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Isomers produced by spontaneous fission of ${}^{252}$Cf have been measured with the VESPA setup, composed of LaBr$_3$(Ce) detectors for fast $\gamma$-ray spectroscopy and an ionization chamber for detecting fission fragments. Identification of the isomers was derived from fission fragment-$\gamma$-$\gamma$ coincidences. This paper presents the half-life of 34 isomeric states measured with this setup, from less than the nanosecond up to tens of microseconds. Two of these isomers are reported for the first time, in ${}^{108}$Tc and ${}^{147}$Ce. In addition to this half-life analysis, the isomers are used to develop and test a nuclear charge calibration of the ionization chamber.

At the FRS Ion Catcher (FRS-IC), projectile and fission fragments are produced at relativistic energies, separated in-flight, energy-bunched, slowed down, and thermalized in the ultra-pure helium gas-filled cryogenic stopping cell (CSC). Thermalized nuclei are extracted from the CSC using a combination of DC and RF electric fields and gas flow. This CSC also serves as the prototype CSC for the Super-FRS, where exotic nuclei will be produced at unprecedented rates making it possible to go towards the extremes of the nuclear chart. Therefore, it is essential to efficiently extract thermalized exotic nuclei from the CSC under high beam rate conditions, in order to use the rare exotic nuclei which come as cocktail beams. The extraction efficiency dependence on the intensity of the impinging beam into the CSC was studied with a primary beam of 238U and its fragments. Tests were done with two different versions of the DC electrode structure inside the cryogenic chamber, the standard 1 m long and a short 0.5 m long DC electrode. In contrast to the rate capability of 10^4 ions/s with the long DC electrode, results show no extraction efficiency loss up to the rate of 2x10^5 ions/s with the new short DC electrode. This order of magnitude increase of the rate capability paves the way for new experiments at the FRS-IC, including exotic nuclei studies with in-cell multi-nucleon transfer reactions. The results further validate the design concept of the CSC for the Super-FRS, which was developed to effectively manage beams of even higher intensities.

The gamma-ray emissions from a radiopure cerium-bromide crystal with a mass of 4381 g were measured for a total of 497.4 d by means of high-resolution gamma-ray spectrometry in the HADES underground laboratory at a depth of 500 m.w.e. A search for 0/2nee and 0/2neb+ double beta decay transitions of Ce-136 and Ce-138 was performed using Bayesian analysis techniques. No signals were observed for a total of 35 investigated decay modes. 90% credibility limits were set in the order of 1e18-1e19 a. Existing constraints from a cerium oxide powder measurement were tested with a different cerium compound and half-life limits could be improved for most of the decay modes. The most likely accessible decay mode of the Ce-136 2nee transition into the 0+1 state of Ba-136 results in a new best 90% credibility limit of 5.0e18 a.

Prompt fission $\gamma$-rays are responsible for approximately 5\% of the total energy released in fission, and therefore important to understand when modelling nuclear reactors. In this work we present prompt $\gamma$-ray emission characteristics in fission, for the first time as a function of the nuclear excitation energy of the fissioning system. Emitted $\gamma$-ray spectra were measured, and $\gamma$-ray multiplicities and average and total $\gamma$ energies per fission were determined for the $^{233}$U(d,pf) reaction for excitation energies between 4.8 and 10 MeV, and for the $^{239}$Pu(d,pf) reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra $\sim$5 MeV of energy is potentially available in the excited fragments for $\gamma$-decay. The measured results are compared to model calculations made for prompt $\gamma$-ray emission with the fission model code GEF. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.

In this paper we have taken into account shell inhomogeneities of the single-particle level spectra in the practical model of the gamma-decay of neutron resonance developed in Dubna. The obtained data confirm a dependence of breaking thresholds for Cooper pairs on a shape of investigated nuclei - a phenomenon noticed earlier without taking into account the shell inhomogeneity.

The double-energy double-velocity ($2E$-$2v$) method allows assessing fission-fragment mass yields prior to and after prompt neutron emission with high resolution. It is, therefore, considered as a complementary technique to assess average prompt neutron multiplicity as a function of fragment properties. We have studied the intrinsic features of the $2E$-$2v$ method by means of event-wise generated fission-fragment data and found severe short-comings in the method itself as well as in some common practice of application. We find that the $2E$-$2v$ method leads to large deviations in the correlation between the prompt neutron multiplicity and pre-neutron mass, which deforms and exaggerates the so called `sawtooth' shape of $\bar{\nu}(A)$. We have identified the treatment of prompt neutron emission from the fragments as the origin of the problem. The intrinsic nature of this deficiency, risk to render $2E$-$2v$ experiments much less interesting. We suggest a method to correct the $2E$-$2v$ data, and recommend applying this method to previous data acquired in $2E$-$2v$ experiments, as well., Comment: 5 pages, 5 figures

The amount of emitted prompt neutrons from the fission fragments increases as a function of excitation energy. Yet it is not fully understood whether the increase in \nu(A) as a function of E_{n} is mass dependent. The share of excitation energies among the fragments is still under debate, but there are reasons to believe that the excess in neutron emission originates only from the heavy fragments, leaving \nu_{light}(A) almost unchanged. In this work we investigated the consequences of a mass-dependent increase in \nu(A) on the final mass and energy distributions. The assumptions on \nu(A) are essential when analysing measurements based on the 2E-technique. This choice showed to be significant on the measured observables. For example, the post-neutron emission mass yield distribution revealed changes up to 10-30%. The outcome of this work pinpoint the urgent need to determine \nu(A) experimentally, and in particular, how \nu(A) changes as a function of incident-neutron energy. Until then, many fission yields in the data libraries could be largely affected, since they were analysed based on another assumption on the neutron emission., Comment: 4 pages, 3 figures, Proc. 2013 International Conference on Nuclear Data for Science & Technology (ND2013), March 4-8, 2013, New York, USA, to be published in Nuclear Data Sheets

Two methods of the total excitation energy (TXE) partition between complementary fission fragments (FF) are compared: one based on the "classical" hypothesis of prompt neutron emission from fully accelerated FF with both fragments having the same residual nuclear temperature distribution,the second one on the systematic behavior of the experimental multiplicity ratio {\nu}H/({\nu}L+{\nu}H) as a function of the heavy fragment mass number AH,the complementary FF having different residual temperature distributions.These methods were applied on six fissioning systems: 233,235U(nth,f), 239Pu(nth,f), 237Np(n5.5MeV,f), 252Cf(SF), 248Cm(SF) and fragment excitation energies,level density parameters,fragment and fragment pair temperatures were compared.Limitations of the "classical" TXE partition method are shown.Residual temperature ratios RT=TL/TH versus AH,local and global parameterizations of RT(AH) for the neutron induced fissioning systems are obtained.Average values of quantities characterizing prompt neutron emission are discussed.A linear decrease of with the mass number of the fissioning nucleus and a linear decrease of the average C parameter with the fissility parameter is obtained.Point by Point (PbP) model calculations validate the RT(AH) parameterizations.The multi-parametric matrix {\nu}(A,TKE) as well as prompt neutron and gamma-ray emission quantities as a function of fragment mass,total average prompt neutron multiplicity and spectrum and prompt neutron multiplicity distribution P({\nu}) were calculated.The global RT(AH) parameterization extends the use of the PbP model to predict prompt neutron emission quantities for fissioning systems without experimental data.An explanation of the less pronounced sawtooth shape of {\nu}(A) and the increase of {\nu}(A) with incident neutron energy only for heavy fragments is given and exemplified by quantitative results of the PbP model.