the synthesis of super heavy elements
TRANSCRIPT
The Synthesis of Super Heavy Elements (SHE)
D. Ackermann, University of Mainz/GSI
Future of Gamma Spectroscopy at LNL: GASP and CLARA Arrays
GAMMA2004
March 3rd 2004
• requirements for the synthesis of SHE
• reaction mechanism studies• fusion/fission excitation function → SHIP, MAIALE+CORSET…• the CN spin distribution → GASP+inner ball, GAMMASPHERE…
• nuclear structure of the SHE: spectroscopy tools • in beam (RDT + γ-γ) → RITU, FMA, PRISMA(gas filled)+CLARA…• ER-α-α/-α-γ(-γ) after separation → SHIP, RITU+GREAT, PRISMA(gas filled)…
• an interesting example: 270Ds
• the basic technical requirement: beam intensity
• CW accelerator• UNILAC upgrade – a first step
208Pb
region der spherically shell stabilised nuclei(„island of stability“)
region of deformed shell stabilised nuclei around Z=108 and N=162
at GSI: Elements 107-112first synthesisedand unambiguouslyidentified
107 – Bh108 – Hs109 – Mt
Shell Correction Energies Eshell in the Region of Superheavy Elements
P. Möller et al.
element 110 recently named
Darmstadtium – Ds
• IUPAC decision - August 2003
• Baptized - December 2003
The 2-step process Fusion - Evaporation
220.0 230.0 240.0 250.0 260.010
-9
10-7
10-5
10-3
10-1
101
Elab [MeV]
σ[m
bar
n]
50Ti + 208Pb ⇒ 258Rf*(HIVAP calculations)
fusion
fission
3n1n 2n
evaporation residues
≈5-7 orders of magnitude
1. CN formation• entrance channel
properties (nuclear structure, deformation…)
2. ER formation• survival • fission competition • vibration-rotation
probes: • Fusion-fission
excitation function (fission and ER-production)
• -distribution...
F.P. Heßberger
Fusion Dynamics and the Spin Distribution
fusionevaporation
fusionfissioncompetition
σ
range of barriers
3n
1n2n
ER
survival via“rotationalstabilisation”?fission ( +1)
Erot( )=2µRb
2
2
Fusion Dynamics and the Spin Distribution
Vb = VCoulomb + VNucl + V
( +1)Erot( )=
2µRb2
0 < < crit
0
crit
Eshell´ = crit < ´crit
compound system entrance channel
r
Vb
2
1 GASP – inner ball (80 BGO-crystals)
CN = (Mγ - Mγs)∆ γ + Mγs∆ γs + iMi∆ i + ∆ gs/m ; i = p, n, α
γ-ray fold
GASP response function
2 GASP – high resolution Ge-detectors
Eγ
3 statistical model(codes like PACE, EVAP,
HIVAP…)
evaporation parameters
Mγ
ER identification spin removed by particles and statistical
γ-rays
Experimental Approach to the Spin Distribution with GASP
Reactions with deformed targets leading to CN in Z = 82 Region
36S+180Hf → 216Ra*34S+168,170Er → 202,204Po*
32S+164Dy → 196Pb*
48Ti+150Nd → 198Pb*
48Ca+150Nd → 198Hg*
→Features to investigate via fusion/fission excitation function and spin distribution
• can rotation stabilize the compound system?σl• the competition of fission and evaporationσfus/fis+σl• the role of deformation for heavy CNσfus/fis+σl• the effect of the shell Z=82 on fusionσfus/fis+σl
48Ca+168Er → 216Ra*48Ca+164Dy → 212Rn*
48Ca+144,154Sm → 192,202Pb*
Fold Distributions with GASP for 64Ni+100Mo
260 MeV
3n
5n
6n
4n
∆fold ≈ 9
246 MeV
2n
4n3n
∆fold ≈ 18
D.Ackermann et al., J. Phys. G 23 (1997)
64Ni+100MoANL/Notre Dame BGO array
260MeV246MeV
∆ ≈ 20
∆ ≈ 10
Fold Distributions with GASP for 34s+170Er → 204Po*
0,0
2,0x104
4,0x104
6,0x104
0,0
5,0x104
1,0x105
1,5x105
2,0x105
0 5 10 15 20 250,0
5,0x104
1,0x105
1,5x105
2,0x105
144 MeV
168 MeV
158 MeV
Yie
ld
3n 4n
34S+170Er
3n 4n 5n
5n 6n
γ ray fold
GASP – inner ball (80 BGO-crystals)
Collaboration for Spin-Distribution Measurements
GSI:S. HofmannF.P. HeßbergerG. Münzenberg (Uni Mainz)M. RuanD. A. (Uni Mainz)
M.G. ItkisG.N. KniajevaE.M. KozulinYu.Ts. OganessianR.N. Sagaidak
FLNR, JINR, Dubna
INFN PadovaD. BazzaccoS. BeghiniE. FarneaR. MenegazzoC. Rossi-AlvarezC. Ur
