Paddy Regan Dept. of Physics University of Surrey, UK E-mail: [email protected]
description
Transcript of Paddy Regan Dept. of Physics University of Surrey, UK E-mail: [email protected]
Deep-Inelastic and Multinucleon Reactions with Discrete
Gammaray Spectroscopy: A Brief Review
Paddy Regan
Dept. of Physics
University of Surrey, UK
E-mail: [email protected]
Physics of neutron-rich nuclei is the evolution of shell structure related to large energy gaps in the nuclear single-particle spectrum.
Reasons to study neutron-rich nuclei include:
1) Evolution of collective modes (vibrations, rotations, superdef ?) from spherical states by altering position in (N, Z, I, Ex) space.
2) Identification of specific orbitals, e.g. via isomers; g-factors; B(E2:I->I-2); shell model, seniority, Nilsson schemes etc.
3) Identifying new nuclear ‘exotica’, e.g., -/proton/-decaying states; new symmetries (e.g., 32), shell closures, shape changes..etc.
• (Some) DIC basics. – Thick or thin targets ? (I, Ex,N, Z) ; isomer gating etc.
• Thin target multi-nucleon transfer reactions:– Neutron-rich C nuclei (Berlin BRS).– N~20, Island of Inversion.– N=32,34 (sub)-shell closures, Se (Z=34, N=50). – 48Ca magic number(s).– N=50 robustness and shell closure.– Rotation/vibration evolution in A~100.– 132Sn region
• Seniority I=10+ isomers, h11/2 neutron hole migration ?• Surface diffuseness, weakening of N=82 shell ?
– A~170-190 K-isomerism and nuclear shape symmetry.– 208Pb at high spins; octupole collective vibrations etc. – U, Th octupole states, (very) high-j intruders (k17/2 etc.)– DIC with RIBs (24Ne beam at GANIL)– TIARA (d,p) etc. in inverse kinematics….
Courtesy,Bogdan Fornal
Courtesy,
Bogdan
Fornal
R.Broda et al., Phys. Rev. C49 (1994)
W. Krolas et al., Nucl. Phys. A724, 289 (2003).
208Pb
64Ni
Advantages and limitations of -ray thick target measurements with DIC
ADVANTAGES
Gamma rays from all reaction products
Gamma rays from the stopped nuclei – narrow lines – easy analysis of coincidences
Detection of cross-coincidences – some potential for identification
LIMITATIONS
Gamma spectra very complicated(hundreds of sources)
Gamma rays from the short lived states smeared out by the Doppler effect (emitted before a product is stopped)
Difficulties of identifications withouta starting point.
Angular distribution of rays almost isotropic
186W186W
3.5 MeV, >3 ms, 16+3.5 MeV, >3 ms, 16+
Off-beam singles, 7h
Total singles, 15 min.
Deep-inelastic reactionsFor K-Isomers with
238U beams
Out-of-beam conditionyields only lines from
the new isomers.
Out-of-beam conditionyields only lines from
the new isomers.
Without an off-beamtiming condition, only
Coulomb excitationlines are seen.
Without an off-beamtiming condition, only
Coulomb excitationlines are seen.
238U at 1600 MeV 186W (16 mg cm-2) μs →ms beam pulsing Argonne/Notre-Dame
array of 12 Ge dets. 1.5 MeV, 18 μs, 7–1.5 MeV, 18 μs, 7–
Courtesy, Carl Wheldon
-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
M . 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.
nano to microsecond isomer tagging ?
Isomer gating very useful in DIC experiments.
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
Wilczynski (‘Q-value loss) Plot A.D.Yamamoto, Surrey PhD thesis (2004)
Can we use the data from the CHICO+Gammasphere expt. to understand the ‘DIC’ reaction mechanism ? A wide range of spins & nuclei are observed.
What about the spin input ?
max
3
1blfmax
3
1tlf
max
3/13/1
0
221
max
1
1
7
2
1
1
7
2
fragments. twoebetween th mom. ang. relative the
and , intosplit is limit, mode rolling In the
25.12
cosec1.4
where, approach,closest of distance by thegiven is
max. issection -cross DIC the whereangle The
. and 219.0
is mom. ang. peripheral max. y theclassicall-Semi
l
AA
ll
AA
l
lll
fmAAE
eZZd
d
grazing
AA
AAVERl
B
T
T
B
blftlf
TBgraz
k
TB
TBCMCM
R. Bock et al., Nukleonika22 (1977) 529
+2p
-2n
+2n
Fold distributions highlight different reaction mechanisms
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
TLFs
BLFs
elastics
PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313
Emission angle of TLFs can give information/selection on reaction mechanism (and spin 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
Temporal separation can clearly identify ‘prompts’ and isomer decays
136Xe + 198Pt
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
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
information and lifetime determination of 195Os isomer decay
New isomer in 195Os identified in GSI projectile fragmentation confirmed ‘in-beam’ CHICO+GAMMASPHERE data.
