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
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2
12
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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.