Au was observed to be 4(2)% longer at 12 K [6], and for 7 Be [electron capture (EC)] decay), an increase of about 1% was reported [7]. Note that electron capture decay rates may depend on the material hosting the radioactive isotope via small modifications of the electron density around the EC-decaying nucleus (see, e.g., [8] and references therein).…”

A GEANT4 Monte-Carlo simulation code for precision spectroscopy

“…in the amplitudes (14)) require the angular distribution coefficientà (see below) to be determined with a precision better than about 1 %. In the past we have performed already several measurements of the angular distribution of β radiation with the LTNO method (17), (18), (19). However, in order to reach the 1 % precision level the method had to be further optimized.…”

Isospin Mixing inZr80: From Finite to Zero Temperature

“…Particular effort is being made to deduce the value of isospin mixing for nuclei in different mass regions [4,5]. Tools are selection rules for the electric dipole (E1) transition in self-conjugate nuclei [6] and the β Fermi transition between states with different isospin [7].For the E1 transitions the giant dipole resonance (GDR), where the maximum E1 strength is concentrated, is ideal for searching for small effects in the breaking of the associated selection rule [8][9][10]. For N ¼ Z nuclei with medium mass, being not stable, the approach that can be used is to form, via fusion reactions, compound nuclei (CN) with N ¼ Z at finite temperature (T) and then deduce isospin mixing at T ¼ 0 using the model of [11] connecting this quantity from T ¼ 0 to finite T.…”