Internal bremsstrahlung of strongly interacting charged particles

A universal theoretical model intended for calculating internal-bremsstrahlung spectra is proposed. In this model, which can be applied to describing nuclear decays of various type (such as alpha decay, cluster decay, and proton emission), use is made of realistic nucleus–nucleus potentials. Theoretical internal-bremsstrahlung spectra were obtained for the alpha decay of the ²¹⁴Po nucleus, as well as for the decay of the ²²²Ra nucleus via the emission of a ¹⁴C cluster and for the decay of the ¹¹³Cs nucleus via proton emission, and the properties of these spectra were studied. The contributions of various regions (internal, subbarrier, and external) to the internal-bremsstrahlung amplitude were analyzed in detail. It is shown that the contribution of the internal region to the amplitude for internal bremsstrahlung generated in nuclear decay via proton emission is quite large, but that this is not so for alpha decay and decay via cluster emission. Thus, a process in which strong interaction of nuclear particles affects the internal-bremsstrahlung spectrum if found.     

New BCS and renormalized QRPA formalism with application to double beta decay

A new analysis of the renormalized proton–neutron quasiparticle random phase approximation based on simultaneous recalculation of the one-body density matrix and the pairing tensor has been used to study the double beta decay. We demonstrated that inclusion of the quasiparticle correlations at the BCS level reduces ground state correlations in the particle–particle channel of the proton–neutron interaction. We also simplified the RQRPA equations significantly obtaining a low-dimensioned set of linear equations for the quasiparticle densities. The formalism was applied to the double beta decay of ⁷⁶Ge. Received: 4 January 1999 / Revised version: 29 March 1999     

Search for tensor couplings in the weak interaction

The existence of exotic couplings in the weak interaction can be tested by a precise measurement of the β-ν angular correlation parameter a in nuclear beta decay. In the case of ⁶He, the ratio of tensor and axial-vector couplings can be determined. The goal of the LPC Trap experiment is to improve the limits on the existence of tensor currents. The LPCTrap setup is installed on the low energy beam line LIRAT of the SPIRAL/GANIL facility. The ⁶He⁺ ions are confined in a novel transparent Paul trap allowing the detection in coincidence of both the β-particle and the recoil ion. The detection setup enables to detect the position and energy of these two particles. The a parameter can then be extracted from the time of flight spectrum of the recoil ions. The first ⁶He⁺ decay events were observed in May 2005 during a commissioning run. Over 10⁵ coincidence events have been recorded during a second run in July 2006.     

Possible contribution of an intermediate-leptoquark-boson mechanism to free-neutron beta decay

A possible mechanism of the virtual intermediate-scalar-leptoquark-boson exchange associated with the contribution of right-handed nucleon currents to free-neutron beta decay is demonstrated. The hypothesis can be extended by considering the realization of the same mechanism in beta decay via the emission of right-handed neutrinos (left-handed antineutrinos). It is shown that a hypothesis of this kind leads to the appearance of scalar and tensor terms in the effective Hamiltonian of weak interaction and that these terms include the right-handed neutrinos. Relevant experimental data are discussed.     

Emission of γ-quanta,electrons, and positrons upon the decay of <Superscript>12</Superscript>N and <Superscript>12</Superscript>B produced in characteristic targets

The emission of γ-quanta, electrons, and positrons upon the decay of ¹²N and ¹²B produced in characteristic targets is calculated within radiation–matter interaction models generated using the GEANT and MCNP simulation software.     

