Download
1 / 44
E N D
Design of a new setup for extraction of reaction products by means of their stopping in gas and subsequent resonance laser ionizationSergey ZemlyanoyFlerov Laboratory of Nuclear ReactionsJoint Institute for Nuclear Research35th meeting of the JINR PAC for Nuclear Physics Jan.26-27, 2012, Dubna.
Programme Advisory Committee for Nuclear Physics34th meeting, 16–17 June 2011 • Valery Zagrebaevpresents the talk: • Possibility for the production and study of heavy neutron-rich nuclei formed in multi-nucleon transfer reactions • The PAC discussed the proposal of the Flerov Laboratory, presented by V. Zagrebaev, on the synthesis of heavy neutron rich nuclei formed in low-energy multi-nucleon transfer reactions. The use of this method opens a new field of research in low-energy heavy-ion physics, namely, the production and study of new neutron rich heavy nuclei playing a key role in the r-process of nucleosynthesis. The development of an experimental set-up based on the method of stopping reaction fragments in gas and on their subsequent selective resonance laser ionization is proposed. With such a method atoms of required elements can be selected. The method is already used in several laboratories for separation and study of light exotic nuclei and fission fragments. Because of the capability of selecting ions of specific atomic numbers, this set-up can also be employed in other studies, like the unknown charge distribution of the products of quasi-fission. The PAC emphasizes that the proposed experimental method is feasible. • Recommendation. • The PAC strongly recommends starting to work on the details of this proposal within the Flerov Laboratory right away.
During period from last PAC session it was performed • Detailed Laser scheme of setup. • Scheme of gas part of setup, consisting of: front end system, gas cell, SPIG system, evacuation system, gas cleaning system etc. • Drawings for all elements of gas part of setup • The different possibilities of Setup position at FLNR U-400M cyclotron have been considered and 2 variants developed more detailed • The International Workshop on “Resonance Laser Separation of Nuclear Reaction Products” was held on 6-7 December at Flerov Laboratory. Leading scientists in this field of research from Leuven, Jyvaskyla, GANIL, CERN, GSI, Mainz and iThemba took part in the Workshop. • During the Workshop the project on production and study of heavy neutron rich nuclei formed in multi-nucleon transfer reactions was discussed along with details of the corresponding setup. The project have been examined by the experts and got their approval.
Schematic view of setup for resonance laser ionization of nuclear reaction products stopped in gas
The scheme of the front end of the LISA mass separator subsystem
The layout of the dual chamber laser ion source gas cell • The aim: (by separating stopping and laser ionization chambers) • Increasing laser ionization efficiency at high cyclotron beam current • Increasing selectivity (collection of survival ions) • Working conditions: • cyclotron – DC • Ion collector – DC • Lasers – transverse or longitudinal Exit hole diameter – 0.5mm/1mm Stopping chamber – 4 cm in diameter Laser ionization chamber – 1 cm in diameter
The ion extraction from the gas cell dE ~ 0.7 eV 4.7MHz 0-500V (-210 V) 1200 V 250V The SPIG consists of 6 rods (124 mm long and a diameter of 1.5 mm) cylindrically mounted on a sextupole structure with an inner diameter of 3 mm. The distance between the SPIG rods and the ion source is equal to 2 mm.
Front end of the LISOL mass separator Cyclotron beam Extraction electrode Laser beams Gas Cell SPIG Gas from purifier
Gas cell and Ion-guide system • General requirements to the ion-guide systems look as follows: • pressure in gas cell: 100–500 mbar depending on the energy of reaction products • and required extraction time; • working gas is He or Ar (the latter looks preferably because its stopping capacity • and efficiency of neutralization are higher); • gas purity not lower than 99,9995%; • cell volume is about 100–200 cm3; • vacuum in intermediate camera not worse than 10-2 mbar; • vacuum in the entrance into the mass separator is 10-6 mbar; • Some specific requirements, stipulated by the use of the resonance laser ionization, • should also be taken into account: • gas cell should be two-volume to separate the area of thermalization and neutralization • from the area of resonance laser ionization; • extraction of ions from the cell and driving them into the mass separator have to be provided • by the sextupole radio-frequency system which allows one to increase • the efficiency of the setup and to perform ionization of atoms in the gas jet outside the cell; • the input-output setup must be supplied by the system of optical windows and • by the system of explicit positioning (0.3 mm) of the gas cell, guide mirrors and prisms. • Production cost of the gas cell and ion output systems is about 800 k$.
