Isotope Separator On-line System Research Articles

Recent progress of ISOL facility at RAON

The RAON (Rare Isotope Accelerator complex for ON-line experiments) is currently in the stage of commissioning under the Rare Isotope Science Project (RISP) launched in 2011. RAON will utilize an advanced rare isotope beams produced with a high power target by the Isotope Separation On-Line (ISOL) facility, aiming to deliver high purity and intense, neutron-rich rare isotope beams to the post-accelerator and experimental facilities. The RAON ISOL facility consists of a target/ion source module surrounded by movable shielding blocks in a bunker, remote handling facilities for the target operation, a pre-mass separator, a RFQ cooler buncher, an EBIS charge breeder, and an A/q separator. The installation and alignment of the ISOL facility were completed in June 2021. The target/ion source module allows us to bombard a thick target with a 70 MeV proton beam of RAON, producing a variety of rare isotope beams. Rare isotope beams extracted from the target/ion source can be transported to a pre-mass separator at energies of up to 60 keV, and will be cooled in a RFQ-CB. Cooled ion beams can be sent to two different experimental facilities, such as a Mass Measurement System and a Collinear Laser Spectroscopy in ISOL experimental hall. Alternatively, for post-acceleration of ion beams, the singly charged ion beam of interest can be bunched to 108 ions in RFQ-CB and then delivered to the EBIS charge breeder through the EBIS branch system. The preparation of multi charged ion beams for the post-acceleration using the superconducting LINAC of SCL3 will be carried out through the EBIS charge breeder and A/q separator to match the energy of 10 keV/u with A/q < 6 with the requirement of RAON Injector.The first commissioning experiment of the ISOL system started in March 2021 using the 133Cs and 120Sn stable beams produced from the target container combined with the surface ion source and laser Ion source. The stable beam experiments have demonstrated the overall functioning of the RAON ISOL system, and we are planning to carry out the first RI beam test using the SiC target with 70 MeV proton of cyclotron in the coming months.

Charge breeding experiment of stable ion beams in EBIS charge breeder for RAON facility

The Electron Beam Ion Source (EBIS) charge breeder is used to produce highly charged ions in the Isotope Separation On-Line (ISOL) system of the Rare isotope Accelerator complex for ON-line experiments (RAON). Beam tests of the EBIS are performed using stable Cs and Sn ion beams. 133Cs1+ ions from a test ion source were injected into the EBIS to measure the breeding effect with the electron beam. The resulting relative abundance of 133Cs27+ was 25.0%, and the extraction energy was 49.3 keV/q. A charge breeding test of the 120Sn ions from the Target Ion Source (TIS) of the ISOL system was also carried out. The charge fraction of 120Sn24+ was 23.0%, and the energy was 50 keV/q. These results fulfilled the input beam condition of the RFQ accelerator (A/q < 6 and 10 keV/u). Additionally, 133Cs27+ ions were extracted with a pulse length up to 10 ms (FWHM) by the preliminary pulse-stretching experiment.

Simultaneous acceleration of two kinds of ion beams in the RISP

The Rare Isotope Science Project (RISP) is a research complex consisting of a heavy-ion accelerator, which contains a front-end system, a super-conducting linear accelerator, an isotope separator online (ISOL) system, and an in-flight system. The original purpose of the post-linear-accelerator (post-linac) section was to accelerate either a stable driver beam derived from an electron cyclotron resonance ion source, or an unstable rare-isotope beam from an ISOL system. The post-linac lattice has now been redesigned using a novel and improved acceleration concept that allows the simultaneous acceleration of both a stable driver beam and a radioisotope beam. To achieve this, the post-linac lattice is set for a mass-to-charge ratio (A/q) that is the average of the two beams. The performance of this simultaneous two-beam acceleration is here assessed using two ion beams: \(^{58}{\mathbf{Ni}}^{8+}\) and \(^{132}{} {\mathbf{Sn}}^{20+}\). A beam dynamics simulation was performed using the TRACK and TraceWin codes. The resultant beam dynamics for the new RISP post-linac lattice design are examined. We also estimate the effects of machine errors and their correction on the post-linac lattice.

