Erzeugung exotischer Atomkerne

Kernfusion in Sternen Der Ursprung der Elemente Nukleosynthese nach dem Urknall Neutroneneinfang in Roten Riesensternen oder Supernovae Krebsnebel Supernova beobachtet 1054

M   8M  Roten Riese Weiβer Zwerg Zwiebelschalenstruktur kurz vor Explosion Geburt und Tod der Sterne 8M   M  15M  Supernova II 1.4M   M core  2M  Neutronen Stern M  15M  Supernova IIa M  2M  Schwarzes Loch

number of neutrons number of protons Nucleosynthese in Supernova-Explosionen: Schneller Neutroneneinfang durch instabile (neutronenreiche) Isotope Fusion in Sternen Der Ursprung der Elemente

Reaktionsmechanismen zur Erzeugung radioaktiver Strahlen Protonen-indizierte ReaktionenSchwerionen-induzierte Reaktionen

Fragmentation im Fluge Ionen-Separation on-line „ISOL“

Zwei moderne Methoden zur Erzeugung und Untersuchung seltener Isotope Fragmentation „im Fluge“ (IF): Gestoppte und wiederbeschleunigte Ionen „Ionen Separation Online (ISOL): Relativistische Schwerionenstrahlen Intensive Protonenstrahlen Dünnes Target: Projektilfragmentation Fragmentseparator Speicherring Heißes, dickes Target: Targetfragmentation Ionenquelle Massenseparator geringer Auflösung ss Ionenkühlung Ionenfallen ms - s

Konzepte für ISOL

Oberflächen-Ionenquelle ISOLDE (CERN) Strahl aus dem PS Booster: Verbund aus 4 kleinen Synchrotrons liefert 1 GeV Protonen, 3.2  /s (alle 1.2 s) Some of the targets used at ISOLDE consist of molten metals kept at temperatures from 700 o C and up to about 1400o C. Such targets are characterized by a relatively long release time of the produced isotopes and a typical time constant of the release is about 30 seconds. Faster release times, in the order of one second or less, can be obtained, if target material in the form of refractory metal powder, metals or carbides is used at temperatures above 2000 o C. An expected decrease in the release time due to the "shock-wave" effect of the pulsed proton beam has been observed. Time constants down to some tenths of a second can be reached for the fastest targets.

ISOLDE at the PS-BOOSTER The basic principle of ISOLDE is that radioactive nuclides are produced in spallation, fission or fragmentation reactions with a thick target placed in the external proton beam of 1 GeV. To most nuclear and high-energy physicists, the word "target" evokes the idea of a passive foil or rod, but here the target is, in reality, a small chemical factory that, under intense bombardment, supplies the radioactive beam, that after magnetic analysis, is steered to the experiments. The large range in solids of high-energy protons and also the reactions induced by secondaries are essential in providing ISOLDE with intensities that, in general, cannot be matched by other machines. The proton injector for ISOLDE, the PS Booster, is a stack of four small synchrotrons pre-accelerating protons, delivered by a Linac, to 1 GeV before injection into the CERN Proton Synchrotron (PS). PS in turn supplies particles to all CERN's high-energy machines. The PSB gives one pulse of 3.2*10 13 protons every 1.2 seconds. Up to half of the pulses in the 12 pulses long super cycle to the PS is brought to bombard the ISOLDE target. This gives an equivalent of about 2 microA dc beam. The transfer of ISOLDE from the 600 MeV dc proton beam at the CERN SC to the time structure, with a short high density proton pulse at low repetition rate, increased the release time of the produced radioactivity from the target. This increased predominantly the production of very short-lived species and makes the ISOLDE beam bunched. In addition it allows "background free" experiments between the pulses because the neutrons, which are the main sources of background, die out in the first 100 ms after the beam burst. The target technique developed at the SC ISOLDE is, in most cases, directly applicable with the new beam.

