Spectroscopy of 166W and 167W and alignment effects in very neutron-deficient tungsten nuclei

High-spin states in ¹⁶⁶W and ¹⁶⁷W were populated by the reactions ¹⁴²Nd(²⁸Si,4n)¹⁶⁶W, ¹⁴²Nd(²⁸Si,3n)¹⁶⁷W and ¹⁴⁷Sm(²⁴Mg,4n)¹⁶⁷W. From the γ-decay the yrast band and a side band (with assumed negative parity) were identified to high spins. There is evidence for a second side band in ¹⁶⁷W. The observed backbend of the yrast sequences and band-crossing anomalies in the side bands are discussed in conjunction with cranked-shell-model calculations. A systematic comparison is made between the yrast bands of ^166,167,168W in order to understand the structure of the second backbend in ¹⁶⁸W.     

States of167Ho from the decay of neutron rich nuclide167Dy

Theβ ^?-decay of ₆₆ ¹⁶⁷ Dy produced through the fast neutron reaction¹⁷⁰Er(n, α)¹⁶⁷Dy has been investigated by using several kinds of detectors and a high-capacity two-parameter recording system. The half-life andβ ^?-decay energy of¹⁶⁷Dy were determined to beT _1/2 = 6.20 ± 0.08min andQ _β-=2.35±0.06, respectively. The observed level scheme of ₆₇ ¹⁶⁷ Ho (completely unknown previously) contains 12 states, among them a 6.0±0.1 μsM2 isomer at 259.3 keV. On the basis of theoretical and systematic considerations combined with multipole determinations, the following Nilsson model assignments are proposed for the lowest states of¹⁶⁷Ho: 0 keV (7?/2 [523]), 259.3 keV (3+/2[411]), 319.8 keV (5/2 3+/2[411]), 392.5 keV (1+/2[411]), 410.0 keV (3/2 1+/2[411]), 569.7 keV (3?/2{7?/2[523], 2⁺}). Theβ-decay proceeds mainly to the proposed gamma-vibrational state at 569.7 keV with an anomalously low logft value 5.4, indicating similarity between the microscopic structures of this state and the famous ¦K ₀?2¦ gamma vibration of¹⁶⁵Ho.     

Structure of β-decay Strength Function <Emphasis Type="Italic">S</Emphasis><Subscript>β</Subscript>(<Emphasis Type="Italic">E</Emphasis>) in Halo Nuclei

It is shown that when the parent nucleus has nn Borromean halo structure, then after Gamow–Teller (GT) β^–-decay of parent state or after M1 γ-decay of Isobar Analogue Resonance (IAR) the states with np tango halo structure or mixed np tango + nn Borromean halo structure can be populated. Resonances in the GT β-decay strength function S_β(E) of halo nuclei, may have np tango halo structure or mixed np tango + nn Borromean halo structure. Correct interpretation of halo structure is important in experiments on β-decay study, interpretation of M1 γ-decay of IAR, and charge-exchange nuclear reactions analysis.     

A test for time-reversal violation in allowed isospin-hindered beta-decay

A method is proposed for the detection of T-violation in allowed isospin-hindered β-decay which is relatively simple from the point of view of theoretical analysis and which introduces an amplication of the T-violating effect of ≈ 10². As an example a β-decay in ¹³⁴Cs is studied.     

Magnetic moments and GT-type β-decay matrix elements in nuclei with a LS doubly closed shell plus or minus one nucleon

The magnetic moments and GT-type β-decay matrix elements of nuclei with an ¹⁶O core plus (minus) one nucleon and with a ⁴⁰Ca core plus(minus) one nucleon are studied from the point of view of configuration mixing in terms of second order perturbation theory. It is found that the effect of the mixing of highly excited configurations through a tensor force is essential to explain the large reduction of the GT-type β-decay matrix elements. It is also found that modulus of the isovector parts of the gyromagnetic ratio, g_τS and g_τl, are appreciably reduced by the configuration mixing.     

