Journal of Nuclear and Radiochemical Sciences,Vol. 3, No. 1, pp. 173–177, 2002

173

Recent Results from Heavy Element Research at JYFL
M. Leino∗
University of Jyväskylä, Department of Physics, P.O. Box 35, FIN-40351 Jyväskylä, Finland
Received: January 14, 2002; In Final Form: January 14, 2002
The gas-filled recoil separator RITU in conjunction with germanium detector arrays and the SACRED conversion
electron array has been used for studies of nuclear structure in the region around 254 No. Rotational spectra have been
extracted using in-beam measurements with recoil gating or recoil decay tagging. Results from completed in-beam
γ-ray studies of 252,254 No as well as preliminary data from in-beam conversion electron measurements of 253,254 No
and γ-ray studies of 250 Fm are presented. These measurements give strong support to the prediction that nuclei inthis region of the nuclear chart are quadrupole-deformed in their ground state with β2 ∼ 0.27. There are indicationsof an upbend occurring in the moment of inertia of 252 No and 250 Fm at a frequency around 180 keV. Future prospects
for these studies as well as for focal plane decay spectroscopy in the transfermium region using RITU are discussed.

1. Introduction
Almost 20 years ago, the surprising experimental result was
obtained that the even-even nuclide 260 Sg has a much longer
spontaneous fission half-life than expected.1, 2 Soon afterwards,
α decay of the even-even nuclide 264 Hs was also observed.3
These results were incompatible with predictions based on calculations which reproduced rather well the lifetime systematics
of lighter nuclei (see e.g. Reference 4).
A long standing prediction is that a region of spherical superheavy nuclei which are stabilised by shell effects should exist.
It has also been known for a long time that a deformed shell closure at neutron number N = 152 has an effect on spontaneous fission half-lives of the actinides.5 However, such deformed shells
were not expected to have a strong enough effect to stabilise
superheavy nuclei. It was only after the above mentioned experimental findings that the idea of deformed superheavy nuclei
emerged.6 Many detailed calculations have been performed, and
it is now a well established theoretical result that, in particularin the region surrounding the “doubly magic” nuclide 270 Hs, deformed superheavy nuclei should exist.7, 8
For many years after the synthesis of 260 Sg and 264 Hs, among
others, there was only little experimental evidence of the deformation. In even-even nuclei, some of the lowest-lying levels
were known from α- or β decay. Examples are 248,250 Cf, in which
the 2+ , 4+ , and 6+ levels of the ground state rotational band wereobserved in α decay of 252,254 Fm (Ref. 9). In both daughter nuclei, also the 4+ → 2+ and 2+ → 0+ γ rays were observed. Another example is 256 Fm where the low-lying level structure wasstudied via β decay of the 7.6 h high-spin 256 Es isomer.10 In thiscase, the ground state rotational band could be observed up to
the 8+ state. The measured excitation energies of the 2+1 states
for the isotopes 248 Cf, 250 Cf, and 256 Fm are 41.5 keV, 42.8 keV,and 48.3 keV, respectively. These excitation energies are indicative of strong deformation of these nuclei. One should notethat total internal conversion coefficients for E2 transitions arehigh in this region of nuclei and at these transition energies.11
For example, for a 2+ → 0+ E2 transition with an energy around50 keV, the total conversion coefficient is on the order of 1000
for Fm (Z = 100). Thus, in Reference 10, the energy of the 2+
level was extracted as the difference between energies of lessconverted transitions.
The heaviest nuclide for which Coulomb excitation measurements have been performed is 248 Cm which was studied via
the bombardments 58 Ni,136 Xe + 248 Cm (Ref. 12). Levels of theground state band were observed up to 22+ , and the diagonal E2
matrix elements were measured up to spin 20h̄. These matrix elements provide the most direct and unambiguous evidence and∗E-mail: matti.leino@phys.jyu.fi. FAX: +358-14-260 2351.

