recent nuclear structure and reaction dynamics studies using mutlinucleon transfer reactions paddy...
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Recent Nuclear Structure and Reaction Dynamics Studies Using Mutlinucleon Transfer Reactions
Paddy Regan
Dept. of Physics
University of Surrey,UK
E-mail: [email protected]
Laser Physics Letters 1 (2004) 317-324
Outline of Talk
• Thin target multinucleon transfer reactions:– 100Mo+136Xe : alignments, E-GOS plots and some reaction
mechanism info.– 198Pt+136Xe: 136Ba I=10+seniority isomers, effective charges and
some reaction mechanisms– 184W K-isomers and –4p transfer
• Future Aims/ Plans.– 170Dy (ish)– N=50 (ish)
Main physics interest in neutron-rich nuclei is based on the EVOLUTION OF SHELL STRUCTURE and the appearance of
‘large gaps in the nuclear single-particle spectrum’.
Reasons to study neutron-rich nuclei
1) Evolution of collective modes (vibrations, rotations, superdef ?) from spherical states by altering (N,Z,I, Ex).
2) Identification of specific nucleonic orbitals, e.g. via isomeric decays, g-factors, B(E2:I->I-2), effective charges, shell model descriptions, seniority schemes, deformed (Nilsson) schemes etc.
3) Identifying new nuclear ‘exotica’, e.g., the unexpected, beta-decaying high-spin states, new symmetries (e.g., 32), neutron ‘skins’, new shell closures, shape changes etc.
2)12( LModified from Introductory Nuclear Physics, Hodgson, Gadioli and Gadioli Erba, Oxford Press (2000) p509
Aim? To perform high-spin physics in stable and neutron rich nuclei. Problem: Fusion makes proton-rich nuclei.Solutions? (a)fragmentation (b) binary collisions/multi-nucleon transfer
See eg. Broda et al. Phys. Rev Lett. 74 (1995) p868Juutinen et al. Phys. Lett. 386B (1996) p80Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23Krolas et al. Acta. Phys. Pol. B27 (1996) p493Asztalos et al. Phys. Rev. C60 (1999) 044307
CCMMAX
MAX
TB
TLF
VER
L
LAA
L
2
2
31
2
1
1
7
2
:limit Rolling
-1
cos-1
by calculated then is correctionDoppler The
coscoscoscossinsinsinsin)cos(
where
)cos(r.r
by given is angleray -fragment/ the
k )cos( , j )sin()sin( ,i )cos()sin(
k, and j i, rsunit vectoCartesian For
2
2,1'
2121212112
122121
1,2
1,2
EE
rr
rzryrx
z
x
y
Simon et al., Nucl. Inst. Meth. A452, 205 (2000)
BLF
TLF
beam tlftlf
blfblf
Ge
TOF ~5-10 ns.ns-s isomers can de-excite in bestopped by CHICO position detector. Delayeds can still be viewedby GAMMASPHERE.
Rochester Group
100Mo + 136Xe @ 700 MeV GAMMASPHERE + CHICOPHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
Can see clearly to spins of 20ħ using thin-target technique.
Can we use the data from the CHICO+Gammasphere expt. to understand the ‘DIC’ reaction mechanism ? A wide range of spins & nuclei are observed.
Crossing and alignments well reproduced by CSM, although AHVs
24
24
2 :Rotor
0 : Vibrator
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242
),1(2
:Rotor
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:Vibrator
22
22
J
J
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n
JR
JR
J
JJER
JEJJE
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PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502
E-GOS plot appears to indicate that Vibrator-Rotator phase change is a feature of near stable (green) A~100 nuclei.
BUT….what is the microscopic basis ?
‘Rotational alignment’ can be a crossing between quasi-vibrational GSB & deformed rotational sequence.(stiffening of potential by population of high-j, equatorial (h11/2) orbitals).
PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502
50
82
[550]1/2-
1h11/2
1g9/2
[541]3/2-
What about odd-A nuclei….are the h11/2 bands ‘rotational’ ?
See PHR, Yamamoto, Beausang, Zamfir, Casten, Zhang et al., AIP Conf. Proc. 656 (2002) p422
‘Weak Coupling’
E/(I-j) E-GOS extension for odd-A
Suggests 11/2- band is anharmonic, -soft rotor?
BUT seems to work ok for +ve parity bandsvib ->rotor following(h11/2)2 crossing.
case. 0 even)-(even for the toreduces which
22
2
24 by, simplified becan This
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jI
E
jI
jRER
RKIRjI
jjIE
jIRjI
jE
jI
jI
I
I
I
EIR
jGOSE
j
jII
Carl Wheldon (HMI-Berlin) has suggested extension of E-GOS by ‘renormalising’ the rotational energies at the bandhead.
If the band-head spin of a sequence is given by j then substituting Ij in place of I, one obtains,
seems to work ok, h11/2 bands now look like rotors,
Even-Even yrast sequences and odd-A +ve parity only show rotational behaviour after (h11/2 )2 crossing….
