Isotope Separation On-Line Method Research Articles

Production of neptunium and plutonium nuclides from uranium carbide using 1.4-GeV protons

Accelerator-based techniques are one of the leading ways to produce radioactive nuclei. In this work, the isotope separation on-line method was employed at the CERN-ISOLDE facility to produce neptunium and plutonium from a uranium carbide target material using 1.4-GeV protons. Neptunium and plutonium were laser-ionized and extracted as 30-keV ion beams. A multireflection time-of-flight mass spectrometer was used for ion identification by means of time-of-flight measurements as well as for isobaric separation. Isotope shifts were investigated for the 395.6-nm ground state transition in ${}^{236,237,239}\mathrm{Np}$ and the 413.4-nm ground state transition in ${}^{236,239,240}\mathrm{Pu}$. Rates of ${}^{235--241}\mathrm{Np}$ and ${}^{234--241}\mathrm{Pu}$ ions were measured and compared with predictions of in-target production mechanisms simulated with geant4 and fluka to elucidate the processes by which these nuclei, which contain more protons than the target nucleus, are formed. ${}^{241}\mathrm{Pu}$ is the heaviest nuclide produced and identified at a proton-accelerator-driven facility to date. We report the availability of neptunium and plutonium as two additional elements at CERN-ISOLDE and discuss the limit of accelerator-based isotope production at high-energy proton accelerator facilities for nuclides in the actinide region.

β - and γ -spectroscopy study of Pd119 and Ag119

Neutron-rich $^{119}\mathrm{Pd}$ nuclei were produced in fission of natural uranium, induced by 25-MeV protons. Fission fragments swiftly extracted with the Ion Guide Isotope Separation On-Line method were mass separated using a dipole magnet and a Penning trap, providing mono-isotopic samples of $^{119}\mathrm{Pd}$. Their ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay was measured with $\ensuremath{\gamma}\ensuremath{\gamma}$- and $\ensuremath{\beta}\ensuremath{\gamma}$-spectroscopy methods using low-energy germanium detectors and a thin plastic scintillator. Two distinct nuclear-level structures were observed in $^{119}\mathrm{Ag}$, based on the $1/{2}^{\ensuremath{-}}$ and $7/{2}^{+}$ isomers reported previously. The ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay work was complemented by a prompt-$\ensuremath{\gamma}$ study of levels in $^{119}\mathrm{Ag}$ populated in spontaneous fission of $^{252}\mathrm{Cf}$, performed using the Gammasphere array of germanium detectors. Contrary to previous suggestions, our data show that the $1/{2}^{\ensuremath{-}}$ isomer is located below the $7/{2}^{+}$ isomer and is proposed as a new ground state of $^{119}\mathrm{Ag}$ with the $7/{2}^{+}$ isomer excitation energy determined to be 33.4 keV. Our data indicate that there are two $\ensuremath{\beta}$ unstable isomers in $^{119}\mathrm{Pd}$, a proposed ground state of $^{119}\mathrm{Pd}$ with tentative spin $1/{2}^{+}$ or $3/{2}^{+}$ and a half-life of 0.88 s and the other one about 350 keV above, having spin ($11/{2}^{\ensuremath{-}}$) and a half-life of 0.85 s. The higher-energy isomer probably decays to the $1/{2}^{+}$ or $3/{2}^{+}$ ground state via a $\ensuremath{\gamma}$ cascade comprising 18.7-219.8-$\mathrm{X}$-keV transitions. The unobserved isomeric transition with energy $X\ensuremath{\approx}100$ keV probably has an $E3$ multipolarity. Its hindrance factor is significantly lower than for analogous $E3$ isomeric transitions in lighter Pd isotopes, suggesting an oblate deformation of levels in $^{119}\mathrm{Pd}$. Oblate configurations in $^{119}\mathrm{Ag}$ are discussed also.

Study of neutron-rich isotopes near N=152 shell closure using Timepix type detectors integrated into the mass separator MASHA

