QED radiative corrections to the decay π<Superscript>0</Superscript>→e<Superscript>+</Superscript>e<Superscript>-</Superscript>

We reconsider QED radiative corrections (RC) to the π⁰→e⁺e^- decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for π⁰→e⁺e^- decay is estimated to be 3.2%, and for η→e⁺e^- decay it is 4.3%. PACS  13.25.Cq; 12.38.Lg; 12.38.-t     

Double-beta decay of <Superscript>100</Superscript>Mo to 0<Superscript>+</Superscript> excited states in <Superscript>100</Superscript>Ru

A brief review on the 2νββ decay of ¹⁰⁰Mo to the 0⁺ excited state in ¹⁰⁰Ru is performed. A weighted-average half-life value for the decay has been obtained, T_1/2 = (6.8 ± 1.2) × 10²⁰ yr. The corresponding average value for the nuclear matrix element was extracted, 0.095 ± 0.009.     

<Superscript>123</Superscript>I → <Superscript>123</Superscript>Te β decay

The β decay of ¹²³I has been calculated within the dynamic collective model developed by the authors earlier. The expression for the reduced matrix element of the weak-interaction Hamiltonian has been used for the partial β decay. The influence of the vacuum fluctuations and creation or annihilation of one or two phonons on the reduced β-decay probabilities is taken into account.     

Dynamical decay process of <Superscript>219, 220</Superscript>Ra<Superscript>*</Superscript> formed in <Superscript>10, 11</Superscript>B + <Superscript>209</Superscript>Bi reactions

The excitation functions for both the evaporation residue and fission have been calculated for ¹⁰B + ²⁰⁹Bi and ¹¹B + ²⁰⁹Bi reactions forming compound systems ^{219, 220}Ra^* , using the dynamical cluster-decay model (DCM) with effects of deformations and orientations of the nuclei included in it. In addition to this, the excitation functions for complete fusion (CF) are obtained by summing the fission cross-sections, neutron evaporation and charged particle evaporation residue cross-sections produced through the axn\ensuremath \alpha xn and pxn\ensuremath pxn (x = 2, 3, 4) emission channels for the ²¹⁹Ra system at various incident centre-of-mass energies. Experimentally the CF cross-sections are suppressed and the observed suppression is attributed to the low binding energy of ^{10, 11}B which breaks up into charged fragments. The reported complete fusion (CF) and incomplete fusion (ICF) excitation functions for the ²¹⁹Ra system are found to be nicely fitted by the calculations performed in the framework of DCM, without invoking a significant contribution from quasi-fission. Although DCM has been applied for a number of compound nucleus decay studies in the recent past, the same is being used here in reference to ICF and subsequent decay processes along with the CF process. Interestingly the main contribution to complete fusion cross-section comes from the fission cross-section at higher incident energies, which in DCM is found to consist of an asymmetric fission window, shown to arise due to the deformation and orientation effects of formation and decay fragments.     

Cluster radioactivity leading to doubly magic <Superscript>100</Superscript>Sn and <Superscript>132</Superscript>Sn daughters

Decay of neutron-deficient ^{128 − 137}Gd parents emitting ⁴He to ³²S clusters are studied within the Coulomb and proximity potential model. The predicted half-lives are compared with other models and most of the values are well within the present experimental limit for measurements (T _1/2 < 10³⁰ s). The lowest T _1/2 value for ²⁸Si emission from ¹²⁸Gd indicates the role of doubly magic ¹⁰⁰Sn daughter in cluster decay process. It is also found that neutron excess in the parent nuclei slows down the cluster decay process. Geiger–Nuttal plots for all clusters are found to be linear with different slopes and intercepts. The α-decay half-lives of ^{148 − 152}Gd parents are computed and are in agreement with experimental data. The role of doubly magic ¹³²Sn daughter in cluster decay process is also examined for various neutron-rich Ba, Ce, Nd, Sm and Gd parents emitting clusters ranging from ⁴He to ³²Si. Alpha-like structures are most probable in the decays leading to ¹⁰⁰Sn, while non-α-like structures are probable in the decays leading to ¹³²Sn. The neutron–proton asymmetry in parent and daughter nuclei is responsible for the reduced decay rate in the decay leading to ¹³²Sn.     

Measurement of the <Superscript>222</Superscript>Rn background in the DEVIS experiment

In the DEVIS tracking experiment that is being performed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow, Russia) and which is devoted to searches for ¹³⁶Xe double-beta decay, the ²²²Rn concentration is measured in xenon samples with different content of the isotope ¹³⁶Xe. The number of probable double-electron events from ²¹⁴Bi decay mimicking the double-beta decay of ¹³⁶Xe is estimated.     

