For certain combinations of protons and neutrons, there is a theoretical expectation that the shape of nuclei can assume octupole deformation, which would give rise to reflection asymmetry or a "pear shape" in the intrinsic frame, either dynamically (octupole vibrations) or statically (permanent octupole deformation). In this paper, I will briefly review the historic evidence for reflection asymmetry in nuclei, describe how recent experiments carried out at REX-ISOLDE are constraining nuclear theory and how they contribute to tests of extensions of the Standard Model, and look at future prospects for this field.
This contribution gives an overview of recent mass measurements performed in the 132 Sn region relevant for the r-process studies. The atomic masses of 121−128 Cd, 129,131 In, 130−135 Sn, 131−136 Sb, and 132−140 Te have been measured with the JYFLTRAP double Penning trap mass spectrometer. Among these, the masses of four r-process nuclei-135 Sn, 136 Sb, 139 Te, and 140 Tehave been experimentally determined for the first time. In addition, the masses of the (11/2 −) isomers in 121,123,125 Cd and 133 Te, (1/2 −) isomers in 129,131 In, and (7 −) isomers in 130 Sn and 134 Sb have been measured and corresponding excitation energies have been determined. The groundstate mass values have been compared to recent Atomic Mass Evaluations and deviations have been found in particular for the states based on beta-decay energies.
Abstract. Data on fission yields and isomeric yield ratios (IYR) are tools to study the fission process, in particular the generation of angular momentum. We use the IGISOL facility with the Penning trap JYFLTRAP in Jyväskylä, Finland, for such measurements on 232 Th and nat U targets. Previously published fission yield data from IGISOL concern the 232 Th(p,f) and 238 U(p,f) reactions at 25 and 50 MeV. Recently, a neutron source, using the Be(p,n) reaction, has been developed, installed and tested. We summarize the results for (p,f) focusing on the first measurement of IYR by direct ion counting. We also present first results for IYR and relative yields for Sn and Sb isotopes in the 128-133 mass range from nat U(n,f) based on γ-spectrometry. We find a staggering behaviour in the cumulative yields for Sn and a shift in the independent fission yields for Sb as compared to current evaluations. Plans for the future experimental program on fission yields and IYR measurements are discussed.
Abstract.A new method to measure the fission product independent yields employing the ion guide technique and a Penning trap as a precision mass filter, which allows an unambiguous identification of the nuclides is presented. The method was used to determine the independent yields in the proton-induced fission of 232 Th and 238 U at 25 MeV. The data were analyzed with the consistent model for description of the fission product formation cross section at the projectile energies up to 100 MeV. Pre-compound nucleon emission is described with the two-component exciton model using Monte Carlo method. Decay of excited compound nuclei is treated within time-dependent statistical model with inclusion of the nuclear friction effect. The charge distribution of the primary fragment isobaric chain was considered as a result of frozen quantal fluctuations of the isovector nuclear density. The theoretical predictions of the independent fission product cross sections are used for normalization of the measured fission product isotopic distributions.
should read as follows:A new method to determine independent yields of fission products has been used in the experiment at the Accelerator Laboratory of the University of Jyväskylä. This method combines the chemical universality of the ion guide technique and the unique properties of a Penning trap. A beam of charged particles is formed by stopping fission products in helium. The Penning trap is employed as a high precision filter to identify parti cles by their mass. The yields of fission products are determined by the ion counting after the trap. The mass resolving power of the method is about 105 with 400 ms excitation time. Such mass resolution allows to sep arate not only nuclides but also isomeric and ground states of nuclei. The independent yields of fission prod ucts are measured in the fission of 232 Th induced by 25 MeV protons. A brief description of the method and experimental results are presented in comparison with theoretical calculations.
Several isomeric yield ratios of fission products in 25 MeV proton-induced fission of 238 U were measured recently at the JYFLTRAP facility. The ion-guide separator on-line method was utilized to produce radioactive ions. The double Penning-trap mass spectrometer was used to separate isomeric and ground states by their masses. To verify the new experimental technique γ-spectroscopy method was used to obtain the same isomeric ratios.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.