Univ. Padova
G. MontagnoliF. Scarlassara
Comenius Univ. Bratislava
S. AntalicG. Berek
LNLM. AxiotisL. CorradiG. De AngelisA. GadeaV. KumarA. LatinaN. MargineanT. MartinezA.M. StefaniniS. SzilnerM. Trotta
Nuclear Structure of the Heaviest Nuclei I: ER-α-α Coincidences: 251No
F.P. Heßberger et al., submitted to EPJ A
Nuclear Structure of the Heaviest Nuclei II: ER-α-α Coincidences: 257DbF.P. Heßberger et al., Eur. Phys. J. A 12, 57-67 (2001)
S. Cwiok, S. HofmannAnd W. NazarewiczNPA A575 (1994)
Experiment:α-α-coincidences
Nuclear Structure of the Heaviest Nuclei III:ER-α-γ Coincidences: 255Rf/253No
F.P. Heßberger, Symposium on Nuclear Clusters, Rauischholzhausen Germany, August 2002
The even-even Isotope 270110 and its decay products 266Hs und 262Sg
8 decay chains:• 2 types with different τα(270110): 0.15ms and 8.6 ms• 3 out of 4 chains complete of the typ:
α-α-fission• 1 γ-ray (218 keV) coincident to the mother decay in chain #7• 7 days of irradiation ⇒ σ = (13±5) pbarn
(for comparison σ(269110) = 15 pbarn)
S. Hofmann et al., Eur. Phys. J. A 10, 2001
k-isomer and Tentative Decay Scheme for 270110
S. Ćwiok and P.-H. Heenen
162
ν[725]11/2-
ν[615]9/2+
ν[613]7/2+
1.34 MeV∆I = 10-
162
ν[725]11/2-
ν[615]9/2+
ν[613]7/2+
1.31 MeV∆I = 9-
Fermi
level
neutrons
tentative decay scheme
270110
266Hs
S. Hofmann et al., Eur. Phys. J. A 10, 2001
Project for a superconducting CW-linacU.Ratzinger et al., University of Frankfurt
• dc beam• 1 < A/q < 7• Ebeam: 4-7.5 MeV/u• ∆Ebeam < ± 3keV/u
Intensity gain:
• Duty cycle 30%→100% 3.5• 28 GHz ECR-source 5-10increased stability (65% → 85)% 1.3• shorter shutdowns (107 d/y → 47 d/y) 1.2
Total gain 25-55
0 5 10 15 20
Z / m
EnergyMeV/u
1.8 2.4 3.3 4.2 5.2 6.1 7.1
CH DTL, supercond.324 MHz 108 MHz
DebuncherIH DTL,108 MHz
1.40.30.003
25 30
RFQ,108 MHz
ECR source
QWR Cavities
normalconducting
superconducting
superconducting
New 28 GHZ ECR Ion SourceGoals : Increasing the average beam intensity on target
Higher intensity in high charge statesHigher duty factor in linac
Semi-empirical scaling law: I(Aq+) ∼ ωECR2
➨ increase of microwave frequency➨ higher magnetic flux density (superconducting)
20 25 30 35 40 45 500,1
1
10
100
1000
inte
nsity
(eµA
)
Xe charge state
28 GHz SC-ECRIS (2007)(extrapolated)
14 GHz GSI-CAPRICE II (1990)
New Front-end for the High Charge State Injector
New RFQ-structure:• gain of the duty factor• higher injection energy• increased acceptance
Additional 28 GHz-ion-source:• intensity gain of factor two• higher charge states for increased duty factor
LEBT – Laminated magnets:• redundance for ion sources• preparation for future pulse to pulse operation with different ion-species
50% duty factor → intensity-gain factor x2
High Duty Cycle RF-Operation of the GSI- High Charge State Injector (HLI) and the Alvarez-accelerator
Rebuncher
Alvarez
Presently:duty factor (beam)= 25 % (rf: 35 %),A/ξ ≤ 8
Upgrade:(new RFQ-structure, higher charge state from 28 GHz-ECR)
A/ξ ≤ 6.5, duty factor = 50 % (rf: 60 %)
Performance of all rf-tube-amplifiers ([email protected] MW, IH+RFQ+Single Gap@200 kW, Rebuncher@ 4 kW) is sufficient to meet the requirements
Rebuncher
The SHIP group
GSI: The collaboration
JINR-FLNR Dubna, Russia:
A.G. PopekoA.V. Yeremin
University Bratislava, Slovakia
Š. ŠaroS. Antalic (Ph.D. student)G. Berek (Ph.D. student)B. Streicher (Ph.D. student)
University Jyväskylä, Finland:
M. LeinoJ. Uusitalo
S. HofmannF.P. HeßbergerR. MannG. Münzenberg (Univ. Mainz)P. Kuusiniemi (Postdoc)B. Sulignano (Ph.D. student)D. A. (Univ. Mainz)
B. Lommel (targetlab)B. Kindler (targetlab)
H.-G. Burkhard (mechanics)H.-J. Schött (elektronics)