K. Vierinen

The ion guide isotope separator on-line, IGISOL

Abstract A new ISOL method, the IGISOL (Ion Guide Isotope Separator On-Line), permits thermalized primary recoil ions produced in nuclear reactions to be run directly through a mass separator without a conventional ion source. It allows a fast (≳ 100 μs) separation of various radioactive isotopes of both volatile and nonvolatile elements. The overall separation efficiencies measured for heavy nuclides produced in light ion induced reactions are up to 10%. The shortest-lived activity identified in an on-line separation is the 182 μs isomeric state of 207Bi.

Beta decay of Tz = −12 nuclides 51Fe and 55Ni: A new approach to on-line isotope separation

Abstract The mirror beta decays of 51 Fe (J π , T = 5 2 − , 1 2 ) and 55 Ni (J π , T = 7 2 − , 1 2 ) have been studied with the ion guide isotope separator on-line-system. The measured half-lives of 310 ± 5 ms for 51 Fe and 208 ± 5 ms for 55 Ni differ significantly from previouslreported values. In the case of 51 Fe, an allowed decay branch with a (5.0 ± 1.3)% intensity to the 7 2 − state at 237 keV in 51 Mn was observed. The deduced Gamow-Teller matrix elements are compared with values calculated using the empirical ( f 7 2 ) n shell model.

Delayed particle emission following the β+ decay of 28P and 32Cl

Abstract Thin sources of 28 P and 32 Cl were prepared by depositing recoil atoms from the reactions 28 Si(p, n) 28 P and 32 S(p, n) 32 Cl with a helium jet onto a fast transport tape. Delayed particle spectra were measured with high resolution using Si(Au) surface barrier detectors. Six proton groups and ten α-particle groups in the energy ranges 0.4 MeV E p E α 28 P. Six proton groups and eleven α-particle groups in the energy ranges 0.7 MeV E p E α 32 Cl. Absolute intensities of the individual proton and α-particle transitions were determined and corresponding upper limits for the log ft values of the precursor β + transitions were calculated. The total proton and α-particle branching ratios are 1.3 × 10 −5 and 8.6 × 10 −6 for 28 P and 2.6 × 10 −4 and 5.4 × 10 −4 for 32 Cl, respectively. The observed particle groups were assigned to excited levels known from resonance reaction studies in 28 Si and 32 S. Ratios of the partial widths for α-particle and proton emission, Γ α /Γ p were determined for four levels in 28 Si and for one level in 32 S; upper limits are given for several other levels. New evidence for spin-parity assignments is discussed. Partial decay schemes are presented for 28 P and 32 Cl.

Beta decay and delayed proton emission of a new nuclide 59Zn

Abstract The β + decay of a new nuclide 59 Zn has been identified by β-delayed proton and γ-ray emission. Two γ-rays and 15 proton groups have been associated with the decay of 59 Zn. The total proton branching ratio was measured to be (2.3 ± 0.8) × 10 −4 . A half-life of 210 ± 20 ms was measured for 59 Zn. The superallowed β-branch to its mirror, the J π = 3 2 − ground state of 59 Cu, was shown to be (93 ± 3)%. Absolute log ft values for β-transitions associated with the observed delayed proton groups were calculated and an experimental β-transition strength function was obtained.

Beta decay of 40Sc to proton and alpha-particle unbound states in 40Ca

Delayed charged particle emission associated with the precursor nuclide 40Sc was studied by use of the He-jet technique. Altogether 40 proton groups (1.0 MeV < Ep < 3.7 MeV) and 21 α-particle groups (2.0 MeV < Eα < 4.6 MeV) were observed. Total proton and α-particle branching ratios were measured to be (4.4±0.7) × 10−3 and (0.17±0.05) × 10−3, respectively. Association of the delayed particle emitting levels with the levels observed in resonance reaction studies is discussed. The fact that the most prominent α-particle groups do not have a counterpart in resonance reaction data suggests collectivity or a cluster configuration for the emitting levels. Log ft values (upper limits) for β+ transitions to particle emitting levels were deduced from the measured absolute intensities of the proton and α-particle transitions. Beta strength function is qualitatively discussed in terms of a simple shell-model description.

Beta-delayed particle emission of 36K

Abstract 36 Ar targets of 19 μg cm 2 thickness were made by a sandwich technique in which a 70 nm layer of Al was evaporated onto the implanted Al surface between five successive implantations of 36 Ar ions. The sources of 36 K were prepared by depositing the recoil atoms from the 36 Ar(p, n) 36 K reaction by means of a helium jet onto a fast transport tape. The measured delayed particle spectra revealed 11 proton groups (0.5 MeV E p E α 36 K. Total proton and α-particle branching ratios were measured to be 4.8 × 10 −4 and 3 × 10 −5 , respectively. Partial level widths and reduced proton and α-particle transition widths were determined for several individual levels with the aid of additional results from resonance reaction studies.

Features of the β-decay of 93mRu to proton emitting states in 93Tc

Abstract The 10.8 s, 1 2 − isomer of 93Ru is shown to be a β-delayed proton precursor. The absolute branching ratio for this decay mode is determined to be (2.7 ± 0.5) × 10−4. The measured total decay energy of 93mRu is 7.070 ± 0.085 MeV. The delayed proton spectrum has prominent peaks at 2.481, 2.534 and 2.557 MeV, indicating structural effects in the β-strength distribution. This structure is discussed in terms of a π g 9 2 → v g 7 2 spin-flip transition across the closed N = 50 nucleon shell. The level structure of 93Tc was also studied by the 92Mo(p, γ)93Tc resonance reaction in the proton energy range 2.00 MeV

Studies of Weak Beta-Delayed Protons Emitted in the Decay of Odd-Z, Tz = -3/2 Nuclei

Radioactive decay of Tz = - 3/2 nuclides, 27P and 31Cl, predicted to be weak β-delayed proton precursors, have been looked for. Two proton groups having energies of 989 ± 15 and 1528 ± 20 keV and a half-life of 150 ± 25 ms were associated with the decay of 31Cl. The search for 27P is still under way, but the first qualitative results are briefly discussed.

Observation of beta-delayed protons in the decay of 31Cl

Abstract Beta-delayed protons have been observed from the decay of the T z = − 3 2 nucleus 31Cl produced via the 32S(p, 2n) reaction. The energy of the observed proton group was measured to be 989 ± 15 keV and it was found to decay with a half-life of 150−20+25 ms.

High resolution Gamow-teller strength measurement via β-decay of 65Ge

The β+ decay of 65Ge was studied by β-delayed proton and γ-ray emission. The He-jet technique was used. Altogether 28 proton groups (1.0 MeV<Ep<2.1 MeV) were observed with proton energy resolution of about 10 keV. The proton spectrum apparently consists of discrete proton groups due to a selective population of excited states of 65Ga by Gamow-Teller β+ decay. The total proton branching ratio was measured to be (1.1±0.3)×10−4. Upper limit of log ft values for beta transitions associated with the observed delayed proton groups and γ-rays were calculated and an experimental beta transition strength function was obtained. The single level structure of 65Ga was studied by the 64Zn(p, γ)65Ga resonance reaction in the proton energy range 1.1 MeV<Ep<2.1 MeV with 1.0 keV overall energy resolution and about 170 resonance levels were observed. Angular distribution and resonance decay measurements were done to study the nature of selected single levels and decay properties of low energy levels. The proton binding energy of 65Ga was measured to be Bp = 3943.0±1.0 keV.