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The β-decay properties of ground-state and isomer of 103In were investigated by means of γ-ray spectroscopy. The half-lives of 103g In and 103m In were determined to be 60 ± 1 s and 34 ± 2 s, respectively. Out of 149 γ transitions ascribed to the decay of 103g In, 104 have been placed in a decay scheme including 55 excited states of 103g Cd. The main part of the resulting distribution of the Gamow-Teller strength B(GT) is associated with the feeding of 103Cd levels at excitation energies around 3 MeV. This observation can be interpreted as a sign of dominant feeding of three-quasiparticle states in 103Cd, which correspond to the 1+(πg 9/2 −1 , vg7/2)⊗πg9/2 shell-model configuration spread over many levels. The sum of the B(GT) values deduced from the present γ-ray data amounts to 0. 34, which provides a lower limit to the total Gamow-Teller strength. The B(GT) distribution for 103In decay is compared to the corresponding experimental results for 105,107,109In and to theoretical predictions for 99,101In. The latter were calculated by using an advanced spherical shell model. The β-branching ratio for the 103m In decay is estimated and compared with the relevant values for the neighbouring indium isotopes including 101In whose half-life was determined to be 14. 9 ± 1.2 s.

By using mass-separated sources, positrons as well as β-delayed protons and γ-rays were measured from the β-decay of 102 In ( T 1 2 = 22 ± 1 s ) and 100 In ( T 1 2 = 6.1 ± 0.9 s ). In particular, the average β + (β + + EC ) ratio for the decay of 102 In was measured to be 0.76(4) and the level scheme of 102 Cd was extended. Whereas no direct β + EC feeding of the identified 102 Cd levels was observed, there is evidence for population of 102 Cd states at high excitation energy followed by statistical γ-decay. This feature, which has been deduced on the basis of the measured positron spectrum and the measured β + (β + + EC ) ratio of the 102 In decay, is compared to the decay properties of the heavier odd-odd indium isotopes 104 In, 106 In and 108 In, and is also used to interpret the observed β-delayed proton data of 102 In and 100 In. For the first time, large-space shell-model calculations have been performed for the Gamow-Teller decay of heavy odd-odd nuclei. The decay results from these calculations are in good overall agreement with the gross decay properties of 102 In and 100 In deduced from the experiment.

The fine structure in the alpha decay of even-even Po, Pb, Hg and Pt isotopes has been studied. Feeding towards low-lying 0+ states in the 196,198Po, 190,192,194Pb, 182,184Hg and 176,178,180Pt isotopes is observed. The energy systematics of the positive parity states in the light Po isotopes indicates the appearance of shape coexistence in these nuclei as well. The hindrance factors of the alpha decay towards the excited 0+ states has been interpreted in a two-level mixing calculation. It offers a probe for the identification of the proton particle-hole character of the 0+ states in this region and strongly supports the persistence of the Z = 82 shell closure in the light Pb isotopes.

Fine structure has been observed in the [alpha] decay of [sup 202]Rn, [sup 194,196,198]Po, [sup 186,188]Pb, and [sup 180,182,184]Hg and has led to the identification of low-lying 0[sup +] states in [sup 198]Po, [sup 190,192,194]Pb, [sup 182,184]Hg, and [sup 176,178,180]Pt. The large variation in the hindrance factors of the [alpha] decay to the exicted 0[sup +] state is a proof for the persistence of the [ital Z]=82 shell closure at the neutron-deficient side. Comparing the reduced widths of the [alpha] decays to the ground and excited states offers a unique way to probe the proton particle-hole character of the 0[sup +] states in this region.

The total cross section for the N-13(d, n)O-14g.s. reaction has been measured with N-13 radioactive beams at laboratory energies of 8.2, 12.0, 16.2, and 28.5 MeV. A spectroscopic factor of 0.9 is obtained from a distorted-wave Born approximation analysis of this transfer reaction. The astrophysical S factor for the N-13(p,gamma)O-14 reaction is calculated using the experimentally known resonance parameters for the resonant contribution and the direct-capture model with the experimental spectroscopic factor for the non-resonant contribution.

Chemically purified and mass-separated Rn isotopes are used to deduce the [alpha] branching ratios of the Po daughter nuclei. The obtained values are systematically lower than the previously known values. Combined with more accurate measurements of the half-lives of the neutron-deficient Po isotopes, a precise set of partial [alpha]-decay half-lives is obtained. The [alpha]-decay energies of some Po and Rn isotopes have also been remeasured. The [alpha] branching ratios of the Rn nuclei can be deduced from the [alpha] intensity of the At daughter nuclei, provided their branching is known. This makes it possible to present in a coherent way the partial [alpha]-decay half-lives and the [alpha]-reduced widths of a long chain of Po and Rn isotopes and to compare them with theory. Evidence is emerging that, for the very neutron-deficient Po isotopes, mixing of intruder configurations into the ground state is slowing down the [alpha] decay.

