0000000000133910
AUTHOR
P.p. Jauho
Status report of the Jyvaskyla ion guide isotope separator on-line facility
The ion guide isotope separator facility IGISOL of the University of Jyvaskyla has been moved to the new K-130 heavy ion cyclotron laboratory. The totally reconstructed facility is described in detail. The primary beams and targets, helium pumping, separator beam line construction and separator beam diagnostics are discussed. The spectroscopy stations are introduced with illustrative examples from the research program, including beta-delayed proton and neutron spectroscopy, gamma-ray spectroscopy with and without arrays, conversion electron spectroscopy, collinear laser spectroscopy and nuclear level lifetime spectroscopy.
Collective structure of the neutron-rich nuclei, 110Ru and 112Ru
Abstract The collective structure of 110 Ru and 112 Ru has been studied at the IGISOL facility through the beta decay of 110 Tc and 112 Tc. Neutron-rich technetium isotopes were produced by the 238 U(p, f) reaction at 20 MeV bombarding energy. The new isotope 112 Tc was found to decay with a half-life of 280(30) ms. The observed energies of the 2 + and 4 + ground state band levels in 108,110,112 Ru are almost the same. However, a steady energy decrease of the proposed gamma band head is observed with increasing neutron number, suggesting importance of triaxiality in these nuclei. In fact, only in 192 Os the second 2 + state has been observed at lower excitation than in 112 Ru. The static de…
Discovery of New Fission Product Activities in the A=110–118 Mass Region
Neutron rich nuclei around the mass A=100 have recently attracted both theoretical and experimental interest since they are expected to form a new region of strong deformation. In contrary, very little experimental information is available in the adjacent transitional region A= 110–118. Due to expected isomerism in this region both low and high spin states can be studied via beta decay in many nuclei. The studies of these nuclides have many experimental difficulties. They are only weakly produced in thermal neutron induced fission and because all the elements in this mass region (Tc, Ru, Rh, Pd) have very high melting points they have not been available as beams of on-line isotope separator…
Status report of the SARA IGISOL used in the study of the 238U(α 40 MeV, ƒ) reaction
Abstract A new ion guide isotope separator on-line (IGISOL), operating with the SARA facility, has been constructed. Using the 238U(α 40 MeV, ƒ) reaction to produce very neutron-rich radioisotopes, all mass chains from A = 96 to 122 have been scanned by conventional methods of nuclear spectroscopy. Provided the stopping volume is separated from the primary beam, it has been proved that the yield is nearly proportional to the He pressure. In addition to the usual advantages (quasi-independence from physical and chemical properties of elements), this makes IGISOL a powerful technique for high energy recoil products. During the experiments the boundary of known neutron-rich nuclei was reached …
Separation of fission products by the ion guide fed isotope separator, IGISOL
Abstract The performance of the ion guide method in the on-line mass separation of fission products has been investigated. Activity was produced by bombarding nat. U targets with a beam of 20 MeV protons. All the mass chains from A = 95 through A = 120 have been scanned using conventional methods of nuclear spectroscopy. No chemical selectivity in the separation was observed; isotopes of highly nonvolatile elements from yttrium to palladium were produced with efficiencies equal to those for the more volatile ones. The boundary of known neutron-rich nuclides was reached throughout the mass region from A = 106 to A = 118. During the course of this preliminary study the new isotope 116 Rh was …
Electron-transporter spectrometer for on-line isotope separator
Abstract ELLJ — a conversion-electron and beta-ray spectrometer for an on-line isotope separator - is described. The instrument is a broad-range, high-transmission device consisting of a two-coil magnetic transporter plus a cooled Si(Li) detector. The spectrometer was designed to perform several kinds of coincidence measurements. A number of representative spectra of fission-product activities separated on-line at the IGISOL facility demonstrate the performance of the spectrometer.
Independent and cumulative yields of very neutron-rich nuclei in 20 MeVp- and 18–41 MeVd-induced fission ofU238
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…
First observation of the beta decay of117Pd and the discovery of a new isotope119Pd
In this paper we wish to report the first direct observations of the beta decays of117Pd and of a new isotope119Pd. The measuredβ-half-life is 4.3±0.3 s for117Pd. For119Pd, the existence of two beta-decaying states with the same half-life but of opposite parity cannot be excluded. The measured half-life for119Pd is 0.92±0.13 s. The observed beta half-lifes are in good agreement with the QRPA predictions. The observed level structure of117Ag and119Ag are discussed in the frame of the level systematics of the known odd Ag isotopes closer to stability.
