The decay properties of 3.25 min 169Hf and 2.05 min 167Hf

The decays of 3.25 min ¹⁶⁹Hf and 2.05 min ¹⁶⁷Hf have been studied with high-resolution Ge(Li) and Si(Li) detectors. The total decay energy of ¹⁶⁹Hf determined from our experimental $\text{K}\text{β}{}^{\mathrm{+}}$ ratio is 3.29^+0.05_?0.13 MeV. The allowed unhindered character of the main β-branches in the decay of both isotopes allows unique Nilsson model assignments.     

Evidence for an isomeric state in 216Th

A new α-line with E_α = 9.912±0.020 MeV is assigned to an isomeric state in ²¹⁶Th. It decays with a half-life of $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 180±40 μ}\text{s}$. There are indications for a dominating γ-branch.     

Gamma-ray multipolarities in 206Pb studied by gamma-gamma directional correlations

Gamma-gamma directional correlations have been measured in the decay of ²⁰⁶Bi. Using a multichannel goniometer with 2 Ge and 6 NaI detectors the directional correlations have been measured for 17 cascades in ²⁰⁶Pb. From the results, electromagnetic multipole mixing ratios are deduced and limits to transition strengths are estimated.     

Coulomb excitation in 180Hf

Coulomb excitation studies have been performed to measure transition probabilities of collective quadrupole vibrational states in ¹⁸⁰Hf. The I = 2 level of the K^π = 2⁺ collective γ-band is established at 1200.5 keV with B(E2)_exc = (11.0 ± 1.1) × 10^?50e² · cm⁴ (3.6 ± 0.4 s.p.u.). The angular distribution of the de-exciting γ-rays from this level yields δ = 9.6⁺²²_?5.8 or, less likely, 0.7 ± 0.2 for the 1107.2 keV 2_γ⁺ → 2_g⁺ transition. The B(E2)_exc for any K^πI = 0⁺2 stateorother 2⁺ states up to 1500 keV is less than 5 × 10^?51e² · cm⁴ (< 0.2. s.p.u.).     

Vibrational transitions in 182W

Directional correlation measurements (e-e, e-γ) have been performed on ¹⁸²W. The multipole mixing ratios have been measured for the 2_γ⁺2?2_g⁺0 and 4_γ⁺2?4_g⁺0 transitions and a 6⁺6-6_g⁺0 transition in the decay of ¹⁸²Ta and ¹⁸²Re. The mixing ratio of the 2_β⁺0-2_g⁺0 transition is discussed. A strong mixing of the 4_β⁺ and 4_γ⁺ states is suggested.     

Gamma transitions in 59Ni following the β+ decay of 59Cu

The γ-ray decay spectrum of 82 s ⁵⁹Cu produced by the ⁵⁸Ni(p, γ) ⁵⁹Cu reaction has been studied with a 40 cm³ Ge(Li) detector. The number of γ-rays now known for this decay has more than doubled. Additional direct β⁺ branches to the 1679.7($\text{5}\text{2}{}^{\mathrm{?}}$), 2414.8($\text{3}\text{2}{}^{\mathrm{?}}$) and 2681 keV states of ⁵⁹Ni have been identified with log ft values of 5.5, 5.5 and 6.0, respectively. A major change is the reassignment of the 1340.4 keV γ-ray to a 1679.7 → 339.3 keV transition. A limit of log $\text{ft ≧ 6.9}$ is given for the direct feeding of the 1337($\text{7}\text{2}{}^{\mathrm{?}}$) keV state, together with limits for direct population of other energetically available states. The new weak γ-ray branches found for the 878.0, 1301.5 and 1679.7 keV levels are in excellent agreement with the recent theoretical calculations of Glaudemans et al.     

Possible evidence for shape isomeric γ-decay in μ− atoms of 238U

A search for the γ-decay of the shape isomer in muonic ²³⁸U excited by radiationless transitions has been performed. Seven delayed transitions in the energy region of 700 to 3200 keV have been observed with a large Ge(Li) detector. Two transitions with E_γ = 2215 and 3131 keV have been attributed to the decay of the shape isomeric state into levels in the first well. The isomeric shift of the second minimum E₁₁ ≈ 600 keV in the presence of the muon and the decrease of the lifetime of the shape isomer to τ = 12 ± 2 ns give arguments in favour of the connection of shape isomerism with large quadrupole deformations.     

Levels and transitions in 131Xe studied by the decay of oriented 131I

Sources of ¹³¹I were prepared by implantation in iron foils. Nuclear orientation of these sources was obtained by cooling them to temperatures of 30 to 50 mK using a dilution refrigerator and saturating the iron by an external magnetic field. Anisotropies of angular distributions of eleven γ-transitions in ¹³¹Xe have been measured, yielding the following results: the levels at 405 and 637 keV are $\text{3}\text{2}$⁽⁺⁾ and $\text{7}\text{2}$⁽⁺⁾ states and the assignment $\text{5}\text{2}$⁽⁺⁾ for the level a keV is confirmed. Deduced values of E2/M1 multipole mixing ratios are (energies in keV): ?0.5 ≦ δ(318) ≦ + 0.2; δ(364) = ?4.53±0.12; + 0.2 ≦ δ(405) ≦ +2.0; δ(723) = +0.207 ± 0.005. The allowed β-decay branch to the level at 637 keV is for at least 90% of the Gamow- Teller type.     

