Transcript Document 7538403

Future Challenges Using Decay
Spectroscopy with Projectile
Fragmentation and In-Beam Deep
Inelastic Reactions
Paddy Regan
Dept. of Physics
University of Surrey,UK
E-mail: [email protected]
Outline of Talk
• (Some) Physics questions in heavy neutron-rich nuclei.
• Thin target multinucleon transfer reactions:
–
–
100Mo+136Xe
: reaction mechanism info.
198Pt+136Xe: 136Ba Ip=10+seniority isomers, effective charges.
• Projectile-fragmentation isomer spectroscopy.
– The Stopped Beam RISING Campaign, some physics aims.
– g-factors and BaF2 timing below isomers.
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,Ip, 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., a32),
neutron ‘skins’, new shell closures, shape changes etc.
How do we study the heavy neutron-rich ?
• Multi-nucleon transfer reactions:
– Backed/thick target technique (made famous by Broda, Fornal,
Krolas (Crakow group) + Daly, Janssens, Khoo, Lunardi et al.,)
• Projectile-fragmentation reactions:
– Isomer spectroscopy (made famous by Pfützner, Rykaczewski,
Grzywacz, Janas, Lewitowicz et al., & the Warsaw Group).
In both cases, the reaction mechanism is not fully
studied and experiments are needed in order to
set the limits of both of these techniques.
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
Rolling limit :
Modified from Introductory
Nuclear Physics, Hodgson,
Gadioli and Gadioli Erba,
Oxford Press (2000) p509
LTLF
2
1
 
7  1   AB AT 1
LMAX
2 R 2
ECM  VC 

2

(2 L  1)p 2

L
3  MAX

See eg.
Broda et al. Phys. Rev Lett. 74 (1995) p868
Juutinen et al. Phys. Lett. 386B (1996) p80
Wheldon et al. Phys. Lett. 425B (1998) p239
Cocks et al. J. Phys. G26 (2000) p23
Krolas et al. Acta. Phys. Pol. B27 (1996) p493
Asztalos et al. Phys. Rev. C60 (1999) 044307
For Cartesian unit vecto rs i, j and k,
x  r sin(  ) cos( ) i , y  r sin(  ) sin(  ) j , z  r cos( ) k
the fragment/  - ray angle is given by
r1.r2  r1r2 cos(12 )
where
cos(12 )  sin 1sin  2 sin 1sin 2  cos1 cos 2   cos1cos 2
The Doppler correction is then calculated by
z
E  E
'
1 -  cos
1 -  
1,2
1, 2
2
1,2
2
y
2
1
1
x
Simon et al., Nucl. Inst. Meth. A452, 205 (2000)
Ge
TLF
beam
Rochester Group
tlf,tlf
blf,blf
BLF
TOF ~5-10 ns.
ns-s isomers can
de-excite in be
stopped by CHICO
position detector. Delayed
s can still be viewed
by GAMMASPHERE.
100Mo
+ 136Xe @ 700 MeV GAMMASPHERE + CHICO
PHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329
Can we use the data from the CHICO+Gammasphere expt.
to understand the ‘DIC’ reaction mechanism ?
A wide range of spins & nuclei are observed.
R.Broda et al., Phys. Rev. C49 (1994)
Wilczynski (‘Q-value loss) Plot
A.D.Yamamoto,
Surrey PhD thesis (2004)
Gating on angle
gives a dramatic
channel selection in
terms of population.
Relative Intensities
of 6+->4+ yrast
transitions in
TLFs (relative to
100Mo) for 136Xe
beam on 100Mo
target at
GAMMASPHERE
+ CHICO.
Fold distributions highlight different reaction mechanisms
+2p
-2n
+2n
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
Emission angle of TLFs can give information/selection
on reaction mechanism (and maybe spins input ?)
198Pt
+136Xe, 850 MeV
J.J. Valiente-Dobon, PHR,
C.Wheldon et al., Phys. Rev.
C69 (2004) 024316
J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316
84
nano and microsecond isomers
83
on gated 198Pt+136Xe with
82
GAMMASPHERE+CHICO
110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 81
DIC
80
79
78
77
76
75
74
73
N/Z compound
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85
59
58
57
56
55
54
53
52
51
50
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313
136Xe+198Pt reaction beam-like fragment isomers.
128Te
130Te
131I
133I
132Xe
136Xe
138Ba
137La
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313
136Xe+198Pt Target-like fragment isomers
184W
195Os
185Re
192Pt
191Os
198Pt
192Os
193Au
Identification of new ‘seniority’ isomer in 136Ba, N=80 isotone.
T1/2=91(2) ns
J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316
N=80 isotonic chain, 10+ isomers, (nh11/2)-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 decay
also depends
on structure
of final state
N=80, (nh11/2)-210+ isomers
Ex, Ip=11/2 N=81
Ex, Ip=10
N=80
Energy of N=80
Ip=10+ isomers
correlates with
energy increase
of 11/2- single
neutron in
N=81 isotones.
Increase in 10+
energy, plus
expansion of
proton valence
space means
8+ yrast state
now (mostly)
NOT (nh11/2)-2
for Z>54
Pair Truncated Shell Model
Calculations (by Yoshinaga,
Higashiyama et al. Saitama)
predict yrast 8+ in 136Ba
no longer mostly (nh11/2)-2
but rather, (pd5/2)2(pg7/2)2
Expect neutron ‘seniority scheme’
for (nh11/2)-2 ‘j2’ mutliplet
configuration at N=80 (e.g. 130Sn).
132Te, 134Xe
have proton excitations
due 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. energies
used in 136Ba SM calcs
h11/2
2.760
d5/2
0.963
g7/2
0.000
Protons, max. seniority 2
spin = 6 ħ (from (pg7/2)2.
Seniority 4 states though
can have up to
7/2 + 5/2 + 5/2 +3/2 = 10 ħ
Production target
In-Flight Technique Using Projectile Fragmentation
Central focus, S2
Final focus, S4
primary beam
Pb @ 1GeV/u
TO F  
dipole, B
A Be