quantitative data on quadrupole collectivity in nuclei.12
It is not easy to extend such measurements to heavier elements. Lack of stable, or long-lived, target or source material
prevents Coulomb excitation and decay studies. Traditionally,
heavy ion evaporation reactions (HI, xn) have produced extensive data from in-beam studies on collective properties e.g. in
the rare earth region. In the region of heavy elements, thesestudies were for a long time impossible to conduct because of
the severe background arising from fission products. This problem was essentially solved with the employment of RDT (Recoil Decay Tagging) techniques.13, 14 In these measurements, anin-beam detector system is coupled to a recoil separator. Only
such in-beam events are accepted for study which are accompanied by a delayed coincidence with a separated nucleus identified through its characteristic (α- or proton-) decay. A variationof this method, called recoil gating, makes use of a delayed coincidence between the in-beam event and a heavy recoil particle,
identified as a fusion product through its energy and possibly
also other measured parameters such as time of flight.
When the RDT or recoil gating method are used, the limitation comes from the reaction cross section. For the observation of the ground state band of heavy even-even nuclei, thepresent limit is on the order of 100 nb (see e.g. Reference 15).
With stable targets, cross sections for (HI, xn) reactions fall below this limit around the element fermium with Z = 100 (see e.g.
Reference 16). On the other hand, when actinide targets andvery asymmetric reactions are made use of, the separator transmission is small. A notable exception comes from the use of
the doubly magic 48 Ca projectile with targets around the doubly magic 208 Pb (Ref. 17, 18). For cold fusion reactions, i.e.
(48 Ca, 1–2n) evaporation reactions, cross sections on the order of
0.1–1 µb allow in-beam measurements in the region surrounding 254 No. In the following, recent work on the structure of Fmand No nuclei using the methods of RDT and recoil gating at
the Department of Physics, University of Jyväskylä (JYFL), is
described. Finally, some future possibilities concerning both inbeam and decay spectroscopy studies will be discussed.
2. Experimental Details
All of the studies described here have been performed using the JYFL gas-filled recoil separator RITU.19 RITU was
designed for the study of the heaviest man-made elements but,mainly due to insufficient beam intensities previously available
at JYFL, has mostly been used for the study of neutron-deficientnuclides in the W–Th region and for the experiments described
here. In in-beam experiments, the maximum beam intensity islimited by the counting rate in the γ- or conversion electron detectors and is typically on the order of 1–10 pnA. A primaryreason for using a gas-filled separator is the high transmission

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

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

JUROSPHERE + RITU preliminary

+
+

+

+

18 - 16

14 - 12++16 - 1415+

12 - 10

+

+
+

+
+

20

Fm Kβ
+

Fm Kα225

10 - 8Fm Kα1

30

8-6

35

+

The first in-beam γ-ray experiment on transuranium nuclei
performed at JYFL was the study of 254 No, produced in the reaction 208 Pb(48 Ca, 2n).21 The cross section for this reaction has
been determined to be about 2 µb in several experiments (seee.g. References 17, 18). Slightly earlier, the same reaction had
been used at Argonne National Laboratory to study 254 No using
Gammasphere and the Fragment Mass Analyzer (FMA).22 The
main differences in these two experiments were the efficienciesof the setup. Gammasphere has a γ-ray detection efficiency of
10% at 1.3 MeV while the efficiency of the SARI array used at
JYFL was 1.7%. The smaller efficiency of SARI was compensated for by the use of the highly efficient gas-filled separator at
JYFL, and the overall performances of the setups were comparable in these essentially singles γ-ray experiments. In these two
experiments, the bombarding energy was chosen for maximal
production of 254 No which occurred at approximately 20 MeV
excitation energy.
The result of these experiments, and of one more study performed at Argonne, using a slightly higher excitation energy(approximately 23 MeV) to enhance the population of high-spinlevels23 was the following: The ground state rotational band wasobserved up to spin 20h̄ showing that 254 No can sustain at least
this amount of angular momentum without fissioning. The observation of the rotational band was clear evidence of groundstate nuclear deformation. A quantitative estimate of the degreeof deformation was extracted as follows: Due to large conversion coefficients of low-energy γ-ray transitions in No nuclei,
the lowest transitions 4+ → 2+ and 2+ → 0+ could not be seen in
the γ-ray spectra. By making a Harris parameter fit to the observed transition energies, the excitation energy of the 2+ level
was extracted. The result was 44.2(4) keV.21 By using global
systematics of 2+ energies of even-even nuclides,24, 25 the valueof the quadrupole deformation parameter β2 = 0.27(3) was determined.21
After these pioneering experiments, the main experimental
goals were the following: (i) Extension of the knowledge ofeven-even systems. (ii) Study of odd-mass cases to gain information on single-particle properties. (iii) Observation of conversion electrons to determine excitation energies of low-lying
states. Some of the progress made at JYFL along these lines will
be discussed in the following.
3.1. Gamma-ray RDT Experiment on 252 No. A straightforward extension of the study of even-even No isotopes was
the in-beam γ-ray RDT measurement26 on 252 No, produced witha cross section of 300 nb in the reaction 206 Pb(48 Ca, 2n). This
experiment was performed using the JUROSPHERE II array
which consisted of 15 Eurogam phase I detectors, 5 Nordball

