New transitions in the β-decay of 36Ca

The β-decay of the T _z = - 2 nucleus ³⁶Ca was studied at the LISE3 magnetic spectrometer at GANIL. Two new proton-emitting states have been detected and the other nine known βp and βγ transitions have been remeasured with improved resolution. A simulation with the GEANT code has been applied to this experimental setup. A comparison with shell model calculations is given. Received: 19 September 2000 / Accepted: 28 February 2001     

СПЕКТР КОНВЕРСИОННЫ Х ЭЛЕКТРОНОВ Lu171 И Lu172

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Conversion electron spectrum of Lu¹⁷¹ and Lu¹⁷²

     

Exploring the uncertainties in theoretical predictions of nuclear β-decay half-lives

Nuclear β-decay half-lives are predicted based on an empirical formula and the mass predictions from various nuclear models.It is found that the empirical formula can reproduce the nuclearβ-decay half-lives well,especially for short-lived nuclei with T_1/2<1s.The theoretical half-life uncertainties fromβ-decay energies and the parameters of the empirical formula are further investigated.It is found that the uncertainties of the half-lives are relatively large for heavy nuclei and nuclei near the neutron-drip line.For nuclei on the r-process path,the uncertainties for those with N=126 are about one order of magnitude,which are much larger than the uncertainties for those with N=50 and 82.However,theoretical uncertainties from the parameters of the empirical formula are relatively small for the nuclei on the r-process path,which indicates that the empirical formula is very suitable for predicting theβ-decay half-lives in r-process simulations.     

β-decay matrix elements from the study of asymmetric emission from polarised nuclei: γ-tagging – a new method for complex β-decay

A new method is introduced designed to facilitate study of matrix elements in complex β-decay through the measurement of asymmetric β-emission from a low-temperature polarised source. The method involves coincident detection of the β-emission with subsequent γ-transitions to tag the β-spectrum component. The method is demonstrated by application to the decay of ¹⁴⁰La. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calculations of the β-decay half-lives of neutron-deficient nuclei

In this work,β~+/EC decays of some medium-mass nuclei are investigated within the extended quasiparticle random-phase approximation(QRPA),where neutron-neutron,proton-proton and neutron-proton(np) pairing correlations are taken into consideration in the specialized Hartree-Fock-Bogoliubov(HFB) transformation.In addition to the pairing interaction,the Br¨uckner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions.Calculations are performed for even-even proton-rich isotopes ranging from Z =24 to Z =34.It is found that the np pairing interaction plays a significant role inβ-decay for some nuclei far from stability.Compared with other theoretical calculations,our calculations show good agreement with the available experimental data.Predictions of β-decay half-lives for some very neutron-deficient nuclei are made for reference.     

Non-yrast states of 132Ce polutated in β-decay

Non-yrast low spin states of the nucleus ¹³²Ce were studied by means of γ-spectroscopy following the β-decay of the ground and medium spin isomeric states of ¹³²Pr. The activity was produced with the reaction ¹¹⁷Sn(¹⁹F,4n) ¹³²Pr at the Cologne FN TANDEM accelerator. The γγ coincidences and singles spectra were measured with the OSIRIS cube spectrometer. The β-decay of ¹³²Pr populates states with spins up to 6ħ and excitation energies up to 4.4 MeV in ¹³²Ce. Besides ground and quasi-gamma bands, an excited band based on the 0₂⁺ state and many other low-lying states were observed. The γγ angular correlations were analyzed to assign spins and parities to the excited states, and to determine the multipolarities of the γ-transitions. We found dominant E2 transitions in the quasi-gamma band and from the quasi-gamma band to the ground band. The experimental data are compared with calculations using the Interacting Boson Model (IBM). Good agreement is reached in the vicinity of the O(6) limit.     

Nuclear β-decay. II

A general expression for the beta-decay transition amplitude is evaluated, using the decomposition of the nuclear current matrix element into beta-decay form factors as obtained in the previous paper. For the electron radial wave functions the finite nuclear size is taken into account. Formulas for the spectrum shape factor and the polarisation are calculated.     