Q cu
degrader
degrader
scint
MW=x,y
scint
catcher
DE(Z2)
Use FRS@GSI or LISE3@GANIL to ID nuclei.
Transport some in isomeric states (TOF~ x00ns).
Stop and correlate isomeric decays with nuclei id.
eg. R. Grzywacz et al. Phys. Rev. C55 (1997) p1126 -> LISE
C.Chandler et al. Phys. Rev. C61 (2000) 044309 -> LISE
M. Pfützner et al. Phys. Lett. B444 (1998) p32 -> FRS
Zs. Podolyak et al. Phys. Lett. B491 (2000) p225 -> FRS
M. Pfützner et al. Phys Rev. C65 (2002) 064604 -> FRS
scint
(veto)
8+ isomer in 78Zn,
real evidence of
78Ni shell closure.
J.M.Daugas et al.
Phys. Lett.
B476 (2000) p213
Heaviest odd-odd,N=Z gammas, isobaric analog states ?
86Tc, C. Chandler et al. Phys. Rev. C61 (2000) 044309
Can perform
spectroscopy at
rates of few ions
per hour.
M. Mineva et al. Eur. Phys. J. A11 (2001) 9
135Te
136Sb
Use FRS to select projectile
fission products (forward
boosted ones). Note
transmission a few %.
T1/2=565(50) ns state in
136Sb (Z=51, N=85)
Prompt ‘flash’ is a limiting
problem for isomer
Fragmentation.
Reduces effective Ge
efficiency by factor of 3-4 !
(Partial) Solution ?
Use a low-Z (e.g., plastic stopper)
Background from the stopping down of the fast ions:
Simulated by
P. Detistov Surrey/Sofia
M.Pfutzner,M.Hellstrom et al.
208Pb
217Ac,
215Ra,
212Po,
29/2+, 1μs
43/2-, 800ns
18+, 65s
many μs isomers
expected
N=126, holes in 208Pb
region
(pg9/2)-2 ‘2j’ multiplet
(and isomer) in
130Cd (Z=48, N=82)
should look like
98Cd (Z=48, N=50)
A real test of valence
anaolgue scheme.
Do with fission fragments.
(pg9/2)-2
Best K-isomer?
Doubly-mid-shell nucleus, 170Dy
N=104, Z=66 (Np.Nn=352=Maximum!).
Appears to be a correlation between
fn values and NpNn for K=6+ isomers
in A~180 region.
(see PHR, Oi, Walker, Stevenson & Rath,
Phys. Rev. C65 (2002) 037302)
170Dy
 T1
fn   2 W
 T1
 2
exp
1
n
 ,