Measurement of the parity non-conservation in nuclear forces in 75As, 171Tm,and 175Lu and of the polarized bremsstrahlung from 51Cr, 170Tm, 177Lu,and 198Au

The circular polarization P of γ-rays from unpolarized sources of ⁷⁵Se, ¹⁷¹Er, and ¹⁷⁵Yb of strengths ? 500 Ci has been measured with a Compton polarimeter of the radial transmission type. Eight NaI crystals and a four-fold current integration system were used to simultaneously record the data in four independent channels. The results are: P = ?(1.8 ± 6.0) × 10^?5 for the 401 keV transition in ⁷⁵As (the experimental error is ± 1.5 × 10^?5, the remaining part is due to the uncertainty in the decay scheme of ⁷⁵Se), P = (0.8 ± 1.5) × 10^?4 for the 296 keV and 308 keV transition in ¹⁷¹Tm, and P = (5.7 ± 0.8) × 10^?5 for the 396 keV transition in ¹⁷⁵Lu. The last value confirms the parity non-conservation in nuclear forces. The polarimeter was calibrated with bremsstrahlung from ¹⁷⁰Tm. The correction for polarized bremsstrahlung was given special attention. Correction factors are derived for ⁵¹Cr, ¹⁷⁷Lu, and ¹⁹⁸Au from a comparison of the measured and calculated bremsstrahlung yields.     

The quadrupole moments of the 5− states in 116Sn, 118Sn and 120Sn

The quadrupole interaction frequencies $\text{ω}{}_0\text{=}\text{3eQ}{}_1\text{V}{}_{\mathrm{zz}}\text{41(21-1)}\text{h}\text{?}$ in the 5^? state of ¹¹⁸Sn have been measured by time differential perturbed angular correlation technique in Sn, Sb and (95% Sn+5% Sb) environments. The ω₀ for ¹¹⁶Sn was determined in Sn environment only. With the help of the known electric field gradient ¹) of Sn in a Sn lattice the quadrupole moments have been deduced as $\text{Q(5}{}^{\mathrm{?}}\text{,}{}^{118}\text{Sn}\text{) = ±0.10(4) b}\text{and}\text{Q(5}{}^{\mathrm{?}}\text{,}{}^{116}\text{Sn}\text{) = ±0.165(60)}\text{b}$. These values together with the known²) quadrupole moment of the analogous 5^? state in ¹²⁰Sn are interpreted in terms of the pure single-particle model. The data exhibit the expected strong systematic variation of Q_I with the number of particles in the h_{$\text{11}\text{2}$}. subshell which is being filled with 1, 3 and 5 neutrons in ¹¹⁶Sn, ¹¹⁸Sn, and ¹²⁰Sn, respectively.     

Decay of 48K, 49K and 50K

The ⁴⁸K, ⁴⁹K and ⁵⁰K nuclides have been produced in high energy fragmentation and analyzed by mass spectroscopy techniques. Their half-lives have been measured as 6 ± 1 s, 1.1 ± 0.3 s and and 0.7 ± 0.3 s, respectively. The γ-rays from their radioactive decay have been observed and the corresponding γ-intensities measured. The nuclide ⁵⁰K is shown to be a delayed neutron emitter. The antianalog states in the daughter Ca nuclei with a $\text{(1d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?}}$ neutron configuration, preferentially populated in the β-decay, have been located. The corresponding $\text{1d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ neutron single-particle energy is found to remain approximately constant for these neutron-rich Ca isotopes.     

Beta decays of 25Na, 25Al and 29Al

The radioactivities ²⁵Na, ²⁵Al, and ²⁹Al were produced in the ²³Na(t, p)²⁵Na, ²⁴Mg(d, n)²⁵Al, and ²⁷Al(t, p)²⁹Al reactions using a 3.5 MV Van de Graaff. γ-radiations were measured by means of a target-transfer system and a Ge(Li) detector with or without Compton suppression. Decay schemes derived for ²⁵Na and ²⁹Al are in general agreement with earlier results, but with improved accuracy of branching ratios and much sharper limits on the intensities of certain unobserved β- and γ-ray transitions. Precision measurements of the energies of principal γ-rays gave results in keV for the listed decaying bodies as follows: ²⁵Na ? 1611.716(11); ²⁵Al ? 1611.708(11); and ²⁹Al ? 1273.361(9). The energy determinations of the ²⁵Mg 1612 keV γ-transition measured in the decays of ²⁵Na and ²⁵Al differ by 8 ± 9 eV.     

The 6.05 MeV 0+ state in 16O: A shape isomer

A variational calculation predicts the existence of a quadrupole deformed isomeric state in ¹⁶O, which may be associated with the observed rotational band starting at 6.05 MeV. Calculated B(E2) value and strength in the ¹⁸O(p, t) reaction support this interpretation.     

