New Isomers from Fast Fragmentation Reactions Dr. Paddy Regan Dept. of Physics University of Surrey,...
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Transcript of New Isomers from Fast Fragmentation Reactions Dr. Paddy Regan Dept. of Physics University of Surrey,...
New Isomers from Fast Fragmentation Reactions
Dr. Paddy Regan
Dept. of Physics
University of Surrey,
Guildford, GU2 7XH, UK
primary beamPb @ 1GeV/u
Production target
Central focus, S2Final focus, S4
E(Z2)cu
eB
Q
A
FTO
catcher
degraderdegrader
dipole, B
scintscint
MW=x,y
scint(veto)
Use FRS (or LISE3) to ID exotic 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. Pfutzner et al. Phys. Lett. B444 (1998) p32 -> FRS
Heaviest odd-odd,N=Z gammas, isobaric analog states ? 86Tc, C. Chandler et al. Phys. Rev. C61 (2000) 044309
8+ isomer in 78Zn, real evidence of 78Ni shell closure.J.M.Daugas et al. Phys. Lett.
B476 (2000) p213
136Sb
135Te
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)
M. Mineva et al. Eur. Phys. J. A11 (2001) p9-13
Gamma-gamma analysis on 200Pt isomer (21 ns!), Caamano et al. Nucl. Phys. A682 (2001) p223c; Acta Phys. Pol. B32 (2001) p763
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)
First id of ‘doubly mid-shell’ nucleus, 170Dy (N=104, Z=66). K=6+ isomers predicted for well deformed N=104 nuclei. TRS calcs (F.Xu) predict a very ‘stiff’, highly deformed prolate nucleus. Could be the best K-isomer?
Data from M.Caamano et al.
Proton drip line isomer physicsfrom 208Pb fragmentation.N=74 chain of K=8- isomers.Next in chain would be 140Dy, proton decay daughter of (deformed) 141Tb.
Isomers orginally seen in fusion-evap (ANU data)A.M.Bruce et al. Phys.Rev. C50 (1994) p480and C55 (1997) p620
2
3/22
22
2
)1(exp
ratio,isomer predicts model off-cut sharp
1
3
3
210178.0
, 2
)1(exp
2
12
fJ jth
p
ppf
ffjj
JJdJPR
A
AAAA
JJJP
m
M. de Jong et al. Nucl. Phys. A613 (1997) p435
M. Pfutzner et al. Phys. Rev. C & Acta. Phys. Pol. (submitted)
iitot
i
fii
effimp
tot
b
ttG
TOFTOF
FGbN
NR
1
expexp
11
expF
, )1(
0
2
2
22
1
11
Isomeric Ratio Calculations
M. Pfutzner et al. Acta. Phys. Pol. & Phys. Rev. C, (submitted)
Prompt flash knocks out a large portion of the detectors….effectively reduces the gamma efficiency by upto 80%! Need digital electronics and time stamping
The problem
Single ion selected by the fragment separator
time
coun
ts
0
plastic
Ge detector
trigger,time start
prompt isomer decay room background
thick Al stopper
Energy 100 MeV/uR 60 mg/cm2 Al
Probability to detect prompt radiation is large.
In a standard set-up only the first gamma is recorded.
DGF detection scheme
A1 A2 A3 A4
Ionization chamberL2
R4R2
L4Plastic scintillators
FRSsecond stage
Energy loss, DE
Beam
Position x2 - TAC(L2-R2) -
Position x4 - TAC(L4-R4) -
TAC(L2-L4) - TAC(R2-R4) -
TOF -
Gate logic
P a r t i c l e i d e n t i f i c a t i o n
DGF 1, 2
Clover detectors
Gamma energy, EG
Gate logic
D e c a y s p e c t r o s c o p y
DGF 3, 4, 5
Beam macrostructure
time [s]
Storing datain memory buffers
Readout
time [s]
microstructure
100 s
Gate
Ions
Gammas
Other ways to get around the gamma-flash problem?
Segmented germanium detectors and digital electronicsfor each individual segment.
EURYSIS 6 x 6 germanium, Surrey/Liverpool/Darebury UK Gamma-Ray Tracking Project.
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.
Neyens, Georgiev et al. RNB5 conference, in press,. Nucl. Phys. A
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.
J. Garces Narro et al. Phys Rev. C63 (2001) 044307
Implant fragments into Si strip detector…if N=Z, stop beam for 1second and wait…..
BIL gatedAll
T=1 ground states in heavy odd-odd N=Z
Summary and Forward Look• New nuclear structure
– along N=Z line (86Tc, Chandler et al.)
– around 78Ni (78Zn, Daugas et al.)
– from fission fragments (136Sb, Mineva, Hellstroem et al.)
– ‘terra incognita’ 190W, 195Os, 200,201,202Pt…170Dy? (Podolyak, Caamano et al.)
• Reaction information
– Isomeric ratios give estimate of spin input, imply useful tool for high-spin physics (Pfutzner et al).
• Developments in Techniques
– Digital electronics for gamma-flash (eg. 136Sb)
– Gamma-tracking with segmented detectors (Pearson, Dobon et al.)
– Fast timing to order gamma-rays in cascade (BaF2 Mach et a.)
– g-factors using TPAD method (Neyens, Georgiev et al.)
– Active stoppers for electron conversion (72,74Kr etc. Becker et al.) and beta, alpha, proton decays tags (GREAT).
• All in the RISING project@GSI.