Journal of Nuclear and Radiochemical Sciences,Vol. 3, No. 1, pp. 9–12, 2002

9

Production of Super Heavy Elements at GANIL: Present Status and Perspectives
S. Grévy∗,a and FULIS collaboration: N. Alamanos,b N. Amar,a J. C. Angélique,a R. Anne,cG. Auger,c F. Becker,c R. Dayras,b A. Drouart,b J. M. Fontbonne,a A. Gillibert,b D. Guerreau,cF. Hanappe,a R. Hue,c A. S. Lalleman,c T. Legou,a R. Lichtenthäler,d E. Liénard,a W. Mittig,bF. De Oliveira,b N. Orr,a G. Politi,e Z. Sosin,f M. G. Saint-Laurent,c J. C. Steckmeyer,a C. Stodel,cJ. Tillier,a R. de Tourreil,c A. C. C. Villari,c J. P. Wieleczko,c and A. WielochfaLPC, IN2P3-ISMRa-Université, Caen, F-14050, Franceb
DAPNIA/SPhN, CEA Saclay, Gif-sur-Yvette, Francec
GANIL, Caen, Franced
IFUSP, São Paulo, BrazileUniversità di Catania, ItalyfIns. Fyziki Uniw., Krakow, Poland
Received: November 30, 2001; In Final Form: November 30, 2001
Experiments on the production and study of superheavy nuclei have been undertaken at GANIL taking advantagesof the powerful velocity filter LISE3 and the high intensity ECR ion sources. A complete setup has been built: —reaction chamber containing large rotating wheels, — slits and beam profiler at mid-filter, — detection chamberwith time-of-flight and Silicon detectors for identifying evaporation residues and their decay products. The response
was checked via fusion reactions with known cross sections producing known α-decay chains and fission fragments.
Excellent transmission of evaporation residues and rejection factor for the primary beam were obtained. This device
is presented together with the results obtained in our last experiments and our future plans are discussed.

1. Introduction

has also started recently.

An experimental program dedicated to the study of Super
Heavy Elements (SHE) started at GANIL in order to take advantages of the performances of the accelerator and of the powerfulvelocity filter LISE3.
Indeed because of the very low cross sections for the production of SHE (from 1 µbarn for Z = 100 to 1 pbarn for
Z = 112),1 very high intensity ECR ion sources delivering about
one particle-µA (6.27 ×1012 projectiles/s) or more should be
used. The second important point is the separation between the
projectiles and the complete fusion evaporation residues (ER)emitted at forward angle after the production target. Originally,
the LISE3 Wien filter2 was designed to improve the separationof exotic nuclei produced by fragmentation of the projectile andselected by the LISE spectrometer. Then, an important work has
been done to adapt it to fusion experiments improving its ability
to work with very high primary beam intensities.
An experimental setup composed of a dedicated rotating target, beam diagnostics, time detectors, and a set of Si detectors(for the implantation and decay products) has been developed.
Finally a digital electronics is under development to reach extremely short decay times in the order of few µ-seconds.
The response of the whole setup was checked via fusion reactions with known cross sections and α-decay chains: 204,206
87 Fr
nuclei formed via 86 Kr + nat Sb with cross sections of 10 to300 µbarn.4 These equipments were then used for an experiment dedicated to the system 86 Kr on 208 Pb and the transmission
and the rejection factor of the Wien filter were precisely measured in an experiment dedicated to the production of the Sg
element (Z = 106) through the system 54 Cr + 208 Pb. Comparison
with known values for the excitation energy function1 allowed tocheck the excellent transmission together with an high rejection
factor.
An experimental program has been established for the production of new elements and/or new isotopes with two principal
axes: — i — the use of the inverse kinematics with a beam of
Lead and — ii — the use of the neutron-rich 76 Ge as projectile.
Another program dedicated to the study of the properties of SHE