High-lying excited states in <Superscript>10</Superscript>Be from the <Superscript>9</Superscript>Be(<Superscript>9</Superscript>Be,<Superscript>10</Superscript>Be)<Superscript>8</Superscript>Be reaction

A transfer-reaction experiment of ⁹Be(⁹Be, ¹⁰Be)⁸Be was performed at a beam energy of 45 MeV. Excited states in ¹⁰Be up to 18.80 MeV are produced using missing mass and invariant mass methods. Most of the observed high-lying resonant states, reconstructed from the α + ⁶He and t + ⁷Li decay channels, agree with the previously reported results. In addition, two new resonances at 15.6 and 18.8 MeV are identified from the present measurement. The 18.55 MeV state is found to decay into both the t + ⁷Li_g.s. and t + ⁷Li* (0.478 MeV) channels, with a relative branching ratio of 0.93 ± 0.33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.     

Photonuclear Reactions on Bypassed Nuclei <Superscript>84</Superscript>Sr and <Superscript>92</Superscript>Mo

The yields of photonuclear reactions on mixtures of natural isotopes of strontium and molybdenum that result in the formation and decay of bypassed nuclei ⁸⁴Sr and ⁹²Mo are measured and compared to theoretical results obtained using the TALYS code and calculations in the combined model of photonucleon reaction (CMPR). The need is demonstrated to consider isospin splitting in cases of photoproton reactions. The yields of the ⁹²Mo(γ,p)⁹¹mNb, ⁸⁴Sr(γ,p)⁸³Rb reactions that make the main contribution to the formation and decay of ⁸⁴Sr and ⁹²Mo in the p-process of nucleosynthesis differ from the TALYS and CMPR results by several hundred percent.     

Low-spin states in <Superscript>182</Superscript>Os and K<Superscript>π</Superscript> = 0<Superscript>+</Superscript>, 2<Superscript>+</Superscript> excited bands

Excited states in ¹⁸²Os were populated by the β⁺/EC decay of ¹⁸²Ir following mass separation. Gamma-ray and conversion electron spectroscopy techniques were employed. Monopole (E0) contributions were determined in transitions populating the ground-state band. A systematic study of the low-spin structures in the Os isotopes is presented and a detailed analysis in the framework of a microscopic configuration mixing approach is performed.     

Aspects of radiative K<Superscript>+</Superscript><Subscript>e3</Subscript> decays

We re-investigate the radiative charged kaon decay K^±→π⁰e^±ν_eγ [K_e3γ ^±] in chiral perturbation theory, merging the chiral expansion with Low’s theorem. We thoroughly analyze the precision of the predicted branching ratio relative to the non-radiative decay channel. Structure dependent terms and their impact on differential decay distributions are investigated in detail, and the possibility to see effects of the chiral anomaly in this decay channel is emphasized. PACS 13.20.Eb; 11.30.Rd; 12.39.Fe     

Precision electron-gamma spectroscopic measurements in <Superscript>75</Superscript>As

The decay of ⁷⁵Se to levels of ⁷⁵As has been studied using an HPGe detector for gamma-ray and a mini-orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 18 gamma rays and 16 conversion electron lines reported for the first time. New results also include E2 multipolarity assignment for the 81 keV transition, M1 assignment to three newly observed transitions and M1 + E2 for the 617 keV transition. A revised ⁷⁵As level scheme is constructed using the Ritz combination principle through the computer code GTOL. While confirming the existence of 10 well-established levels, two levels at 587 and 859 keV are newly placed into the decay scheme of ⁷⁵Se. The interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly placed 586.8 keV 1/2^- and 859.9 keV 1/2⁺ levels are studied in the light of the Interacting Boson-Fermion Model.     

Precise measurement of the energy of γ rays excited in <Superscript>191</Superscript>Pt decay

The energy differences for 19 pairs of γ rays are measured with a γ spectrometer. The first γ transition in each pair is excited in decay of ¹⁹¹Pt, and the second transition, accompanying the decay of ¹⁸²Ta or ¹⁹²Tr is a third-order nuclear spectroscopic normal. The energies of nine ¹⁹¹Ir levels and 36 γ-ray photons accompanying decay of ¹⁹¹Pt, were determined with high accuracy on the basis of these data.     

