Possibility for the production and study of heavy neutron-rich nuclei formed in multi-nucleon transfer reactions

proposal for a new project at FLNR

V. Zagrebaev for PAC meeting,

16 June 2001

Unexplored area of heavy neutron rich nuclei

fusion fragmentation fission

r-process and heavy neutron rich nuclei

(1) difficult to synthesize (2) difficult to separate

Transfermium elements

(1) no more alpha-decays !

(2) problem of Z identification

Multi-nucleon transfer reactions

as a method for synthesis of heavy neutron rich nuclei and

Stop in gas with subsequent resonance laser ionization

as a method for extracting required reaction products (with a given Z value)

Production on NEW heavy nuclei in the region of N=126

“blank spot”

Production on new heavy nuclei in the

Xe + Pb

collisions

Simulation of typical experiment in the laboratory frame

Test experiment demonstrated good agreement with our expectations

Schematic view of the setup for resonance laser ionization of nuclear reaction products stopped in gas

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 (750 k$)

- laser system

(900 k$)

- mass-separator

(300 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.

Required beams of accelerated ions

(the ion beams available at FLNR are well satisfied our requirements) Ions:

16,18 О, 20,22 Ne, … 48 Ca, 54 Cr, …, 86 Kr, 136 Xe, 238 U (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 10 13 pps).

Beam spot at the target:

3–10 mm in diameter (not very important).

Beam emittance:

20 mm mrad.

Targets:

different, including actinides Th, U, Pu, Am, Cm.

At target thickness 0.3 mg/cm 2 , ion beam of 0.1 p m A and efficiency of the facility of 10% we will detect

1 event per second

at cross section of 1 microbarn

Similar setups at other laboratories

(Jyväskylä: JYFL and ISOLDE)

Similar setups at other laboratories

(Louvain-la-Neuve Radioactive Beam Facility) CYCLONE 110 CYCLONE 30 CYCLONE 44

LISOL Laser System LASER ION SOURCE

Front end of the LISOL mass separator Cyclotron beam Extraction electrode SPIG Gas Cell Gas from purifier

Max. Rep. Rate – 200 Hz Laser System Excimer lasers Dye lasers SHGs Reference cell

Yu.Kudryavtsev, SMI06, March 27 28, 2006

Towards LIS, 15 m

4/20

Similar setups at other laboratories

Japan, Tokai, KEK, RNB group of Miyatake

(setup for 136 Xe + 208 Pb experiment)

A-, Z-separation

People already involved into discussion of the project Leuven: Jyväskylä : GSI: Mainz: Manchester: FLNR:

M. Huyse, Yu. Kudryavtsev, P. Van Duppen Juha Äystö, Iain Moore, Heikki Penttilä Michael Block, Thomas Kühl Klaus Wendt Jonathan Billowes, Paul Campbell V. Zagrebaev, S. Zemlyanoi, E. Kozulin and others

Laser system

type Dye laser Ti:Sapphire Eximer laser CVL output power, (average) main & harmonics: (2 nd ), {3 rd & 4 th }, Wt 3, (0.3) 2, (0.2), {0.04} 30 30-50 Nd:YAG (80-100) pulse frequency, Hz pulse length, ns wave length, ns 10 4 10 4 400 10 3 -10 4 10 4 10-30 30-50 10-20 10-30 10-50 213 - 850 210 - 860 308 510.6 & 578.2

532

Production cost of the laser system with three-step resonance ionization (combined with the corresponding optic scheme) is about

900 k$.

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 energy of reaction products and required velocity of their extraction; • working gas is He or Ar (the latter looks preferably because its stopping capacity and effectiveness of neutralization are higher); • gas purity not lower than 99,9999%; • cell volume is about 100–200 sm3; • vacuum in intermediate camera not worse than10-2 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 be also taken into account:

• gas cell should be two-volume to separate the area of thermalisation 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 sextopole (quadrupole) radio-frequency system which allows one to increase the effectiveness 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

750 k$.

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: • turning angle 40о–90о, • turning radius of about 1–1.5 m, • focal length of about 1 m, • rigidity of about 0.5 Т/m.

Mass resolution is the only critical parameter which should be not less than 1500 (4000 is theoretically feasible). 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

300 k$.