2. Experimental Setup∗Corresponding author. E-mail: grevy@in2p3.fr. FAX: +33-(0)231-45-25-49.

A general overview of the experimental setup, from the reaction chamber to the detection setup is presented in Figure 1.
2.1. Reaction Chamber. The reaction chamber contains
two 67 cm diameter wheels bearing 35 targets (5.0 ×1.5 cm2each) and rotating up to 2000 RPM, allowing targets with low
melting temperature (like Pb or Bi) to sustain very intense primary beams. The second wheel support carbon stripper foils inorder to re-equilibrate the charge state of evaporation residues.
The time structure of the beam is synchronized with the rotation.
Two smaller wheels allow us to run with targets having higher
melting temperatures. A Si detector continuously monitors thestatus of each target via elastic scattering reactions.
2.2. Wien Filter. The LISE3 Wien filter has crossed magnetic and electric fields in a rather compact geometry and its angular acceptance is ±36πmrad. It is divided into two identicalhalves and is followed by a dipole magnet. Several modifications were found to be necessary for fusion experiments: — i —the upper plate in the first half of the filter was moved up by
2 cm in order to deflect the beam without hitting the electrode.
The beam is now stopped on a new water-cooled collimator, —ii — two pairs of independently movable slits and a beam profiler were installed at mid-filter. An additional background suppression can be performed using the last dipole magnet locatedbetween the Wien filter and the detection chamber. The transmission of fusion nuclei from the target position through thequadrupoles, filter, and final dipole was studied via a simulation
code.3 The optics are checked and the Wien filter is calibratedusing low energy ions (0.35 MeV/u to have the same speed thanER’s after the target).
2.3. Detectors. The detection setup (see Figure 2) is composed of two Galottes (carbon foils + MCP’s time detectors) and
13 Si detectors. The time detectors are used in order to tag all theevents (ER’s or background) coming from the beam. Since theefficiency of Galotte for light particles might not be 100%, twoof them are used. Then, the “implantation events” are those with
an implantation energy signal in coincidence with both Galottes
whereas the “α” or fission events are those in anti-coincidence.
The implantation detector is a 300 µm thick Si 48 × 48 strips.

c 2002 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 6/30/2002

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J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

The distance between the strips is reduced (∼45 µm) to have adead zone inferior to 5%. Two of them are mounted on a movable arm. When emission of α particles or fission fragments is
identified via electronics, the beam is immediately stopped for ashort while during which the first implantation detector is moved
out of the beam and the second implantation detector comes in,then the beam is sent again. This technique allows us to waitfor very long decay times in the first implantation detector, being completely free of background coming from the beam. The
ER’s are implanted at a depth of approximately 10 µm which issmaller than the range in Si for α particles with energy above
2.5 MeV. Then, in order to measure the full energy of the α
particles emitted at backward angles which escape the implantation detector, a set of 8 Si detectors is mounted in a ‘tunnel’
geometry. With this configuration, the efficiency for full α energy goes up from 55 to 95%. A ‘face’ Si detector is placed in
front of the ‘out of beam’ implantation detector in order to play
the same role, the efficiency being then 100%. A veto Si detector is placed after the implantation detector to eliminate thebackground of light particles coming from the beam. All the Si
detectors are mounted on copper supports and can be cooled toreduce the electronic noise.
2.4. Data Acquisition and Electronics. Specific electronics and data acquisition systems were developed. We use for thedata acquisition a complete VXI system for which the standard
dead-time is around 150 µs. In order to reduce it, a multi-trigger
logic with 2 sets of converters (ADC’s) is working in the following way: the hard trigger provided by the electronics enters
into two GMT (Ganil Master Trigger) modules, T1 and T2. Incase of usual counting rate, all the triggers are treated as ‘T1’
and the events are registered into the first set of converters. Thisway is exactly the same as the usual one used in many experiments. The same signals are also duplicated into the second setof converters but are not yet considered by the acquisition. In
case of a new trigger comes during the dead time of GMT1, it is
now treated by GMT2 (as a trigger ‘T2’) while GMT1 continues
to deal with the preceding event. The minimum time between
two events is then about 30 µs. This procedure was tested witha strong α source before the experiment. The used converters
are new 14-bits ADC’s which allow to have a good resolution
for α particles (less than 50 keV) together with a large range ofenergy, between 300 keV and 250 MeV (necessary for spontaneous fission events).
A fast analysis program allows us to identify ‘on line’ αdecay chains or spontaneous fission and then to stop the beamand move out the implantation detector (see sect. 2.3).
A complete read out digital electronics is actually under development to be able to reach extremely short decay times, inthe order of few µs keeping good energy resolution (less than
50 keV) on a large energy range from 1 MeV to 1 GeV. This new
digital electronics will be placed after the analog front-end elec-

Figure 1. Schematic drawing of the experimental setup including,from left to right, the reaction chamber with the rotating target and stripper foils, the Q-poles and the LISE3 Wien filter between them, the last
dipole and the detection chamber with time and Si detectors.