Dobon, Wheldon, Regan et al.,
M.Caamano, P.M.Walker, PHR et al., Eur. Phys. J. A (2005)
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
J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316
N=80isotone
10+
N=80 isotonic chain, 10+ isomers, (h11/2)-2I=10+
Q. Why does Ex(10+) increase while E(2+) decreases ? 91(2) ns
Energy of N=80 I=10+ isomers correlates with energy increaseof 11/2- singleneutron hole 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., PR C69 (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
BRS+EUROBALL
Energy
Z
Carbon gate
Doppler correction from energy in BRS
Add-back included
1818O at 90 O at 90 MeV on on 99Be (98 Be (98 μg.cmμg.cm-2-2)) BRSBRS= = ±12.5±12.5° ° → ±45.5→ ±45.5°° Euroball: 15 clusters, 26 clovers (209 crystals)Euroball: 15 clusters, 26 clovers (209 crystals) Unique-Z id., position to 1 mm, energy of recoilUnique-Z id., position to 1 mm, energy of recoil Particle-γ, particle-γ-γ and particle-particle-γ-γParticle-γ, particle-γ-γ and particle-particle-γ-γ
coincidencescoincidences
Courtesy, Tzany Kokolova
S. Lunardi, Acta. Phys. Pol. B36 (2005) 1301
CLARA
S. Lunardi, Acta. Phys. Pol. B36 (2005) 1301A. Gadea et al., J. Phys. G (2005) in press
S. Lunardi, Acta. Phys. Pol. B36 (2005) 1301
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
24Ne
Deep Inelastic Collision reaction with light exotic beamPopulation of exotic Ne-F-O isotopes
Report of the E421S experiment (spokeperson F.Azaiez):aim of the experiment
• cross section measurements• spectroscopy Ne-O-F
DIC with RIBs!A new era ?
courtesy, Giovanna Benzoni
Report of the E421S experiment:Experimental details
• reaction: 24Ne @ 7.923 MeV/A + 208Pb (10.9 mg/cm2) 24Ne5+ , Ibeam ~ 1.5 . 105 pps
beam on target for 7 days
• setup: Vamos + EXOGAMVamos @ 45°
EXOGAM 11 detectors(2 without Compton shield)
Typical count rates:
• Ions: 30/min Total Ion counts: 7*24*60*30 = 302400 cross section determination is feasible
• Ion-gamma coincidence 70/h Total Ion-gamma coinc. 7*24*70 = 11760
only spectroscopy of inelastic ch.
courtesy, Giovanna Benzoni
Report of the E421S experiment:very preliminary spectraID-plot
E
E (a.u)
NeFONaE
(a.
u.)
Ne (inelastic)
3 days of statistics (~ 1/2)
Conditions:-Si-gamma coincidence- Prompt gamma peaks- calculated v/c
Ana
lysi
s in
pro
gres
sWorking on mass separation
courtesy, Giovanna Benzoni
Report of the E421S experiment:future
F
Ne
24Ne ~ 500 mb
26Ne ~ 80 mb(2n pick up)
23F ~ 20 mb(1p removal)
Beam intensity required to study weaker channels
• to get to more exotic Ne isotopes ~ 106
• to get to F 5.106
• to get to O ~ 107
courtesy,
Giovanna Benzoni
TIARA
courtesy, Wilton Catford
Experimental Results for 24Ne(d,p)25Ne Transfer with TIARA
TIARA
25Ne
(d,p)
10 MeV/u
Courtesy, Wilton Catford
• DIC physics…. – Neutron-rich C nuclei (Berlin BRS).– N~20, Island of Inversion.– N=32,34 (sub)-shell closures, Se (Z=34, N=50). – 48Ca magic number(s).– N=50 robustness and shell closure.– Rotation/vibration evolution in A~100.– 132Sn region
• Seniority I=10+ isomers, h11/2 neutron hole migration ?• Surface diffuseness, weakening of N=82 shell ?
– A~170-190 K-isomerism and nuclear shape symmetry.– 208Pb at high spins; octupole collective vibrations etc. – U, Th octupole states, (very) high-j intruders (k17/2 etc.)– DIC with RIBs (24Ne beam at GANIL)– TIARA (d,p) etc. in inverse kinematics….