The MASHA facility [1–3] was developed as a high precision mass-spectrometer for heavy and super heavy elements with masses up to 450 a.m.u. It uses ISOL (Isotope Separation On-Line) method. Its unique properties opens great prospective for the investigation of neutron-rich nuclei produced in multinucleon transfer reactions. Mainly nuclei near the neutron N = 126 and N = 152 shell closures are of great interest. This region of nuclei is not so far thoroughly enough investigated while its research has direct relation to the synthesis of super heavy elements. As is known the island of stability close to super heavy elements (Z = 112–118) exists due to the shell effects in nuclei. More detailed investigation of these shell effects can greatly help in the synthesis of next super heavy elements. Heavy neutron rich radon isotopes were produced in the multinucleon transfer reaction 40Ar + 232Th at Flerov Laboratory of Nuclear Reactions, Dubna. Radon isotopes with given masses were detected using two types of detectors: a multi-strip well-type detector (made in Canberra) and a position-sensitive quantum counting hybrid pixel detector of the Timepix type [1]. The latter detector has an array of 256×256 square pixels each with a pitch size of 55 μm for the full sensitive area 14×14 mm2. Radon isotopes implanted into the detector emit then alpha and beta particles until they reach the stable or long-lived isotopes at the end of their decay chains. The positions of radon isotopes, the tracks, times and energies of the beta particles were measured and analyzed. New software for the particle recognition and data analysis of the results obtained from the experiment was developed and used. It has been proven that MASHA + Timepix setup is a powerful instrument for investigation of neutron-rich isotopes far from stability limits.

Development of a prototype radio-frequency system for a radio-frequency quadrupole cooler buncher in the rare isotope science project.

Radioactive ion beams produced using the isotope separation on-line method in the Rare isotope Accelerator complex for ON-line (RAON) experiment are to be delivered with a beam emittance of around 3 π mm mrad, an energy spread of less than 10 eV, and a short beam bunch width of around 10 µs to meet the requirements of an electron beam ion source charge breeder. A radio frequency quadrupole cooler buncher (RFQ-CB) will be used to meet the beam quality requirements mentioned above. Our target bunching capacity of RFQ-CB is 108 ions/bunch for various ion species. Such a high bunching capacity requires an RF amplitude of ∼3 kV and a frequency range of 1.5-4.5 MHz in our RFQ-CB design. We designed and tested the prototype RF system composed of a helical resonator, a high-power RF amplifier, and high-voltage probes. To reduce heat load to the high voltage probes, we employed vacuum capacitors serially connected to the ends of helical resonators. In the experiment, we confirmed that our 4.5-µH helical resonators made of a 12-mm copper tube and variable vacuum capacitor with a capacitance range of 120-1120 pF can produce required voltages and frequencies using a 100-W RF amplifier. As a result, with 2.5-W RF output power, we obtained the maximum voltage amplitude of 1 kV at 4.5 MHz, which is equivalent to 6.4 kV with 100-W RF output power.

The ISOLPHARM project: ISOL-based production of radionuclides for medical applications

Radionuclides for radiopharmaceuticals can be produced in cyclotrons or nuclear reactors. Each of these production modes has serious issues, such as high target costs, production of long-lived wastes and contaminants, expensive separation. For this reason, new methods are under consideration for the production of highly pure radionuclides. The ISOL (Isotope Separation On-Line) method is the major technique for the production of radioactive ion beams for nuclear physics applications. The SPES-ISOLPHARM project at INFN-LNL (Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Legnaro) is a feasibility study for the production of medical isotopes exploiting the ISOL method. The ongoing activities concerning a recent experiment focused on 111Ag, a study performed in collaboration with Padova and Trento Universities, is presented.

Thermal stability of nanometric TiC-carbon composites: effects of carbon allotropes and Zr milling impurities

In the ISOL (Isotope Separator OnLine) method a target at high temperatures (up to 2300 °C), is bombarded with high energy protons in order to produce isotopes through nuclear reactions which are simultaneously extracted from the target, ionized and delivered to physics experiments. Due to the enhanced isotope release properties of nanosized porous materials, titanium carbide-carbon porous nanocomposites have been developed at CERN and tested up to 1500 °C. In the interest of the ISOL application, in this study we extended the range of temperatures up to 1800 °C, to test the sintering hindering capabilities of different carbon allotropes. Carbon black was the most effective with the smallest TiC crystallite size: <80 nm at 1800 °C. Additionally, using thermodynamic modelling, ex-situ X-ray powder diffraction and in-situ gas phase analysis, we show that there are interesting additional phase and lattice parameter changes due to the ZrO2 impurities from the attrition milling.

The current status of the MASHA setup

The MASHA setup designed as the mass-separator with the resolving power of about 1700, which allows mass identification of superheavy nuclides is described. The setup uses solid ISOL (Isotope Separation On-Line) method. In the present article the upgrade of some parts of MASHA are described: target box (rotating target + hot catcher), ion source based on electron cyclotron resonance, data acquisition, beam diagnostics and control systems. The upgrade is undertaken in order to increase the total separation efficiency, reduce the separation time, of the installation and working stability and make possible continuous measurements at high beam currents. Ion source efficiency was measured in autonomous regime with using calibrated gas leaks of Kr and Xe injected directly to ion source. Some results of the first experiments for production of radon isotopes using the multi-nucleon transfer reaction 48Ca+242Pu are described in the present article. The using of TIMEPIX detector with MASHA setup for neutron-rich Rn isotopes identification is also described.