Theα decay of mass-separated188Pb and180,182Hg has been studied at the GSI on-line mass separator. Alpha singles spectra as well asα-X-t andα-e-t coincidence events were collected. Fine structure in theα decay of188Pb was measured for the first time, feeding the 21+ and 02+ states in184Hg. Theα decay of180,182Hg feeds low-lying states in176−178Pt. One of these states could be identified as a 0+ state. The deexcitation pattern could be established. As a by-product an alpha-decay scheme of180Au towards levels in176Ir is given.

The {sup 206}Fr{r arrow}{sup 202}At{r arrow}{sup 198}Bi, {sup 204}Fr{r arrow}{sup 200}At{r arrow}{sup 196}Bi, and {sup 202}Fr{r arrow}{sup 198}At{r arrow}{sup 194}Bi {ital a}-decay chains have been studied by standard spectroscopic techniques using an on-line isotope separator. All the studied doubly odd isotopes have at least two isomers, which decay by a combination of the following decay modes: {ital a} emission, {beta}{sup +}/EC (electron capture) decay, and internal transition (IT). The internal transition, a highly retarded {ital E}3, is the {ital j}-forbidden transition between the ({pi}{ital h}{sub 9/2}{direct product}{nu}{ital i}{sub 13/2}){sub 10}{sup {minus}} and the ({pi}{ital h}{sub 9/2}{direct product}{nu}{ital f}{sub 5/2}){sub 7}{sup +} states. The {ital B}({ital E}3) values of these IT's together with their energy behavior as a function of the neutron and proton number, compared to the energy difference between the 13/2{sup +}({nu}{ital i}{sub 13/2}) and 5/2{sup {minus}}({nu}{ital f}{sub 5/2}) states in the odd-mass Pb isotones, indicate that these proton-neutron-coupled states have a rather pure shell-model character.

Theα-branching ratios (bα) of192,190,188Pb are measured using mass-separated sources. Different experimental set-ups are used — one detector as well as two detector set-ups — thereby detecting theα particles from the parent and/or viaα decay formed daughter nuclei, theβ-delayed gamma radiation from the parent and/or viaβ decay formed daughter nuclei and the Tl KX rays from electron capture decay. Values forbα of 6.2(6) 10−5 and 4.0(4) 10-3 were found for192,190Pb respectively. For188Pb, limits on thebα values were obtained: 0.03

An off-line release study N-13 (T1/2 = 9.96 min) produced by a proton induced reaction on a graphite target (POCO-graphite EDM3, density = 1.84 g/cm3, grain size approximately 3-mu-m) has been performed. The activation energy for the diffusion process is determined to be 6.15(16)x10(5) J/Mol. With this acitivation energy, extraction efficiences for N-13 are obtained at different temperatures and are compared to on-line measured extraction efficiencies.

In this paper we wish to report on the first observation of the beta decay of the very neutron-rich nucleus 117Rh. It was produced via 23 MeV proton-induced fission of U-238 using the ion guide setup of the LISOL separator. A beta half-life to 0.44 +/- 0.04 s was measured for this nucleus from the decay of the beta-coincident K x rays of Pd. The half-lives of neutron-rich Rh isotopes are compared with the newest model calculations. Three gamma rays of 34.6, 131.7, and 481.6 keV were found to be associated with the decay of 117Rh. Its proposed beta-decay scheme and the decay of the recently discovered 19 ms isomer in 117Pd imply spin and parity of 11-/2 for the isomer fed directly in fission.

The alpha-decay of mass separated Bi-190,192,194,196 isotopes has been studied with the LISOL on-line separator. Time sequential alpha-singles spectra were taken and for Bi-190,192,194, alpha-Xt and alpha-gamma-t coincidences were collected. Transition probabilities of levels in Tl-186,188,190 were measured using a fast timing alpha-gamma-t and alpha-e-t coincidence set up. The alpha-decay of 196Bi and the beta-decay of 190Bi are observed for the first time. In all the Bi nuclei presently studied, unhindered alpha-decay of Bi starting from the high- (10-) and low-spin (3+) isomer populating intruder-based states in Tl was observed. The excitation energy of these intruder states is comparable with the intruder states in the neighboring odd-even and even-even nuclei.

