Search

Decay properties of highly-charged radioactive ions can differ from the ones established for neutral atoms. In this contribution we review recent results and future plans for investigations of two-body beta decays of highly-charged ions. Special attention is given to orbital electron capture decay of few-electron ions.

The yrast and near-yrast level scheme of light neutron-rich 143La ( Z = 57 , N = 86 ) is reinvestigated and expanded and that of 144La ( N = 87 ) is proposed for the first time by measuring prompt γ rays from the spontaneous fission of 252Cf at Gammasphere. Spins/parities are assigned to the lowest-lying levels of 143,144La based on the early studies of β − decay, and the assignments for high-spin levels of 143,144La are made by measuring internal conversion coefficients and following the level systematics of the neighboring heavier La isotopes and even–even Ba and Ce nuclei. The B ( E 1 ) / B ( E 2 ) ratios, energy displacements δ E ( I ) and rotational frequency ratios ω − ( I ) / ω + ( I ) of the new parity-doublets of 143,144La indicate that octupole deformations/correlations also develop in these nuclei. The band-crossings observed in a rotational frequency range of 0.31 to 0.34 MeV for the two even-parity bands in 143La but being absent in 144La are interpreted as due to alignment of a pair of i 13 / 2 neutrons in 143La.

Direct photons were measured with the PHENIX experiment in p + p , d + Au , and Au+Au at s N N = 200 GeV . To tackle the p T region below 5 GeV/c, direct photons were measured through their internal conversion into e + e − in Au+Au collisions.

Nuclear excitation by electron transition (NEET) has been observed for 193 Ir in K -shell photoionization, following a previous measurement for 197 Au. We detected internal conversion electrons emitted by decaying excited nuclei of 193 Ir in time spectroscopy using a silicon avalanche photodiode. The incident synchrotron X-rays were monochromatized and scanned around the iridium K -edge ( Δ E = 0 eV ). At energies of between Δ E = + 105 and + 344 eV , an increase of event rates due to nuclear excitation was observed at a level of 2.2-times higher than the standard deviation of the background measured at energies of between Δ E = − 3 and − 324 eV . The NEET probability at Δ E = + 128 eV was obtained to be ( 2.8 ± 0.4 ) × 10 −9 , which is less than one tenth of the probability for NEET on 197 Au.

The probabilities P KK of double K -shell vacancy production per K electron capture decay and per K internal conversion of 109 Cd and 207 Bi have been determined by means of the double- and triple-coincidence experiments using Kα X-ray and K internal conversion. For 109 Cd we find P KK (EC) = (4.2 ± 0.5) × 10 −5 and P KK (IC) = (4.32 ± 0.46) × 10 −5 , and for 207 Bi, P KK (EC) = (2.54 ± 0.50) × 10 −5 . The observed X-ray energy shifts of the hypersatellite Ag ( Kα 1 H ) X-ray and the hypersatellite Pb ( Kα 1 H ) X-ray lines are 545±15 eV and 1238±45 eV, respectively.

The structure of 193Ir was investigated using the 191Ir(2nth,γ)_and 192Os (d,nγ) reactions. High resolution γ and internal conversion spectrometers as well as different Compton-suppressed spectrometers were used. The collective structures are interpreted within the framework of the asymmetric rotor model. The results are also compared to IBFA-1 and IBFA-2 calculations.

The suppression of the nuclear matrix elements describing the two-neutrino nuclear double beta decay mode is studied in the context of a schematic model. The model is able to reproduce the features of extended calculations performed with realistic interactions. It is shown that the dominant mechanism leading to the suppression of the relevant nuclear matrix elements is the destructive interference between “spin-flip”- and “non-spin-flip”-like contributions to the transitions. Detailed results are shown for the case of the 2νββ ground-state-to-ground-state transition 76 Ge → 76 Se.

A combination of the proton-induced fission of 238 U and the on-line mass separation based on the ion-guide technique has been applied in the study of neutron-rich Mo-isotopes. The decays of 106,108 Mo have been studied by using gamma-, beta-, X-ray and conversion-electron spectroscopy. The decay scheme of 106 Mo has been revised and a beta-decay half-life of 8.73(12) s has been measured for this nucleus. A beta-decay half-life of 1.09(2) s and a decay energy of 5120(40) keV have been measured for 108 Mo. The decay scheme of 108 Mo has been constructed and altogether 29 new transitions have been placed in the decay scheme. The beta-decay strengths of 102,104,106,108 Mo have been deduced from the experimental data and are compared with the Gamow-Teller strength obtained from a macroscopic-microscopic calculation. The role of the asymptotic quantum numbers in the context of the allowed beta decay is discussed. Additionally, the experimental half-lives and the decay energies are compared to the recent half-life and atomic-mass predictions.