Specifications of the pump station located in the basement: • Pumping system: RUVAC WH 7000 roots pump with SCRELINE SP630 backing pump • (from Oerlikon Leybold Vacuum Gmbn) is taken as example. • Electrical power for the prepump : 3 X 380V, 11 kW • Electrical power for the pump: 3 X 380V, 18 kW • Weight : 1300 kg, • Noise level : 80 dB(A) - pumps to be placed in the basement with sound isolation panels • Pumping station is placed on the high voltage platform (40kV) and electrical power for roots and • backing pumps comes via the isolation transformer. • - A metal fence with a door and safety switch has to be installed around the pumping station. • - Vacuum gauges and the meter have to be foreseen in the basement.
The pump station 3 roots pump station at HV platform Isolating transformer for HV platform
Gas purifier MonoTorr Phase II 3000 SAES Pure Gas, Inc. Flow meter Brooks Instrument 5860S 0.08 - 8 ln/min Towards gas cell Ar Grade 5.5 (99.9995%) Oil-free, small pump station The scheme of the gas handling and purification system The gas purity is a key issue for efficient running of the laser ion source. The gas handling system has to be designed to supply and to control the gas flow into the gas cell. Electro-polished stainless steel tubes and metal-sealed valves have to be used in order to reduce the outgasing and the "memory effect". The system should be bakeable up to 2000C with temperature control and be pumped by a separate small oil-free pumping station. High-purity argon gas is additionally purified in a getter-based purifier to the sub-ppb level.
Mass separator • All extracted ions have charge state +1 because only neutral atoms are ionized to this state • by the lasers while all “non-resonant” ions are removed by electric field before reaching • the area of interaction with laser radiation. In this case the extracted particles can be easily • separated by masses in dipole magnet. • For low-energy (30–60 keV) beams of +1 charged ions no specific requirements are needed • for the dipole magnet. It could be a standard magnet separator similar to ISOLDE II, • for example: • Bending angle 40о–90о, • Bending radius of about 1–1.5 m, • Focal plane length of about 1 m, • Rigidity of about 0.5 Т.m. • Dipole gap about 50-60 mm • Mass resolution is the only critical parameter which should be about 1500. • Camera of the separator must have an optical input if collinear laser ionization • is used with the sextupole ion-guide (SPIG). • Production cost of such mass separator is about 250 k$.
Mass separator Most important specifications: Magnet Weight : 1800 kg, Bmax :0.76 T Cooling water flow: 400 l/h, pressure drop = 4 bar Cooling water: 15 degrees Magnet power supply Weight : 250 kg Output : max 300A/25V AC main input: 3 X 380V, 18.5A Cooling water flow: 120 l/h, pressure drop=3bar Vacuum system 4 turbo pumps (at front end, lens chamber, entrance of the magnet, dispersion chamber): for example Edwards STP1003C,Water cooled, 100 l/h per pump Two Prepumps, for example Pfeiffer MVP160-3 can be placed in the basement - Total flow for cooling water: min. 1000 l/h - Compressed air to drive small actuators and vacuum valves - Total electrical power needed : ~20 kW
Comparison dye vs. possible Ti:Sa system Dye Ti:Sa 2x Dye 2x Ti:Sa Ti:Sa 3x Ti:Sa 3x Dye 4x Ti:Sa Dye
l– meter The (almost) optimum RILIS Laser System Nd:YAG Dye 2 SHG Dye 1 THG SHG Master clock NarrowbandDye RILIS Dye Laser System GPS/HRS Delay Generator RILIS Ti:Sa Laser System Target & Ion Source Nd:YAG Ti:Sa 3 Faraday cup Ti:Sa 2 Ti:Sa 1 SHG/THG/FHG l– meter pA – meter
Laser system Nd:YAG laser specification (EdgeWave GmbH) • Maximal average power: 90 W and 36 W respectively; • Repetition rate: 10-15 kHz; • Pulse duration: 8-10 ns. • Divergence parameter of the green beam: M2 = 1.4; • Electrical power 3.6 kW including 1.6 kW for the water chiller. Credo dye laserspecification (Sirah) • Maximal average power: 20 W at fundamental wavelength, 2 W at 2nd harmonics; • Line width: 12 GHz • Pulse duration: ~7 ns • Remote control of wavelength with stabilization to an external laser wavelength meter. Production cost of the laser system with three-step resonance ionization (combined with the corresponding optical scheme) is about 950 k$.