Independent and cumulative yields in nearly symmetric fission have been measured for the first time by bombarding $^{238}\mathrm{U}$ with 20-MeV protons and with 18-, 25-, and 41-MeV deuterons. Isobaric charge dispersion has been determined in the A=110, A=112, and A=114 mass chains and, from asymmetric fission, in the A=80 mass chain. The average isobaric charges in the p+U reaction were 44.01\ifmmode\pm\else\textpm\fi{}0.20 (A=110), 45.15\ifmmode\pm\else\textpm\fi{}0.15 (A=112), and 45.74\ifmmode\pm\else\textpm\fi{}0.15 (A=114). The widths (standard deviations) of the charge dispersion curves were 0.82\ifmmode\pm\else\textpm\fi{}0.08 (A=112) and 0.54\ifmmode\pm\else\textpm\fi{}0.08 (A=114). The average charges are roughly 0.3 unit higher than those calculated on the basis of the unchanged charge distribution model. The ground-state branch in the beta decay of $^{80}\mathrm{Ge}$ was determined to be 65%. Altogether some 15 new neutron-rich isotopes have been found, the newest one being $^{114}\mathrm{Ru}$ with a half-life of 0.53\ifmmode\pm\else\textpm\fi{}0.06 s. An ion guide facility was used to separate the isobaric chains on-line from other fission products. Typical cumulative yields in a mass chain were on the order of 1000 atoms/\ensuremath{\mu}C, but for new isotopes independent yields as low as a few atoms/\ensuremath{\mu}C could be observed.

Theβ-strength function of104Cd is studied in theβ+/EC decay of mass-separated104In. The determination of theβ+ feeding and theβ+/β+EC ratio is the result of the simultaneous measurement of beta and gamma rays in one semiconductor beta-spectrometer. Information on the strength function near theQEC value is obtained from the detection of high-energyγ rays. The total observedβ strength amounts up to 10% of the Extreme Single-Particle Shell Model value. A strong enhancement in theβ+/EC feeding to a group of levels around 5.6 MeV shows the influence of the Gamow-Teller Resonance.

The β-decay properties of ground-state and isomer of 103In were investigated by means of γ-ray spectroscopy. Their half-lives were determined to be 60±1 s and 34±2 s, respectively. 149 γ transitions were ascribed to the decay of 103gIn. The main part of the resulting distribution of the Gamow-Teller strength B(GT) is associated with the feeding of 103Cd levels at excitation energies around 3 MeV. The sum of the B(GT) values deduced from the present γ-ray data amounts to 0.34, which provides a lower limit to the total Gamow-Teller strength. The β-branching ratio for the 103mIn decay is estimated and compared with the relevant values for the neighbouring indium isotopes including 101In whose half-life was determined to be 14.9±1.2 s.

The EC/ β + decay of 105 Sn was reinvestigated by using 58 Ni(5 MeV/u) + 50 Cr reactions, chemically selective on-line mass separation and γ-ray spectroscopy. The half-life of 105 Sn has been determined as 34 ± 1 s. Out of 104 γ transitions ascribed to the 105 Sn decay, 89 have been placed in the decay scheme including 52 excited states of 105 In. From the EC/ β + feeding of individual states, the distribution of the Gamow-Teller (GT) strength has been derived. It is shown that the main part of the GT strength is associated with the feeding of 105 In levels having excitation energies above 3 MeV. This observation can be interpreted as a sign of dominant feeding of three-quasiparticle states in 105 In, which correspond to the π( g 9 2 ) −1 νg 7 2 νd 5 2 shell-model configuration spread over many levels. The sum of the GT strength deduced from the present gamma-ray data of B Σ (GT) = 1.46 provides a lower limit to the total GT strength. Many weak transitions, mainly from high-energy levels, may not have been detected in this study and therefore part of the strength may be missed. An indirect support for this conclusion has been obtained from the analysis of the indium KX-rays intensity. This analysis indicates about 50% contribution of the electron-capture to the beta decay of 105 Sn, which is interpreted as a sign of a predominant feeding of the high-energy 105 In states with B Σ (GT) ⩾ 3. The observed GT distribution and strength will be compared to results obtained from a finite-Fermi-system theory and a large-basis shell-model calculation. The core-polarization and higher-order hindrance factors will be discussed.

The EC/β+-decay of the odd-odd nucleus100Ag was studied by means of total absorptionγ-ray spectrometry. Most of the Gamow-Teller strength was found to be concentrated at an excitation energy of 5.6 MeV in100Pd, the FWHM of this resonance being 1.5 MeV. The measured strength distribution which is interpreted within the BCS approximation as being due to the dominant population of four-quasiparticle excitations, resembles the distribution predicted by an advanced shell-model calculation for the98Ag →98Cd decay.