6-4

3. In-beam γ-ray and Conversion Electron Experiments

and 7 TESSA detectors (all Compton-suppressed) with an efficiency of 1.7% at 1.3 MeV γ-ray energy. The spectrum quality
was much better than with the SARI array which consisted offour unshielded clover detectors, and thus the ground state rotational band could again be observed up to spin 20h̄ in spite of
the significantly reduced reaction cross section as compared to
the 254 No experiment.
3.2. Gamma-ray RDT Experiment on 250 Fm. The mostrecent investigation in this field performed at JYFL was an inbeam γ-ray RDT experiment on the structure of 250 Fm. This
isotope was produced in the reaction 204 Hg(48 Ca, 2n)250 Fm forwhich a peak cross section on the order of 1 µb was measured
at an excitation energy of 23 MeV. The targets were 204 HgS andhad a thickness of 300–600 µg/cm2 . Prompt γ rays from thetarget were detected using the JUROSPHERE IV germanium
detector array which was similar to the JUROSPHERE II arraydescribed in sect. 3.1. At the focal plane there was, in addition
to the usual position sensitive stop detector, a Time-Of-Flightdetector27 for the identification of fusion products. The combined Time-Of-Flight and energy gate (for the signal in the stop
detector) provided very clean conditions for separating fusion
products from other heavy particles. Thus, decay tagging was
only used to confirm the identification of the origin of γ rays.
Preliminary results from this experiment28 are given in the following.
In Figure 1 the preliminary recoil gated total γ-ray spectrum
is shown. In addition to γ-ray peaks, Fm X-ray peaks around
100 keV energy can be seen in the spectrum. A cascade of E2
γ-ray transitions in the ground state rotational band has beententatively identified as shown. As in the cases of 252,254 No(Ref. 21, 26), the 4+ → 2+ and 2+ → 0+ transitions are too weak
to be seen due to internal conversion. The spin assignments
shown are the only ones which lead to a meaningful Harris parameter fit of the transition energies.
3.3. Conversion Electron RDT Experiments on 253,254 No.
As mentioned above, internal conversion coefficients are large
for low-energy transitions in the transfermium region. As an
example, the total conversion coefficients for the 4+ → 2+ and2+ → 0+ transitions in 254 No are around 1000 and 30, respectively. Thus, it is highly desirable to measure conversion electrons in-beam for these nuclei. Several problems, foremost ofwhich is the very intense background of delta electrons coming from the target, have prevented such measurements. This
problem was recently overcome at JYFL by using a high voltage barrier electrode in conjunction with the SACRED electron
spectrometer29 and RITU. Details of the setup are discussed
in a forthcoming publication.30 Briefly, the current version of
SACRED makes use of a segmented 25-unit electron detector
which is located almost collinearly upstream from the RITU target, i.e. at 177.5 degrees from the beam direction. Conversion

Countsof such devices which is based on charge and velocity focusingof the reaction products.20
The determination of the transmission of recoil separators is anotoriously difficult task. In-beam experiments provide an accurate method for such a determination using the ratio of the number of γγ to recoil-γγ coincidences for a particular fusion product. For the reactions described here, RITU efficiencies on theorder of 25–45% have been estimated, depending on the losses
caused by multiple scattering in the Time-of-Flight detector incase such a device was used in front of the focal plane.
The filling gas used in RITU is helium, and typical gas pressures are 0.5–1.0 mbar. The separator gas volume is isolated
from the beam line vacuum using a gas window which is typically carbon with a thickness of around 50 µg/cm2 . The carbon
window and the helium gas increase the count rate of Ge detectors used in in-beam γ-ray experiments. Partly for that reason,
differential pumping has recently been installed at RITU. However, in all of the experiments described here, a gas window wasstill used.

Leino

10
5
0

0

100

200

300

400

500

Gamma-ray energy [keV]
Figure 1. Preliminary recoil-gated singles γ-ray spectrum of 250 Fm
produced in the reaction 48 Ca + 204 Hg and measured using RITU in conjunction with the JUROSPHERE IV Ge detector array.28 The spin assignments are tentative.