The multiplicity of KX-rays originating from the conversion of quasi-continuum transitions feeding non-collective discrete states in 143Eu was determined to be about 0.2 per cascade. This implies that the contribution of M1 transitions to the quasi-continuum is much larger than usually expected, possibly as a result of the presence of highly collective M1 bands in this nucleus. Alternatively, this may be a signature of the presence of E0 transitions. Much lower values of the multiplicity of KX-rays were measured for the quasi-continuum transitions feeding a strong E2 cascade in the same nucleus.

High-spin states in doubly odd nuclei of 124Cs, 126Cs and 124La have been investigated by gamma ray spectroscopy. Rotational bands of pih11/2 x nuh11/2 configuration have been assigned by the block ...

K X-ray spectra of 40 18 Ar+ 51 23 V, 59 27 Co, 62 28 Ni fusion evaporation residues are measured in coincidence with γ-rays, protons and α-particles. The spectra are separated into prompt components due to ionization of the target atom by the projectile (PI) and delayed components due to internal conversion of γ-rays deexciting the residues (IC). K-shell ionization probabilities in half-trajectory collisions, P PI 1 2 , are deduced. The results are compared with numerical evaluation of two mechanisms producing K-shell vacancies during the collision: the direct ionization of the target atom by the projectile and the transfer of the K-shell vacancy from the projectile to the K-shell of the united atom. The elemental distribution of cross sections for nuclear reaction products were determined as a by-product from the yields of the PI K X-ray components.

Internal conversion coefficients of transitions in 180 Os have been measured using a superconducting, solenoidal electron spectrometer, operated in the lens mode. The high energy resolution and efficiency allow a precise measurement of the conversion coefficients of the 528 keV yrast transition. The values obtained, α K = 0.015(2), α L = 0.004(1) define pure E2 multipolarity. Taken with the measured γ-ray angular distribution, the conversion coefficient leads to an unambiguous assignment of 16 + → 14 + for the 528 keV transition.

High-spin states in 109In have been investigated using the 107Ag(α, 2nγ)109In reaction. In-beam measurements of γ-ray excitation functions, γ-γ coincidences, γ-ray angular distributions and linear polarizations and lifetimes were performed with Ge(Li) detectors to establish the level scheme. Internal conversion electron spectra have been recorded with a mini-orange spectrometer to determine the conversion coefficients of the transitions in 109In. The level structure of 109In shows strong resemblances with the one of 111In. The properties of several levels in both nuclei are described adequately in terms of a g 9 2 proton hole coupled to excitations of the adjacent Sn cores. However, the observation of the J π = 19 2 + isomeric state (T 1 2 = 210 ms ) in 109In cannot be reconciled with this simple picture. Negative-parity bands can only partly be explained in the usual models.

Electromagnetic transitions between low-lying states in the odd proton nuclei 59 141 Pr 82 , 61 143 Pm 82 , 61 144 Pm 83 and 61 145 Pm 84 with neutron numbers N ≈ 82 were studied by means of in-beam electron-gamma spectroscopy. The triple-focusing electron spectrum selector (TESS) was used to measure in-beam conversion electrons. The TESS, giving very good electron line spectra with small background, was found to be very powerful for in-beam spectroscopy. Accurate values for the internal conversion coefficients (ICC) were obtained by measuring simultaneously both conversion electrons and γ-rays. M2, E3 and some other multipolarities were uniquely assigned from the ICC for the γ-transitions between low-lying states. Properties of these transitions and energy levels are discussed. Analyses of the M2 and E3 transition rates gave, respectively, an isospin-spin (magnetic) core polarization effect and an octupole core polarization effect. The l -forbidden M1 transitions were analyzed in terms of the tensor terms.

The mirror nuclei in the f 7/2 shell offer an excellent possibility for systematic studies of various nuclear properties. These nuclei decay by a strong mixed Fermi and Gamow-Teller decay to the ground state of the daughter nucleus and by weak Gamow-Teller decays to the excited states. The accurate determination of the Gamow-Teller strength provides a sensitive test for the nuclear shell-model calculations.

