Transcript Document

In detail: ap process
Ge (32)
Ga (31)
Zn (30)
Cu (29)
Ni (28)
333
Co (27)
Fe (26)
3132
Mn (25)
Cr (24)
2930
V (23)
Ti (22)
25262728
Sc (21)
Ca (20)
2324
K (19)
Ar (18)
2122
Cl (17)
S (16)
17181920
P (15)
Si (14)
12C
a+a+a
1516
Al (13)
14O+a
17F+p
Mg (12)
14
Na (11)
17F+p
18Ne
Ne (10)
18Ne+a …
11 1213
F (9)
O (8)
9 10
N (7)
Alternating (a,p) and (p,g) reactions:
C (6)
For each proton capture there is an
7 8
B (5)
Be (4)
(a,p) reaction releasing a proton
Li (3)
5 6
He (2)
Net effect: pure He burning
3 4
H (1)
0 1 2
3a reaction
ap process:
Mass known < 10 keV
Recent progress in mass measurements
Mass known > 10 keV
Only half-life known
seen
Measure:
 decay properties
 gs masses
 level properties
 rates/cross sections
ISOLTRAP
Rodriguez et al.
NSCL Lebit
Bollen et al.
ANL CPT
Savard et al.
JYFL Trap
NSCL Set of experiments
use (p,dg) to determine
level structure
Reaction rates:
• direct measurements difficult
• “indirect” methods:
• Coulomb breakup
• (p,p)
• transfer reactions
stable beams and RIBS
Figure: Schatz&Rehm, Nucl. Phys. A,
 Guide direct measurements
 Huge reduction in uncertainties
 If capture on excited states matters
only choice
Nuclear physics needed for rp-process:
• b-decay half-lives (ok)
(in progress)
• masses
(just begun)
• reaction rates
Xe (54)
I (53)
Te (52)
Sb (51)
Sn (50)
In (49)
Cd (48)
Ag (47)
Pd (46)
Rh (45)
Ru (44)
5758
Tc (43)
Mo (42)
Nb (41)
Zr (40)
Y (39)
Sr (38)
mainly (p,g), (a,p)
56
5455
Rb (37)
Kr (36)
Br (35)
Se (34)
53
5152
4950
As (33)
Ge (32)
Ga (31)
Zn (30)
45464748
424344
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)
some experimental information available
(most rates are still uncertain)
Theoretical reaction rate predictions difficult near
drip line as single resonances dominate rate:
Hauser-Feshbach: not applicable
Shell model: available up to A~63 but large
uncertainties (often x1000 - x10000)
Li (3)
He (2)
5 6
H (1)
3 4
n (0)
2
0 1
(Herndl et al. 1995, Fisker et al. 2001)
 Need rare isotope beam experiments
H. Schatz
Techniques with rare isotope beams
21Na
1) Direct Measurements
+ p  22Mg
Bishop et al. 2003 (TRIUMF)
For p-capture
only 2 cases so far !
 Need RIA
2) First step: indirect techniques
with low intensity rare isotope beams
Many developed at a number of facilities:
(ANL, GSI, MSU, ORNL, RIKEN, Texas A&M, …)
Example: 32Cl + p  33Ar*  33Ar + g
Resonant enhancement through states in 33Ar ?
H. Schatz
NSCL Experiment: Clement et al. PRL 92 (2004) 2502
Doppler corrected g-rays
in coincidence with 33Ar in S800 focal plane:
34Ar
g-rays from predicted 3.97 MeV state
33Ar
excited
Plastic
d
33Ar
level energies measured:
3819(4) keV (150 keV below SM)
3456(6) keV (104 keV below SM)
reaction rate (cm3/s/mole)
stellar reaction rate
with
shellexperimental
model only data
x 3 uncertainty
x10000 uncertainty
temperature (GK)
H. Schatz
Stellar Enhancement Factor
SEF =
1/2+
Dominant
resonance
5/2+
MeV
4.190
3.819
this work
7/2+
2+
90 keV
stellar capture rate
ground state capture rate
5/2+
1+
32Cl
3.456
3.364
3.343
NON Smoker
33Ar
 direct measurement of this rate is not possible – need indirect methods
 SEF’s should be calculated with shell model if possible
H. Schatz
Mass ejection in X-ray bursts ? Weinberg, Bildsten, Schatz 2005
Winds can eject <1% of accreted mass
Does convection zone reach into the
outer layers that get blown off ???
 Wind ejects ashes in
radius expansion bursts
for wide range of parameters
Neutron star interior
Temperature (K)
wind
?
surface
Column density (g/cm2)
wind
H. Schatz
Reaction flow during burst rise in pure He flash
12C(a,g)
bypass
(a,p)
13N
16O
slow
(p,g)
12C
Need protons as catalysts
(~10-9 are enough !)
Source: (a,p) reactions
and feedback through bypass
 Increases risetime
 Triggers late reexpansion of
convection zone
 enhances production
of heavy elements vs. carbon
H. Schatz
Composition of ejected material
28Si
32S
Weak p-capture
on initial Fe seed
 Observable with current
X-ray telescopes
 in wind
 on NS surface
as spectral edges
 Explanation for enhanced
Ne/O ratio in 4U1543-624,
4U1850-087, … ???