Ion-production efficiency of a singly charged ion source developed toward a 11C irradiation facility for cancer therapy.

The ion-production efficiency of a newly developed singly charged ion source (SCIS) has been investigated to discuss the possibility of it being used in an isotope separation on-line system that provides 11C ions for heavy-ion cancer therapy with simultaneous verification of the irradiation field using positron emission tomography. The SCIS uses a low-energy hollow electron beam to produce singly charged carbon ions efficiently. To deliver sufficient 11C ions to the treatment room from a limited amount of 11C molecules, which are produced from a boron compound target and proton-beam irradiation via the 11B(p,n)11C reaction, the SCIS must have high ion-production efficiency. To realize this high efficiency, the SCIS was designed using a three-dimensional particle-in-cell code in previous work. With the fabricated SCIS, we performed experiments to measure the efficiency of producing CO2 + ions from nonradioactive 12CO2 molecules and C+ ions from nonradioactive 12CH4 molecules. We found that the SCIS achieved efficiencies of εC+ =4×10-3 (0.4%) for C+ production and εCO2 + =0.107 (10.7%) for CO2 + production.

Singly charged ion source designed using three-dimensional particle-in-cell method.

A singly charged ion source (SCIS) has been designed using a newly developed three-dimensional particle-in-cell (PIC) code. The SCIS is to be used in an isotope separation on-line (ISOL) system that provides 11C ions for heavy-ion cancer therapy with simultaneous verification of the dose distribution using positron emission tomography. The SCIS uses low-energy electron beams to produce singly charged carbon ions efficiently and maintain a high vacuum in the ISOL system. Because the SCIS has to realize a production efficiency of 1% if its carbon ions are to be used in the ISOL system, a suitable design for the SCIS was investigated by using the developed PIC code to study the beam trajectories of the electrons and extracted ions. The simulation results show that hollow electron beams are produced in the designed SCIS resulting in a high effective electron current. The results also predict that the designed SCIS would realize ion-production efficiencies (IPEs) of ε SCIS ≃ 6.7% for production from CO2 gas and ε SCIS ≃ 0.1% for C+ production from CH4 gas. Moreover, to examine the validity of the developed code and confirm that the SCIS was able to be designed appropriately, the space-charge-limited current of the electron gun and the total IPE obtained by adding the IPEs of each ion were compared between the experiment and the simulation.

Development of an EBIS charge breeder for the Rare Isotope Science Project

In Korea, a heavy ion accelerator facility called RAON is being designed to produce various rare isotopes for the Rare Isotope Science Project (RISP) (Jeong, 2016) [1], (Moon, 2014) [2]. This facility is designed to use both In-flight Fragment (IF) and Isotope Separation On-Line (ISOL) techniques in order to produce a wide variety of RI beams for nuclear physics experiments. An Electron Beam Ion Source (EBIS) will be used for charge breeding of Rare Isotope (RI) beams in the ISOL system. The charge-to-mass ratio (q/A) of the RI beams after charge breeding is ≥1/4. The highly charged RI beams will be accelerated by a linac post-accelerator and delivered to a low energy (∼18MeV/u) experimental hall or the IF system. The RAON EBIS will use a 3A electron gun and a 6T superconducting solenoid for high capacity, high efficiency, and short breeding time. In front of the charge breeder, an RFQ cooler-buncher will be used to deliver a bunched beam with small emittance to the EBIS charge breeder. The main design of the RAON EBIS has been carried out on the basis of several beam analyses and technical reviews. In this paper, current progress of the development of the RAON EBIS charge breeder will be presented.

Start-to-end simulation with rare isotope beam for post accelerator of the RAON accelerator

The RAON accelerator of the Rare Isotope Science Project (RISP) has been developed to create and accelerate various kinds of stable heavy ion beams and rare isotope beams for a wide range of the science applications. In the RAON accelerator, the rare isotope beams generated by the Isotope Separation On-Line (ISOL) system will be transported through the post accelerator, namely, from the post Low Energy Beam Transport (LEBT) system and the post Radio Frequency Quadrupole (RFQ) to the superconducting linac (SCL3). The accelerated beams will be put to use in the low energy experimental hall or accelerated again by the superconducting linac (SCL2) in order to be used in the high energy experimental hall. In this paper, we will describe the results of the start-to-end simulations with the rare isotope beams generated by the ISOL system in the post accelerator of the RAON accelerator. In addition, the error analysis and correction at the superconducting linac SCL3 will be presented.