The isotope 74 Br was produced as the daughter of 74 Kr. This production mode leads to a 74 Br isomer whose half-life was measured to be 25.3 ± 0.3 min. A decay scheme based on the 85 observed β-delayed γ-rays suggests the spin assignment (0, 1) − . Previous detailed studies have reported a 41.5 ± 1.5 min, 4 − isomer of 74 Br which is produced directly in nuclear reactions. There is no indication which of the two isomers represents the ground state of 74 Br.

A new isomer with a half-life of 62 ± 5 ms was observed in 205Po by the reaction 209Bi (p, 5n)205mPo. Prompt and delayed spectra of γ-rays and internal conversion electrons were measured using Ge(Li) and Si(Li) detectors. The 1461 keV isomer decays by an E3 transition with an energy of 580.8 keV and the spin-parity is assigned as 19 2 − .

It is shown that electron capture to β + decay ratios are insensitive to the induced tensor interaction.

The energy dependence of the asymmetry in the beta decay of 8 Li to the first excited state of 8 Be has been measured. Expectations based on the conserved-vector-current hypothesis and the spherical shell model are in good agreement with the measured asymmetry for beta energies above ∼5 MeV. No second class currents are needed to explain the data but the present experiment is not a very sensitive test.

The radioactive decay of 7.4 min 203 At to 203 Po has been studied with mass separated sources from the UNISOR facility. Time-sequenced spectra of γ-rays. X-rays, and conversion electrons were obtained, together with γγt, γXt, e − γt, and e − Xt coincidence data. A decay scheme has been constructed that incorporates approximately 90% of the decay intensity assigned to 203 At. All excited states below 1 MeV have been assigned unique spin-parity values, and the observed level scheme can be qualitatively understood in terms of a particle-core weak coupling description. The ground-state decay energy has been deduced to be Q EC = 5.06 ± 0.20 MeV from γ-ray-gated EC/β + ratios.

Half-lives of several low-lying levels in 157, 159, 161 Er have been measured using isotopically separated sources of Tm produced by the ISOCELE facility at Orsay, France. Delayed coincidences between internal conversion electrons or between conversion electrons and gamma quanta have been registered. Absolute reduced transition probabilities of γ-transitions have been deduced and compared with single-particle estimates and theoretical values found from model calculations including the Coriolis mixing of states.

Excitation functions of γ-rays from the 75 As(p, n) 75 Se reaction were measured with 2.0 to 3.6 MeV protons to establish the level scheme of 75 Se up to about 1.5 MeV excitation energy. Internal conversion electrons following the same reaction were measured at 4.5 and 5.0 MeV proton energy. Using theoretical predictions of the statistical compound nucleus model together with deduced internal conversion coefficients, unique spin assignments were obtained for the 112.5( 7 2 + ), 427.9( 5 2 − ) and 663.9( 5 2 − ) keV levels. Probable spins were proposed to the 286.6 ( 3 2 − for one of the doublet and 5 2 − or 7 2 − for the other), 579.4 ( 1 2 − or 3 2 − , 585.8( 9 2 − or 11 2 − and 747.6 ( 5 2 − or 7 2 − ) keV levels. Alow-lying 9 2 + level was tentatively assigned at 133.2 keV energy. It was found that a low-lying 1 2 − level which appears systematically in other odd Se nuclei is absent in 75 Se.

The intensity ratio of K and L X-rays arising from internal conversion of the 74.38 keV M3 isomeric transition in 191 Os has been measured with a thin source made by electron microscopy staining techniques. The resulting α K = 119 ± 12 agrees with the theoretical value of 115 calculated using a nuclear structure parameter λ = 9.4 ± 0.5. No anomaly due to proximity of the transition energy to threshold was observed.