Analysis of Energy Transfer and Concentration Quenching in Sm3+-Activated Borate GdB3O6 Phosphors by Means of Fluorescence Dynamics

This article reports on the optical properties of Sm³⁺-activated GdB₃O₆ phosphors based on the measurement of their photoluminescence spectra and luminescence decay curves. Energy transfer from Gd³⁺ to Sm³⁺ and the concentration quenching of the Sm³⁺ ion emission are investigated. From the photoluminescence spectra and decay curves, the energy transfer from Gd³⁺ to Sm³⁺ is confirmed. The concentration quenching of the Sm³⁺ ion emission can be ascribed to resonant cross-relaxation. The interaction between the Sm³⁺ ions is derived of the electric dipole–dipole type through fitting the data with the Inokuti-Hirayama model. The critical distances and energy transfer microparameter for the transfer processes are given. The decay curves of Sm³⁺⁴G_5/2 level exhibiting a buildup and decay process also confirm the energy transfer from Gd³⁺ to Sm³⁺ and between Sm³⁺ ions.     

Studies of weak interaction effects by laser spectroscopy of short-lived atoms

Laser-induced nuclear orientation has been used to make sub-Doppler-resolution measurements of a nuclear isomer^85mRb that has a lifetime of only a microsecond. The technique succeeds because the sampled atoms remove themselves before equilibrating. This paper describes two cases in which pre-equilibrium removal of atoms can prevent thermal equilibrium from obscuring information about the weak interaction that is present in the velocity profile of atoms as they recoil following beta decay. It should be possible to measure electron-antineutrino angular correlations in the beta decay of⁸⁵Kr, and to look for beta decay of tritium into an atomic bound state of³He-a fundamental effect predicted by weak interaction theory but never observed.     

Neutrinorückstoßexperiment am Li8

The beta-decay of Li⁸→Be^8*→2α is especially suitable in neutrino recoil experiments on account of the large beta-decay energy available and on account of the subsequent break up of Be^8* into two α-particles. For the angular correlation between the antineutrino and the α-particle one obtains for our counter geometry and a Gamow-Teller interaction the angular distributionw(v)dv=(1+b v/c 0.707 cosv)dv, whereb=?1 for axial vector interaction (A) orb=+1 for tensor interaction (T) and wherev is the angle between the direction of emission of the antineutrino and the α-particle. The measurement of the energy difference of the two α-particles in the Be^8* decay, when the direction of the emission of the beta-particle is fixed, defines the angular correlation coefficientb. In this experiment the value ofb is found to be equal to ?1.12±0.20, which shows axial vector interaction in the Gamow-Teller decay.     

Status and prospects of searches for neutrinoless double beta decay

The simultaneous beta decay of two neutrons in a nucleus without the emission of neutrinos (called neutrinoless double beta decay) is a lepton number violating process which is not allowed in the Standard Model of particle physics. More than a dozen experiments using different candidate isotopes and a variety of detection techniques are searching for this decay. Some (EXO‐200, Kamland‐Zen, and GERDA) started to take data recently. EXO and Kamland‐Zen have reported first limits of the half life for ¹³⁶Xe. After a decade of little progress in this field, these results start to scrutinize the claim from part of the Heidelberg–Moscow collaboration to have observed this decay. The sensitivities of the different proposals are reviewed.     

Mirror transitions and second class currents

Theoretical implications of observed mirror asymmetry in nuclear beta decay are examined, taking into account CP violation and internal symmetries. The second class induced tensor current is shown not to be responsible for the observed asymmetry, which must be the result of multinucleon or meson exchange effects. The result is general and holds for all values of momentum transfer. Possible two nucleon transitions are discussed. Mirror asymmetry in the Σ−Λ decay cannot be produced by SU(3) octet currents or single quark currents in the quark model even if such second class currents exist.     

Gamma-ray emission in competition with neutron emission in the beta decay of Br

Evidence is presented for the existence of a γ-ray at 5594.7±0.6 keV following beta decay of ⁸⁷Br. This observation indicates population of neutron unbound levels in ⁸⁷Kr from which photon emission competes successfully with neutron emission.     