The SPES High Power ISOL production target

SPES (Selective Production of Exotic Species) is a facility under construction at INFN-LNL (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro), aimed to produce intense neutron-rich radioactive ion beams (RIBs). These will be obtained using the ISOL (Isotope Separation On-Line) method, bombarding a uranium carbide target with a proton beam of 40MeV energy and currents up to 200 μA. The target configuration was designed to obtain a high number of fissions, up to 1013 per second, low power deposition and fast release of the produced isotopes. The exotic isotopes generated in the target are ionized, mass separated and re-accelerated by the ALPI superconducting LINAC at energies of 10AMeV and higher, for masses in the region of A = 130amu, with an expected rate on the secondary target up to 109 particles per second. In this work, recent results on the R&D activities regarding the SPES RIB production target-ion source system are reported.

Thick target for high-power ISOL facilities

The future frontier of the Isotope Separation On-Line (ISOL) method is to increase the intensity of the Radioactive Isotope Beams (RIB) by many orders of magnitude in order to satisfy challenging experiments such as Rn-Electric Dipole Moment, Fr-Parity Non Conservation…and in general for radiative proton-capture relevant for nuclear astrophysics processes. The most direct method to obtain higher RIB intensity is to increase the driver beam intensity. New techniques were developed such as composite targets, where the target material is deposited onto a high thermal conductive substrate allowing a better heat dissipation. Combined with high-power target using radial finned for radiative cooling, these targets are capable of dissipating up to 20kW depending on the target material operating temperature. Another method to increase RIB intensity is the use of indirect ISOL method, where secondary particle beam (n or γ) interacts with a fissile target material. By decoupling the power deposition in the system composed of a converter and ISOL target allows for much higher primary beam power. Indirect ISOL-target method permit reach several hundred of kW to MW of driver beam power, allowing the production of intense fission products beams. This paper reviews the thick ISOL target approach for producing intense radioactive ion beams.

Target materials for exotic ISOL beams

The demand for intensity, purity, reliability and availability of short-lived isotopes far from stability is steadily high, and considerably exceeding the supply. In many cases the ISOL (Isotope Separation On-Line) method can provide beams of high intensity and purity. Limitations in terms of accessible chemical species and minimum half-life are driven mainly by chemical reactions and physical processes inside of the thick target. A wide range of materials are in use, ranging from thin metallic foils and liquids to refractory ceramics, while poly-phasic mixed uranium carbides have become the reference target material for most ISOL facilities world-wide. Target material research and development is often complex and especially important post-irradiation analyses are hindered by the high intrinsic radiotoxicity of these materials. However, recent achievements have proven that these investigations are possible if the effort of different facilities is combined, leading to the development of new material matrices that can supply new beams of unprecedented intensity and beam current stability.

Development of target ion source systems for radioactive beams at GANIL

The GANIL facility (Caen, France) is dedicated to the acceleration of heavy ion beams including radioactive beams produced by the Isotope Separation On-Line (ISOL) method at the SPIRAL1 facility. To extend the range of radioactive ion beams available at GANIL, using the ISOL method two projects are underway: SPIRAL1 upgrade and the construction of SPIRAL2. For SPIRAL1, a new target ion source system (TISS) using the VADIS FEBIAD ion source coupled to the SPIRAL1 carbon target will be tested on-line by the end of 2013 and installed in the cave of SPIRAL1 for operation in 2015. The SPIRAL2 project is under construction and is being design for using different production methods as fission, fusion or spallation reactions to cover a large area of the chart of nuclei. It will produce among others neutron rich beams obtained by the fission of uranium induced by fast neutrons. The production target made from uranium carbide and heated at 2000°C will be associated with several types of ion sources. Developments currently in progress at GANIL for each of these projects are presented.

Direct 1+→N+ conversion of stable alkali ions using an electron cyclotron resonance ion source

The production of radioactive ions using the Isotope Separation On-Line method gives rise, in most cases, to singly charged ions. In order to perform experiments with postaccelerated radioactive ion beams, these ions have to be multicharged. We describe here a new compact design for a charge breeder that will be coupled to the production target of SPIRAL1 at GANIL. We present recent results obtained offline with stable alkali ions (Na, K, Rb, and Cs) on the SIRa test bench. Particularly, 1(+) to N(+) conversion efficiencies and conversion times are presented. Several points have been identified for the improvements of the present performances.