Double-beta decay of <Superscript>150</Superscript>Nd to the first 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript>Sm

Two-neutrino-double-beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with a 400-cm³ low-background HPGe detector. Data analysis for 11320.5 h shows an excess of events at 333.9 and 406.5 keV. This allows us to estimate the half-life of the investigated process as [1.4 _?0.2 ^+0.4 ±0.3(syst.)]×10²⁰ yr.     

Structure of excited states of <Superscript>123</Superscript>Te

The β decay of ¹²³I has been calculated within the dynamic collective model developed by the authors earlier. The expression for the reduced matrix element of the weak-interaction Hamiltonian has been used for the partial β decay. The influence of the vacuum fluctuations and creation or annihilation of one or two phonons on the reduced β-decay probabilities is taken into account.     

Double-beta decay of <Superscript>150</Superscript>Nd to the first 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript> Sm: Current state

Two-neutrino double-beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with the 400-cm³ low-background HPGe detector. Preliminary data analysis for 6843 h shows an excess of events at 333.9 and 406.5 keV. If this excess is assigned to the investigated transition, then its half-life can be estimated at [1.2 _?0.3 ^+0.5 ±0.4(syst.)]×10²⁰ yr.     

Light-charged-particle emission from hot <Superscript>32</Superscript>S<Superscript>*</Superscript>formed in <Superscript>20</Superscript>Ne + <Superscript>12</Superscript>C reaction

Inclusive energy distributions for light charged particles (p , d , t and have been measured in the ²⁰Ne (158, 170, 180, 200 MeV) + ¹²C reactionsintheangularrange$10^°$ - - $50^°$.Exclusivelight-charged-particleenergydistributionmeasurementswerealsodoneforthesamesystemat158 MeVbombardingenergybyin - planelightchargedparticle - - fragmentcoincidence.Pre - equilibriumcomponentshavebeenseparatedoutfromprotonenergyspectrausingthemovingsourcemodelconsideringtwosources.ThedatahavebeencomparedwiththepredictionsofthestatisticalmodelcodeCASCADE.Ithasbeenobservedthatsignificantdeformationeffectswereneededtobeintroducedinthecompoundnucleusinordertoexplaintheshapeoftheevaporated$d$,$t$energyspectra.Forprotons, evaporatedenergyspectrawereratherinsensitivetonucleardeformation, thoughangulardistributionscouldnotbeexplainedwithoutdeformation.Thedecaysequenceofthehot$³²S$nucleushasbeeninvestigatedthroughexclusivelight - - charged - particlemeasurementsusingthe$²⁰Ne$$(158 MeV) + $¹²C reaction. Information on the sequential decay chain has been extracted through a comparison of the experimental data with the predictions of the statistical model. It is observed from the present analysis that exclusive light-charged-particle data may be used as a powerful tool to probe the decay sequence of hot light compound systems.     

Inverse-beta-decay reaction in the antineutrino flux from the fragments of <Superscript>232</Superscript>Th and <Superscript>233</Superscript>U fission

The energy spectra of antineutrinos produced in the beta decay of fragments originating from ²³³U and ²³²Th fission induced by neutrons are calculated. The relevant cross sections and the spectra of positrons produced in inverse beta decay are found. This study was motivated by the hypothesis (discussed over the past decade)t hat a self-sustained chain reaction proceeds at the center of the Earth (“georeactor”). According to the author of this hypothesis, the georeactor provides energy necessary for maintaining the Earth’s magnetic field. It is ²³⁵U and, probably, ²³²Th and ²³³U that serve as a nuclear fuel in this reactor. Data obtained in the present study can be guidelines in future experiments aimed at testing the hypothesis of the georeactor and at estimating the composition of its nuclear fuel within the development of geophysical and astrophysical investigations based on the observation of antineutrino fluxes in nature.     

Double beta decay of <Superscript>150</Superscript>Nd to the First 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript>Sm

Two neutrino double beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with the 400 cm³ low-background HPGe detector. Data analysis for 11320.5 h shows the excess of events at 333.9 and 406.5 keV. This makes it possible to estimate the half-life of the investigated process as [1.4 _?0.2 ^+.04 (stat)±0.3(syst)]×10²⁰yr.     

On the phenomenon of oscillatory decay of the <Superscript>125m</Superscript>Te isomer

The radioactive decay curve of the ^125mTe nucleus is measured in the environment of stable ¹²⁵Te nuclei representing a Mössbauer resonant screen. Thorough analysis shows that the decay of the ^125mTe nucleus corresponds to the standard exponential law with half-life T_1/2≈58 days without oscillations.