(ratios ~1 – ISM 0.18)
H. Schatz
Step 2: Deep ocean burning: Superbursts
Neutron star surface
H,He
gas
ashes
ocean
outer
crust
Inner
crust
~ 20m, r=109 g/cm3
H. Schatz
The origin of superbursts – Ashes to Ashes
Accreting Neutron Star Surface
Radiation transport H,He
~10s ~hours
~1 m
fuel
~ x1000 longer burst duration
~ x1000 longer recurrence time
~ x1000 more energy
Thermonuclear H+He burning
(rp process)
gas
ashes
~10 m
ocean
~100 m
outer
crust
~1 km
10 km
Inner
crust
core
Deep burning ?
 long duration through
longer radiation transport
 long time to accumulate
means long recurrence time
more material
means more total energy
by same factor
for same MeV/u)
Ashes to ashes – the origin
of superbursts ?
54
52
50
48
68
44
42
62
40
(Cumming & Bildsten 2001)
38
36
54
34
30
44
28
34
20
14
20 22
16 18
8
14
6
10 12
4
0
2
4
6
48
~ 55%
Energy
44
48
24
26 28
8
42
62
38
36
54
34
36
30
44
28
30
24
38
Time:
1.041e-04 s
20
Temperature: 180.850 GK
20 22
10
16 18
8
14
6
10 12
4
0
0
2
4
6
34
8
(Schatz, Bildsten, Cumming, ApJ Lett. 583(2003)L87
46
48
24
40
36
32
16
12
60
42
26
~ 45% Energy
14
56
58
64 66
50 52
32
2
68
40
22
10
0
46
32
18
2
60
46
40
38
22
16
52
50
42
26
12
56
58
54
64 66
50 52
32
24
Burst peak (~7
70
46
Carbon can explode
deep in ocean
30
Puzzle:
The
ocean is too
cold s
Time:
1.076e+03
Temperature:
ignition about
every
6.607
GK10 years
instead of every year
as observed
26 28
Energy generation in Superbursts
(plus C->Ni fusion)
And nuclear power plants
only place in cosmos ?
on earth
Energy generation
everywhere else in comos:
• Stars
• X-ray bursts, Novae
H. Schatz
Step 3: Crust burning
Neutron star surface
H,He
gas
ashes
ocean
outer
crust
Inner
crust
ashes
~ 25 – 70 m
r=109-13 g/cm3
Surface of accreting neutron stars
Neutron star surface
Hydrogen,
Helium
X-ray bursts
1m
gas
10m
Ocean (palladium?
Zinc?)
Crust of rare isotopes
Inner
crust
D. Page
ashes
Crust processes
106Pd
Known mass
4.8 x 1011 g/cm3
106Ge
56Fe
1.8 x 1012 g/cm3
68Ca
2.5 x 1011 g/cm3
56Ar
72Ca
4.4 x 1012 g/cm3
1.5 x 1012 g/cm3
34Ne
Haensel & Zdunik 1990, 2003
Gupta et al. 2006
Crust processes
Recent mass
measurements
at GSI
(Scheidenberger et al.,
Matos et al.)
Recent mass
measurements
at Jyvaskyla
(Hager et. al. 2006)
Known mass
Recent mass
measurements
at ISOLTRAP
(Blaum et. al.)
Q-value
measurement
at ORNL
(Thomas et al. 2005)
Recent TOF mass
measurements
at MSU
(Matos et al.)
Reach of next generation
Rare Isotope Facility FRIB
(here MSU’s ISF concept)
(mass measurements)
NEW JINA Result: S. Gupta,
E. Brown, H. Schatz,
K.-L. Kratz, P. Moeller 2007
Electron capture into excited
states increases heating
by up to a factor of ~10
Excitation energy
of main transition
Increased
heating
Enhanced crust heating
New heating
enhanced by x 5-6
Former estimate
 Heats entire crust and increases ocean temperature from 480 Mio K to 500 Mio K
Impact of new crust modeling on superbursts
Can the additional heating from EC into excited states make the crust hot
enough to get the superburst ignition depth in line with observations ?
Almost:
Ignition depth
Without excited states
Inferred from
observations
Mass number of crust composition (pure single species crust)
H. Schatz
Observables: transients in quiescence
Low crust conductivity, normal core cooling
KS 1731-260 (Wijands 2001)
Bright X-ray burster for ~12 yr
Accretion shut off early 2001
Is residual luminosity cooling
neutron star crust ?
 If yes: probe neutron star !
(Ouellette & Brown 2005)
(Rutledge 2002)
High crust conductivity, enhanced core coolin
H. Schatz
Comparison with observations during quiescence
M. Ouellette
Low crust conductivity
Normal core cooling
High crust conductivity
Normal core cooling
Low crust conductivity
Enhanced core cooling
High crust conductivity
Enhanced core cooling
(data from Wijnands 2004)

but: a superburst has been observed from KS 1731-260
this indicates a hotter crust and low crust conductivity
(Brown 2004)
H. Schatz
Superbursts as probes for NS cooling
Superburst ignition depth (Ed Brown, to be published)
(for accretion rate of 3e17 g/s and X(12C)=0.1)
Low crust conductivity
High crust conductivity
Recurrence times
(observed ~ 1yr)
1.4 yr
3.1 yr
5.2 yr
“regular” core cooling
27 yr
“enhanced” core cooling
 Recurrence time depends on crust conductivity and core cooling
 Observations require LOW conductivity and no enhanced cooling (incl. KS1731-260)