n  D  
Extrapolation suggests
isomer in 170Dy lives for
hours….could be
beta-decay candidate.
?
N=104 isotones,
K=6+ energy
172Hf, 174Yb, 174Hf, 176Hf,
178Hf, 178W
K=6+ isomers
Xu, Regan, Walker et al
First id of ‘doubly mid-shell’
nucleus, 170Dy (N=104, Z=66).
Data from M.Caamano et al.
33 ns isomer in 195Os (last
stable 192Os), useful test of
structure in prolate/oblate
shape coexistence region.
194Os Wheldon et al. Phys.
Rev. C63 (2001) 011304(R)
BaF2 ‘fast timing’ data from H. Mach et al. Contribution to ENAM 2001
Allows an ordering of the
gammas under isomer
from their (~ps) lifetimes.
From Henryk Mach et al., 96Pd.
Use (BaF2,BaF2) coincidences below isomers to get B(E2) values
( & order gamma-transitions)
96Pd
H. Mach et al.,
g-factors from fragmentation
isomers
Basic idea, put isomer in B-field.
Perturbation of gamma-ray
angular distribution depends on
induced Torque.
Rate of precession gives Larmor
frequency, which gives g-factor.
‘Wiggles’ in count ratio between
different angles from 13/2+ isomer,
T1/2= 354(2)ns in 69Cu.
G.Georgiev EPJA20 (2004) p93;
See poster by Steve Mallion
J. Phys. G28 (2003) p2993
50 delegates, ~ 20 presentations, 4 working groups…..
Stopped Beam Physics Workshop, Guildford 29-30th March 2004
Major campaign using ‘retired euroball’ detectors
for fragmentation-based nuclear
spectroscopy.
Stopped-Beam Campaign to
study decays from isomers and
following beta-decay.
First call for proposals (deadline was last week),
three proposals initially submitted for ‘isomer only’ study
1) A~110 neutron-rich Zr,Mo,Ru,Pd (Alison Bruce)
2) A~140 proton drip-line, proton decay daughters (Dave Cullen)
3) N=126, ‘south’ of 208Pb (Zsolt Podolyak)
+ g-factor letter of intent (Gerda Neyens)
‘Active stopper’ experiment planned for next EA (170Dy, 130Cd, etc.)
International Conference
On NUclear STructure,
Astrophysics &
Reactions
University of Surrey,
Guildford, UK
5-8 January 2005
http://www.ph.surrey.ac.uk/cnrp/nustar05
Happy Birthday Rafal !!
PHR, Valiente-Dobon, Wheldon et al., Laser Phys Letts. 1 (2004) 317
Crossing and alignments well reproduced by CSM, although AHVs
Smith, Walker et al., Phys. Rev.
C68 (2003) 031302
50
Kinematics and angular mom.
input calcs (assumes ‘rolling
mode’) for 136Xe beam on
100Mo target.
40
%>Ecoul
30
Ltlf (roll)
20
10
79
0
73
3
0
62
0
Linear
(%>Ecoul)
Estimate ~ 25hbar in TLF
for ~25% above Coul. barrier.
For Eb(136Xe)~750 MeV, in lab
blf~30o and tlf~50o.
67
7
v/c graz tlf
60
100Mo
+136Xe (beam)
DIC calcs.
50
blf_graz
40
tlf_graz
lmax/10
30
20
10
0
E_beam (MeV)
620 648 677 705 733 761 790
Gamma-gamma analysis on 200Pt
isomer (21 ns!), M. Caamano et al.
Nucl. Phys. A682 (2001) p223c;
Acta Phys. Pol. B32 (2001) p763
stripping effect to extend lifetime
Z. Podolyak et al.,
Low spin
~1 ms
PROTON RICH
I=43/2
76Rb
69Se
67Ge
Chandler et al. Phys. Rev.
C61 (2000) 044309
Search for long (>100ms) K-isomers in neutron-rich(ish) A~180 nuclei.
high-K
mid-K
j
low-K
K
Walker and Dracoulis
Nature 399 (1999) p35
K - sel. rule :
D  D
N104 also a
good number
for K-isomers.
(Stable beam) fusion limit
makes high-K in neutron
rich hard to synthesise
Prompt flash knocks out a large
portion of the detectors….effectively
reduces the gamma efficiency by upto
80%! Need digital electronics and time
stamping
M. de Jong et al. Nucl. Phys. A613 (1997) p435
 J ( J  1) 
2J 1
 ,
Pj 
exp  
2
2