ISOLDE at the PS-BOOSTER The basic principle of ISOLDE is that radioactive nuclides are produced in spallation, fission or fragmentation reactions with a thick target placed in the external proton beam of 1 GeV. To most nuclear and high-energy physicists, the word "target" evokes the idea of a passive foil or rod, but here the target is, in reality, a small chemical factory that, under intense bombardment, supplies the radioactive beam, that after magnetic analysis, is steered to the experiments. The large range in solids of high-energy protons and also the reactions induced by secondaries are essential in providing ISOLDE with intensities that, in general, cannot be matched by other machines. The proton injector for ISOLDE, the PS Booster, is a stack of four small synchrotrons pre-accelerating protons, delivered by a Linac, to 1 GeV before injection into the CERN Proton Synchrotron (PS). PS in turn supplies particles to all CERN's high-energy machines. The PSB gives one pulse of 3.2*10 13 protons every 1.2 seconds. Up to half of the pulses in the 12 pulses long super cycle to the PS is brought to bombard the ISOLDE target. This gives an equivalent of about 2 microA dc beam. The transfer of ISOLDE from the 600 MeV dc proton beam at the CERN SC to the time structure, with a short high density proton pulse at low repetition rate, increased the release time of the produced radioactivity from the target. This increased predominantly the production of very short-lived species and makes the ISOLDE beam bunched. In addition it allows "background free" experiments between the pulses because the neutrons, which are the main sources of background, die out in the first 100 ms after the beam burst. The target technique developed at the SC ISOLDE is, in most cases, directly applicable with the new beam.

The laser ion source has been developed to ionize isotopes of elements which could not be ionized efficiently by any of the other types of ion sources or to obtain a purified beam. This is possible because the laser ion source works only on the atoms of the element the laser wavelengths are tuned for (chemical selectivity), the isobaric contamination is therefore reduced down to small amounts, which are caused by surface ionization inside the tube where laser ionization takes place and which needs moderate heating. The laser system consists of copper vapor lasers, tunable dye lasers and non linear crystals for frequency doubling or tripling offering the possibility for most efficient two or three step ionization. The plasma ion source is used to ionize elements that cannot be surface-ionized. The plasma is produced by a gas mixture (typical Ar and Xe) that is ionized by electrons being accelerated between the transfer line and the extraction electrode by supplying an anode voltage of about 130 V. For the optimization of this process an additional magnetic field is used (SRCMAG). Plasma ion sources have been used in combination with most target materials.

The surface ion source is the simplest set-up for ionizing atoms produced in the target. The ionizer consists only of a metal tube ("line"), for example tantalum or tungsten, which has a higher work function than the atom that should be ionized. Depending on the line's material it can be heated up to 2400 o C. Surface ion sources have been used in combination with most of the different target materials. The heart of an on-line isotope separator is its target and ion source. The target should assure a fast liberation of the radioactive nuclei produced in large amounts of target material. The combination with the ion-source should be able to produce an ion beam which preferably should only contain isotopes from one chemical element. The development of this experimental technique is a field of radiochemistry, which also involves metallurgy, high temperature chemistry and surface physics. The ISOLDE group has developed many different advanced target-ion-source combinations, which have allowed the users of the facility to study radioisotopes from more than 60 different elements. the elements for which beams are available at ISOLDE today are indicated in the periodic table, which also allows to obtain information on the produced quantities. Some of the targets used at ISOLDE consist of molten metals kept at temperatures from 700 o C and up to about 1400 o C. Such targets are characterized by a relatively long release time of the produced isotopes and a typical time constant of the release is about 30 seconds. Faster release times, in the order of one second or less, can be obtained, if target material in the form of refractory metal powder, metals or carbides is used at temperatures above 2000 o C. An expected decrease in the release time due to the "shock-wave" effect of the pulsed proton beam has been observed. Time constants down to some tenths of a second can be reached for the fastest targets.

The ISOLDE PS-Booster facility is equipped with two isotope separators. The General Purpose Separator (GPS) is designed to allow three beams, within a mass range of ± 15%, to be selected and delivered to the experimental hall. The magnet is double focussing H-magnet with a bending angle of 70° and a mean bending radius of 1.5 m. The mass resolving power is M/  M=2400. The second separator, the High Resolution Separator (HRS), is equipped with two bending C-magnets with bending angles 90° and 60° degrees, respectively. At the moment one single mass, with a resolution of about M/  M=5.000, can be separated routinely with the HRS separator. The calculated beam profiles for the masses 99, 100 and 101 are shown in the figure. It will be possible to achieve a maximal resolution of more than Separatoren an ISOLDE (CERN)

Konzepte für Separation im Fluge

Erzeugung hochgeladener Isotope an der GSI

Beispiel: 78 Ni

B  -  E - B  Separation Method

Reichweite und Energieverlust geladener Teilchen in Materie nach Bethe-Bloch

Der Fragmentseparator der GSI

GSI: Kombination von relativistischen Ionenstrahlen, Fragmentseparator und Speicherring (oder Neutronendetektor)