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Identification of Element 107 by α Correlation Chains

Z. Phys. A - Atoms and Nuclei 300, 107-108 (1981)
Short Note
f~r Physik A /~l,l.~,tl ! I~.~
and Nuclei
Springcr-Verlag 1981
Identification of Element 107 by 9 Correlation Chains
G. Miinzenberg, S. Hofmann, F.P. Hegberger, W. Reisdorf,
K.H. Schmidt, J.H.R. Schneider, and P. Armbruster
Gesellschaft fdr Schwerionenforschung, D-6100 Darmstadt,
Federal Republic of Germany
C.C. Sahm
ftir Kernphysik, Technische Hochschule,
D-6100 Darmstadt, Federal Republic of Germany
B. Thuma
II. Physikalisches Institut, Universitfit Giegen,
D-6300 Giel3en, Federal Republic of Germany
Received April 3, 1981
The production of nuclei at the upper end of the
periodic table in heavy ion fusion reactions is
limited by the high fissility of the compound
system. Formation cross-sections decrease
rapidly with increasing excitation energy. With
targets near the double magic 2~ and neutron
rich metal ions like 5OTi or 54Cr as projectiles,
fusion close to the barrier yields weakly excited
compound systems with excitation energies of less
than 25 MeV. The asymmetry of the target-projec-
tile combination is still sufficient to expect no
dynamic effects on the barrier. Consequently,
the irradiation of 2O9Bi with 54Cr as proposed by
Oganessian et al /1/ is up to our present knowl-
edge the most appropriate reaction to synthesize
element 107 by heavy ion fusion.
With the velocity filter SHIP /2/ for separation
and surface barrier detectors for identification
/3/ of the fusion products we can investigate the
predominant decay modes, spontaneous fission and
decay over the entire expected halflife range
down to us with low background from other
Up to now in experiments to produce element 107
only spontaneous fission was observed. Oganessian
et al. /I/ found two spontaneous fission activ-
in bombardments of 2O9Bi with 54Cr. One
with a halflife of (1-2) ms, which was assigned
to the 2n channel. The other activity with a
halflife of 5 s was explained by an unobserved
decay of 261107 leading to 257105 which was
regarded to undergo spontaneous fission with the
corresponding halflife.
The aim of our experiment was to produce element
107 in the same reaction and to identify the iso-
topes unambiguously by correlated a decay chains
to known transitions. We also investigated the
reaction 5OTi on 209Bi to find the unknown
daughter decays of element 105 and Lr.
Experimental Setup
The S4Cr beam from the UNILAC linear accelerator
had an average intensity of 6 x 1011 particles/s.
The ion source was operated with isotopically
enriched material. 209Bi targets with an average
thickness of 660 ug/cm 2 had been evaporated on a
30 ug/cm 2 carbon foil and covered with a 30
~g/cm carbon film for radiative cooling. They
were mounted on a rotating wheel to stand the
high beam intensities /4/. Target thickness was
monitored by Rutherford scattering.
After in-flight separation by SHIP, the evapor-
ation residues passed two large area detectors
for time-of-flight measurement and were im-
planted into a bench of 7 position sensitive
surface barrier detectors. The point of the
identification method is that all decays belong-
ing to a decay chain which starts from any inci-
dent evaporation residue have to occur at its
position of implantation within a window given by
the detector resolution. Correlation times are
limited by the rates of random events within this
position window. The detectors are cooled to
268 K and have an energy resolution of 27 keY
FWHM, the position resolution is 0.3 mm FWHM.
The evaporation residues are separated with
efficiencies of about 20%. The response of the
surface barrier detector for ~ decays is 50%, as
the evaporation residues are implanted close to
the detector surface and about half of the
particles escape. For an average beam current
of 6 x 1011 particles per second, 20 events per
nanobarn and day are implanted into the detector
array. The expected formation cross sections
for isotopes of element 107 range in the order of
0.1 nb /1/.
From preceding experiments with 4~ on 208pb,
5OTi on 2~ and 2~ we estimated an effec-
tive Coulomb radius parameter of (1.42• fm,
therefore we irradiated with 4.85 MeV/u and
4.95 MeV/u. To ensure that our projectile
energies were above the interaction barrier, we
observed the symmetric component of the mass
distribution in a scattering chamber at 45 o with
a time-of-flight measurement using surface
barrier detectors /5/.
108 G. Mfinzenberg et al.: Identification of Element 107
Experimental Results
A group of six distinguished ~ decays was found.
Five of them in the interval between 10,350 keV
and 10,400 keV are observed (1-13) ms after im-
plantation of the evaporation residue. One decay
has an energy of 9,704 keV and a correlation time
of 165 ms.