Grévytronics (preamplifiers) and the main idea of such an approachis to adapt a dedicated processing to each event on a very large
dynamical range and without limitation due to the recovery timeof the preamplifier.
3. Experimental Results
3.1. Experiment on 86 Kr + 208 Pb System. In July 1999,
the BGS-Berkeley group reported the observation of 3 eventsof the new element Z = 118 identified by α decay with chainsof 6 α’s.5 The reported cross section was much larger than expected (∼2 pb) and the same system studied with the velocity
filter SHIP at Darmstadt did not lead to the observation of thiselement,7 justifying to repeat this experiment at GANIL in December 1999. Since GANIL is able to deliver an high intensity
beam of 86 Kr (15 µA with charge 10+, i.e. nearly 1013 projectiles/s), our idea was to confirm (or not) Berkeley’s result and,in the case of a positive answer, to obtain additional information: — i — be able to reach shorter decay times (by the use of
fast electronics, see sect. 2.4) for possible α decay before theminimum time of 120 µs in the Berkeley experiment, — ii —wait for very long decay times (by the use of movable implantation detectors, see sect. 2.3), — iii — since ER’s may be createdin an isomeric state which decays via electron capture followedby an electron cascade with an unknown half-live modifying theionic charge and strongly reducing the transmission in the caseof the GSI experiment, the carbon stripper foils were in our experiment located at a distance from the target 3 times larger thanin the SHIP experiment.
With a total accumulated dose of 1.1 ×1018 ions at
5.27 MeV/u on targets of 300 µg/cm2 , we didn’t observe any
event corresponding to the decay of element 118.
The result of Berkeley was recently retracted.6
3.2. Experiment on 54 Cr + 208 Pb System. In order to measure precisely the transmission and the rejection factor of the
LISE3 Wien filter for SHE’s, an experiment dedicated to the production of the 106 Sg element through the system 54 Cr on 208 Pb
was performed at GANIL in December 2000. With a primarybeam intensity of 40 nAp and 2 incident energies (4.698 and4.756 MeV/u), we observed 10 events of 261
106 Sg (1 neutron evaporation channel) and 2 events of 260
106 Sg (2 neutrons evaporation
channel). The decay chains were identified by position correlation between the implantation of the ER and the decay events in
the implantation detector. Comparison with the known excitation energy functions1 makes possible to deduce a transmission
efficiency above 60% together with a power of suppression of

Figure 2. Schematic view of the detection setup implanted at the end of
the LISE3 spectrometer. It is composed by 2 time detectors (Galotte), 2
movable implantation Si detectors, a set of 8 Si detectors for the tunnel,
1 veto Si detector behind the ‘in beam’ implantation, and 2 Si detectors(face) to recover the products (α or fission fragment) escaping the ‘outof beam’ implantation detector.

Production of Super Heavy Elements at GANIL

J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

11

TABLE 1: Summary of the different possible reactions using 207, 208 Pb beams on various targets. ZCN and ACN are respectively the atomic
number and mass of the compound nucleus, E∗bass being the excitation energy at the Bass barrier.
208

Z CN
Target
50
104
Ti
51 a
105
V
54
106
Cr
55
107
Mna
58
108
Fe
59
109
Coa
64
110
Ni
65
111
Cua
70
112
Zn
71
113
Ga
76
114
Ge
75
115
As
82
116
Se
81
117
Br
New reactions (in italic).
a
New path.
b
Production of new isotope.

