On-Line Isotope Mass Separator

ISOLDE ( Isotope Separator On Line Device) is an operated since 1967 means for generating radioactive ion beams, which has been based since 1992 at the Proton Synchrotron Booster (PSB ) of CERN. With the proton beam of a plurality of radioactive nuclides PSB can be produced by chemical elements 70 in particular heated materials (targets). These are - after they emerge from the targets - ionized in different ways, accelerated and separated due to their different masses by means of magnets. Over 700 different ion beams with partially 1000 ions per second can so generated and the material and biological sciences are made available several experiments of atomic and nuclear physics as well.

History

First successful experiments for the continuous production and separation of short-lived radioactive nuclides were carried out in the early 1950s at the Niels Bohr Institute in Copenhagen. Here, a cyclotron was combined with an isotope separator. This technology has opened up new research opportunities and motivated leading European nuclear physicists in the early 1960s to propose the construction of a plant at the Synchro - Cyclotron (SC ) at CERN. Once the project and the final approval by the former CERN Director General Victor Weisskopf end of 1964 the building was begun in the following year. The underground facility at CERN and the isotope separator at the University of Aarhus was built. On October 16, 1967, the first experiment could be carried out at the ISOLDE facility above. In the early years, several new isotopes of the elements krypton, xenon, mercury and radon could be identified; A first publication appeared in 1969.

Between 1972 and 1974, the first major changes were needed at ISOLDE by increasing the intensity of the 600 MeV proton beam of the SC. Now it has been worked with the 100-fold greater intensity of the proton beam to the target, thereby reducing the number and intensity of ion beams could be increased. In the early 1980s received ISOLDE another target with magnetic separation, but due to the limited space of the ion beam was directed into the hall of the SC, where another experimental area for ISOLDE arose. With the anticipated closure of the SC in the late 1980s was thinking about a relocation of ISOLDE to another particle; In 1990 it was decided to erect a new building complex on Proton Synchrotron Booster (PSB ) of CERN. The SC gave his last beam in December 1990 and in May 1992, the new location of ISOLDE was inaugurated; on 26 June 1992, the first experiment with the 1 GeV beam of the Proton Synchrotron Booster could be performed.

1994 is for selectively ionizing the laser system Rilis (Resonance Ionization ion laser source ) are used, by whose means the desired chemical elements can be selectively ionized. This allows the separation of isobaric nuclides, which would not be possible due to the same extent by the separation magnet. The end of 2001 was taken with REX - ISOLDE post-accelerator for a ion beams provided by ISOLDE with a maximum energy of 60 keV in operation, which accelerated the ions to energies of up to 2.2 MeV. The energy could later be increased to up to 3.1 MeV and for a further remodeling are for 2014 energies up to 5.5 MeV targeted. Main users of these high-energy ion beams is the experiment MINI BALL.

Operation

The radioactive nuclides are with the proton beam of the PSB - produced by nuclear fission or spallation in a container filled with the target material container - with energies of 1.0 or 1.4 GeV. The container is typically an existing tantalum cylinder 20 cm in length and 2 cm in diameter, whose longitudinal axis is aligned horizontally and parallel to the proton beam. The introduced into the container materials, such as solid and liquid metals, carbides or oxides, electrically heated up to 2500 ° C so as to an efficient and rapid discharge of the nuclides produced from a mounted on top of the container opening to be guaranteed (about 1 to 30 s ).

The opening is connected by a channel (transfer line ) to the so-called ion source (ion source). It consists either of tantalum, copper, or quartz glass, and other suitable materials. The channel is also heated and, in some nuclides to a first selection are ( thermochromatography ). After leaving the nuclides are ionized by three different methods. The ion sources in the surface, plasma or resonant laser ionization is used.

The ions are then separated by means of deflection due to their different masses and ultimately found four ion beams of high purity with energies up to 60 keV available experiments. Two separators come each with its own target zone for use; the General Purpose Separator (GPS ) which has a bending magnet and three separate ion beams and provides alternating the High Resolution Separator (HRS ) with two bending magnets, which only generates an ion beam. The existing of the target and ion source units are housed in a specially shielded and protected area ( target zone) and are changed due to the radioactive radiation generated by mobile robots. The units used are up to the decay of the radiation dose to safe levels ( cira one year) stored behind shields in the access corridors of the robot and during maintenance periods disposed of.