Nuclear β-decay. I

In order to clarify the validity of the theory of nuclearβ-transition a new formulation is given. The nuclear properties are contained in form factors, arising from a decomposition of the matrix element of the V-A operator for nuclear states. The connection of these form factors with nuclear physics matrix elements is tabulated. The total transition amplitude can be written as an integral over these form factors folded with off-shell amplitudes for elastic and inelastic electron scattering on nuclei.     

Relativistic and atomic effects in the K-shell ionization of an atom during β-decay

A theoretical investigation is performed on the K-shell self-ionization of an atom during nuclear decay, taking screening and relativistic effects into account. The atomic potential chosen is the Taites potential, an approximation of the Thomas-Fermi potential. It is shown that taking screening into account in the given isotopes does not have any considerable influence on the total probability of self-ionization, whereas the contribution of relativistic effects in heavy isotopes is more significant, being of order (Z)². The role of the mechanism of direct -particle collision with electrons of the atomic shell in the self-ionization process is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 27–32, May, 1982.     

Gamow-teller transitions in β-decay of 66 146 Dy80

The β-decay of¹⁴⁶Dy₈₀ was studied by γ-ray and conversion electron spectroscopy following on-line mass separation. 58 % of the β-decay proceeding to a group of levels close to 2 MeV excitation is attributed to GT-decay of (πh ₁₁ ^2/2 )₀₊ pairs populating (πh_11/2νh_9/2νj ₀ ^?2 )1⁺ states in¹⁴⁶Tb₈₁. The total decay strength is significantly higher than found in¹⁴⁸Dy₈₂ decay, which arises from GT-transitions involving the ν-holes.     

Neutrinoless double β-decay without Majorana neutrinos in supersymmetric theories

Mechanisms for neutrinoless double β-decay, which do not require intermediate Majorana neutrinos, are discussed in the context of supersymmetric models with R-parity violating interactions. The resulting currents are of the S, P, T type rather than those familiar from the V - A theory. The effective transition operators associated with such currents are constructed. The present experimental limits are then used to provide additional constraints for some of the parameters of supersymmetric models.     

Semi-gross theory of nuclear β-decay

The gross theory of β-decay is refined to take into account shell effects of the parent nuclei, and the resulting theory is named semi-gross theory. In this theory, the one-particle energy distribution in the parent nucleus is taken to have structures, and the one-particle strength function is assumed to depend on the quantum numbers of the initial state of the decaying nucleon. β-decay (partial) half-lives are calculated for 1659 nuclides, and the results are compared with experimental data as well as with those calculated by the gross theory. The β-decay strength functions are shown for two selected nuclides, and briefly discussed. These numerical studies confirm that the semi-gross theory includes some part of the shell effects correctly, although there still remain deviations of the theoretical results from experimental data, which should, at least partly, be due to shell effects of the daughter nuclei. Comparison of the present results with microscopic theories shows that the overall accuracy of the semi-gross theory is comparable with those of the microscopic theories.     

Precision nuclear β-decay half-life measurements

Precise measurements of the intensities of superallowed Fermi β decays between 0^?+? analog states provide a demanding test of the electroweak standard model. At ISAC, nuclear β-decay lifetimes are measured with high-precision (<0.05 %) by direct β counting using a 4π continuous flow gas proportional counter coupling to a fast tape transport system. This facility has provided the most precise half-life measurements for several superallowed β emitters including: ²⁶Al^m, ³⁸K^m, ⁶²Ga and ⁷⁴Rb.     

Competition between α-decay and β-decay for heavy andsuperheavy nuclei

In this work, the β-stable region for Z≥90 is proposed based on a successful binding energy formula. The calculated β-stable nuclei in the β-stable region are in good agreement with the ones obtained by Möller et al. The half-lives of the nuclei close to the β-stable region are calculated and the competition between α-decay and β-decay is systematically investigated. The calculated half-lives and the suggested decay modes are well in line with the experimental results. The decay modes are mostly β^--decay above the β-stable region. Especially for Z≤111, all the decay modes are β^--decay. Regarding the nuclei above the β-stable region, α-decay and β^--decay (α+β^-) can occur simultaneously when Z≥112. This is a very interesting phenomenon. The competition between α-decay and β-decay is very complex and drastic below the β-stable region. The predictions for half-lives and decay modes of the nuclei with Z=107-110 are presented in detail.     