EURISOL High Power Targets

Modern Nuclear Physics requires access to higher yields of rare isotopes, that relies on further development of the In-flight and Isotope Separation On-Line (ISOL) production methods. The limits of the In-Flight method will be applied via the next generation facilities FAIR in Germany, RIKEN in Japan, and RIBF in the United States. The ISOL method will be explored at facilities including ISAC-TRIUMF in Canada, SPIRAL-2 in France, SPES in Italy, ISOLDE at CERN, and eventually at the very ambitious multi-MW EURISOL facility [1]. ISOL and in-flight facilities are complementary entities. While in-flight facilities excel in the production of very short lived radioisotopes independently of their chemical nature, ISOL facilities provide high Radioisotope Ion Beam (RIB) intensities and excellent beam quality for 70 elements. Both production schemes are opening vast and rich fields of nuclear physics research.

Development of a 1+∕N+ setup for the production of multicharged radioactive alkali ions in SPIRAL

In the framework of the production of radioactive ion beams by the isotope separator online method, a new system has been developed at GANIL/SPIRAL I to produce multicharged alkali ions. The principle, referred to as the "direct 1+/N+ method," consists of a surface ionization source associated with a multicharged electron-cyclotron-resonance ion source without an intermediate mass separator. This new system has been tested online using a (48)Ca primary beam at 60.3 A MeV. The experimental evidence of the direct 1+/N+ process has been obtained for a potential difference between the two sources of 11 V and with a 1+/N+ charge breeding efficiency of 0.04% for (47)K(5+). This value is significantly lower than the value of 6% obtained for stable K ions with the standard 1+/N+ method. A possible explanation is given in the text.

Resonant laser ionization of radioactive atoms

Intense radioactive ion beams are produced by the isotope separation on-line method. The resonance ionization laser ion source (RILIS) can provide the chemical selectivity to separate beams with reduced isobaric contamination. The hot cavity RILIS at ISOLDE (CERN) uses copper vapor laser pumped dye lasers for the resonant transitions. Up to now 22 elements have been ionized with efficiencies of the order of 10%. Additional elements have been ionized with similar RILIS set-ups at the Institute of Spectroscopy (Troitsk), IRIS (Gatchina), Mainz University and TIARA (Takasaki). Ideas are discussed for future developments of this type of RILIS, which could further improve the efficiency, selectivity, rapidity of release and stability of the operation. The RILIS can also be applied for atomic spectroscopy studies of exotic radioactive isotopes, which are produced at rates of few atoms per second only. An interesting parallel is shown to the atomic vapor laser isotope separation (AVLIS), a large-scale application of resonance ionization, which could be used for the isotope enrichment of macroscopic amounts: tens of kg per h.

Intense radioactive-ion beams produced with the ISOL method

For fifty years the isotope separation on-line (ISOL) technique has been used for the production of radioactive-ion beams (RIBs). Thick-target ISOL facilities can provide very intense RIBs for a wide range of applications. The important design parameters for an ISOL facility are efficiency, rapidity and selectivity of all steps of the separation process. To achieve the anticipated beam intensities with the next-generation RIB facilities, the production rate in the ISOL target has to be increased by orders of magnitude. This is only possible by adapting the projectile beam for optimum production cross-sections and simultaneously minimizing the target heating due to the electronic stopping power of charged-particle projectiles. ISOL beams of 75 different elements have been produced up to now and further beam development is under way to produce a still greater variety of isotopes and to improve existing beams in intensity and purity.

ISOLDE target and ion source chemistry

For the production of radioactive ion beams by means of the ISOL (isotope separation on-line) method in which the nuclei of interest are stopped in a thick target, chemistry plays a crucial role. It serves to separate the nuclear reaction products in atomic or molecular form from the bulk target and to transfer them efficiently to an ion source. This article gives an overview of ISOLDE radiochemical methods where targets (liquid metals, solid metals, carbides and oxides) and ion sources are optimized with respect to efficiency, speed and chemical selectivity. Rather pure beams of non-metals and volatile metals can be obtained with a temperature-controlled transfer line acting as thermo-chromatograph. For less volatile metals the temperature of the target and ion source units needs to be kept as high as possible, but a selective ion source can be used: positive surface ionization for metals with ionization potentials below about 6 eV and the RILIS (resonance ionization laser ion source) technique for most other metals.

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.