One of the measured decay chains leading to the
known decay of 25~ is shown in fig. I. The
MeV/u) 10,367 keel 3 ms '
9 176 keV I ~ual
keV/~3"8 s
~2.1 s
7 457
Fig. i*
others are partly incomplete because of the 50%
detector response. Another chain ends in 2S0Md
decay. Consequently, the chains start from
262107 formed by In evaporation. The decay chain
of fig. i follows an evaporation residue within a
position of 0.3 mm on the position sensitive
dectector. The evaporation residue has been im-
planted with an energy of 18.6 MeV, in good
agreement with the value of about 17 MeV calcu-
lated for the reaction and our detector system.
This energy is about 30% higher than the energy
of implanted Bi-recoils which is (14• MeV.
Moreover, the velocity has been checked twice: by
SHIP as well as by the time-of-flight. Except
the decay of 284Lr all decays of the chain were
observed in the background free beam pause of the
accelerator. The table shows a summary of our
data from 54Cr on 2~ In addition, we ob-
served one spontaneous fission with a correlation
time of 4.3 s.
The ~ decays of
and also 251107 lead to
unknown isotopes of 105 and Lr. 258105 can be
produced in S~ on 2~ irradiations by evap-
oration of one neutron (Fig.2). At 4.75 MeV/u we
observed decays of (9,18g_+35) keV and (9,066-+35)
keV with (4.0~+{:~) s halflife and (8,468• keY
L" CN ~3.1 s CN
keV~ ~&2 s
7,148 k~ V"
542 s
Fig. 2*
with (18~I~) s halflife corresponding to 258105
and 25~Lr respectively in good agreement to the
data from 262107 shown in the table. We observed
9 spontaneous fission events with a halflife of
(1.6~81~) s at (4.65-4.85) MeV/u irradiations.
At 4.85 MeV/u and 4.95 MeV/u decay chains from
257105 ending in the sequence 249Md- 245Es
appeared, while the 258105 and 254Lr decays dis-
Our results show the discovery of the m decay of
element 107. The ~ chains end in known transi-
tions of 25~ and 25~ respectively, indi-
cating the observation of the isotope 262107
formed by the In channel from the compound nu-
cleus 263107. This is also most likely from the
excitation energy of the compound system of less
than 18 MeV for 4.85 MeV/u specific irradiation
energy /6/. The step in m decay energies from
258105 to 262107 seems to be unusally high. So we
may speculate that the 10,376 keV decay corre-
sponds to an isomeric state. The 9,704 decay
which fits better to ~ decay systematics then
would be the ground state transition of 262107.
The possibility that the observed m decays may
origin from transfer products can be excluded:
The observed decay chain does not fit to known
transitions, the evaporation residue is well de-
fined to be heavier than a transfer nucleus near
Bi and the length of the decay chain would re-
quire a transfer of at least 4 ~ particles,
whereas no ~ decay of 21~p0, 212At, or 213Rn in-
dicating at least a transfer of few nucleons has
been found. The ms fission activity of (I-2) ms,
assigned to the 2n channel by Oganessian /1/ has
not been observed at our projectile energies.
No. of
Isotope Energy/keV • TI/2 events
262107 10,376• (4.7 t~.~) ms 5
9,704• (115 +23t~ ms I
258105 9,181• (1.8 +~'~) s 3
9,104• - I
284Lr 8,446• (10 C~) s 3
2S~ 7,435• (i 386 +900~
S 2
2S~ 7,740• (152 +3o~ s 1
Observed decays of 54Cr on 2~ irradiations
(x• keY error for absolute calibration included)
1. Oganessian, Yu.Ts., et al.: JETP Lett. 23
No. 5, 277 (1976)
2. MUnzenberg, G., et al.: Nucl. Instrum. Meth.
161, 65 (1979)
3. lq-6-i~mann, S., et al.: Z. Physik A291, 53
4. Marx, D, et al.: Nucl. Instrum. Meth. 163,
15 (1979)
5. Sahm, C.-C. et al.: Z. Physik A297, 241(1980)
6. Wapstra, A.H., Bos, K.: Atomic~a Nuclear
Data Tables 19, 177 (1977); Liran, S. Zeldes,
N.: Univ. Je~alem, Int. Rep. (1976)
*Examples of sequences of ~ decays with time
intervals between observed decays and
corresponding energies.
... The velocity filter SHIP was built for in-flight separation and studies of superheavy isotopes produced in fusion-evaporation reactions [50]. It is well-known for the discovery of the elements with proton number Z = 107 − 112 [52][53][54][55][56]. Figure 3.1 illustrates the electrostatic and magnetic components of the separator. ...
... The difference between the single frequency ratios obtained by applying the linear interpolation method and the weighted mean frequency ratio is shown in Fig. 6.7 a. The solid line indicates the mean frequency ratio which is R = 0.96724017 (52) and the shaded band represents the 1σ uncertainty. In Fig. 6.7 b, the temporal evolution of the cyclotron frequencies of 133 Cs + and 257 Rf 2+ is shown. ...
