Transcript Slide 1

b-delayed proton-decay for nuclear
astrophysics
Livius Trache
Cyclotron Institute
Texas A&M University
EURISOL User Group Workshop, Florence, Jan 2008
Indirect methods in NPA (w, w/o RNB)





Coulomb dissociation
Transfer reactions (ANC method)
Breakup of loosely bound nuclei
Trojan Horse Method
Others – (other) spectroscopic info: Jp, Eres, G


to estimate direct terms: Jp, l, config mixings … variae
resonances (Jp, Eres, G’s) – variae, including




b-decay
b-delayed p-decay
Reaction spectroscopy …
resonant elastic scatt., etc.
A. Coc – OMEG07
!!!
A. Coc – OMEG07
!!!
Summary
b-decay of 23Al → 22Na(p,g)23Mg
 b-delayed proton decay of 23Al

Production and separation
 Decay measurements: b, g, p

b- and b-delayed p-decay of 31Cl →
30P(p,g)31S
 Connection to EURISOL physics

A challenge: missing g-rays from 22Na
Gamma-ray space-based telescopes
to detect current (on-going)
nucleosynthesis
Astrophysical g-ray emitters 26Al,
44Ti, … and 22Na
Satellites observed g-rays from 26Al
(T1/2=7 ·105 y), 44Ti, etc., but not
from 22Na (2.6 y) (COMPTEL,
INTEGRAL)!
20Ne(p,g)21Na(p,g)22Mg(b,n)22Na
Depleted by 22Mg(p, g)23Al ?!
Depleted by 22Na(p, g)23Mg ?!
22Mg(p,g)23Al - cross section
dominated by direct and resonant
capture to first exc state in 23Al
22Na(p, g)23Mg dominated by
resonant capture
22Na
3+
β+
2+
γ (1.275 MeV)
0+
22Ne
Explosive H burning in novae
&
IAS in Tz=-3/2 nuclei
Isospin mixing
GT strength distribution
MARS
In-flight RB production
24Mg
23Al
48A MeV
40A MeV
Purity: 90%, or >99% after en degrader
Intensity: ~ 4000 pps
First time - very pure & intense 23Al
(p,2n) reaction
Primary beam 24Mg @ 48A MeV – K500 Cycl
Primary target LN2 cooled H2 gas p=1.6 atm
Secondary beam 23Al @ 40.2A MeV
b decay study of pure RB samples
Betas and beta-gamma coincidences
parent
k
5
d=49 mm
g
b
i
b+
HpGe detector
j
Plastic
scintillator
0
Nb 
daughter
Goal: determine the beta decay scheme
the beta branching ratios: Nbi /Ntot
and absolute log ft
b
 b 0 N b 0 +  b 1 N b 1 +  b 2 N b 2 + ... + daughter + imp 
4p 


