Transcript Possibility for the production and study of heavy neutron

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
fission
fragmentation
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: 16,18О, 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: 20 mm mrad.
Targets: different, including actinides Th, U, Pu, Am, Cm.
At target thickness 0.3 mg/cm2, ion beam of 0.1 pmA
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 ION
SOURCE
Laser System
Front end of the LISOL mass separator
Cyclotron beam
Extraction
electrode
Gas Cell
SPIG
Gas from purifier
Laser System
Max. Rep. Rate – 200 Hz
Excimer lasers
Dye lasers
SHGs
Reference cell
Yu.Kudryavtsev,
SMI06, March 2728, 2006
Towards LIS, 15 m
4/20
Similar setups at other laboratories
Japan, Tokai, KEK, RNB group of Miyatake
(setup for 136Xe + 208Pb experiment)
A-, Z-separation
People already involved into discussion of the project
Leuven:
M. Huyse, Yu. Kudryavtsev, P. Van Duppen
Jyväskylä :
Juha Äystö, Iain Moore, Heikki Penttilä
GSI:
Michael Block, Thomas Kühl
Mainz:
Klaus Wendt
Manchester:
Jonathan Billowes, Paul Campbell
FLNR:
V. Zagrebaev, S. Zemlyanoi, E. Kozulin and others
Laser system
type
output power,
(average) main &
harmonics:
(2nd ), {3rd & 4th}, Wt
pulse
frequency, Hz
pulse length,
ns
wave length,
ns
Dye laser
3, (0.3)
104
10-30
213 - 850
Ti:Sapphire
2, (0.2), {0.04}
104
30-50
210 - 860
Eximer
laser
30
400
10-20
308
CVL
30-50
103-104
10-30
510.6 &
578.2
Nd:YAG
(80-100)
104
10-50
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$.
Mass separator
All extracted ions have charge state +1 because only neutral atoms are ionized to this state
by the lasers while all “non-resonant” ions are removed by electric field before reaching
the area of interaction with laser radiation. In this case the extracted particles can be easily
separated by masses in dipole magnet.
For low-energy (30–60 keV) beams of +1 charged ions no specific requirements are needed
for the dipole magnet. It could be a standard magnet separator similar to ISOLDE II,
for example:
• turning angle 40о–90о,
• turning radius of about 1–1.5 m,
• focal length of about 1 m,
• rigidity of about 0.5 Т/m.
Mass resolution is the only critical parameter which should be not less than 1500
(4000 is theoretically feasible).
Camera of the separator must have an optical input if collinear laser ionization
is used with the sextupole ion-guide (SPIG).
Production cost of such mass separator is about 300 k$.