Recent Results from Heavy Element Research at JYFL

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

electrons from the target are guided to SACRED by using a setof four solenoidal coils. The efficiency of the device was measured to be approximately 8% for electrons with energies around200 keV. A high voltage electrode with typically 40 kV negative
potential prevents the passage of low-energy delta electrons to
the SACRED silicon detector. In order to achieve high vacuumin the barrier region, two gas windows with additional pumping
in the space between the two foils was employed.30
Two measurements on No isotopes were performed with thissetup. In the first one, RDT conversion electrons from 254 No
were collected using the reaction 208 Pb(48 Ca, 2n) at 20 MeV excitation energy.31 The target thickness was 430 µg/cm2 and thebeam intensity, limited by the count rate in the SACRED silicondetector, was 2 pnA. Altogether around 2400 254 No nuclei werecollected in a 70 h bombardment. The total recoil gated electron spectrum is shown in Figure 2. The low-energy part of thespectrum is affected by the −40 kV high voltage barrier. The
conversion electron peaks corresponding to the E2 transitions
have been identified as shown. In particular, a triplet of peaks
identified as arising from the 4+ → 2+ transition gives a transition energy of 101.72(15) keV, confirming the result from theγ spectroscopy measurements where an energy of 102.0(3) keV
was determined by extrapolation. The 2+ → 0+ transition still
remains unobserved due to the effect of the high voltage barrier.
In another experiment, conversion electrons were measured
from the reaction 207 Pb(48 Ca, 2n)253 No. A preliminary spectrumof recoil gated electrons is shown in Figure 3 (top panel). Whilethe data do not allow detailed interpretations, some preliminary
conclusions may be drawn: The ground state and three predicted
lowest single-particle states in 253 No according to Reference 7
are 9/2− [734], 7/2+ [624], 5/2+ [622], and 1/2+ [620]. If it is assumed that the quadrupole moment of 253 No is identical to thatof 254 No, rotational model calculations can be performed to produce a level scheme for 253 No. Figure 3 shows the results of simulations32 based on such a calculation. The intrinsic gK factor
of an individual state depends sensitively on the single-particle
configuration and determines, on the other hand, the nature of
the transitions to be observed. Here in particular, negative gK
values favour M1 intra-band transitions while positive gK values
enhance the cross-over E2 transitions. The E2 transitions areless converted than the M1 transitions which may allow theirobservation in a γ-ray investigation. Of the four band heads
mentioned above, the only one leading to a large positive gK
value (+0.28) is the 7/2+ state. The predicted 9/2− [734] groundstate leads to the negative gK value of −0.25. As can be seenfrom the two simulated spectra in Figure 3, the converted M1
transitions from the band based on the 9/2− state are in muchbetter qualitative agreement with the experimental data than thetransitions from the band based on the 7/2+ state. This obser-

vation is complementary with results from a γ-ray experiment
performed at Argonne using Gammasphere and the FMA whichshows evidence for a rotational band built on the 7/2+ singleparticle state.33
4. Discussion
The extraction of the quadrupole deformation parameter β2
on the basis of extrapolated 2+1 excitation energies and the global
systematics24, 25 certainly involves uncertainties. Nevertheless,by using the same method for a set of isotopes, some systematic trends can be discussed. Scrutiny of the 2+ energies directly, which appear to be quite reliable also when extracted
by extrapolation, should already be fruitful. For example, according to Sobiczewski et al.,8 254 No should have the lowest
2+1 energy among all nuclei in this region. This expectation isbased on the effect of the closed N = 152 shell which should
reduce the effect of pairing correlations and thus increase themoment of inertia for this nuclide. The extracted 2+1 energies
are the following (calculated values8 are given in parentheses):
250
Fm, 43.5 keV (43.9 keV); 252 No, 46.5 keV (44.5 keV); 254 No,
44.2 keV (41.6 keV). These values lead to the following β2 deformation parameters: 250 Fm, 0.273; 252 No, 0.260; 254 No, 0.264.
The relative uncertainty of all values is approximately 10%.21(The value given here for 252 No differs from that given in Reference 26 where somewhat different systematics were used. For
the sake of consistency, the same method which was also employed in Reference 21 is used here for all nuclides.) The excitation energies are in good agreement with those calculated
by Sobiczewski et al.8 although the difference between energies of 250 Fm and 254 No is smaller than predicted. If the same
method is used to extract the β2 values for Cf isotopes with
N = 150 and N = 152 for which the 2+ energies have been directly measured,9 the results are 0.280 (248 Cf) and 0.274 (250 Cf).
In this case there is also no significant effect seen at N = 152.
For No isotopes, the experimentally determined deformation
values are in good agreement with results calculated using themacroscopic-microscopic method7, 34, 35 which typically yields
values of β2 ∼ 0.25.
The dynamic moments of inertia deduced for 250 Fm and
252,254
No are shown in Figure 4. The data for 250 Fm are based
30
SACRED + RITU
20