Structure of nuclei near100Sn and theπg 9/2 →vg 7/2 Gamow-Teller beta decays

Selected properties of the Gamow-Teller beta decay of even nuclei near¹⁰⁰Sn have been studied. Two theoretical models were used: a self-consistent Hartree-Fock-Bogolyubov approach with the Skyrme interaction and a shell-correction model with a Woods-Saxon average field and monopole pairing residual interaction. Calculations reproduce fairly well both theQ _EC values and the average energies of theI ^π=1⁺ states fed directly in the decay. It is shown that the observed energy splitting between the 1⁺ states cannot be associated with a stable deformation of a final doubly-odd nucleus. The calculated pairing factors are used to estimate the 0⁺ → 1⁺ GT transition strength in the neighbourhood of doubly-magic ₅₀ ¹⁰⁰ Sn₅₀.     

Order-α radiative correction to 6He and 32Ar β decay recoil spectra

Order-α model independent radiative correction results to the ⁶He → ⁶Li and ³²Ar → ³²Cl β decay recoil spectra are presented. The effects of these corrections on the electron-neutrino correlation parameter (a_eν) and the induced tensor form factor are discussed (taking into account the most important experimental details of these measurements). In the case of ⁶He beta decay, the shift of the a_eν value due to our radiative correction calculation is larger than the total experimental error of the last, precise measurement. The order-Zα² radiative correction of the recoil spectrum is also estimated. Recoil-order formulae are given for the beta energy - recoil energy Dalitz distribution and the recoil spectrum.     

Angular momentum and energy dependence of fission andn,p,4He emission from194Hg compound nucleus

Spin and temperature dependence of the fission and particle emission is studied for¹⁹⁴Hg. The compound nucleus is described using the Strutinsky shell correction approach extended for finite angular momenta and temperature. The shell corrections to the potential energy, free energy and the angular momentum are calculated using the Woods-Saxon average field. Results are compared with the experimental data and show a good qualitative agreement. It is found that the inclusion of the shell effects is necessary to understand the decay properties of¹⁹⁴Hg even for temperatures as high as 1.5–2.0 MeV.     

Decay of heavy and superheavy nuclei

We present here, an overview and progress of the theoretical works on the isomeric state α decay, α decay fine structure of even–even, even–odd, odd–even and odd–odd nuclei, a study on the feasibility of observing α decay chains from the isotopes of the superheavy nuclei Z = 115 in the range 271 ≤A ≤ 294 and the isotopes of Z = 117 in the range 270 ≤A ≤ 301, within the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The computed half-lives of the favoured and unfavoured α decay of nuclei in the range 67 ≤Z ≤ 91 from both the ground state and isomeric state, are in good agreement with the experimental data and the standard deviation of half-life is found to be 0.44. From the α fine structure studies done on various ranges of nuclei, it is evident that, for nearly all the transitions, the theoretical values show good match with the experimental values. This reveals that CPPMDN is successful in explaining the fine structure of even–even, even–odd, odd–even and odd–odd nuclei. Our studies on the α decay of the superheavy nuclei ^271?294115 and ^270?301117 predict 4 α chains consistently from ^284,285,286115 nuclei and 5α chains and 3α chains consistently from ^288?291117 and ²⁹²117, respectively. We thus hope that these studies on ^284?286115 and ^288?292117 will be a guide to future experiments.     

Effect of pressure on luminescence properties of Sm3+ ions in potassium niobate tellurite glass

Emission spectra and decay properties of the ⁴G_5/2 level of Sm³⁺ ions in TeO₂+K₂O+Nb₂O₅ glass have been measured as a function of pressure upto 14.6 GPa at room temperature. A progressive red shift in the barycentres of ⁴G_5/2→⁶H_J (J=9/2, 7/2 and 5/2) emission bands and increase in splitting of these bands have been observed with increasing pressure. The luminescence decay profile of the ⁴G_5/2 level at ambient condition shows a nearly single exponential nature and with increase in pressure it becomes gradually non-exponential associated with a decrease in lifetime. The non-exponential decay curves are well-fitted to the Inokuti–Hirayama model for S=6, indicating that the interaction for cross-relaxation energy transfer between Sm³⁺ ions is of dipole–dipole type. The results obtained after release of pressure reveal that there is a small hysteresis.     