Recent great impact by an Isotope Separator On-Line (ISOL) in nuclear and radiochemistry.

On April 9 2015, the Letter article titled "Measurement of the first ionization potential of lawrencium, element 103" is now published at News and Views on Nature (2015) which has been performed by our remarkably Japanese colleagues of nuclear and radiochemistry at JAEA (Japan Atomic Energy Agency). In this review, the author will state that the isotope separator on-line (ISOL) our regularly used, one of mass separation techniques, with a thermal surface ionization makes possible for determining the ionization potential of lawrencium based on the fruitful fundations of developing the ISOL system until now and also ever studying searches for unknown nuclei and these nuclear decay properties around actinide region in the past 20 years.

A singly charged ion source for radioactive ¹¹C ion acceleration.

A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive (11)C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source was found to have favorable performance as a singly charged ion source.

Beam dynamics simulations of post low energy beam transport section in RAON heavy ion accelerator.

RAON (Rare isotope Accelerator Of Newness) heavy ion accelerator of the rare isotope science project in Daejeon, Korea, has been designed to accelerate multiple-charge-state beams to be used for various science programs. In the RAON accelerator, the rare isotope beams which are generated by an isotope separation on-line system with a wide range of nuclei and charges will be transported through the post Low Energy Beam Transport (LEBT) section to the Radio Frequency Quadrupole (RFQ). In order to transport many kinds of rare isotope beams stably to the RFQ, the post LEBT should be devised to satisfy the requirement of the RFQ at the end of post LEBT, simultaneously with the twiss parameters small. We will present the recent lattice design of the post LEBT in the RAON accelerator and the results of the beam dynamics simulations from it. In addition, the error analysis and correction in the post LEBT will be also described.

RFQ design for the RAON accelerator’s ISOL system

The heavy-ion accelerator RAON has the advantage of having both an in-flight (IF) and an isotope separator on-line (ISOL) system. Two radio frequency quadrupoles (RFQs) will be installed in the RAON: the main linear accelerator (LINAC) RFQ will be used to accelerate the two-charge state 238U for the IF system, while the post-accelerator RFQ will be used to accelerate low-current isotope beams from the ISOL system. In this paper, the post-accelerator RFQ design for the ISOL system is reported. A beam current of 1 pμA was used, and the input beam and the output beam energies were 5 keV/u and 400 keV/u, respectively. Moreover, the design was optimized by reducing the total length and power, adjusting the beam quality. To quantify the influence of thermal expansion on the frequency, we calculated the frequency difference according to deference between the vane’s tip and the body’s diameter.

Achromatic and isochronous lattice design of P2DT bending section in RAON accelerator

In RAON heavy ion accelerator, generally, the In-flight Fragmentation (IF) and Isotope Separation On-Line (ISOL) systems are employed in order to produce various isotope beams. Out of the isotope beams, the beams generated by the ISOL system are transported from the low energy linac SCL3 to the high energy driver linac SCL2. The post-accelerator to the driver linac transport (P2DT) section that consists of the charge stripper section, the 180° bending section, and the SCL2 matching section is placed between the SCL3 and the SCL2. In this P2DT section, however, the transverse and longitudinal emittance growth can aggravate the beam acceptance of the SCL2. Besides, the growth at the P2DT 180° bending section is considered a significant issue because of the unexpected achromatic effect. Therefore an achromatic and isochronous lattice design should be devised to prevent the transverse and longitudinal emittance from increasing while the multi-charge beams flow through the bending section. This study reports an improved design for the achromatic and isochronous lattice up to the second-order. After satisfying the first-order achromatic and isochronous condition by adjusting the field strength of quadrupoles with this design, the simple and efficient method will be utilized with the aim of getting the minimum number of sextupoles. The research on the collimator for the charge selection at the bending section will be also represented by using the designed lattice.

