JAERI Tandem Accelerator Research Articles

Radiochemical Studies of the Transactinide Element, Rutherfordium (Rf) at JAERI

are reviewed. The transactinide nuclide 261 Rf has been successfully produced in the reaction 248 Cm( 18 O, 5n) at the JAERI tandem accelerator. The excitation function of the reaction has been measured with a rotating wheel catcher apparatus and the maximum production cross section has been determined to be about 13 nb. On-line ionexchange experiments on Rf together with the group-4 elements Zr and Hf in acidic solutions have been conducted with a rapid ion-exchange separation apparatus. From the systematic study of the anion-exchange behavior of Rf, it has been found that the properties of Rf in HCl and HNO3 solutions are quite similar to those of Zr and Hf, definitely confirming that Rf is a member of the group-4 elements. However, we have observed an unexpected chemical behavior of Rf in HF solutions; the fluoride complex formation of Rf is significantly different from those of Zr and Hf. The current progress in the Rf aqueous chemistry is briefly summarized and prospects of extending chemical studies of transactinide elements at JAERI are considered.

Negative Parity Bands and Signature Splitting Inversion in80Rb

High spin states in 80Rb were studied via the 65Cu+19F,66Zn+18O and 68Zn+16O reactions. The 75-MeV19F, 76-MeV 18O and 80-MeV 16O beams were provided by theCIAE HI-13 Tandem accelerator and the JAERI Tandem accelerator. The promptγ-γ coincidence and the directional correlation from orientednuclei (DCO) were measured by the detector arrays in CIAE and JAERI.Twenty-three new states with 28 new transitions have been assigned to80Rb. The states were observed up to spins of 20+ and 22− in theα = 0 branch for the positive and negative parity yrast bandsrespectively. The negative parity non-yrast bands were significantlyextended up to spins of 22− and 15−. The band crossingswith frequencies 0.51 MeV and 0.61 MeV in the α = 0 cascade were observed forthe first time. The signature splitting was observed in bothnegative parity bands. The signature inversions at spins of about7 ℏ and 15 ℏ were observed.

Nuclear Decay Properties of the Neutron-Deficient Actinides

Nuclear decay properties of the neutron-deficient actinide isotopes 233,234,235,236Am and 237,238Cm have been investigated using a gas-jet coupled on-line isotope separator at the JAERI tandem accelerator facility. Alpha-decays of 233,235,236Am and 237,238Cm produced in the 6Li-induced reactions on 233,235U and 237Np targets have been observed with unambiguous mass identification, and the new isotopes 233Am and 237Cm have been identified for the first time. Alpha-particle energies, Qα values, half-lives and α-branching intensities were determined and the observed α decays of 233Am and 235Am are regarded as the favored transition.

Measurement of Mass Yield Distributions in Proton-Induced Fission of Minor Actinides

Fission product yields of low-energy proton-induced fission of minor actinides, 237Np, 241Am, 243Am and 248Cm, were measured by γ-ray spectrometry in order to construct the mass yield distributions. Enriched targets of the minor actinides were irradiated by proton beams with the energies of 25 and 30 MeV for several hours at the JAERI tandem accelerator. About 40 fission products were measured and their formation cross sections were determined. Systematic trends of the mass yield distributions in the fission of the minor actinides are discussed quantitatively.

Electronic excitation effects on secondary ion emission from a foil of conducting material bombarded by high energy heavy ions

It is recognized that high electronic excitations play an important role in the damage process of solid targets by high-energy heavy ions. However, the conversion mechanism of the energy of the excited electrons into kinetic energy for target atom displacement is not well understood. In order to investigate the electronic excitation effects of high energy heavy ions in solids, we have studied the secondary ions mass spectra from thin conductive solid targets irradiated by swift heavy ion beams from the JAERI tandem accelerator in the energy region where the electronic stopping power is dominant. The results show the importance of the electronic excitation effect even in simple metallic (Cu) target. It is suggested that Coulomb explosion is the major mechanism of producing columnar defects along the incident ion path.

Performance of the multiple target He/PbI 2 aerosol jet system for mass separation of neutron-deficient actinide isotopes

A multiple target He/PbI 2 aerosol jet system coupled with a thermal ion source was installed in the isotope separator on line (JAERI-ISOL) at the JAERI tandem accelerator facility. The neutron-deficient americium and curium isotopes produced in the 233,235 U( 6 Li, xn) and 237 Np( 6 Li, xn) reactions were successfully mass-separated and the overall efficiency including the ionization of Am atoms was evaluated to be 0.3–0.4%. The identification of a new isotope 237 Cm with the present system is reported.

