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.     

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.     

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.     

Decay of the new isotope167W

Theα- and β-decay of the new isotope¹⁶⁷W were observed in the reaction of 191 MeV³⁶Ar with¹³⁶Ba using a helium-jet and a fast tape-transport system. The identification is based on coincidences with tantalum X-rays and excitation function measurements. The measured half-life is 19.9(5) s. A decay scheme comprising 12 levels was constructed from γγ-coincidences. The β-decay is discussed within experimental and calculated level systematics. Alpha-rays with energy 4.55(2) MeV were assigned to¹⁶⁷W.     

Isospin-forbidden β-decay of 28Mg

We have measured the branching ratio for the isospin-forbidden Fermi β-decay of ²⁸Mg to the 0.972 MeV 0⁺, T = 1 level in ²⁸Al. This decay occurs through an admixture of the 0⁺, t = 2 analog state at 5.992 MeV into the anti-analog level at 0.972 MeV. A charge-dependent matrix element of 17.0_?5.8^+4.3 keV is deduced from the observed (0.21 ± 0.12)% branch. Comparisons are made with matrix elements deduced in other nuclei. An analysis based on a simple shell model with fourfold degenerate Orbitals indicates the importance of the two-body Coulomb interaction in isospin mixing in nuclei with more than one valence proton.     

Spin exchange polarization and measurement of the hyperfine splitting of short-lived8Li

Free⁸Li (T _1/2=0.84 sec) atoms were polarized by spin exchange with optically pumped rubidium vapour. The⁸Li nuclei were produced by the reaction⁷Li(d, p)⁸Li in a thin LiF target. They recoiled into helium which was used as a buffer gas for optical pumping as well. Nuclear polarization up to 2% was detected by β-decay asymmetry. Rf transitions between hfs levels of the atomic ground state yielded the hfs separation ΔW=382.543(7) MHz. The nuclear spin assignmentI=2 was confirmed.     

The beta decay of 18N and T = 2 states of mass 18

The ¹⁸N(β^?)¹⁸O decay was observed via the ⁹Be(¹⁸O, p2α)¹⁸N reaction, utilizing helium-transport techniques and Ge(Li) spectroscopy. In addition to the previously reported β-decay to the ¹⁸O 4456 keV level (J^π = 1^?) branches were observed to levels at excitation energies (in keV) of 1982 (J^π = 2⁺). 5530(2^?), 6198(1^?). 6350(2^? or 1⁺), 6880(0^?), and 7771(2^?). The percentage β-branches, in order of increasing excitation energy, are 3.9 ± 1.5, 54.6 ± 1.0, 3.1 ± 0.4, 1.4 ± 0.2, 2.2 ± 0.3, 14.8 ± 0.8 and 5.0 ± 0.5. respectively, with 15 % assumed on the basis of calculations to proceed to non-γ-emitting states. These measurements allow definite assignments J^π = 1^? for the ¹⁸N ground state and J^π = 0^? for the ¹⁸O 6880 keV state. Additional measurements determine the ¹⁸N half-life to be T_{1 2} = 624 ± 12 ms. A shell-model calculation for mass 18 was carried out in a full 1?ω basis. The predictions for the T = 2 energy level spectrum and for ¹⁸N β-decay are discussed.     

Isospin impurity of 64Ga ground state

It is well known that the observation of a nonzero Fermi matrix element for a β-transition between states that differ in isospin can provide information about the relative isospin purity of the states involved. We have determined the log ft value for the 0⁺ → 0⁺ (ΔT ≠ 0) β-transition in ${}^{64}\text{Ga}\text{→}{}^{64}\text{Zn}$ decay as 6.516 ± 0.020. From this log ft value, we have deduced |M_F| = (43.4 ± 1.1) × 10^?3, |α| = (21.7 ± 0.6) × 10^?3 and |〈V_CD〉| = 41.7 ± 1.1 keV, where M_F,α² and 〈V_CD〉 represent the Fermi matrix element, isospin impurity and Coulomb matrix element, respectively. The Coulomb matrix element of 41.7 keV found for ⁶⁴Ga is one of the largest known from β-decay experiments. The experimental procedure involved a careful measurement of the intensity of the annihilation radiation relative to that of the other γ-rays from ⁶⁴Ga decay. As a by-product, we have obtained an improved ⁶⁴Ga decay scheme. We have also summarized the existing information on the isospin impurities of nuclear states as deduced from β-decay experiments.     