High-spin states in odd-mass Te nuclei were studied by means of the (α, 2n), ( 3 He, 3n) and (d, 2n) reactions. Using in-beam spectroscopic methods γ-ray energies, intensities, excitation functions, time and angular distributions and γ-γ coincidences were measured. Also, for 121 Te, measurements of the linear polarization of γ-rays and internal conversion electron spectra were performed. Level schemes of odd-mass Te nuclei (A = 117–121) were established Up to spin values of J =232. The predominantly excited level sequences, built on the112 − states, are compared with the ground state bands in doubly even Te nuclei. The systematics of decoupled112 − bands in the Z = 50 region is given. Deviations of the level spacings for maximum aligned states of the h 112 ⊗ R multiplets from those of the g.s. bands in the neighbouring core nuclei can be observed. The energetically favoured coupling to J max−1 may be caused by the blocking effect due to the Pauli principle or by dynamical shape fluctuations. The h ]112 ] level systems of the Te nuclei are furthermore compared with particle-core coupling calculations where different models for the core are tested, such as the rigid triaxial rotor, the soft rotor including hexadecapole deformation, and the γ-unstable potential. Each model assumption leads to a rather good agreement with the experimental level energies.

The decay of 193Os to 193Ir has been studied by γγ angular correlations. Inconsistencies between previous angular correlations, internal conversion coefficients, and nuclear orientation angular distributions have been satisfactorily resolved by the present results. These data are used to derive a set of E2M 1 multipole mixing ratios of the transitions between low-lying states. The resulting electromagnetic transition moments are compared with calculations based on the Nilsson model with Coriolis mixing and on the interacting boson-fermion model.

The level structure of 117 Sb was investigated in the reactions 115 In(α, 2nγ) 117m Sb, 117 Sn(d, 2nγ) 117m Sb and 117 Sn(p, nγ) 117m Sb. In order to confirm level sequences and to assign spins and parities to levels populated in the decay of the isomeric three-particle state T 1 2 = 340 μs), prompt and delayed γ-ray spectra, lifetimes, γ-γ coincidences, γ-ray angular distributions, conversion electrons and excitation functions were measured. The spin 25 2 + of the isomeric state can be explained by the three-particle configuration [ π( d 5 2 ); v( h 11 2 ) 2 10 + ] 25 2 + . This is supported by the experimentally determined g -factor of g = O .115 ± 0.006. Other levels in 117 Sb can be interpreted as particle states coupled to anharmonic vibrations of the core. The existence of an excited 9 2 + [404] quasirotational band is experimentally proved and is supported by calculations of the equilibrium deformation.

The relative intensities of the K-shell internal conversion electrons above 800 keV from the decay of 182 Ta(115 d) have been studied. These measurements were made with a π √2 iron-free, magnetic, electron spectrometer with observed resolutions of 0.075 to 0.20%. Relative γ-ray intensities were also determined on Ge(Li) detector systems. These data were combined to obtain K-shell conversion coefficients for 21 transitions. The estimated uncertainties are as small as 0.5% for the relative electron intensities and 0.8% for the conversion coefficients. Multipole mixing ratios are determined for a number of the transitions.

The nucleus 110In has been studied via the reactions 107Ag(α, nγ)110In at 14.5 and 17 MeV, and 110Cd(p, nγ)110In at 7.5 MeV bombarding energy. Gamma-ray and γγ-coincidence measurements have been performed. Energies and relative intensities of 137 transitions in 110In have been determined. A more complete level scheme, containing 53 levels, has been deduced. From this new level scheme, the energy separation of the Jπ = 7+1 ( T 1 2 = 4.9 h ) ground state and the Jπ = 2+1 ( T 1 2 = 69.1 min ) isomer has been deduced to be 62.08±0.04 keV. The electron spectrum from the (α, nγ) reaction was measured with a superconducting magnetic spectrometer. Internal conversion coefficients of 30 transitions have been determined. Spins and parities have been deduced on the basis of the multipolarity of γ-transitions, and other arguments. Lifetime measurements were peformed by delayed coincidence and DSA methods. The energies and electromagnetic properties of the 110In states were calculated using the interacting boson-fermion-fermion/odd-odd truncated quadrupole phonon model. Several approximate proton-neutron multiplet states were identified and the unusual energy splitting of the πg −1 9 2 , ν g 7 2 multiplet was reproduced.

Delayed γ-rays from 98 Tc have been observed following pulsed proton beam bombardment of an enriched 98 Mo target. The energies of the delayed γ-rays are 43.5 ± 0.5 keV and 21.8 ± 0.1 keV. Also seen are delayed Tc X-rays. These radiations all have the same half-life which has been measured to be 14.6 ± 0.7 μs. The 21.8 keV γ-ray is identified as the first excited state to ground state transition. An estimate of the internal conversion coefficients of the 21.8 and 43 keV decays suggests that both transitions are M1.