Direct mass measurements of neutron-rich zirconium isotopes up toZr104

Atomic masses of radioactive zirconium isotopes from {sup 96}Zr to {sup 104}Zr have been measured with a relative accuracy of {<=}5x10{sup -7} using a Penning trap coupled to the ion guide isotope separator on-line system. The obtained two-neutron separation energies show strong local correlation in relation to the shape change and shape coexistence between N=58 and 60.

EBIS as charge breeder for radioactive ion beam accelerators

The numerous forthcoming post-accelerators for radioactive ions produced with the isotope separator on-line (ISOL) technique all have a need for an efficient method to accelerate the precious primary ions. By including an Electron Beam Ion Source (EBIS) as a charge breeder after the radioactive ion production stage, a short and compact linear accelerator can be employed as a result of the increased ion charge-to-mass ratio. In view of the constraints on a post-accelerator for radioactive beams, an EBIS appears to be an attractive solution. It is independent of the element injected, and an overall efficiency as high as 30% for the peak charge state can be attained. The mean charge state of the extracted ion beam is easily varied by changing the breeding time and the beam has excellent properties (time structure and emittance) for LINAC injection. Furthermore, the extraction of a bunched beam improves the signal-to-noise ratio for low-intensity beams and the UHV inside the source permits the mass separation of very weak radioactive beams from the residual gas contamination. With a high electron-beam density, the breeding time can be kept short, so decay losses are minimized. To obtain a high efficiency for a charge breeding EBIS, it is advantageous if the beam from the ISOL system is bunched and has its emittance reduced before injection. To achieve this a Penning trap can be introduced in front of the EBIS. The space-charge limit of the Penning trap restricts the number of ions per bunch to a couple of orders of magnitude lower than the constraint set by the EBIS. A positive side effect though, is that a mass selection can take place inside the trap. In this article the above listed features will be discussed. As an example, the charge breeding system for the REX-ISOLDE post-accelerator will be introduced. In addition, future possible developments of an EBIS leading to shorter breeding times, the acceptance of a continuous beam, and an increased number of charge-bred ions, will be discussed.

Half-life and configuration of the 1/2+ intruder state in203Bi

The decay properties of theJπ=1/2+,Eexc=1,098 keV state in203Bi were studied. The state was populated via the204Pb(p, 2n) reaction and the activity was studied with the ion guide isotope separator on-line system IGISOL. The half-life of the 1/2+ state was measured to beT1/2=303 ±5 ms. From this value the partial half-lives of the three depopulating branches 1/2+ →7/2− (E3), 1/2+→5/2− (E3 +M2) and 1/2+→9/2 g.s. − (M4) were deduced. Since all the transitions are configuration forbidden in first order, a detailed study of second-order shell-model configuration mixing could be performed.

Cross sections of the 63Cu(p, 3n)61Zn and the 63Cu(p, p3n)60Cu reactions

Cross sections of the reaction 63Cu(p, 3n)61Zn (T12 = 1.48 min) have been measured for proton energies from 30 to 47 MeV with an isotope separator on-line (ISOL) attached to a cyclotron. The method of the cross section measurement with the ISOL system has been developed. The cross sections obtained by the ISOL method agreed with those by the stacked foil method. In addition, cross sections of the 63Cu(p, p3n)60Cu (T12 = 24 min) reaction have been measured by the stacked foil method at proton energies up to 52 MeV.

〔50〕 放射性核による核分光学の動向

The present status of nuclear spectroscopy with the use of radioactive nuclides as seen from the side of instrumentation and experimental methods is reviewed. It is remarked that the current status of progress in nuclear instrumentation is mainly due to improvements seen in the precision and rapidity of measurements. The impact brought upon γ-ray spectroscopy by the introduction of Ge detectors with its marked precision is described in connection with the resulting revelation of the complexity of the nuclear decay scheme. Mention is made of the tendency toward the use of multichannel detection equipment to increase the rapidity of measurements, an example being the multicounter goniometer in angular correlation measurements. The necessity of an on-line irradiation facility or an isotope separator on-line system (ISOL system) is emphasized for the studies of short lived nuclei. Plans for the future are presented.