The β-decay of 91Sr

Both the continuous β-mray spectrum and the internal conversion electron spectrum of ⁹¹Sr have been studied with a π√2 magnetic spectrometer. The measurements yield an intensity of 30.8% for the first-forbidden unique β-decay to the ground state and a Q-value of 2.684 ± 0.004 MeV. The measured internal conversion coefficient of the 555.6 keV isomeric transition in ⁹¹Y is in excellent agreement with the theoretical value for an M4 transition. Seven less intense internally converted transitions were also studied. The results verify the J^π assignments of earlier studies and also provide new information for the transitions from which level structure configurations can be proposed.     

Half-life and α-ray energy of146Sm

Up-to-date α-decay data of the double-even,N=84 isotones are presented, including the presently remeasured values for¹⁴⁶Sm. For this nuclide a half-life,T _1/2 =1.031 (45) ×10⁸ y, and α-ray energy, E_α=2455(4) keV, were measured. The significance of these data for the subshell closure atZ=64 observed in α-decay is discussed.     

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.     

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.     

Anregung gebundener Atomzustände durch die plötzliche Zentralfeldänderung beim β−-Zerfall des Kerns

By the sudden change of nuclear charge during β^?-decay the daughter-ion is ionized or excited with probabilities of the order of some percent; other processes in the electron shell may be neglected, therefore unperturbed excitations can be measured by detecting photons emitted from the decaying excited atomic states in delayed coincidence with β^?-particles as is shown in an earlier paper for the Kr 85-β^?-decay. More extensive measurements of the photonemission after this decay give results in good agreement with theoretical predictions. Mostly such photons are observed, which can be emitted after a monopol-excitation, for which the selectionrulesΔ J=0 andΔ l=0 are valid. The total excitationprobability into both 5p(J=0)-states of Rb II is found to be P(4p?5p)=5,6±1,0%. The lifetimes of these two states are measured (correspondingly) to be τ=7,6 ±0,5 nsec, from which the reduced matrixelements ¦〈5p∥D∥5s〉¦²=18,9±3,2 and ¦〈5p∥D∥4d〉¦²=10,4 ±1,8 a.u. are calculated.     

The decay 150Pr → 150Nd and the anomalous β-band in 150Nd

The β-decay of mass-separated ¹⁵⁰Pr has been studied resulting in a considerably improved level scheme for ¹⁵⁰Nd. Particular care has been taken to evaluate the γ-ray branching ratios from the 2⁺ levels of the β- and γ-bands since the moment of inertia of the β-band in ¹⁵⁰Nd deviates considerably from the systematics of the N = 90 isotones. The deduced relative B(E2) values from the β-band are in keeping with a relatively small deformation for this band.     

The MTV experiment: searching for T-violation in polarized Li-8 at TRIUMF

The MTV experiment (Mott Polarimetry for T-Violation Experiment) is running at TRIUMF, to search for a large T-violating transverse electron-polarization in polarized ⁸Li β-decay. We aim at reaching precision of 10^?4 for the R-correlation, which is defined as a T-violating triple vector correlation in the β-decay rate function. A Mott polarimeter system using a CDC (Cylindrical Drift Chamber) is used to measure the left-right scattering asymmetry in the Mott scattering from a thin metal foil. In the present study, we aim to discuss systematic effects in Mott polarimetry using the CDC.     

Study of the giant gamow-teller resonance in nuclear β-decay: The case of 32Ar

Delayed proton and gamma emissions following the β-decay of ³²Ar have been studied. The half-life of ³²Ar is 98 ± 2 ms, and the T = 2 analogue state in ³²Cl lies at the excitation energy 5036 ± 12 keV. From the intensity of the feeding to this state the proton intensities can be converted to an absolute scale leading to a total proton branching ratio of (43 ± 3)%. From proton-gamma coincidence measurements it emerges that (1.9 ± 0.2)% of the protons lead to the first-excited state in ³¹S. A level scheme up to 8.75 MeV excitation in ³²Cl has been constructed and the Gamow-Teller strength function has been deduced. The result is a renormalization of the axial-vector strength to (49 ± 5)% of the free-nucleon value.     

IsoscalarE2 transition strengths in 10≦A≦48 nuclei

Electric quadrupole transition strengths for the 2 ₁ ⁺ ,T=1→0 ₁ ⁺ ,T=1γ-decay branches are summarized for 10≦A≦42 nuclei. In¹⁰B the corresponding branch has been remeasured by use of the⁹Be(p, γ)¹⁰B resonance reaction atE _p =320 keV; an upper limit of 0.6% is found. The variation of theE2 strengths within each individualT=1 isobaric multiplet reveals the particleor hole-character of the levels involved. The isoscalar 2 ₁ ⁺ →0 ₁ ⁺ transition strengths in 10≦A≦48 nuclei vary between 2 and 20 Weißkopf units showing drastic shell effects. Results for the ratio of neutron and proton matrix elements deduced from analogγ-decay studies and from inelastic pion scattering are compared.     

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.     

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.     

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.