253

+

4 −> 2

Intensity (counts/2 keV)M+

6 −> 4

+

254

L

M

Simulation 1

g K = −0.25

20

No

2

400µ g/cm
40kV barrier
2441 recoils

15+

8 −> 6

10
0Simulation 2

30

+

L

10

+

20

M

10

+

10−> 8MLU

g K = +0.28

0

5

0

50

100

150

200

250

Energy
0

No

0

+

L

preliminary

10

30

20

175

10

50

100

150

200

250

300

350

Energy (keV)
Figure 2. Recoil-gated singles conversion electron spectrum of 254 No
produced in the reaction 48 Ca + 208 Pb and measured using RITU in conjunction with the SACRED spectrometer.31

300

350

400

450

(keV)

Figure 3. Top panel: Preliminary recoil gated conversion electron
spectrum of 253 No produced in the reaction 48 Ca + 207 Pb and measured
using RITU in conjunction with the SACRED spectrometer. Middle
panel: Simulated spectrum (Reference 32, see text for details) using
an intrinsic gK factor of −0.25 for the band head state. Bottom panel:
Simulated spectrum using gK = +0.28.

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

Leino

on preliminary results and are only tentative. Perhaps the moststriking feature of the data is the upbend which occurs for 252 No
at approximately 0.18 MeV rotational frequency but is absent,or occurs at higher frequency, for 254 No. The last data point for250
Fm corresponds to the 18+ → 16+ transition, i.e. two h̄-units
lower than for the two No nuclei. Qualitatively, the behaviour ofthe dynamic moment of inertia of 250 Fm is closer to 252 No than
to 254 No at high spin values while the opposite is true at the lowest data points. The fact that 254 No is more deformed than 252 No
can also be seen from the relative magnitudes of the moments ofinertia at low frequencies.
Several theoretical studies utilising Hartree-Fock-Bogoliubov(HFB) calculations have been performed to explain the experimental observations for 254 No (Ref. 36–38). In Reference 37,
where the agreement with experimental γ-ray energies and kinematic moments of inertia is very good, an upbend and a backbend are predicted at I ∼ 30h̄ and ∼38h̄, respectively. Thesechanges are due to the alignment of πi13/2 and νj15/2 orbitals,
respectively. The theoretical deformation value is β2 = 0.29. In
Reference 36, the dynamic moments of inertia have been calculated for 252,254 No. The calculations reproduce the fact that the
moment of inertia increases faster for 252 No than for 254 No above
a rotational frequency of 200 keV although experimentally, thedifference between the two isotopes is more pronounced. The
obtained deformation parameter36 is 0.264 for 254 No. In Reference 38, using another parametrisation of the Skyrme interaction, a somewhat improved description, as compared with Reference 36, of the dynamic moment of inertia is found for 254 No.
5. Future Possibilities
The study of man-made elements has progressed to a region
where the production cross sections are on the order of 1 pb.
The production of spherical superheavy elements may require
even more sensitive measurements. In such experiments, spectroscopic information to be gained is scarce. However, evenat the level of 10 pb, important data for example on isomericstates can be collected.39 Very efficient and versatile detector
configurations are then needed. An extensive collaboration has
been funded in the U. K. to develop a data acquisition and detec-