Full-text available
This thesis presents high-precision mass measurements of the heaviest nuclides performed with the Penning-trap mass spectrometer SHIPTRAP and technical developments directed towards studies of medium-heavy neutron-deficient isotopes in the region around Sn-100. Direct mass measurements of these exotic nuclei provide important quantities, such as nucleon separation energies, which are used to study the nuclear structure and the synthesis of different chemical elements through nucleon-capture processes. Within this work, high-precision mass spectrometry of No-251, No-254 (Z=102) and Lr-254, Lr-255, Lr-256 (Z=103) was performed at SHIPTRAP by employing the PI-ICR (Phase-Imaging Ion-Cyclotron-Resonance) technique. For the first time, the atomic ground-state masses of the odd-A isotope No-251 and the odd-odd isotope Lr-254 have been measured directly with a precision on the order of 10E−8. Also, the ground-state mass of the superheavy nucleus Rf-257 was determined for the first time. These results are used to benchmark atomic mass models in the vicinity of the deformed neutron shell closure at N=152 and they will indirectly improve the atomic masses of isotopes up to the element darmstadtium (Z=110). The latter will contribute to the investigation of the strength of the shell closure at N=162. In addition, a novel chemical separation technique is proposed to separate Sn-100 from its isobars by taking advantage of gas-phase chemistry inside a gas catcher. The gas catcher has been designed and it will be used as a part of the CISE (Chemical Isobaric Separation) setup to systematically study the gas-phase chemistry.
... This effect has proved to be even more important in the progressive advance along the transactinide row, and the new "cold-fusion" approach was widely exploited in the successive experiments that led to the discovery of 107-109 elements. The first isotope of element 107 (Bh), the short-lived metastable 262 Bh m , was identified at GSI in a fusion reaction of low-energy 54 Cr ions and 209 Bi targets (Münzenberg et al. 1981). ...
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We present an updated version of the 2015-Atlas of Nuclear Isomers \cite{jain2015}, compiling and evaluating experimental data for the isomers with half-life $\ge 10$ $\it{ns}$, together with their spectroscopic properties such as excitation-energies, half-lives, decay modes, spins and parities, energies and multipolarities of isomeric transitions, along with the relevant original references in literature. The current version of Atlas presents many re-evaluated half-lives as compared to the 2015 edition, where values were referred to Nuclear Data Sheets publications, when no new data existed. The ENSDF database \cite{Ensdf}, together with the XUNDL \cite{Xundl} and the NUBASE2020 \cite{Kondev2021} databases have been consulted for completeness, yet, data from original papers from journals were considered in the present evaluation, and the NSR bibliographic database \cite{Nsr} has been searched to ensure that this work is as complete and current as possible. Several useful systematic features of nuclear isomers covered in this Atlas have been discussed. Literature cutoff date for the extraction of data is July 21, 2022.
The production of 243–254No is investigated within the framework of the improved quantum molecular dy- namical model incorporated with a statistical model. The calculated results of the 48Ca+208Pb fusion reaction can reproduce the experimental data well. The impact parameter and the incident energy influence the fusion probability and the lifetime of the neck in fusion reaction process. Furthermore, the evaporation residue cross sections of 40,44,48Ca+208Pb, 20Ne+233,235,238U, 16O+242Pu, and 26Mg+232Th reactions are calculated. From investigation, the more neutrons there are in the projectile or target for the same projectile-target combination, the larger evaporation residue cross sections will be. Six unknown isotopes 243–248No are predicted with maximum evaporation residue cross sections 0.061 pb, 2.250 pb, 0.005 nb, 0.530 nb, 0.432 nb, and 3.518 nb, respectively. The corresponding fusion reactions are 208Pb(40Ca,5n)243No, 208Pb(40Ca,4n)244No, 208Pb(40Ca,3n)245No, 208Pb(40Ca, 2n) 246No, 233U(20Ne, 6n) 247No, and 233U(20Ne, 5n) 248No, respectively.
We have presented the systematics of fusion evaporation with deformation and entrance channel parameters based on 107 experiments in the pre-actinide, actinide, and superheavy region. The experimental evaporation residue cross sections were successfully reproduced by advanced statistical model (ASM) and dinuclear system model (DNS) models. Among the studied entrance channel parameters, the Coulomb interaction parameter z and mean fissility χm influence effectively the fusion reactions. Deformation effects are also included. It can also be concluded that the fusion of two spherical nuclei yields the largest σER. The highest σER that can obtained is dictated by the properties of the entrance channel parameters such as Coulomb interaction parameter and mean fissility parameter. By studying these systematics, we have established an entrance channel and deformation parameter dependent empirical formula for maximum evaporation residue cross sections. The presented formula is useful in determining evaporation residue cross sections of the heavy ion fusion reaction to synthesize heavy and superheavy nuclei.