Relative probabilities of the E0 internal conversion for the K, L, M and N + O shells in the transitions of 154 Gd have been studied in detail with the use of special electron measuring techniques. They were compared with the theoretically predicted values. It turned out that the internal conversion is successively hindered from the outer to the inner shells on the assumption that the conversion for the outer shells is normal.

The nuclear structure of 155Sm has been studied via primary and secondary γ-rays and by internal conversion electrons following thermal neutron capture. Furthermore average resonance neutron capture spectra for various neutron energy ranges were recorded. A detailed level scheme with a complete set of levels with spin 7 2 has been well established up to 1400 keV excitation energy. The neutron binding energy has been determined to be 5807.2(3) keV. The scheme is interpreted in a basis of Coriolis and ΔN = 2 coupled Nilsson states and compared with the less deformed Sm isotopes. A possible additional band coupling via the octupole vibrational mode is discussed.

Relative intensities of internal conversion lines of the 569.6, 897.3, 1063.6 and 1770.2 keV transitions in the decay of 207 Bi were precisely determined by spectrographical measurements with position-sensitive electron detectors installed on the focal plane of the INS iron-free π √2 β-ray spectrometer. Internal conversion coefficients were deduced with the measured relative electron intensities and with the recent precise γ-ray data, where we assumed that the ICC of the 569.6 keV K-line is equal to the theoretical α k (E2) value. The experimental ICC thus obtained were systemati- cally compared with those by Rosel- Fries-Alder- Pauli (RFAP) and found to be satisfactorily in agreement with the theoretical values. L- and M-subshell ratios, and K- through O+P-shell ratios of the 569.6 and 1063.6 keV transitions determined for the first time in the present work were also found consistent with the predictions by RFAP.

Internal conversion coefficients for inner shells of atomic ions of Sn are calculated for various degrees of ionization and compared with neutral atom predictions. The relativistic version of an analytic perturbation theory is used to include screening effects.

An analogy with electron capture allows us to show that the instantaneous state produced by dynamical correlations is frozen in after internal conversion. The exchange correction calculated by using this final state explains the anomalies in the K L internal conversion ratios at low atomic numbers and in the L-subshell ratios at medium and high atomic numbers.

The structure of excited states in 132Sn, fed in the β-decay of 132In, has been investigated. Absolute intensities were deduced from γ-singles measurements. From multi-spectrum analysis of γ-lines the half-life of 132In was determined to be 186 ± 22 ms. A level scheme based on γγ and βγ coincidences is presented. The conversion electron spectrum has been studied and internal conversion coefficients deduced for two low-energy transitions. The total decay energy of 132In was determined, from γ-gated β-spectra, to be Qβ = 13.6 ± 0.4 MeV. A lower limit of 6.968 MeV for the neutron separation energy in 132Sn was deduced from the β-delayed neutron spectrum. The experimental results on the level structure of the doubly closed shell nucleus 132Sn show that the shell model is applicable even far from the valley of stability.

The decay of 5.4 min 174Tm has been investigated using Ge(Li) spectrometers in singles and coincidence measurements. A total of 43 γ-ray transitions, 26 of them not reported before, have been observed following the decay of 174Tm. All transitions could be placed in a level scheme comprising 19 excited states of 174Yb. The Nilsson model has been used to interpret the level structure. The mixing of two-quasineutron and two-quasiproton states is studied and the experimental mixing matrix element is compared with the results of theoretical calculations.

Low-lying states in 96 Tc excited through the 96 Mo(d, 2nγ) reaction have been investigated by means of on-line internal conversion electron and γ-ray spectroscopy. Measured singles spectra and relative excitation functions together with particle-γ and γ-γ coincidences were used to identify and fit the transitions in a level scheme. The low-lying positive-parity states 2 + –7 + and negative-parity states 2 − and 3 − are compared with those appearing systematically in doubly odd 94, 98 Tc and 92–96 Nb isotopes. Comparison is also made with simple shell-model calculations for those nuclei based on the π( p 1 2 , g 9 2 ) p ν ( d 5 2 ) n configuration space and the tendency of the multiplet structure of the wave functions is discussed.

An analysis of 165 Tm decay has shown that precision measurements of the γ-ray and internal conversion electron intensities, in combination with angular correlation measurements, provide additional data useful for the determination of the mixing and intensity ratios of γ-transitions with a small energy difference. The spin of the 589.868 keV state is found to be I π = 1 2 − . Doublet opposite-parity transitions from states at 1103.495, 920.632 and 745.968 keV to levels near 590 keV with an energy difference ΔE = 108 ± 22 eV are identified.