The α decay of mass-separated202Rn is studied at the ISOLDE separator. Time sequential α-singles spectra together with α-X-t and α-e-t coincidence events are collected. Fine structure in the α decay is observed and feeding of a low-lying 0 2 + state at 816 keV in198Po is evidenced. This 0+ state can be interpreted as the bandhead of an intruder-state based deformed band, coexisting with the spherical groundstate band. Mixing between normal and intruder states is discussed. A preliminary α-decay study of200Rn did not yet reveal any fine structure.

By studying the β +/EC and α decay of mass—separated neutron—deficient Hg to Fr nuclei, the spectroscopy group at the Leuven Isotope Separator On Line (LISOL) project collected in recent years extensive systematics on shell—model intruder states in the Pb region 1–10. These shell—model intruder states, leading to shape coexistence, have been identified in odd—proton At, Bi and Tl nuclei 3–4, odd—neutron Pb nuclei 8 9, even — even Pb nuclei 1 2 5 7 and odd—odd Tl nuclei 6 10. A remarkable systematic behavior of the excitation energy of the intruder—based states as a function of neutron number is now evident and several theoretical descriptions have been developed to reproduce this specific trend (see the references 11 to 15 and the contributions to this conference by K. Heyde, R. Bengtsson and N. Tajima).

The fraction of daughter nuclei that recoil out of the catcher foil after α decay of mass-separator implanted mother nuclei is determined experimentally and compared with calculations. The correction that has to be applied on the α-branching ratio, obtained by comparing the mother and daughter activity in one α detector, is at least 20%. Previously published branching ratios can be wrong due to the underestimation of the correction procedure. As an example, the 202 Rn → 198 Po → 194 Pb decay chain is studied.

The191Bim,g →187T1 →183Au a-decay chain has been studied using mass — separated sources. The a — branching ratios have been measured. Out of the reduced a — decay widths, it is clear that the πs1/2 — πS1/2 and πh9/2 → πh9/2 transitions are not hindered although they involve strong shape changes.

The /sup 104/In/sup g/ and /sup 104/In/sup m/ nuclei have been produced by means of the following reactions: /sup 106/Cd(p,3n), /sup 92/Mo(/sup 14/N,2n), /sup 92/Mo(/sup 16/O,p3n), /sup 92/Mo(/sup 20/Ne,3p5n). Their decay has been investigated after mass separation. From ..beta../sup +/, ..gamma.., and x direct spectra and ..gamma..-..gamma..-T, ..gamma..-x-T, and ..beta..-..gamma..-T coincidences, a /sup 104/Cd level scheme has been constructed. The observation of an intense background of statistical ..gamma.. rays, emitted after strong ..beta.. decay to high energy levels, resolves the problems of previously published work concerning ..beta..-ray intensities, spin determinations, and Q/sub EC/ values.

The level structure of 223Ac has been obtained from a study of the α-decay of mass separated 227Pa. Two levels connected by a fast E1 transition and with spin and parity 5+ 2 and 5− 2 were found: they form a parity doublet suggestive of octupole deformation in this nucleus. The Coriolis matrix element obtained for the mixing between the low-lying states is found to be attenuated, in agreement with theoretical expectations for stable octupole deformation.

The fine structure in the α-decay of mass-separated 194,196,198 Po is studied. Feeding to the 0 + ground state and the first excited 0 + intruder state in 190,192,194 Pb is observed. From α-e-t coincidences between the feeding α-ray and the E0 transition, the half life of the 0 + intruder state in 190,192,194 Pb is measured. The mixing between intruder state and ground state is deduced.

A proton bombarded target coupled to an ion source is a key-equipment to produce a cyclotron accelerated Radioactive Ion Beam (RIB). This note concerns the target development for a 13 N ion beam which will be the first one out of a more general project at Louvain-la-Neuve (Report RIB-1988-01). A 30-MeV proton beam of up to 300-μA intensity from the CYCLONE 30 bombards a graphite target to produce the 13 N isotope via the 13 C(p, n) 13 N reaction. Two major problems have to be solved: the extraction and transport of 13 N and the beam-heat dissipation. These aspects are somewhat correlated to the temperature dependence of the 13 N release and to the heat conductivity of graphite. A disk shaped target can be cooled through its side-face or through its back-face, and in fact both designs are explored. The extraction yield of the first one varies with the beam intensity up to a maximum value of 46% at 170 μA. For the second one, which is presently under development, the target temperature can be adjusted by a cooled finger of variable length.

The motivation, experimental setup and status report of the program for producing and accelerating radioactive ion beams at Louvain-la-Neuve are described.