R.Broda et al., Phys. Rev. C49 (1994)
0
10
20
30
40
50
%>Ecoul
Ltlf (roll)
v/c graz tlf
Linear(%>Ecoul)
0
10
20
30
40
50
60
620 648 677 705 733 761 790E_beam (MeV)
blf_graz
tlf_graz
lmax/10
Kinematics and angular mom. input calcs (assumes ‘rolling mode’) for 136Xe beam on 100Mo target.
Estimate ~ 25hbar in TLFfor ~25% above Coul. barrier. For Eb(136Xe)~750 MeV, in labblf~30o and tlf~50o.
100Mo +136Xe (beam) DIC calcs.
+2p
-2n
+2n
Fold distributions highlight different reaction mechanisms
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
Wilczynski (‘Q-value loss) Plot A.D.Yamamoto, Surrey PhD thesis (2004)
Emission angle of TLFs can give information/selection on reaction mechanism (and maybe spins input ?)
TLFs
BLFs
elastics
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
Gating on anglegives a dramatic channel selection in terms of population.
Relative Intensitiesof 6+->4+ yrast transitions in TLFs (relative to 100Mo) for 136Xe beam on 100Mo target at GAMMASPHERE+ CHICO.
198Pt +136Xe, 850 MeV
J.J. Valiente-Dobon, PHR,C.Wheldon et al., Phys. Rev.C69 (2004) 024316
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85
59585756555453525150
757473
76
8483828180797877
N/Z compound
nano and microsecond isomerson gated 198Pt+136Xe withGAMMASPHERE+CHICODIC 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124
J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313136Xe+198Pt reaction beam-like fragment isomers.
131I
133I
128Te
130Te 136Xe
132Xe
138Ba
137La
136Xe+198Pt Target-like fragment isomers
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313
184W
185Re
191Os
192Os
195Os
192Pt
198Pt
193Au
PHR, Valiente-Dobon, Wheldon et al., Laser Phys Letts. 1 (2004) 317
Can see 184-194Os in binary partner channels. i.e.in 2p transfer, up to 14 neutrons evaporated. ( 4n -> 194Os is heaviest known).
198Pt, 2+
136Xe, 2+
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313
138Ce 125Sb
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313
Identification of new ‘seniority’ isomer in 136Ba, N=80 isotone.
J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316
T1/2=91(2) ns
N=80 isotonic chain, 10+ isomers, (h11/2)-2I=10+
Q. Why does Ex(10+) increase while E(2+) decreases ? 91(2) ns
Structure of 8+ final state changes from 134Xe -> 136Ba ?See Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) 024313
Isomer decayalso depends on structureof final state
N=80, (h11/2)-210+ isomers
Energy of N=80 I=10+ isomers correlates with energy increaseof 11/2- singleneutron in N=81 isotones.
Increase in 10+ energy, plusexpansion of proton valencespace means8+ yrast state now (mostly)NOT (h11/2)-2
for Z>54
N=81
N=80
Ex, I=11/2 -
Ex, I=10
Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) 024313
Pair Truncated Shell Model
Calculations (by Yoshinaga,Higashiyama et al. Saitama)predict yrast 8+ in 136Ba no longer mostly (h11/2)-2
but rather, (d5/2)2(g7/2)2
0.000
0.963
2.760
g7/2
d5/2
h11/2 Protons, max. seniority 2spin = 6 ħ (from (g7/2)2.
Seniority 4 states though can have up to7/2 + 5/2 + 5/2 +3/2 = 10 ħ
Expect neutron ‘seniority scheme’for (h11/2)-2 ‘j2’ mutlipletconfiguration at N=80 (e.g. 130Sn).
132Te, 134Xe have proton excitationsdue to g7/2, d5/2 at 0+,2+,4+,6+ but not competing 8ħ and 10ħ states.
Extra collectivity for higher-Z pushes down 0+ and 2+.
Proton s.p. energiesused in 136Ba SM calcs
Search for long (>100ms) K-isomers in neutron-rich(ish) A~180 nuclei.
low-K high-K mid-K j
K
:rule sel. -K
Walker and Dracoulis Nature 399 (1999) p35
(Stable beam) fusion limit makes high-K in neutronrich hard to synthesise
also a good number for K-isomers.
170Dy, double mid-shell, ‘purest’ K-isomer ? (see PHR, Oi, Walker, Stevenson and Rath, Phys. Rev. C65 (2002) 037302)
Max at 170Dy
K=6+state favoured
,
1
21
exp
21
WT
Tf
Best K-isomer?Doubly-mid-shell nucleus, 170DyN=104, Z=66 (Np.Nn=352=Maximum!).Appears to be a correlation betweenf values and NpNn for K=6+ isomers in A~180 region.(see PHR, Oi, Walker, Stevenson & Rath, Phys. Rev. C65 (2002) 037302)
Extrapolation suggestsisomer in 170Dy lives forhours….could be beta-decay candidate.
172Hf, 174Yb, 174Hf, 176Hf, 178Hf, 178W K=6+ isomers
170Dy ?
N=104 isotones, K=6+ energy
Try at PRISMA in 2005
International ConferenceOn NUclear STructure, Astrophysics & Reactions University of Surrey, Guildford, UK5-8 January 2005Payment deadline last Friday (1st October)
http://www.ph.surrey.ac.uk/cnrp/nustar05