2 fj
2 f 

 2  2 / 3 DA3 Ap  DA
2
 f  0.01781    Ap
Ap  1
 3 
sharp cut - off model predicts isomer ratio,
 J ( J  1) 

Rth   Pj dJ  exp  
2


Jm
2

f



M. Pfutzner et al. Phys Rev. C65, 064604 (2002)
Isomeric Ratio Calculations
M. Pfutzner et al.
Phys Rev. C65, 064604 (2002)
R
N  (1  a tot )
N imp eff b FG
,
  TOF1

TOF
2
F  exp   q1
 q 2
 
1
 2 
 
 1
1  2
G  exp  i ti   exp  t f 
  
0
i
bi
i
1  a tot
Pfutzner, Hellstrom, Mineva et al.
J
Vibrator : En  n   , E  
2
2
2


Rotor : E J 
J ( J  1), E  4 J  2
2
2
R
E ( J  J  2)
J
 J 
Vibrator : R 

 0
J
 2 
2 
2  J 
Rotor : R   4   
 4 
2 
J
 2 
PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502
E-GOS plot appears to
indicate that VibratorRotator 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 quasivibrational 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
82
1h11/2
50
[550]1/2-
1g9/2
[541]3/2-
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 bands
vib ->rotor following
(nh11/2)2 crossing.
What about odd-A nuclei….are the nh11/2 bands ‘rotational’ ?
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 Ij in place of I, one obtains,
 2 

E   4 j
2
2
E  4 I  2 I  I  j  4I  j   2
2 

R I  



 R I  j 
I
2 I 
2 I  j 
Ij
  2  E I  j  2  j 
 
This can be simplified by,  4
 R I  K  2   R j  2
I  j  2
 2 
E  jR j  2
E
 RE  GOS 
which reduces to
for the (even - even) j  0 case.
Ij
I
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
Can see clearly to spins of 20ħ using thin-target technique.
Even-Even yrast sequences and odd-A +ve parity
only show rotational behaviour after (nh11/2 )2 crossing….
seems to work ok, nh11/2 bands now look like rotors,
τ = 800 ns, 43/2-, 3.8 MeV
407 keV γ-ray
215Ra
from 206Pb(13C,4n)
Stuchbery et al.
Nucl. Phys. A641 (1998) 401
215Ra
γ-ray spectrum
Z. Podolyak, private communication
from 238U fragmentation
Abrasion-ablation model
(1-2/3)
k=2
“sharp cut-off” approximation:

Rth   P( J )dJ  exp[
Jm
DA>10
J m ( J m  1)
]
2 2f
179W
populated in:
fragmentation of 208Pb at 1 GeV/u
fusion evaporation: 170Er(13C,4n) at 67 MeV
M. Pfutzner, PHR et al. Phys Rev. C65, 064604 (2002)
Higher spins for greater DA.
208Pb
beam at 1 GeV/u allows production of
high-spin isomers,
M. Pfützner et al. Phys Rev. C65 (2002) 064604
High spins
(>35/2)
populated
(
Projectile Fragmentation Reactions
projectile
Final
Excited
fragment
pre-fragment
target
hotspot
Energy (velocity) of beam > Fermi velocity inside nucleus ~30 MeV/u
Can ‘shear off’ different combinations of protons and neutrons.
Large variety of exotic nuclear species created, all at forward angles
with ~beam velocity.
Some of these final fragments can get trapped in isomeric states.
Problem 1: Isotopic identification. Problem 2: Isomeric identification.
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
BLFs
TLFs
elastics
Can see 184-194Os in binary partner channels. i.e.in 2p transfer,
up to 14 neutrons evaporated. ( 4n -> 194Os is heaviest known).
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313
198Pt, 2+
136Xe,
2+
J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313
138Ce
125Sb
Super-FRS yields
215Ra
double mid-shell, ‘purest’ K-isomer ?
(see PHR, Oi, Walker, Stevenson and Rath,
Phys. Rev. C65 (2002) 037302)
170Dy,
Kp=6+state
favoured
Max at 170Dy