Energy levels and γ-ray transitions in 147Pm

Gamma rays emitted in the decay of ¹⁴⁷Nd have been studied using Ge(Li) detectors as singles and coincidence spectrometers. Four new γ-rays of 53.1, 81.15, 149.4 and 191.24 keV have been detected and all incorporated into the decay scheme. Angular correlation measurements for the 275–319, 275–411 and 272–408 keV cascades have yielded the following result: A₂(275–319) = 0.006(2), A₄(275–319) = 0.005(5), A₂(215–411) = ?0.013(17), A₄(275–411) = ?0.008(30), A₂(272–408) = ?0.283(10) and A₄(272?408) = 0.015(18). From these coefficients the E2/M1 mixing ratios of the 272 and 275 keV γ-transitions have been determined to be 0.10(3) and 0.107(7), respectively, and the spin of the 680.43 keV level to be $\text{7}\text{2}$. Theoretical calculations on the intermediate coupling model for harmonic and anharmonic potential functions have been carried out and better agreement with experiment has been obtained for the anharmonic potential function.     

The half-life of 207Bi and decays of 211At and 211Po

The half-life of ²⁰⁷Bi was obtained from the genetic relation between ²⁰⁷Po and ²⁰⁷Bi, and between ²¹¹At and ²⁰⁷Bi. The half-life was found to be 33.4 ± 0.8 y. The half-life of ²⁰⁷Po was determined to be 5.81 ± 0.04 h by following the decay of the characteristic γ-rays from ²⁰⁷Po. The half-life of ²¹¹ At was determined tobe 7.23 ± 0.02 h by following the decay of γ-rays and α-particles from ²¹¹At and ²¹¹Po. The half-lives determined in the present work for ²⁰⁷Po and ²¹¹At agree with the literature although the half-life of ²⁰⁷Bi differs considerably from the currently accepted value of 38 y. The branching ratio of ²¹¹ At decaying through EC and α-decay modes was determined together with the branching ratios of the three α-particles emitted from ²¹¹Po.     

Discovery of a very low-lying 0+ state in 98Sr and shape coexistence implication in 98Sr

Using the on-line mass separator OSTIS for studies of short-lived fission products, we found two modes for the β-decay of ⁹⁸Rb with respective half-lives of 96 and 114 ms. The latter decay populates a 0⁺ state in ⁹⁸Sr at the unusually low energy of 215.5 keV, which is by far the lowest 0⁺ excited state observed in even-even nuclei. The half-lives of the 0⁺ and the 2₁⁺ states in ⁹⁸Sr were found to be respectively 25 ns and 4 ns. The transition probabilities, the reduced E0 matrix element and the observed level structure suggest shape coexistence for ⁹⁸Sr: the spheroidal 0₁⁺ ground state shows a rotational band with the 2⁺, 4⁺, (6⁺) levels, whereas the presumably spherical 0₂⁺ excited state may be connected with the 2⁺ level of a vibrational band. A simple model is proposed.     

181Ta(n, α)178mLu, 178Lu reactions and isomeric states of 17871Lu107

The cross sections for the production of 25 min and 5 min activities due to the isomeric states of ¹⁷⁸Lu, produced by the ¹⁸¹Ta(n, α) reaction, have been measured at four neutron energies in the keV region. From a study of σ_{5 min} (n, α)/σ _{25 min}(n, α) versus E_n, an attempt has been made to assign spins to the 25 min and 5 min isomeric states of ¹⁷⁸Lu.     

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 102Mo

The ¹⁰²Mo activity was obtained by photofission of natural U and thermal-neutron induced fission of ²³⁵U, with subsequent chemical separation of the molybdenum fraction. In addition, nuclei with mass 102 were separated from fission products of ²³⁵U(n_th, f) using the mass separator LOHENGRIN. A decay scheme and absolute γ-intensities are deduced from measured γ-ray, X-ray and γ-coincidence spectra. Logftvalues are calculated. Shell-model calculations for a $\text{(πlg}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^3$$\text{(νlg}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^3$ multiplet have been carried out using effective nucleon-nucleon interactions. The γ-decay between low-lying, low-spin members of this multiplet was studied in detail and compared with the experimental data.     

Average excited state lifetimes in 73Br

Lifetimes in the region of 10^?16 s have been measured for excited states between 4 and 6.6 MeV in ⁷³Br. The states were produced by the β⁺(EC) decay of a mass-separated source of ⁷³Kr, and they decayed by the emission of protons or γ-rays; their lifetimes were measured by the particle X-ray coincidence technique. The data yield information on both γ-ray and proton partial widths as well as on the level density, a level density parameter-a = 13.7 MeV^?1 is obtained. With the level widths so determined, a statistical model calculation yields excellent agreement with the delayed proton spectrum if a smooth gaussian β-strength function is employed. It is concluded, however, that without the lifetime data, β-strength function information could not have been reliably extracted.