140
130

254

tor system called GREAT40 to be used at the focal plane of the
RITU separator. GREAT comprises two Double-sided Silicon
Strip Detectors (DSSD) covering an area of 40 mm by 120 mm
to be used as a stop detector and 32 PIN diodes for detection of
conversion electrons and escaping α particles. A segmented planar Ge detector in combination with a large-volume segmented
Ge detector, both behind the DSSD detector, will be used forthe detection of low- and high-energy γ rays, respectively. Thissystem provides unsurpassed capability for the detection of αγ, α-e− , and also β-γ coincidences. The system is expected tobe commissioned in the year 2002. First experiments will concentrate on the study of α-decay fine structure and isomeric α
decays as well as γ rays from high-K isomers41 in the region
around 254 No.
The study of odd-mass nuclei in the No region may provide
crucial information on single-particle properties, especially regarding predictions concerning the exact location of the next
closed spherical proton shell. In-beam conversion electron spectroscopy is expected to be an important method complementing
γ-ray spectroscopy and focal plane studies. At JYFL, emphasis will be placed on improving the energy resolution of the
SACRED spectrometer and on optimising the electron transport
efficiency.
Finally, it is expected that a Ge γ-ray detector array will beavailable at JYFL in the year 2003, providing an order of magnitude improvement in the detection of γγ coincidences in RDT
studies. This will significantly increase the capability to extend
the ground state rotational band of 254 No to higher spin values
which should shed light on the nature of the quasi-particle alignment properties of this nuclide. It may also be possible to observe the β and γ bands. Tentative evidence of the linking transitions was already seen in the previous measurement.21
Acknowledgement. The experiments described here havebeen performed in collaboration with University of Liverpool,
DAPNIA/SPhN CEA-Saclay, Henryk Niewodniczanski Institute of Nuclear Physics Krakow, GSI Darmstadt, University
of Helsinki, Ludwig Maximilians Universität Munich, and Argonne National Laboratory. This work has been supported by
the Academy of Finland under the Finnish Centre of Excellence
Programme 2000–2005 (Project No. 44875, Nuclear and Condensed Matter Physics Programme at JYFL) and by the European Union Fifth Framework Programme ‘Improving Human
Potential — Access to Research Infrastructure’ (Contract no
HPRI-CT-1999-00044).

No

252

References

No

120

250

Fm

100

(2)

2

I [h /MeV]

110

90
80
70
60
0,05

0,10

0,15

0,20

0,25

Rotational frequency [MeV]
Figure 4. Dynamic moments of inertia determined for 250 Fm (preliminary data28 ) and 252,254 No (Ref. 21, 26).

(1) G. Münzenberg, S. Hofmann, H. Folger, F. P. Heßberger,
J. Keller, K. Poppensieker, B. Quint, W. Reisdorf, K.-H.
Schmidt, H. J. Schött, P. Armbruster, M. E. Leino, and R.
Hingmann, Z. Phys. A 322, 227 (1985).
(2) A. G. Demin, S. P. Tretyakova, V. K. Utyonkov, and I. V.
Shirokovsky, Z. Phys. A 315, 197 (1984).
(3) G. Münzenberg, P. Armbruster, G. Berthes, H. Folger, F.
P. Heßberger, S. Hofmann, J. Keller, K. Poppensieker,
A. B. Quint, W. Reisdorf, K.-H. Schmidt, H.-J. Schött,
K. Sümmerer, I. Zychor, M. E. Leino, R. Hingmann, U.
Gollerthan, and E. Hanelt, Z. Phys. A 328, 49 (1987).
(4) J. Randrup, S. E. Larsson, P. Möller, S. G. Nilsson, K.
Pomorski, and A. Sobiczewski, Phys. Rev. C 13, 229(1976).
(5) R. Vandenbosch and J. R. Huizenga, Nuclear Fission (Academic Press, New York and London, 1973).
(6) A. Sobiczewski, Z. Patyk, and S. Ćwiok, Phys. Lett. B 186,
6 (1987).
(7) S. Ćwiok, S. Hofmann, and W. Nazarewicz, Nucl. Phys. A
573, 356 (1994).