Ngb ( Eij )   gph ( Eij )bijg  b i N b i +   b k N b k bkig + corr 
k i


direct b pop. g from above
b-g coincidence spectrum
5/2+
7/2+
IAS
23Al
BGO
Tighe ea, LBL 1995
Perajarvi ea, JYFL 2000
5/2+
23Al
Proton br. total=1.1%
0.25%
1/2+
0.446(4)s
β+
Qec=12240keV
β+
0.48%
9548
8456
8164
8003
7877
p
22Mg(p,g)23Al
IAS: ft=2140 s +/-5%
7803 IAS 5/2+
7787 (7/2)+
0.38%
22Na
E=207 keV =>
Ep= 198 keV
DE=16 keV
Sp=7580 keV
22Na(p,g)23Mg
6985 5/2+
6575 5/2+
resonances
Most important:
wg7787=2.6(9) meV
2905 (3,5/2)+
2359 1/2+ NO!
2051 7/2+
data from 4 exp:
above
+ Jenkins PRL 2004
+ present data
450 5/2+
0 3/2+
23Mg
Y Zhai thesis
VE Iacob, et al.,
PRC 74, Oct. 2006
Energy degrader
(rotating, motorized)
275 mm
OD F150 mm
thermocooler
connectors
64 mm
>110 mm
E=Ep+kErecoil+<DEb>
18” dia chamber
F=80 mm
p-detector – v. thin Si strip 65 mm
b-detector – thick Si det 1 mm
g-detector – HPGe 70% effic
Pulsed beam
18-Jul-15
Back chamber, flange & detector holder
Isotope selection with MARS
E
Pos ~ q/m
Final cut with focal plane slits
Si 1000 mm
Si strip
61 mm
“HI telescope mode” – control implantation
Signal=EHI
17 mm
Signal=DEHI
HI
Dp/p=+/-0.25%
DE (p)
36°
Signal=DEb
30°
Signal=Ep+DEb
“b-proton mode”
measure simultaneously:
• b-proton and
• b-g coinc.
Si stops protons:
½ 65 mm Ep<1.5 MeV
E (b)
0°
23Al
implantedSecondary beam distribution
Measurements
• g-ray detector calibration – 24Al implanted at p-det
position
• Implantation control in “DE-E mode”
• 23Al b-delayed p-decay – 23Al implanted in p-det
• p-detector b backgr – 22Mg implanted in p-det
• b-detector calibration – 20Na implanted in b-det
• p-detector calibration:
–
–
20Na
(ba) implanted in p-det
21Mg (bp) implanted in p-det
• Off-line Ge det efficiency calibration with sources:
152Eu, 60Co, 137Cs
23Al
- figures from Run0507
E=Ep+kErecoil+<DEb>
20Na
21Mg
Run1107 – Nov. 2007
•
31Cl
decay. Goals:
– b-decay
– b-delayed proton-decay
• Measurements
– b-g and b-p coinc with source in p-det
– b-g coincidences with source stopped in foil
– Calibrations: 32Cl and 29S
31Cl
b-decay - status 2006
t=150(25) ms
MARS
In-flight RB production
32S
31Cl
40A MeV
34A MeV
Purity: > 85 % (at target det)
Intensity: ~ 2-3000 pps
difficult - pure & intense 31Cl
(p,2n) reaction
Primary beam 32S @ 40A MeV – K500 Cycl
Primary target LN2 cooled H2 gas p=2 atm
Secondary beam 31Cl @ 34 A MeV
31Cl
production and separation
31Cl
production and separation
32Cl
31Cl
29S
31Cl
production and separation
31Cl
29S
Y-Z profile of stopped 31Cl
X-Y profile (Beam Spot)
200
4000
5000
IAS
6000
Energy(keV)
10
2
7000
DE 3023.9
SE 3536.3
3620.6
3700.0
3078.7
2235.6
2000
2961.2
2746.1
2615.4
2424.1
2036.1
1000
6285.9
3
1723.2
1779.2
10
SE 5773.4
600
5035.2
4
1248.3
+ -
ee
5
4871.2
10
583.8
0
SE 4523.4
10
4048.4
10
4159.5
4211.5
SE 3536.3
400
3620.6
3700.0
Counts
31Cl
b-g-decay
3000
4000
a)
1
SE=Single Escape
DE=Double Escape
b)
0
8000
31Cl
p-spectra
PRELIMINARY!
29S
p-detector calibration
~ 10 pps, 8 hr measurement
Results 23Al, 31Cl b-delayed p-decay
Technique works well – can go to Ep~200 keV
and, maybe, lower
Can work with lifetimes ~100 ms or less
Very selective: can separate well beam cocktails
(by implantation depths)
Very sensitive: could obtain results for 21Mg, 29S
at rates ~ 1-10 pps in 8 hrs
Strengths:



Good mass separation (MARS)
In-flight production: need 30-50 MeV/u (can be
implanted)
Can work with short lifetimes ~100 ms or less
Nuclear Physics in the rp-process
Xe (54)
I (53)
Te (52)
End:
SnSbTe Cycle
(Schatz 2001)
Sb (51)
Sn (50)
In (49)
Cd (48)
Ag (47)
Pd (46)
Rh (45)
Ru (44)
Adapted from H. Schatz, 2006
5758
Tc (43)
Mo (42)
Nb (41)
Zr (40)
Y (39)
Sr (38)
56
5455
Rb (37)
Kr (36)
Br (35)
Se (34)
53
5152
4950
mass and half-life known
As (33)
Ge (32)
Ga (31)
Zn (30)
45464748
424344
half-life known
41
Cu (29)
37383940
Ni (28)
Co (27)
33343536
Fe (26)
Mn (25)
3132
Cr (24)
V (23)
2930
Ti (22)
Sc (21)
25262728
Ca (20)
K (19)
2324
Ar (18)
Cl (17)
2122
S (16)
P (15)
17181920
Si (14)
Al (13)
1516
Mg (12)
Na (11)
14
Ne (10)
F (9)
11 1213
O (8)
N (7)
9 10
C (6)
B (5)
7 8
Be (4)
seen
rate based
on some
exp. data
Theoretical reaction rate predictions:
Statistical model : not applicable near drip line
Li (3)
He (2)
5 6
H (1)
3 4
n (0)
2
0 1
(Rauscher et al. 1997)
Shell model: available up to A~63 but large
uncertainties (often x1000 - x10000)
(Herndl et al. 1995, Fisker et al. 2001)
EURISOL connection
With EURISOL beams close to p-dripline
(“long lived”) can access more p-rich,
shorter lived isotopes, at higher masses
needed in rp-process – not accessible now
use with in-flight production technique
(“tertiary” beam)
 need 30-50 MeV/u accelerator
 need a good in-flight mass separator

Collaborators
• A Banu, JC Hardy, VE Iacob, M
McCleskey, G Tabacaru, RE Tribble –
Cyclotron Institute, Texas A&M University
• J Aysto, A Saastamoinen, A Jokinen – Univ
of Jyvaskyla
• PJ Woods, T Davinson – Univ of
Edinburgh
• D Jenkins, MA Bentley – Univ of York
• L Achouri, B Roeder – LPC Caen