The layout of laser installation OT1-OT9 – optical tables; Nd:YAG1 and Nd:YAG2 – pump lasers; DL1-DL3 – dye lasers; R1 and R2 – racks for electronics and water chillers; M1-M10, M22 – high power mirrors for 532nm beams; M10-M15 – high power mirrors for 355nm beams; BS1-BS4 – beam splitters for 532nm beams; M16-M21, M23-M25 – mirrors for dye laser beams; T1-T4 – telescopic zoom expanders for 532nm beams; T5 and T6 - telescopic zoom expanders for 355nm beams; L1-L6 – spherical lenses, SM1 and SM2 – spherical mirrors; BD1 and BD2 – beam dumps for IR beams; P1 and P2 – half-wave plates for 355nm; RM1-RM4 – return mirrors for reference beams; RP – reference plane; AlM1 – Al mirror; QP1 – quartz plate; RC – reference cell
Financial plan, k$ Total: 1990 k$
Report of the Experts on the FLNR project on production and study of heavy neutron rich nuclei formed in multi-nucleon transfer reactions by means of their stopping in gas cell and subsequent resonance laser ionization The International Workshop on “Resonance Laser Separation of Nuclear Reaction Products” was held on 6-7 December at Flerov Laboratory of Nuclear Reactions JINR. Leading scientists in this field of research from Leuven, Jyvaskyla, GANIL, CERN, GSI, Mainz, iThemba and Troitsk took part in the Workshop and made contributions on the current status of these investigations in their centers. During the Workshop the FLNR project on production and study of heavy neutron rich nuclei formed in multi-nucleon transfer reactions was discussed along with details of the corresponding setup for extraction of reaction products by means of their stopping in gas cell and subsequent resonance laser ionization. The project was undergone an examination by the experts and got their approval. The discussion on the details of the project has been initiated by the decision of the JINR PAC on Nuclear Physics in June 2011. Experts made a number of recommendations on detailed parts of the project and optimal choosing of setup components: type and initial configuration of laser system, construction of front-end system and gas cell, importance of adequate gas purifying system etc. It was stressed by experts the following: The proposed physics program is rather ambitious. These studies allow investigating unexplored area of heavy neutron rich nuclei, helping to understand the r-process of astrophysical nucleogenesis near the last “waiting point”. The method proposed for production of heavy neutron rich nuclei, namely, the low-energy multi-nucleon transfer reactions, looks promising and adequate; the calculated cross sections of these reactions look quite realistic. The setup proposed, its configuration and components are quite feasible and correspondent the problem. Analogous setups already successfully operated in some facilities for another investigations and reactions type. The chosen laser system (YAG + DYE) with following extension to (YAG +TiSa) allow performing an efficient ionization of new neutron rich isotopes, giving the possibility of their selection by atomic number and even by isomers. Gas cell with indicated main parameters (pressure 100-500 mbar of Ar (He), double chambers) will provide efficient stopping and guiding of reaction products to mass separator. Basic mass separator parameters (with the resolution not less than 1500) fulfill the goal of isotope separation by mass. The total efficiency of setup could be of order from few to tens percent. The setup definitely could be build up during the period not exceeding 3 years (depending on financial schedule). Required funding of amount ~2M$ looks absolutely feasible and reasonable. The all experts strongly recommend constructing this setup at FLNR JINR. Many of experts show an interest to participate in realization of this project and forthcoming experiments. Proponents: V. Zagrebaev, S. Zemlyanoi and E. Kozulin Experts: Michael Block (GSI, Darmstadt, Germany) Valentine Fedosseev (CERN, Switzerland) Iouri Koudriavtsev (KUL, Leuven, Belgium) Nathalie Lecesne (GANIL, Caen, France) Vyacheslav Mishin (ISAN, Troitsk, Russia) Iain Moore (JYFL, Jyväskylä, Finland) Herve Savajols (GANIL, Caen, France) Klaus Wendt (Institut für Physik Johannes Gutenberg-Universität, Mainz, Germany)
On 24 January 2012 the design of setup for extraction of reaction products by means of their stopping in gas and subsequent resonance laser ionization have been consideredby Technical Council of Flerov Laboratory of Nuclear Reactions, JINR and approved.