Startup of transactinide chemistry in JAERI

The transactinide nuclides261Rf and262Db have been successfully produced in the248Cm(18O,5n) reaction at 99 MeV and in the248Cm(19F,5n) reaction at 100, 103, and 106 MeV, respectively, at the JAERI tandem accelerator. The on-line ion exchange experiments with an automated fast and repetitive liquid chromatography separation system were performed in the HNO3/HF system using Rf homologues89mZr and167,165Hf produced in the89Y(p,n) and152Gd(18O,xn) reactions, respectively. The radiotracers88Zr,175Hf, and234Th were also prepared and the distribution coefficients on ion exchange resins were measured systematically in 1-11 M HCl and 1-14 M HNO3with the batch method. It was found that anion exchange experiments of Rf in 8 M HNO3and 9 M HCl provided information useful to extract the ionic radius of Rf and to verify the influence of relativistic effects.

The feature of the JAERI recoil mass separator

A recoil mass separator has been constructed at the JAERI tandem-booster facility. It has a symmetric configuration of Q1Q2-ED1-MD-ED2-Q3Q4-O, where two electric dipoles ED1 and ED2, and a magnetic dipole MD are used to disperse reaction products by their mass/charge ratio ( m q ) and focus their energies. Two quadrupole doublets (Q1Q2 and Q3Q4) are used for focusing reaction products spread spatially. The octupole magnet O is used to correct a non-linearity of the m q dispersion. The m q and energy acceptances are designed to be ±4% and ±12%, respectively. In order to reduce a beam background scattered from the ED1 anode, the anode is split into two parts, so that the primary beam can pass through without hitting the anode. The performance of the recoil mass separator has been tested by using the 127I and 28Si beams from the JAERI tandem accelerator. The capability of the background suppression at the beam direction is excellent and the obtained mass resolution is A ΔA ≅ 300 . By using the recoil mass separator, a new neutron-deficient isotope 209Th has been produced in the reaction of 32S on 182W at beam energy of 171 MeV. An α-decay energy and a half-life of 209Th have been determined to be 8.080(50) MeV and 3.8 −1.5 +6.9 ms, respectively.

JAERI recoil mass separator

Abstract A recoil mass separator has been constructed at the JAERI tandem-booster facility. It has a symmetric configuration of Q1Q2-ED1-MD-ED2-Q3Q4-O, where two electric dipoles ED1 and ED2, and the magnetic dipole MD are used to disperse reaction products by their mass/charge ratio ( m q ) and focus their energies. Two quadrupole doublets (Q1Q2 and Q3Q4) are used for focusing reaction products spread spatially. The octupole magnet O is used to correct a non-linearity of the m q dispersion. The m q and energy acceptances are designed to be ±4% and ±12%, respectively. In order to reduce a background originating from beams scattered from the ED1 anode, the anode is split into two parts, so that the primary beam can pass through without hitting the anode. The performance of the recoil mass separator has been tested by using the 127I and 28Si beams from the JAERI tandem accelerator. The capability of the background suppression at the beam direction is excellent and the obtained mass resolution A ΔA ≅ 300 .

Mass separation of neutron-rich isotopes using a gas-jet coupled thermal ion source

A gas-jet coupled thermal ion source was installed in the isotope separator on line at the JAERI tandem accelerator. It was used for separation of neutron-rich isotopes produced in the reaction 238U(15 MeV-p, fission). The separation efficiencies of the whole system were measured to be 3.3% for 140Cs (T12 = 63.7 s), 2.0% for 144La (T12 = 40.8 s), 2.2% for 148Pr (T12 = 2.0 m), 1.2% for 156Pm (T12 = 26.7 s) and 1.0% for 160Eu (T12 = 44 s). A long sticking time of La atoms on the ionizer surface gave a low efficiency of about 0.1% for 148La (T12 = 1.05 s). The first observation of a new isotope 166Tb was carried out using its monoxide ions from this ion source: T12(166Tb) = 21±6 s.

Measurements of the negative ion beam emittance for the JAERI tandem accelerator

A computer controlled emittance measuring device has been constructed for the JAERI tandem accelerator system. The emittance values were measured in the accelerator beam line for proton, oxygen, silicon, nickel and iodine beams. They were extracted from a negative sputter ion source and accelerated up to 220 keV. In the measurements, the suppression voltage was used to exclude the effects of the secondary electrons emitted from the beam detectors and their surrounding materials. The emittance values together with their associated current intensity distributions were obtained to be satisfactory.