The K-shell ionization cross sections, σ K Z , are determined for Dy atoms produced in bombardments of several Gd targets with α-particles in the energy range 47–130 MeV and of 148, 150 Nd targets with 12 C ions at 65 and 90 MeV. The determination is based on the measured intensity ratios of the characteristic K X-rays of the product atoms to those of the target elements. Analysis of the simultaneously measured discrete in-beam γ-ray spectra allows one to determine ionization cross sections for Dy product atoms, σ Z K ( der ), derived as a sum of the products of the γ-ray intensities times the corresponding K-shell internal conversion coefficients. The measured and the total derived values are found to be identical to within the experimental errors. The partial ionization yields per reaction are analyzed as functions of the average angular momentum left in each exit channel. Strong dependence of these yields on the nuclear structure is found. Moreover, the variation of the yields with the angular momentum is also strongly structure dependent. Properties of the quasicontinuum γ-radiation deexciting the reaction residues are considered. Upper intensity limits are determined for the low-energy magnetic dipole components in this radiation.

We have applied a simple microscopic decay theory to the analysis of the rare decay modes. The absolute decay rates are estimated by using the shell model and resonance formation factors and optical model penetrabilities. The resonance formation factors are deduced from the strong interaction form of the theory where the wave function in the internal region is represented in terms of compound nucleus decay. In order to account fully for the data, the implication of internal degrees of freedom was found to be necessary, but no adjustment of Gamow factor was needed. The results have been discussed in the light of the previously reported results and data.

Seventy-nine γ-rays, three of which are reported here for the first time, have been observed in the decay of 231 Pa. The internal conversion electron spectrum has been studied using a trochoidal spectrometer, and the internal conversion coefficients of transitions between 240 and 410 keV have been determined. The α K values for four of the transitions, viz. those at 243.15, 255.76, 277.10, and 407.80 keV are here reported for the first time. Two levels at 508.9 and 576.6 keV proposed by de Pinho et al . as higher spin states of the case1 2 − (530) rotational band have been confirmed. Reduced transition probabilities of inter- and intra-band transitions have been determined and compared with theoretical predictions. An estimate of Q 0 , g R and g K is presented.

The odd-mass nucleus 107Cd was investigated in the reactions 105 Pd (α, 2 n ) 107 Cd , 107 Ag (d, 2 n ) 107 Cd and 107 Ag ( p, n ) 107 Cd . The constructed level scheme is based on results, obtained from singles γ-ray spectra and excitation functions, from the measurements of delayed γ-rays, of γ-γ coincidences, of internal conversion electrons and of γ-ray angular distributions. Two new isomers were observed. The first one, interpreted as the h 11 2 neutron state at 845.6 keV has a half-life of 67 ± 6 ns. This isomeric state is populated by a strong E2 cascade. Bands built on the other intrinsic states with spins and parities 5 2 + and 7 2 + are not strongly populated. For the second isomeric state at an excitation energy of 2679 keV a half-life of 55±4 ns was determined. This isomer is probably a three-quasiparticle state. Its configuration can be proposed as [π( g 9 2 ) −2 8+ ν( 7 2 ) 1 ] 21 2 + .

Levels in 81 Kr have been studied by the 81 Br(p, n γ) reaction at proton energies from 1.80 to 5.00 MeV. Gamma-ray excitation functions, γ-γ and n-γ coincidence spectra and an internal conversion spectrum have been taken. A level scheme of 81 Kr has been proposed, and spins and parities have been assigned to many low excited states. The half-life of the first excited state (49.4 keV) has been measured to be 8.4±1.0 ns. A simple shell model calculation assuming a 88 Sr core has been carried out and compared with the experimental results.

Protons with energies from 870 keV to 5.4 MeV have been observed following bombardment of a 40 Ca target with 3 He at beam energies of 29.5, 36.5 and 60 MeV, as well as from 40 MeV 3 He bombardment of an 36 Ar gas target. These data, and those resulting from 20 MeV proton bombardment of 40 Ca, permit accurate identification of proton unbound levels in 41 Sc, 37 K, and 40 Ca fed by allowed beta decay from 41 Ti, 37 Ca or 40 Sc, respectively. Absolute ft values have been determined for beta decay to these levels. The half-life of 41 Ti has been remeasured to be 80±2 ms and the log ft for its superallowed decay branch has been found to be 3.35±0.02, indicating an isospin purity for the lowest T = 3 2 state in 41 Sc of ≈ 91 % . The ft values for 37 Ca β + decay are compared to shell-model calculations for beta-decay in A = 37 nuclei.