Levels in165Tm excited by the decay of 9·8 min165Yb

The decay of¹⁶⁵Yb (T _1/2=9·8 min) has been investigated with Ge(Li), Si(Li) and NaI(Tl) detectors, a toroidal -spectrometer and magnetic -spectrographs. The isobarically separated samples produced by the YASNAPP facility at the Dubna Institute were used. The single -ray spectrum, the conversion electron spectrum, prompt and delayed - coincidences have been measured. The decay scheme of¹⁶⁵Yb involving 40 excited states in¹⁶⁵Tm has been proposed. The first members of the rotational bands l/2⁺[411], 3/2⁺[411], 5/2⁺[402], 7/2⁺[404], 1/2^–[541], 7/2^–[523] and 9/2^–[514] have been identified.On leave fromthe Nuclear Physics Institute, e near Prague, Czechoslovakia.On leave fromthe Institute for Nuclear Physics, Uzbek Academy of Sciences, Tashkent,USSR.On leave fromthe Technical University, Dresden, GDR.We should like to thank Professor V. P.Dzhelepov for his support. Our thanks are due to M.Jachim for preparing the mass-separated sources. We are indebted to the electronics team of the measuring centre and to the synchrocyclotron staff of the Laboratory of Nuclear Problems.     

On radiative corrections to the strangeness-conserving β-decay of free baryons

In the work presented, the effect of electromagnetic interactions on the strangeness-conserving β-decay of baryons: neutron, $n \to p + e^ - + \bar \nu + \gamma $ , and hyperon, $\Sigma ^ \pm \to \Lambda ^0 + e^ \pm + \nu (\bar \nu ) + \gamma $ , is visualized. The polarized baryon decay studied, the total decay probability modification, as well as the modifications of the e ^± spectrum and the angular distribution with respect to the polarization vector ξ of the initial baryon (coefficient A), have been calculated. Dependence of the results on the value of the ultraviolet cut-off parameter Λ is elucidated. The spectrum and yield of the γ-radiation accompanying the β-decay is acquired, with special attention being paid to the infrared (soft-photon) radiation. The photon radiation of pions constituting the baryon's “pion cloud” is investigated. The radiative corrections to the total β-decay probability and to the electron energy and angular distributions found in this work proves to be of pivotal importance for obtaining the main characteristics of the weak interaction from experimental data processing.     

Lepton phenomenology and neutrinoless double β-decay in superstring inspired theories

The properties of neutrinos,s-leptons,s-quarks as well as the coloured isosinglet \(\tilde D\) and \(\tilde D^c \) are studied in superstring inspired models. Furthermore the neutrinoless double β-decay process is investigated, including light and heavy majorana neutrinos, as well as the contribution of the exotic Higgs scalars of the theory. From the current experimental limits onov-ββ-decay, useful constraints are imposed on the masses and Yukawa couplings of the theory.     

Competition between α-decay and β-decay for heavy and superheavy nuclei

In this work, the β-stable region for Z 90 is proposed based on a successful binding energy formula.The calculated β-stable nuclei in the β-stable region are in good agreement with the ones obtained by Mo¨ller et al. The half-lives of the nuclei close to the β-stable region are calculated and the competition between α-decay andβ-decay is systematically investigated. The calculated half-lives and the suggested decay modes are well in line with the experimental results. The decay modes are mostly β--decay above the β-stable region. Especially for Z 111,all the decay modes are β--decay. Regarding the nuclei above the β-stable region, α-decay and β--decay(α+β-)can occur simultaneously when Z 112. This is a very interesting phenomenon. The competition between α-decay and β-decay is very complex and drastic below the β-stable region. The predictions for half-lives and decay modes of the nuclei with Z =107–110 are presented in detail.