Studies on fission phenomena induced by charged particles using the JAERI tandem accelerator

Charged-particle-induced fission has been studied using the JAERI tandem accelerator. Characteristics of the symmetric mass division process at high angular momentum are investigated in the region of relatively light mass systems: 37Cl + 68Zn and 16O + 89Y. Observed widths of the mass and total kinetic energy distributions are broader than those expected from the liquid drop model. Pre-scission 4He particles in coincidence with fission products are measured in the 19F+ 197Au reaction. The multiplicity of pre-scission 4He is explained by a statistical model calculation which takes into account the reduced emission barrier for 4He. The correlation between fragment mass and total kinetic energy distributions is studied in proton-induced fission of 232Th using a double velocity TOF spectrometer. The result suggests the presence of two kinds of scission point configurations.

Performance of the heavy-ion magnetic spectrograph “ENMA” on the kinematic correction

A magnetic spectrograph, named ENMA, has been successfully put into operation for heavy-ion reaction studies at the JAERI tandem accelerator. The spectrograph consists of two dipoles, a quadrupole and three multipoles arranged in the form of Q-M1-D1-M2-D2-M3. The kinematic broadening has been well compensated for over the kinematic parameter range from k = 0.4 to 1.15 mainly with a quadrupole field produced by the multipole magnet M2. The energy resolution obtained as a function of the kinematic parameter k is consistent with the value estimated from the contributions due to the target effects, the beam emittance and the intrinsic energy resolution of the spectrograph.

The 1H( 11B,n) 11C reaction as a practical low background monoenergetic neutron source in the 10 MeV region

Neutron source properties of the 1H( 11B,n) 11C reaction were measured for incident 11B energies between 50 and 64 MeV by detecting the neutrons at angles of 0° to 40°. Neutron were produced with high monochromaticity in the range of several MeV to 12 MeV. In addition, the room background is very low because they were collimated to a forward cone according to the kinematical condition. Therefore, this reaction was proved to be a desirable monoenergetic neutron source in the “gap” region and was applied successfully to the neutron physics research at the JAERI tandem accelerator.

Control system for the JAERI tandem accelerator

A new program has been developed and implemented for the automated control of the JAERI tandem accelerator. The new system has shown good reliability since entering service in December 1986.

Extension to the 350-kV negative ion injector for the JAERI tandem accelerator

An extension to the 350-kV negative ion injector for the JAERI tandem accelerator was constructed to minimize loss of the beam time due to changing and tuning the ion sources, and to improve substantially the reliability and personal safety in the accelerator operation. Performance during the first operation over three months is reported and discussed in comparison with the previous performance.

Service lives of long-life carbon stripper foils in the first three years operation of the JAERI tandem accelerator

For three years after the installation of long-life carbon stripper foils in 1982, 82 of them have been used for acceleration of heavy ions at the JAERI tandem accelerator. Their service lives and their conditions after use were investigated.

A compact high voltage isolation transformer for the 350 kV injector of the JAERI tandem accelerator

A compact high voltage isolation transformer insulated by epoxy resin and SF6 gas media was developed and has been successfully used for feeding electricity through a polyethylene insulated cable to the 350 kV injector of the JAERI tandem accelerator for about three years. The insulation level of the transformer and the cable, and the current capacity of the secondary winding were designed to be 500 kV and 58 A at 200 V of 3 phase, respectively.

Scaling of the optical parameters for the JAERI tandem accelerator

A scaling rule of the beam optical parameters was adopted for computer-aided beam transport in the JAERI tandem accelerator. Tests have shown that the computer program can transport a specified beam in a short time using a reference parameter set. Problems of ion source control and accuracy of the optical devices are also discussed.

The JAERI tandem accelerator facility

Installation of the 20 MV heavy ion tandem accelerator, which had been going on since July 1978, was completed and all specifications of ion beam performance were met at terminal voltages ⩽18 MV by June, 1982. Scheduled running of the accelerator for experiments started on September 1, 1982. A brief report on the installation and summaries of the operation in the past 3 years are presented. Improvement and development work at the JAERI tandem accelerator facility during the past 4 years is discussed concerning the ion sources and the extended injector system, the JAERI type long-lived carbon stripper foils, the expansion of hardware and software of the computer system for accelerator control, and the automated control of the accelerator.