Isotopic product distributions in the near symmetric mass region in proton induced fission ofU238
We have studied fission product yields using 19.8 MeV proton induced fission of a thin $^{238}\mathrm{U}$ target and the on-line mass separator IGISOL. The nonselectivity of the separation method used with respect to Z has allowed accurate determination of the yields of symmetric fission for the first time. The cumulative yields for the elements from Z=40 (Zr) up to Z=47 (Ag) have been determined from the beta- and gamma-radioactivity measurements. The independent fission product yield distributions for elements Tc, Ru, and Rh are obtained from the experimental data. An improved theoretical model for calculating mass and independent yields is described and applied. It is found that the char…
Gamow-Teller decay of 118Pd and of the new isotope 120Pd
Abstract With the use of the proton-induced fission of 238 U and the ion guide-fed on-line mass separation, even- A isotopes of palladium with high neutron excess were studied by means of γ-ray and conversion-electron spectroscopy. The decay of 118 Pd was reinvestigated in detail, and evidence for the new isotope 120 Pd, with a half-life T 1 2 = 0.5 ± 0.1 s , was found. As established for 118 Pd and tentatively shown for 120 Pd, the β-decay of these two isotopes proceeds mainly through 0 + → 1 + Gamow-Teller transitions with log ft values between 4.2 and 4.7. The strength of individual transitions has been compared with the predictions of the shell-correction model with a deformed Woods-Sax…
Half-life measurements for neutron-rich Tc, Ru, Rh, and Pd isotopes. Identification of the new isotopesTc111,Ru113, andRh113
The decays of three new neutron-rich nuclides $^{111}\mathrm{Tc}$, $^{113}\mathrm{Ru}$, and $^{113}\mathrm{Rh}$ have been observed at an on-line isotope separator facility. In addition, the beta decays of several other n-rich isotopes with Ag100 have been studied for the first time. The new half-lives reported in this work include: $^{111}\mathrm{Tc}$ [${T}_{1/2}$=0.30(3) s], $^{111}\mathrm{Ru}$ [2.12(7) s], $^{112}\mathrm{Ru}$ [1.75(7) s], $^{113}\mathrm{Ru}$ [0.80(10) s], $^{113}\mathrm{Rh}$ [2.72(22) s], and $^{118}\mathrm{Pd}$ [2.24(17) s]. In general, these results support the microscopic theoretical half-life predictions below Z=50.
New Neutron-Rich Nuclei and Isomers Produced in Symmetric Fisson
The novel method for rapid on-line mass separation, the IGISOL, is described. The method has been shown applicable to mass separation of short-lived proton-induced fission products without any chemical dependence on radionuclide. Recent results on isomeric states with half-lives of the order of milliseconds produced directly in proton-induced fission of 238U and separated with the IGISOL are presented. The future plans for connection of the new K-130 cyclotron of the University of Jyvaskyla with the IGISOL are reviewed.
β-decay of 113Rh and the observation of 113mPd : Isomer systematics in odd-A palladium isotopes
Abstract Decay of 113Rh to the levels of 113Pd was studied at the IGISOL-facility by means of β-, γ- and conversion-electron spectroscopy. The level scheme of 113Pd was constructed using 33 gamma transitions on the basis of observed γγ-coincidence relations and half-life analysis. A β-decay half-life of (2.80±0.12) s was measured for 113Rh. A new 9 − 2 isomeric state with (0.3 ± 0.1) s half-life and excitation energy 81.3 keV was discovered in 113Pd. This state and the other recently observed low-lying 9 − 2 or 11 − 2 isomeric states in 115,117Pd isotopes are directly populated in proton-induced fission. The decay of these isomers is unusually strongly hindered compared with Weisskopf estim…
Gamow-Teller decay of118Pd and of neighbouring even isotopes of palladium
Neutron-rich isotopes of palladium were produced via the fission of238U by 20 MeV protons. These isotopes were selected using the ion guide-fed on-line mass-separator facility IGISOL at Jyvaskyla. Their decays were studied byβ-ray,γ-ray and conversion-electron spectroscopy. For114Pd and116Pd, the decay schemes established previously were confirmed; additionally multipolarities were determined for a few transitions. In the case of118Pd, only an approximate half-life was known from a previous radiochemical experiment. In the present study, 15 gamma transitions were observed, most of which were placed in a decay scheme. The half-life and the decay energy were found to beT1/2=1.9±0.1 s andQβ=4.…
Spin-flip? ? decay of even-even deformed nuclei110Ru and112Ru
Neutron-rich nuclides110Ru and112Ru produced in symmetric fission of238U by 20 MeV protons have been studied at the IGISOL facility by means ofβ-ray,γ-ray and conversion electron spectroscopy. A total of 12 and 6γ-transitions were observed in the decays of110Ru and112Ru, respectively. Multipolarities were determined for a few transitions. The beta decay half-life was determined to be 11.6±0.6 s for110Ru and 1.75±0.07 s for112Ru. As a side product, a new value of 2.1±0.3 s for theβ half-life of the112Rh 1+ state was obtained. The decay energy measured with the plastic scintillator was 2.81 ±0.05 MeV for110Ru and 4.52 ±0.08 MeV for112Ru. The beta decay schemes of110Ru and112Ru isotopes indica…
Beta decay of 108Mo and of neighbouring even Mo-isotopes
Abstract 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 de…
Beta decay of very neutron-rich110Mo studied at the new IGISOL facility
The decay of the new activity110Mo (t1/2=0.30(4).s) has been observed at the new IGISOL separator. Multiscaled singles,β-γ-t and γ-y-t coincidences were recorded. The decay scheme suggests Iπ=2+ for the ground state of the daughter nucleus110Tc. Three 1+ levels are fed with logft values below 5, indicating no drastic change among Mo and Ru decays at the middle of the neutron shell. This experiment confirms the expectation that the new IGISOL facility will allow the identification of one or two new more neutron-rich isotopes per element in this region.
Gamow-Teller Beta Decay of Neutron Rich Tc, Ru, Rh and Pd Isotopes
During recent experiments at the IGISOL-facility several new neutron rich nuclides have been discovered, including the first direct observations of the beta decays of 111Tc, 112Ru, 113Ru, 114Ru, 113Rh, 115Rh, 116Rh and 118Pd. The role of the νg7/2 → πg9/2 transformation in the beta decays of the odd-odd 110–116Rh and the even-even 114–118Pd isotopes is shown to be dominant. The experimental results are compared with shell model calculations including deformation and pairing.