Experiments

In addition to some permanently installed test set-ups, there are annually many smaller experiments, which rely on the variety of radioactive beams of ISOLDE facility. These will be built shortly before the availability of the corresponding rays and later dismantled. Every year there are over 50 different experiments. The permanent experiments are:

• ASPIC ( Apparatus for Surface Physics and Interfaces at CERN ) Is an ultra-high vacuum apparatus for the investigation of the electronic and magnetic properties of thin films - in the order of a few atomic layers - means developed by Hans Frauenfelder Perturbed Angular Correlation (PAC ) spectroscopy of gamma -emitters in solids.
• COLLAPS ( Collinear LAser Spectroscopy) By means of collinear laser spectroscopy in this experiment since the late 1970s (starting at the research reactor in Mainz in 1978 and then from 1980 to 1992 at the former site of ISOLDE ) nuclear ground state properties of short-lived nuclides determines how spin, magnetic and electric moments and charge radius.
• CRIS ( Collinear Resonant Ionization Spectroscopy) In this experiment the co-linear laser spectroscopy is combined with the resonance ionization spectroscopy. Developed in the 1980s method allows not only the study of nuclear ground state properties of short-lived exotic nuclides and the production of radioactive ion beams of high isomeric purity. The current ultra-high vacuum apparatus was constructed and tested between 2008 and 2011, and could be used since 2012 to the first extensive measurements of francium isotopes.
• ISOLTRAP Is a system based on the principle of high-precision Penning trap ion trap mass spectrometer. Since the 1980s, yet the masses could be determined from over 400 short-lived nuclides with a relative accuracy of ~ 5:10 -8. With further improvements, the accuracy was improved to ~ 1.10 -8 and measurability be extended to ions with half-lives down to 50 ms.
• LUCRECIA Is a total absorption ( gamma ) spectrometer (TAS ) for determining the gamma radiation of daughter nuclide in excited states according to a beta decay. Destination, the exact determination of which are usually held in a cascade transition from daughter nuclides in the ground state. Advantage of the design is the avoidance of occurring in other high-resolution gamma spectrometers Pandemonium effect, which does not allow an accurate determination of the energy states of the daughter nuclides.
• MINI BALL Is an operated since 2002 high-resolution gamma spectrometer consisting of 24 high-purity germanium single crystals, which are arranged spherically around the collision zone and electrically divided to increase the spatial resolution in six segments. In each case three of the crystals are shown in a cryostat to a detector. These can be mounted on a special frame in a variable number and flexibility at different positions. To study the properties of exotic nuclides the ions produced by ISOLDE are using a linear accelerator (REX - ISOLDE ) speeds up to 3 MeV and for a Coulomb excitation (electromagnetic excitation by inelastic collisions ) studied the atomic nuclei emitted in the collision zone gamma radiation.
• NICOLE ( Nuclear implantation into Cold On Line Equipment) This experiment consists of a large 3He - 4He dilution refrigerator, cooled in the ferromagnetic films of up to 10 milli- Kelvin and in which then the ion beams are steered. The implanted radioactive ions undergo spin polarization with spin -lattice relaxation times between hours and milliseconds. This has been running since 1988 experiment, the angular distribution of the emitted during the decay particles is determined as a function of the induced nuclear polarization and so, for example, examines the parity violation in beta decay, in addition to studies using nuclear magnetic resonance spectroscopy.
• WITCH ( Weak Interaction Trap for Charged particles ) Is an experiment to investigate properties of the electroweak interaction. Main concern is to determine the recoil energy of the daughter nuclides beta decay, which allows conclusions to the beta - neutrino correlation. These generated by ISOLDE ions are cooled by means of several Penning traps and recorded the distribution of recoil energies with a downstream spectrometer. Was started in 2004 with the construction of the experiment and after a few setbacks could from 2009 first results.