Pb beam
ACN
258
259
262
263
266
267
272
273
278
279
284
283
290
289

207

E∗bass / MeV
23
25
22
24
21
23
17
19
12
13
9
13
3
7

the primary beam and scattered projectiles of ∼2 ×1010 , corresponding to a counting rate of 5–10 Hz in the implantation
detector.
4. Short and Middle Range Perspectives
4.1. Inverse Kinematics
4.1.1. Method. The use of the inverse kinematics (heavy
projectile on light target) has been tried at GANIL in June 1999
and will be used in spring 2002 on the system 208 Pb + 54 Cr to
8
produce 261,260
106 Sg isotopes. This technique presents several assets in comparison with direct kinematics.
— i — The target thickness is no longer limited by multiple
scattering of the ER’s and it becomes possible to use thicker
targets covering an excitation energy range of typically 10 MeV
instead of 3–4 MeV. The counting rate is then maximized andthe gain in time can be very important. Indeed, in the search
for new isotopes or new elements, the incident energy depends
strongly on the mass defects which differ in different mass tables
by several MeV whereas the excitation function is rather narrow.
— ii — The ER’s are more strongly focused at forward angles
resulting in a better transmission through the LISE3 filter.
— iii — Because of the higher energy after the target, theionic charge distribution of ER’s is better estimated and its relative width is smaller. Here again the transmission is favoured.
— iv — Finally, the quality of the data is better: due to thedeeper implantation depth, the energy deposited by the ER’s ishigher, both fission fragments are stopped and escaping α particles lose more than 2 MeV and then cannot be missed.
The main drawback of this approach concern the velocity difference between the beam and the ER’s which is much smaller
than in direct kinematics. Then, higher electric and magnetic
fields are necessary in the Wien filter. With the new power supplies installed this year, the LISE3 filter will be able to get thesame spatial separation at mid-filter as in direct kinematics.
4.1.2. Use of 208Pb Beam. Several systems can be studied
for different purposes (summarized in Table 1):— i — New paths to known isotopes with 208Pb: Produce thesame isotopes of the odd-Z compound nuclei than ER’s formed
at GSI with a 209 Bi target.1 Here, two points are of interest:
first, measure and then compare the cross sections which will
give a clue to the respective roles of macroscopic and structure
effects: charge asymmetry of the entrance channel and closed
shells effects. Secondly, produce ER’s in different levels, especially isomeric states.
— ii — New isotopes with 207Pb: Produce isotopes lighterby 1 neutron than the ones known for several elements: 260
107 Bh,Target
50
Ti
51
V
54
Cr
55
Mnb
58
Fe
59
Cob
64
Ni
65
Cub
70
Znb
71
Ga
76
Ge
75
As
82
Se
81
Br

265
271
111, and 276 112.
109 Mt,Pb beam
ACN
257
258
262
262
265
266
271
272
277
278
283
282
289
288

E∗bass / MeV
23
25
22
24
20
22
16
18
12
13
9
13
2
6

For the last two cases, a chain of 3
α’s will be observed before reaching a known isotope, i.e. 3 newisotopes will be observed in one event.
— iii — New elements: Above Z = 109 the counting rates arevery low. For 277 112, measurements were made at one beam energy only, not necessarily at the maximum of the excitation function. The broader energy coverage provided by inverse kinematics may reveal a larger cross section. Moreover, the 1n channel
cross section decreasing quickly with Z, it may be that the 0n
cross section becomes larger even through the fusion probability
drops very much at the corresponding incident energy. Added
to the uncertainty on the compound nucleus mass defect, the exploration of a broad range of incident energies corresponding to
0n + 1n channels leads to lengthy measurements at several incident energy in direct kinematics: 6 beam energies were tried for
Se + Pb at GSI in the search of element 116 (Ref. 1) whereas an
excitation energy range of 12 MeV or more can be covered witha single incident energy in inverse kinematics.
The main interest of using 76 Ge
4.2. Use of 76
32 Ge Beam.
beam is the direct cold fusion production of the element 273 110
using a 198 Pt target.9 Indeed, this isotope has been observedin 3 events only through the decay of element 277 112 andpossibly 3 events by direct production in hot fusion reaction(34 S + 244 Pu = 273 110 + 5n). A very large range of α-decay energies, from 9.18 to 11.17 MeV with lifetimes from 0.11 to 170 ms
have been observed. What we propose is to make a precise α
spectroscopy of this isotope since the population of different levels (especially isomeric states) may be due to overreaching thedeformed shell N = 162. This would require a “large” number of
events.
A more general interest for the 76 Ge beam is provided by theaccessible region of production. Indeed, it makes possible, us205
ing targets ranging from 192
76 Os to 81 Tl, to produce elements 108
to 113 heavier by two neutrons (except for element 111) than
the isotopes produced using Pb/Bi targets with beams ranging
from 48 Ca to 70 Zn (Ref. 1). Clearly, comparing with Pb/Bi based
reactions, the entrance channel is more symmetric and there are
no closed shells, the cross sections will be then reduced. But on
the other hand, the accessible compound nuclei are richer by 2
neutrons (except for element 111) and this will be in favour ofthe cross sections.
An estimation of the reduction factors (see Figure 3) can bemade using the compound nucleus 220 Th produced via different
entrance channels having similar Bass barriers4, 10–12 : 18 Ar + 72 Hf
and 30 Zn + 60 Nd systems have no closed shells and the more
symmetric system has a cross section smaller by a factor 14.