The de-excitation of the 215 keV 7 2 + and 324 keV 5 2 + levels in 97 Tc, as observed in 97 Ru decay, was studied by means of internal conversion electron spectroscopy and the delayed electron-electron coincidence technique. From L-subshell intensity ratios, the E2 content in the 108 and 215 keV transitions were found to be (65 ± 12)% and (7 ± 4)%, respectively. The obtained level mean-lives were 0.75 ± 0.09 ns for the 324 keV level and 74 ± 15 ps for the 215 keV level.

The rotational bands built on the excited 112− levels in 191Au and 193Au were investigated in (α,4n) reactions with in-beam γ-ray and conversion electron spectroscopy. Half-lives of the rotation-aligned levels in these bands were determined from e−e− time spectra, which were measured with a new double-orange spectrometer. In addition, some information on the magnetic moments of the rotation-aligned levels was obtained from integral perturbed angular distribution measurements. Finally, the previously unknown low-energy 312− → 272− transition in 191Au was identified from conversion electron measurements. From these data it is concluded that the rotation-aligned Hg cores have predominantly νvi1322 structure, contrary to the earlier suggestion of a πh1122 core structure.

The γ-spectrum of the 70Zn(p. nγ)70Ga reaction was measured with Ge(Li) spectrometers at proton bombarding energies of 3, 3.5 and 4 MeV. 47 γ-rays were assigned to 70Ga and the energies (Eγ) and relative intensities (Iγ) of γ-rays were determined. The electron spectrum of the reaction was measured with high-transmission superconducting-magnet-transporter Si(Li) and mini-orange Si(Li) spectrometers. Internal conversion coefficients were determined for eight 70Ga transitions. The level scheme of 70Ga, γ-branching ratios, multipolarity of transitions, level spins and parities were deduced. The energies of low-lying 70Ga levels were calculated on the basis of the parabolic rule derived from the cluster-vibration model. This calculation provided a simple classification of several multiplet states in 70Ga for the first time.

The decay scheme of 40 min 120 Xe has been investigated using isotopically separated sources produced by the ISOLDE facility at CERN. A total number of 202 γ-transitions has been observed in this decay; 188 of them have been placed in a level scheme involving 34 excited states in 120 I. Most of these levels are based on the results of γ-γ coincidence experiments with two Ge(Li) detectors. Internal conversion coefficients have been obtained with a Si(Li) detector and a magnetic spectrometer. The half-life of 4 low-lying levels in 120 I has been measured by delayed coincidence techniques. From these measurements, partial half-lives for some transitions have been deduced and are compared with the single-particle estimates. Two E2 transitions are strongly enhanced.

A study has been made of K − meson interactions at rest in the CERN 1.1 m 3 heavy liquid bubble chamber filled with a mixture of hydrocarbons. The data are used to determine (i) the internal conversion probability, C ( Σ − ), of Σ − hyperons produced in association with π + mesons by K − meson interactions in carbon nuclei, (ii) the relative emission frequencies of ( Σ + π − ) and ( Σ − π + ) pairs, E ( Σ + π − / Σ − π + ), and the emission frequency E ( Σ ± π ∓ /K − ), of ( Σ ± π ∓ ) pairs per K − meson absorption in carbon, (iii) the branching fraction, P ( Σ − π + /K − ), for the primary process K − + p → Σ − + π + in carbon and (iv) the trapping probability, T ( Λ °), for Λ ° hyperons produced by Σ − hyperon interactions in carbon nuclei. The results are: C ( Σ − ) = 0.38 ± 0.03, E ( Σ + π − / gS − π + ) = 1.25 +- 0.09, E ( Σ ± π −+ /K − ) = 0.164 ± 0.006, P ( Σ − π + /K − ) = 0.127 ± 0.004 and T ( Λ °) = 0.13 ± 0.04, where the errors quoted are statistical and correspond to one standard deviation. Possible systematic errors were estimated to be at most of the same order of magnitude as the statistical uncertainties.