Recent Results from Heavy Element Research at JYFL
(8) A. Sobiczewski, I. Muntian, and Z. Patyk, Phys. Rev. C 63,
034306 (2001).
(9) I. Ahmad and J. L. Lerner, Nucl. Phys. A 413, 423 (1984).
(10) H. L. Hall, K. E. Gregorich, R. A. Henderson, D. M. Lee,D. C. Hoffman, M. E. Bunker, M. M. Fowler, P. Lysaght,
J. W. Starner, and J. B. Wilhelmy, Phys. Rev. C 39, 1866
(1989).
(11) F. Rösel, H. M. Fries, K. Alder, and H. C. Pauli, At. Data
Nucl. Data Tables 21, 91 (1978).
(12) T. Czosnyka, D. Cline, L. Hasselgren, C. Y. Wu, R.
M. Diamond, H. Kluge, C. Roulet, E. K. Hulet, R. W.
Lougheed, and C. Baktash, Nucl. Phys. A 458, 123 (1986).
(13) E. S. Paul, P. J. Woods, T. Davinson, R. D. Page, P. J. Sellin,
C. W. Beausang, R. M. Clark, R. A. Cunningham, S. A.
Forbes, D. B. Fossan, A. Gizon, J. Gizon, K. Hauschild,I. M. Hibbert, A. N. James, D. R. LaFosse, I. Lazarus,
H. Schnare, J. Simpson, R. Wadsworth, and M. P. Waring,
Phys. Rev. C 51, 78 (1995).
(14) R. S. Simon, K.-H. Schmidt, F. P. Heßberger, S. Hlavac, M.
Honusek, G. Münzenberg, H.-G. Clerc, U. Gollerthan, and
W. Schwab, Z. Phys. A 325, 197 (1986).
(15) D. G. Jenkins, M. Muikku, P. T. Greenlees, K. Hauschild,
K. Helariutta, P. M. Jones, R. Julin, S. Juutinen, H.
Kankaanpää, N. S. Kelsall, H. Kettunen, P. Kuusiniemi,
M. Leino, C. J. Moore, P. Nieminen, C. D. O’Leary, R. D.
Page, P. Rahkila, W. Reviol, M. J. Taylor, J. Uusitalo, andR. Wadsworth, Phys. Rev. C 62, 021302(R) (2000).
(16) H. Gäggeler, T. Sikkeland, G. Wirth, W. Brüchle, W.
Bögl, G. Franz, G. Herrmann, J. V. Kratz, M. Schädel, K.
Sümmerer, and W. Weber, Z. Phys. A 316, 291 (1984).
(17) H. W. Gäggeler, D. T. Jost, A. Türler, P. Armbruster,W. Brüchle, H. Folger, F. P. Heßberger, S. Hofmann,
G. Münzenberg, V. Ninov, W. Reisdorf, M. Schädel, K.
Sümmerer, J. V. Kratz, U. Scherer, and M. E. Leino, Nucl.
Phys. A 502, 561c (1989).
(18) Yu. Ts. Oganessian, V. K. Utyonkov, Yu. V. Lobanov, F.
Sh. Abdullin, A. N. Polyakov, I. V. Shirokovsky, Yu. S.
Tsyganov, A. N. Mezentsev, S. Iliev, V. G. Subbotin, A.
M. Sukhov, K. Subotic, O. V. Ivanov, A. N. Voinov, V.
I. Zagrebaev, K. J. Moody, J. F. Wild, N. J. Stoyer, M.
A. Stoyer, and R. W. Lougheed, Phys. Rev. C 64, 054606(2001).
(19) M. Leino, J. Äystö, T. Enqvist, P. Heikkinen, A. Jokinen,
M. Nurmia, A. Ostrowski, W. H. Trzaska, J. Uusitalo, K.
Eskola, P. Armbruster, and V. Ninov, Nucl. Instrum. Methods B 99, 653 (1995).
(20) M. Leino, Nucl. Instrum. Methods B 126, 320 (1997).
(21) M. Leino, H. Kankaanpää, R.-D. Herzberg, A. J. Chewter,
F. P. Heßberger, Y. Le Coz, F. Becker, P. A. Butler, J. F.
C. Cocks, O. Dorvaux, K. Eskola, J. Gerl, P. T. Greenlees,
K. Helariutta, M. Houry, G. D. Jones, P. Jones, R. Julin,
S. Juutinen, H. Kettunen, T. L. Khoo, A. Kleinböhl, W.
Korten, P. Kuusiniemi, R. Lucas, M. Muikku, P. Nieminen,
R. D. Page, P. Rahkila, P. Reiter, A. Savelius, Ch. Schlegel,
Ch. Theisen, W. H. Trzaska, and H.-J. Wollersheim, Eur.
Phys. J. A 6, 63 (1999).
(22) P. Reiter, T. L. Khoo, C. J. Lister, D. Seweryniak, I. Ahmad,
M. Alcorta, M. P. Carpenter, J. A. Cizewski, C. N. Davids,
G. Gervais, J. P. Greene, W. F. Henning, R. V. F. Janssens,
T. Lauritsen, S. Siem, A. A. Sonzogni, D. Sullivan, J.
Uusitalo, I. Wiedenhöver, N. Amzal, P. A. Butler, A. J.
Chewter, K. Y. Ding, N. Fotiades, J. D. Fox, P. T. Greenlees,
R.-D. Herzberg, G. D. Jones, W. Korten, M. Leino, and K.
Vetter, Phys. Rev. Lett. 82, 509 (1999).