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Dieses Kapitel beschreibt die Vorkommen, Herstellverfahren, Eigenschaften und Anwendungen der Elemente der zehnten Nebengruppe des Periodensystems (Nickel, Palladium, Platin und Darmstadtium) und ihre wichtigen Verbindungen. Nickel wurde 1751 entdeckt, Palladium 1803, und Platin dagegen war zumindest in legierter Form schon in Altägypten bekannt. 1994 konnten die ersten Atome des Darmstadtiums erzeugt werden.
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Results are presented of experiments on the synthesis of the 107th element. Bombardment of ²°⁹Bi by ⁵⁴Cr has revealed new spontaneously fissioning emitters with half-lives approx.5 sec and approx.2 msec. Different control experiments using the crossing-reaction method give grounds for assuming that activity with Tâ/â approx.5 sec is due to the spontaneous fission of the isotope ²⁵⁷105, which is formed as a result of the ..cap alpha.. decay of the isotope ²⁶¹107, which has a half-life of about 2 msec in a noticeable fraction of the events (approx.20%) and experiencing spontaenous fission. (AIP)
A target wheel rotating synchronously with the pulsed heavy ion beam of the GSI UNILAC is described. Isotopically enriched Pb targets of 4.5 × 1.5 cm2 and of thicknesses of 0.5 to 1.2 mg/cm2, covered with thin C layers on both sides, were mounted on the wheel and irradiated by up to 2 × 1012 s−1 Ar ions of 5 MeV/u on a beam spot of 0.25 cm2 without being destroyed. The total particle dose on the targets was 4 × 1016 ions.
Based on a least-squares fit to experimental data for all nuclides for which data are available and on estimates obtained from systematics for many other nuclides, we present a table of atomic masses, of mass excesses, of total binding energies, and of beta-decay energies, the last three quantities in energy units.
Very neutron deficient isotopes in the Hf-Re region were produced by bombarding targets of107, 109Ag,nat, 108, 110Pd, and103Rh with58Ni accelerated by the linear accelerator UNILAC at GSI. After separation from the projectile beam by the velocity filter SHIP, the fusion products were implanted with their full recoil energy into a silicon surface barrier detector. The subsequent alpha decay of the implanted ions was measured with the same detector. In some of the experiments the evaporation residues were implanted into a position sensitive silicon surface barrier detector. With a newly developed position and time correlation technique parent daughter relationships, half lives, and branching ratios of a large number of isotopes could be determined. In the investigated reactions the eleven new isotopes161–164Re,160W,157–161Ta, and156Hf could be identified. The measuredQ values, half lives, and a branching ratios are discussed. Two new high energy. transitions of (7,40810) keV and (7,80415) keV were also found with half lives of 2.7 ms and 0.52 ms, respectively.A tentative mass and atomic number assignment givesA=153–156 andZ=70–72. The energies of the excited isomeric states are between 2 MeV and 3 MeV. From the systematics of alpha ground state transitions in even nuclei a hindrance of 105 can be deduced for both transitions, possibly indicating orbital angular momenta on the order of 10 for the alpha emitting states. The isomers are proposed to belong to shell model isomers beyond146Gd.
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The velocity filter SHIP installed at the UNILAC (GSI Darmstadt) is described. It is used for the investigation of neutron deficient nuclei generated by heavy ion induced fusion. The two stage filter separates unretarded reaction products emerging from a thin target with high efficiency and low background of primary beam particles. For reaction products covering an angular range of 3° in horizontal and vertical directions and a velocity range of 10% the transmission is between 30% and 60%. The separation time is of the order of 10−6s. High suppression of primary particles by factors of 107-1011 permits the investigation of reaction products in the direction of the primary beam. α-active reaction products have been implanted into a surface barrier detector and identified by their decay.A description of the ion optical principles, technical details and the performance of SHIP is given.
Atomic Data Nuclear Data Tables19
  • A H Wapstra
  • K Bos
  • S Liran
  • N Zeldes
  • C.-C Sahm
Sahm, C.-C. et al.: Z. Physik A297, 241(1980)
  • G Munzenberg
MUnzenberg, G., et al.: Nucl. Instrum. Meth. 161, 65 (1979)
Atomic~a Nuclear Data Tables 19
  • A H Wapstra
  • K Bos
  • S Liran
  • N Zeldes
Wapstra, A.H., Bos, K.: Atomic~a Nuclear Data Tables 19, 177 (1977); Liran, S. Zeldes, N.: Univ. Je~alem, Int. Rep. (1976)