Study of multinucleon transfer (MNT) reactions of 136 Xe Pt for production of exotic nuclei

Transcription

1 16 th ASRC International Workshop Mar. 19, 2014 Study of multinucleon transfer (MNT) reactions of 136 Xe Pt for production of exotic nuclei Contents Y.X. Watanabe (KEK) 1. Introduction (MNT reactions for nuclear production) 2. KEK isotope separation system (KISS) 3. MNT measurements of 136 Xe Pt 4. Summary 1

2 Nuclear production by MNT reactions Xe Pb (E cm = 700 MeV) n-stripping Xe Pb (E cm = 700 MeV) p-stripping (from projectile to target) 154 Xe p-pickup 136 Xe 118 Xe n-pickup (from target to projectile) 136 Xe Pb (E cm = 450 MeV) C.H. Dasso et al., Phys. Rev. Lett. 73, 1907 (1994). V. Zagrebaev and W. Greiner, Phys. Rev. Lett. 101, (2008). L. Corradi et al., J. Phys. G: Nucl. Part. Phys. 36, (2009). 2

3 Neutron-rich nuclei around N=126 Atomic number Neutron number H. Grawe et al., Rept. Prog. Phys. 70 (2007)1525. Lifetime measurements around N=126 Astrophysical environments for r-process atomic number Hg 194 Pt 195 Pt 196 Pt 193 Ir 192 Os years T 1/2 30 days T 1/2 < years 10 minutes T 1/2 < 30 days T 1/2 < 10 minutes unknown 198 Pt 203 Tl 198 Hg 199 Hg 200 Hg 201 Hg 202 Hg 197 Au p-pickup 204 Pb MNT 206 Pb 207 Pb 208 Pb 205 Tl 204 Hg 136 Xe Pt n-stripping 207 Tl 206 Hg 205 Au 204 Pt 203 Ir 202 Os 201 Re 200 W neutron number 3

4 MNT reactions of 136 Xe Pt GRAZING calculation A. Winther, Nuclear Physics A572, 191 (1994); A. Winther, Nuclear Physics A594, 203 (1995). TLF: 136 Xe Pt (8 MeV/A) σ (mb) 136 Xe : 2 pna 198 Pt : 7.2 mg/cm pps for 202 Os 0.1 pps for 200 W Atomic number 198 Pt 202 Os Low and broad energies Large and broad emission angles Efficient collection using a gas cell system Large contamination of isobars 202 Os ~ 0.3% Contamination ~ 99.7% Z selection Neutron number N=126: The production channels are rare channels The separation of A and Z is essential for the measurement of rare channel products. Laser Ion-source with argon gas-cell 4

5 KEK isotope separation system (KISS) Detection system 3 detection stations Tape-transport system Multi-layered plastic scintillators Ge detectors β-decay measurements E2 & E3 experimental halls in RIKEN Nishina Research Center Mass separator (A selection) Extraction chamber High voltage (30 kv) All apparatus except for detection system was already installed. Under commissioning for efficiency and selectivity. Gas catcher system Target ( 198 Pt) MNT reaction Gas cell (Ar gas, neutralization) Laser resonance ionization (Z selection) 5

6 MNT reactions 64 Ni (6.1 MeV/A) U L. Corradi et al., Physical Review C59 (1999) p +1p projectile-like fragments 6p 5p 4p 3p 2p 1p 0p Measurements Calculations (GRAZING) Discrepancy of centroids of the isotopic distributions and absolute cross sections of them becomes larger as number of transferred protons increase 6

7 MNT measurements of 136 Xe Pt at GANIL 198 Pt (1.3 mg/cm 2 ) Target MWPPAC Quadrupoles VAMOS++ EXOGAM 10 CLOVER detectors grazing angle TLF γ-rays 500 kev total photo-peak efficiency 10% MWPPAC Drift Chambers 2 Ionization Chamber Silicon Wall PLF Trajectory Path length, Angles (θ, φ), Bρ Velocity Energy loss Total kinetic energy Q, Mass, Z 7

8 Charge and mass distributions of PLF Q / Q ~ 1 / 70 M / M ~ 1 / 200 M / Q = Bρ / v Q = 2 E / Bρ v M = Q i M / Q 8

9 600 Z identification of PLF de(mev) Z Energy (MeV) Energy (MeV) Z / Z ~ 1 / Z 9