Conclusion • At target thickness 0.3 mg/cm2, ion beam of 0.1 pmA and setup efficiency of 10% we would be able to detect 1 event per second at cross section of 1 microbarn • It allow as to measure decay properties at least 1 new isotope per day • It is sufficiently not only for measurement of typical nuclear characteristics (like half-life times, decay schemes, etc.), but also for determining of nuclear charge radii (and moments) with using in-source laser spectroscopy.
People involved into developing and discussion of this SETUP project Leuven:M. Huyse, Yu. Kudryavtsev, P. Van Duppen Jyväskylä:Juha Äystö, Iain Moore, Heikki Penttilä CERN:Valentin Fedosseev GSI:Michael Block, Thomas Kühl GANIL:Nathalie Lecesne, Herve Savajols Mainz:Klaus Wendt Manchester:Jonathan Billowes, Paul Campbell IS RAN Troitsk:Vyacheslav Mishin FLNR:V. Zagrebaev, S. Zemlyanoi, E. Kozulin, and others
People involved into developing and discussion of this SETUP project Thank you for your attention
r-process and heavy neutron rich nuclei • difficult to synthesize • difficult to separate
Production of NEW heavy nuclei in the region of N=126(Zagrebaev & Greiner, PRL, 2008) “blank spot”
IGISOL – Ion Guide Isotope Separation on line Time profiles of laser-ionized stable Ni-58 from the filament Ni filament He SPIG ~1994 40 kV mass separator + + + Laser beams cyclotron beam target 3-10 mg/cm2 Weak beam, 1nA, 1ms Delay time - down to 10 ms (He) Refractory elements - ! Strong beam, 1uA,20ms Laser-produced Ni ions recombine in a plasma created by a primary beam >99% are neutral We have to provide for radioactive atoms: 1. Efficient laser ionization 2. Survival of laser-produced ions in a volume around the exit hole
Required beams of accelerated ions(the ion beams available at FLNR are well satisfied our requirements) Ions:16,18О, 20,22Ne, …48Ca, 54Cr, …86Kr, 136Xe, 238U (i.e., quite different depending on the problem to be solved). Beam energies:4,5 – 9 MeV/nucleon (slightly above the Coulomb barrier) Beam intensity: not restricted (up to 1013 pps). Beam spot at the target: 3–10 mm in diameter (not very important). Beam emittance:20pmm mrad. Targets: different, including actinides Th, U, Pu, Am, Cm.
The setup consists of the following elements (units) - front end system including: gas cell, system for extraction of the cooled ion beam, electrostatic system for final formation and acceleration of the ion beam (800 k$) - laser system (950 k$) - mass-separator (250 k$) - system for delivery and cleaning of the buffer gas inside the gas cell, - vacuum system, - high voltage and radio frequency units, - diagnostic and control systems for the ion beam.
Schematic view of setup for resonance laser ionization of nuclear reaction products stopped in gas
Laser System Max. Rep. Rate – 200 Hz Excimer lasers Dye lasers SHGs Reference cell Yu.Kudryavtsev, SMI06, March 27-28, 2006 Towards LIS, 15 m 4/20
off Cyclotron on on Laser off on Separator Pulsed operation mode Energy (eV) 4 0 LISOL Laser Ion Source Towards mass separator SPIG –210V Target (~ mg/cm2) Exit hole Cyclotron beam Ion source selectivity - Laser ON/OFF: 30-80 for proton-induced fission reactions 100-200 for fusion evaporation reactions Ar 500mbar Ar/He from gas purifier Filament Plasma created in the cell does not allow to collect not neutralized ions and causes recombination of laser-produced ions Gas cell for fusion reactions Laser beams • Thermalisation in a buffer gas cell (500 mbar Ar/He) • Neutralisation (>99%) • Resonant laser ionization: Z-selection (isomer) • Extraction using gas flow, transport using RF ion guide • Mass separation: A/Q selection