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J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

Grévy90% by EC on 251 Fm. Since the ground state parity and spinof the first level of 251 Fm are known, ground state of 251 Fm andpossibly of 255 Lr could be determined. The experimental setup
will be adapted with a tunnel of Si detectors to detect conversion
electrons and a set of Ge clover detectors from Exogam will be
added in a close geometry.
Acknowledgements. The authors would like to acknowledge
all the technicians and engineers from mechanics, detector, andelectronic groups who made possible this experimental program,
especially at LPC Caen, GANIL, and Saclay. We are also indebted to the target laboratories of LNS Catania, IFU Sao Paulo,
GSI Darmstadt, and IPN Orsay for the excellent quality of theirproducts. The users support group (Service des aires) and theaccelerator staff of GANIL should be mentioned for their continuous support and efficient performances at all stages of thiswork. Finally, a great help was provided by the data acquisitiongroup GIP (GANIL) for the electronics and by the CHARISSA
collaboration for lending us their VXI ADC’s.
References

Figure 3. One neutron channel cross sections measured for 208 Pb and209
Bi targets in direct kinematics.7 The crosses represent our estimations
using a 76 Ge beam (see text sect. 4.2 for details).

Assuming a steady variation with the charge asymmetry, the expected cross sections for 20 Ca + 70 Yb and 40 Zr + 50 Sn are estimated. The actual cross sections are much higher, by a factor 6
and 23 respectively, due to the role of the closed shells.13 These
factors may now be used to estimate the reduction factor whichapplies when the same CN is formed on 76 Ge based reactions incomparison with Pb/Bi based reactions. The loss of shell effects
is estimated to reduce the cross section by one order of magnitude (represented by a solid arrow in Figure 3). At Z = 106,
the decrease of asymmetry reduces the cross section by a factor
about 12 (represented by a dashed arrow in Figure 3) whereas
this asymmetry disappears for 76 Ge + 208 Pb reaction producing
element 114.
An estimation of the gain in the cross section due to the neutron richness can be made also considering the Th isotopes. Detailed measurements show that 2 more neutrons in the CN increase the residue cross section by a factor 9.12 As seen in Figure 3, the gain for Z = 110 using 64 Ni beam instead of 62 Ni isin the order of 5. In our estimation for 76 Ge beam, we consider an average factor of 7 (represented by a solid arrow on
Figure 3). Then, the estimated cross sections are represented
by solid crosses. They are smaller than the Pb/Bi based crosssections.
4.3. Study of the Structure of the Super Heavy Elements.
A new experimental program is proposed at GANIL14 on the
study of transfermium isotopes by the use of spectroscopic information in order to have a better understanding of their shellstructure. This program is going to start with the α, γ, and electron spectroscopy of 251 Md and 251 Fm. 251 Md is populated by
the α decay of 255 Lr produced in the 2 neutrons channel of the48
Ca + 209 Bi fusion evaporation reaction. The 251 Md should decay with less than 10% by α decay on 247 Es and with more than(1) S. Hofmann and G. Münzenberg, Rev. Mod. Phys. 72, 733(2000).
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Gelletly, AIP Conf. Proc. 495 (AIP, New York, 1999),
p. 137.
(8) J. Péter for the FULIS collaboration, Proposal for GANIL
experiment E339b(09-2000).
(9) C. Stodel for the FULIS collaboration, Proposal for GANIL
experiment E369a(09-2000).
(10) C. C. Sahm, H.-G. Clerc, K.-H. Schmidt, W. Reisdorf, P.
Ambruster, F. P. Hessberger, J. G. Keller, G. Münzenberg,
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