Scheme of the β-decay of <Superscript>234</Superscript>Th

The scheme of the β-decay of ²³⁴Th is still not completely clear. Only the upper bound (10 keV) of the energy of the isomeric transition from level T_1/2 = 1.17 min of the ²³⁴Pa nucleus is known, and the correspondence between gamma quanta of several energies emitted in the β-decay of ²³⁴Th and specific nuclear levels of ²³⁴Pa has not been established. In this work, the isomeric transition energy of 2.6 ± 0.5 keV is determined via the γ-spectrometry of a ²³⁴Th source in γγ-coincidences, and a new ²³⁴Pa level populated in the β-decay of ²³⁴Th is introduced.     

New features in the systematics of low-spin states in170–178W

Excited states in the range of even tungsten isotopes, from¹⁷⁰W to¹⁷⁸W, populated in the β-decay of^170–178Re parents have been identified using γ-ray singles and coincidence techniques, utilising the high efficiency of a Compton-suppressed array, and conversion electron systems. Many new states at low excitation energies have been identified, complementing the level schemes previously established from in-beam studies. The new states include excited O⁺ states in¹⁷⁰W,¹⁷²W,¹⁷⁴W,¹⁷⁶W and¹⁷⁸W. A large body of data on decay properties, spins and parities, and relative E2 and E0 matrix elements has been obtained. The properties of theK ^π=0⁺ (quasi-β) bands are compared with similar bands observed in light osmium, platinum and mercury isotopes, which have been attributed to shape coexistence.     

Gamma-ray decay from the analogue state of the Ca g.s.

The γ-decay from three fine-structure components of the ⁴⁹Ca ground state analogue has been investigated. Angular distributions have been measured for the decay from the strongest component. Absolute γ-widths are found from the γ-spectra, and the proton and neutron widths from fits to the ⁴⁸Ca(p, p) and (p, n) excitation functions. A group of eight states with E_x around 7 MeV is found to carry a significant part of the M1 strength. A comparison with the β-decay from ⁴⁹Ca has been made.     

β-decay studies of the neutron-rich 18,21N isotopes

The β-decay studies of neutron-rich ^18,21N isotopes have been performed using β-n, β-γ, and β-n-γ coincidence methods. The ^18,21N ions were produced by the fragmentation of the ²²Ne and ²⁶Mg beams, respectively, on a thick beryllium target. The time of flight of the emitted neutrons following the β-decay of ^18,21N was measured by a neutron detector system with wide energy detection range and low-energy detection threshold. In addition, several clover germanium detectors were used to detect the β-delayed γ-rays. The half-lives of the β-decays of ¹⁸N and ²¹N were determined to be (619±2) ms and (82.9±7.5) ms, respectively. Several new β-delayed neutron groups were observed with a total branching ratio of (6.98±1.46)% and (90.5±4.2)% for ¹⁸N and ²¹N, respectively. The level schemes of ¹⁸O and ²¹O were deduced. The experimental Gamow-Teller β-decay strengths of ¹⁸N and ²¹N to these levels were compared with the shell model calculations.     

Levels in182W populated in the decay of182Ta

Theγ-rays emitted in theβ-decay of¹⁸²Ta have been reinvestigated with improved statistics in attempting to clarify the reported new levels at 1460.41, 1592.98, 1620.36, 1712.29 and 1762.91 keV in¹⁸²W observed in theβ-decay of¹⁸²Ta. The present study demonstrated that the fifteen newγ-rays, which were used to support the existence of the five new levels, are not relevant to theγ-decay of¹⁸²Ta. Therefore the five new levels are not populated in this decay. Additionally, theγ-ray with an energy of 1035.6 keV (0 ₂ ⁺ →2 ₁ ⁺ ) deexciting theβ-band head in¹⁸²W is observed for the first time in the present decay study and the previous tentative placement of the 351.0 keVγ-ray in the level scheme is confirmed by the present coincidence measurements.     

