Mass measurements on radionuclides along the potassium isotope chain have been performed with the ISOLTRAP Penning trap mass spectrometer. For 35 K (T 1/2 = 178 ms) to 46 K (T 1/2 = 105 s) relative mass uncertainties of 2×10 −8 and better have been achieved. The accurate mass determination of 35 K (δm = 0.54 keV) has been exploited to test the Isobaric Multiplet Mass Equation (IMME) for the A = 35, T = 3/2 isospin quartet. The experimental results indicate a deviation from the generally adopted quadratic form.

An experimental set-up is described for the precise measurement of the recoil energy spectrum of the daughter ions from nuclear beta decay. The experiment is called WITCH, short for Weak Interaction Trap for CHarged particles, and is set up at the ISOLDE facility at CERN. The principle of the experiment and its realization are explained as well as the main physics goal. A cloud of radioactive ions stored in a Penning trap serves as the source for the WITCH experiment, leading to the minimization of scattering and energy loss of the decay products. The energy spectrum of the recoiling daughter ions from the ¬-decays in this ion cloud will be measured with a retardation spectrometer. The principal aim of the WITCH experiment is to study the electroweak interaction by determining the beta-neutrino angular correlation in nuclear ¬-decay from the shape of this recoil energy spectrum. This will be the first time that the recoil energy spectrum of the daughter ions from ¬-decay can be measured for a wide variety of isotopes, independent of their specific properties. IntroductionThe standard model of the electroweak interaction is very successful in describing the interaction both qualitatively and quantitatively. However, it contains many free parameters and ad hoc assumptions. One of these is that from the five possible types of weak interactionsvector (V), axial-vector (A), scalar (S), tensor (T) and pseudoscalar interaction (P) -just V and A interactions are present at a fundamental level. Together with maximal parity violation this has led to the well known V A structure of the weak interaction. Most experimental limits for the S and T coupling constants in the charged current sector are rather weak, though [1,2,3,4],

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The atomic masses of the neutron-deficient radioactive rubidium isotopes [74][75][76][77]79,80,83 Rb have been measured with the Penning trap mass spectrometer ISOLTRAP. Using the time-of-flight cyclotron resonance technique, relative mass uncertainties ranging from 1.6 × 10 −8 to 5.6 × 10 −8 were achieved. In all cases, the mass precision was significantly improved as compared with the prior Atomic-Mass Evaluation; no significant deviations from the literature values were observed. The exotic nuclide 74 Rb, with a half-life of only 65 ms, is the shortest-lived nuclide on which a high-precision mass measurement in a Penning trap has been carried out. The significance of these measurements for a check of the conserved-vector-current hypothesis of the weak interaction and the unitarity of the Cabibbo-Kobayashi-Maskawa matrix is discussed.

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The atomic masses of 76,77,80,81 Sr and 129,130,131,132 Sn were measured by means of the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. 76 Sr is now the heaviest N = Z nucleus for which the mass is measured to a precision better than 35 keV. For the tin isotopes in the close vicinity of the doubly magic nucleus 132 Sn, mass uncertainties below 20 keV were achieved. An atomic mass evaluation was carried out taking other experimental mass values into account by performing a least-squares adjustment. Some discrepancies between older experimental values and the ones reported here emerged and were resolved. The results of the new adjustment and their impact will be presented.

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