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

177(23) P. Reiter, T. L. Khoo, T. Lauritsen, C. J. Lister, D.
Seweryniak, A. A. Sonzogni, I. Ahmad, N. Amzal, P.
Bhattacharyya, P. A. Butler, M. P. Carpenter, A. J. Chewter,
J. A. Cizewski, C. N. Davids, K. Y. Ding, N. Fotiades, J.
P. Greene, P. T. Greenlees, A. Heinz, W. F. Henning, R.-D.
Herzberg, R. V. F. Janssens, G. D. Jones, H. Kankaanpää,
F. G. Kondev, W. Korten, M. Leino, S. Siem, J. Uusitalo,
K. Vetter, and I. Wiedenhöver, Phys. Rev. Lett. 84, 3542
(2000).
(24) L. Grodzins, Phys. Lett. 2, 88 (1962).
(25) S. Raman, C. W. Nestor, Jr., S. Kahane, and K. H. Bhatt,
At. Data Nucl. Data Tables 42, 1 (1989).
(26) R.-D. Herzberg, N. Amzal, F. Becker, P. A. Butler, A. J. C.
Chewter, J. F. C. Cocks, O. Dorvaux, K. Eskola, J. Gerl, P.
T. Greenlees, N. J. Hammond, K. Hauschild, K. Helariutta,
F. Heßberger, M. Houry, G. D. Jones, P. M. Jones, R. Julin,
S. Juutinen, H. Kankaanpää, H. Kettunen, T. L. Khoo, W.
Korten, P. Kuusiniemi, Y. Le Coz, M. Leino, C. J. Lister, R.
Lucas, M. Muikku, P. Nieminen, R. D. Page, P. Rahkila,
P. Reiter, Ch. Schlegel, C. Scholey, O. Stezowski, Ch.
Theisen, W. H. Trzaska, J. Uusitalo, and H. J. Wollersheim,
Phys. Rev. C 65, 014303 (2001).
(27) H. Kettunen, P. T. Greenlees, K. Helariutta, P. Jones, R.
Julin, S. Juutinen, P. Kuusiniemi, M. Leino, M. Muikku,
P. Nieminen, and J. Uusitalo, Acta Phys. Pol. B 32, 989(2001).
(28) R.-D. Herzberg, M. Leino, J. Styczen, Ch. Theisen et al. (tobe published).
(29) P. A. Butler, P. M. Jones, K. J. Cann, J. F. C. Cocks, G. D.
Jones, R. Julin, and W. H. Trzaska, Nucl. Instrum. Methods
A 381, 433 (1996).
(30) H. Kankaanpää et al. (to be published).
(31) R. D. Humphreys et al. (to be published).
(32) P. A. Butler (private communication, 2001).
(33) P. Reiter, Habilitationsschrift, Ludwig-MaximiliansUniversitat Munich (2001) (unpublished).
(34) Z. Patyk and A. Sobiczewski, Nucl. Phys. A 533, 132(1991).
(35) P. Möller, J. R. Nix, W. D. Myers, and W. J. Swiatecki, At.
Data Nucl. Data Tables 59, 185 (1995).
(36) T. Duguet, P. Bonche, and P.-H. Heenen, Nucl. Phys. A 679,
427 (2001).
(37) J. L. Egido and L. M. Robledo, Phys. Rev. Lett. 85, 1198
(2000).
(38) H. Laftchiev, D. Samsœn, P. Quentin, and J. Piperova, Eur.
Phys. J. A 12, 155 (2001).
(39) S. Hofmann, F. P. Heßberger, D. Ackermann, S. Antalic,
P. Cagarda, S. Ćwiok, B. Kindler, J. Kojouharova, B.
Lommel, R. Mann, G. Münzenberg, A. G. Popeko, S. Saro,
H. J. Schött, and A. V. Yeremin, Eur. Phys. J. A 10, 5(2001).
(40) P. A. Butler, A. J. Chewter, H. Kankaanpää, R.-D.
Herzberg, F. Becker, J. F. C. Cocks, O. Dorvaux, K. Eskola,
J. Gerl, P. T. Greenlees, N. Hammond, K. Helariutta, F. P.
Heßberger, M. Houry, R. D. Humphreys, A. Hürstel, G. D.
Jones, P. M. Jones, R. Julin, S. Juutinen, A. Keenan, H.
Kettunen, T. L. Khoo, W. Korten, P. Kuusiniemi, Y. Le Coz,
M. Leino, R. Lucas, M. Muikku, P. Nieminen, R. D. Page,
T. Page, P. Rahkila, P. Reiter, A. Savelius, Ch. Schlegel, C.
Theisen, W. H. Trzaska, J. Uusitalo, and H. J. Wollersheim,
Acta Phys. Pol. B 32, 619 (2001).
(41) A. Ghiorso, K. Eskola, P. Eskola, and M. Nurmia, Phys.
Rev. C 7, 2032 (1973).