The α-decay rate of 188Pb

As part of our investigation of the reported anomalous α-decay rates of even-even lead nuclei with A ≦ 192 we have measured the α-decay branching ratio of ¹⁸⁸Pb. The isotope was produced in the ¹⁸⁰W(¹⁶O, 8n) reactions, and its decay properties were investigated with the use of the Oak Ridge on-line isotope separator facility. Gamma-ray and α-particle spectra were measured with the detectors placed in calibrated geometries. From these measurements the ¹⁸⁸Pb α-decay branching ratio was determined to be (22 ± 7)%, a value about seven times greater than that available in the literature. This result, together with our recent data for ¹⁹⁰Pb and ¹⁹²Pb, is discussed within the context of α-decay-rate systematics in the lead region.     

Probability of K-shell auto-ionization in the β−-decay of 143Pr

The K-shell auto-ionization probability in the β^?-decay of ¹⁴³Pr has been measured in a new method using a curved-crystal spectrometer. A value of (2.88 ± 0.20) × 10^?4 was obtained for the number of K-shell vacancies per β^?-decay. This result is compared with previous results and with theory.     

Activation measurement of the3He(4He,γ)7Be reaction

The energy integrated absolute cross section of the³He(⁴He,γ)⁷Be reaction has been determined by an activation measurement, using the branching of the⁷Be 53.44d β-decay to the 478 keV state in⁷Li and its subsequentγ-decay. Depending on the branching ratio used (10.4% or 15.4%) we obtain a zero-energy nuclear cross section factor ofS(0)=0.56±0.03 keV·barn orS(0)=0.38±0.03 keV·barn, respectively.     

β-γ-Zerfall des 5+-Niveaus in In 116 und γ-Verzweigungsverhältnisse in Sn 116

The γ-spectrum, emitted in the β-γ-decay of the 5⁺ state of In 116, has been measured with a Ge(Li)-detector. 19 unknown transitions in Sn 116 have been found, most of which could be fitted uniquely into the established level scheme. A new β-transition (logft=5.6) to the 3,096 keV level has been found. Branching ratios are given and a possible band structure in Sn 116 is discussed.     

The Internal Bremsstrahlung Accompanying the β-Decay from 185W

The internal bremsstrahlung (IB) spectrum accompanying the β-decay from ¹⁸⁵W radionuclide has been measured. The obtained spectrum was analyzed into its constituting gamma lines taking into account all the proper corrections. The analyzed spectrum was compared with those theoretically calculated. The experimental results for the IB probability were found to be in good agreement with theoretical calculations especially with the shape corrected modified KUB theory of Nilsson up to 357.7 keV.     

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.     

Asymmetrie des β-Zerfalls und NMR von28Al,38Cl und116In nach dem Einfang polarisierter Neutronen

Polarized²⁸Al,³⁸Cl and¹¹⁶In nuclei have been produced by capture of polarized thermal neutrons. The nuclear magnetic resonance has been observed by measuring the asymmetry of the β-decay. The nuclear magnetic moments were found to be μ(²⁸Al)=2.789(1) nm and μ(³⁸Cl)=2.05(2) nm (uncorrected). The β-decay asymmetry of¹¹⁶In has been observed in superconducting In-metal.     

Beta-decay properties of exotic nuclei and the astrophysical r-process

The r-process abundances are evaluated with the use of three different β-decay models, i.e., the second version of the Gross Theory, the semi-Gross Theory and a QRPA approach. The necessary Q_β-values, as well as the neutron separation energies, are obtained from the TUYY, ETFSI and FRDM mass predictions. A comparison is made among the β-decay half-lives predicted by these β-decay models for the nuclei on a typical r-process path, as well as among the resulting r-process abundances.     

Q values in β+-decay, (p,n) and (3He,t) reactions

Atomic excitation corrections to Q-values in β⁺-decay determined by (p, n) and (³He, t) reactions are shown to be comparable to current experimental precision, but too small to account for observed discrepancies.     

Non-yrast level structure of35Nd via beta decay of135Pm

The isotope¹³⁵Nd has been studied through the β-decay of mass-separated¹³⁵pm. He-jet transported samples without mass-separation were also studied. The parent¹³⁵Pm has isomers with β-decay half-lives of 40±3 s and 49±3 s. The low-lying non-yrast structure of¹³⁵Nd is shown to consist of a group of levels which decay to a 65.1-keV isomeric level which is not reached in the yrast cascades.