Roles of tensor and isoscalar pairing interactions in β-decay calculations for possible r-process waiting point nuclei with N ~ 82 and 126

In this study, we adopt the self-consistent Hartree-Fock-Bogoliubov (HFB) theory with the proton-neutron quasi-particle random phase approximation (pnQRPA) based on the Skyrme force for calculation of the β^? decay half-lives for nuclei with N ~ 82 and 126 on possible r-process paths. In the calculations, the Skyrme interaction (e.g., SKO') is adopted, and the tensor interaction is added self-consistently in both HFB and QRPA calculations. We systematically study how the half-life is changed by varying the strength of the triplet-even (TE) and triplet-odd (TO) components as well as the IS pairing. We find that a variation in strength of the IS pairing of approximately 20% does not produce a substantial effect on β-decay rates with or without the tensor force, while a strength variation of the TO tensor force considerably affects the change in the β-decay half-lives for the very neutron rich N ~ 82 and 126 isotonic chains. In addition, with the inclusion of the tensor force, the GT decay becomes dominant for very neutron-rich nuclei.     

Angular distribution of tensor polarizations in 2H(α, 5Heg.s)p from the sequential decay reaction 2H(α,p)5Heg.s(α)n

The sequential decay reaction ²H(α,p)⁵He^g.s(α)n has been studied at E_α = 22.5 MeV in kinematically complete p-α coincidence experiments with special regard to the tensor moments of even rank of the intermediate state ${}^5\text{He}{}^{\mathrm{<mtext>3</mtext><mtext>2?</mtext>}}$. From the measured absolute differential cross section of this reaction, the angular distributions of the second step for the ⁵He^g.s c.m. production angles from 45.6 to 119.8 were extracted. By applying Welton's formalism to the second step the tensor moments of even rank of the intermediate ⁵He system were deduced and compared to calculations in the cluster-model formalism. They as well as the absolute differential cross sections for ²H(α,pα)n were found to be in good agreement with the sequential decay model. Small deviations seem to arise from Coulomb interaction between p and α in the final channel and from the restriction to partial waves l ≦ 2.     

Luminescence and decay times of CsI:In+

Luminescence spectra of single crystals of CsI:In⁺ excited in the A(304 nm), B(288 nm), C(268 nm) and D(257 nm) absorption bands have been studied in the temperature range 4.2–300 K. Excitation in the A band at 4.2 K gives rise to the principal emission at 2.22 eV accompanied by a partly-overlapping weak band at 2.49 eV. An additional emission band at about 2.96 eV is observed on excitation in the B, C or D bands. Yet another emission band located at 2.67 eV is excited only in the D band. The relative intensities of the bands are very sensitive to excitation wavelength as well as to temperature. The origin of all these bands is assigned in terms of a model for the relaxed excited states (RES). All the luminescence spectra were resolved into an appropriate number of skew-Gaussian components. Moments analysis leads to a value of (1.35 ± 0.02) × 10¹³ rad s^-1 for the effective frequency (ω_eff) of lattice vibrations coupled to the RES. At the lowest temperature, the radiative decay times of each of the intracenter emission bands (2.22, 2.49 and 2.96 eV) show a slow decay ( ～ 10–100 μs) and a fast decay ( ～ 10–100 ns). The 2.96 eV band, which is assigned to an emission process which is the inverse of the D-band absorption, exhibits a single decay mode ( ～ 10 μs). The intrinsic radiative decay rates (k₁, k₂), the one-phonon transition rate (K) and the second-order spin-orbit splitting (D) for the RES responsible for the principal emission are: k₁ = (6.0±-0.3)×10³ s^-1, k₂ = (1.33±-0.06)×10⁵ s^-1, K = (2.4±-0.4)×10⁷ s^-1 and D = (13.8±-0.5) cm^-1.