10 65 Z -Adistribution of PLF 136 Xe Pt (8 MeV/A) Atomic number n-stripping p-pickup 136 Xe Ni Pb (6.1 MeV/A) n-pickup 58 Ni Mass number Contribution of p-pickup and n-stripping channels was observed. c.f. n-pickup and p-stripping channels dominate in 58 Ni Pb. L. Corradi et al., Phys. Rev. C66, (2002) 10

11 Isotopic distributions of PLF (0, ±1p, ±2p transfer) σ(a.u.) 0n Measurements Correction for missing events GRAZING before evaporation GRAZING after evaporation p-pickup: Larger cross section Heavier distribution 1p +1p σ(a.u.) σ(a.u.) σ(a.u.) 2p σ(a.u.) +2p 11

12 Isotopic distributions of PLF (±3p, ±4p transfer) 3p +3p σ(a.u.) σ(a.u.) σ(a.u.) 4p σ(a.u.) +4p E lab = 8 MeV/A (55% higher than the Coulomb barrier) Highly damped collision Large contribution of neutron evaporation Measurements Correction for missing events GRAZING before evaporation GRAZING after evaporation 12

13 TKEL (MeV) All events Z -Ndistribution of PLF for different TKEL θ(degree) TKEL = MeV Pure binary kinematics was assumed Evolution of Z-N distribution (50 MeV window) Z/N equilibrium (compound system) TKEL = MeV TKEL = MeV TKEL = MeV TKEL = MeV TKEL = MeV TKEL = MeV 13

14 Z -Ndistribution of PLF at low TKEL TKEL = MeV Almost no neutron transfer is favored on average. Proton pickup is a little bit favored. 14

15 Evolution of centroids of distributions 300 MeV TKEL 0 TKEL MeV Measurements Derived primary centroids (Evaporation energy: 12 MeV/neutron) TKEL = 300 MeV : PLF s are populated along the Z/ Nequilibrium line Neutron stripping (pickup) accompanies proton stripping (pickup) 15

16 Derived Z -Ndistribution of TLF for different TKEL All events TKEL (MeV) θ(degree) TKEL = MeV Z/N equilibrium TKEL = MeV TKEL = MeV TKEL = MeV TKEL = MeV TKEL = MeV TKEL = MeV 16

17 Summary MNT reactions have been proposed for production of exotic nuclei We are advancing the KISS project Lifetime measurements around N=126 nuclei from astrophysical interest Nuclear production by the MNT reaction between 136 Xe and 198 Pt MNT measurements were performed at GANIL for 136 Xe Pt reaction PLF s were detected by VAMOS : Q/ Q= 1 / 70, M/ M= 1 / 200, Z/ Z= 1 / 60 Z-A distribution Contribution of p-pickup and n-stripping channels was observed Isotopic distributions were deduced for each proton transfer channel p-pickup channels larger than p-stripping channels were observed Neutron stripping (pickup) seems to accompany proton stripping (pickup) on average Evolution of isotopic distributions as increasing TKEL were studied Distribution gradually evolves from quasi-elastic regime to deep-inelastic regime Lower TKEL (~0) : Proton pickup is a little bit favored Almost no correlation between neutron transfer and proton transfer High TKEL (~300 MeV): In parallel to Z-N equilibrium of compound system Large effect of neutron evaporation Neutron stripping (pickup) accompanies proton stripping (pickup) according to Z-N ratio of the compound system Low TKEL reaction would contribute to the production of neutron-rich TLF s 17

18 Collaboration KISS project KEK Y. Hirayama, N. Imai, H. Ishiyama, S.C. Jeong, H. Miyatake, M. Oyaizu, Y.X. Watanabe Seoul National University Y.H.Kim Tsukuba University M. Mukai, S. Kimura RIKEN M. Wada, T. Sonoda K.U. Leuven P. Van Duppen, Yu. Kudryavtsev, M. Huyse MNT measurements at GANIL KEK Y. Hirayama, N. Imai, H. Ishiyama, S.C. Jeong, H. Miyatake, Y.X. Watanabe Seoul National University S.H. Choi, Y.H. Kim, J.S. Song GANIL M. Rejmund, C. Schmitt, A. Navin, G. de France, E. Clement Torino University G. Pollarolo LNL L. Corradi, E. Fioretto Padova University D. Montanari IPN M. Niikura, D. Suzuki Osaka University H. Nishibata, J. Takatsu 18