Alex Murphy

Alex Murphy 1/2 Day IOP meeting on Supernovae 1

Alex MurphyAlex Murphyhttp://www.ph.ed.ac.uk/nuclear/http://hepwww.rl.ac.uk/ukdmc/ukdmc.html/

Experimental Nuclear Astrophysics Relevant to Supernovae


Nuclear Astrophysics

Interstellar gas

Nuclear Reactions Stellar stability

Rise in T and

pp-chainsCNO cycles

s-process

Thermonuclear runaway

Triple HCNO

Breakoutrp-processp-processr-process

Explosive nucleosynthesis

Gravitational collapse

Formation of stars

pp-chains


Thermal energy distribution For ions – use MB statistics Novae: up to 2-3 x108 K X-ray bursts: up to 2-3 x109 K Supernovae: up to 1010 K

Nuclear Physics in Stars

The rate at which reactions occur is determined by the overlap of the thermal energy distribution and nuclear cross sections

Relevant energies 10keV - 10 MeV

Cross sections Typically below Coulomb barrier

Low cross sections Resonant processes dominate

Low density of states Indirect methods can be useful

Need to know energies, spins, widths


What we do and how we do it

LOGSCALE

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Focus of recent research…

Explosive astrophysical environments Novae, X-ray bursters, exotic scenarios

Typically we have been concentrating on proton rich side, A<30 This is largely for technical reasons

(H)CNO cycles Breakout from CNO processing rp-processing…


Example of what we do… Novae

Masssive star (e.g. Red Giant) More massive star expands… Outer layers transferred to compact object

movie Layer of H builds up on top of evolved

material (e.g. C/O/…) Slow accretion rate leads to degeneracy Conditions for a thermonuclear runaway High temperatures and short timescales

Ejecta Elemental composition Gamma ray emission…?


Gamma-ray production in Novae

Clayton & Hoyle Ap. J. 494 (1974) – direct observation of -rays in novae ejecta

Intensity of an observed -ray flux would provide a strong constraint on novae modelling.

Need to know the relevant reaction rates! 21Na(p,)22Mg

Nucleus Emission Nova type

13N 862 s 511 keV CO

ONe

18F 158 m 511 keV CO

ONe

7Be 77 d 478 keV CO

22Na 3.75 yr 1275 keV ONe

26Al 1.0x106 yr 1809 keV ONeINTEGRAL: launched Oct ’02

Nucleus Emission Nova type

13N 862 s 511 keV CO

ONe

18F 158 m 511 keV CO

ONe

7Be 77 d 478 keV CO

22Na 3.75 yr 1275 keV ONe

26Al 1.0x106 yr 1809 keV ONe


Example: Novae

Why is this reaction important?

Synthesis of 22Na in ONe novae 20Ne(p,)21Na(p,)22Mg(+)22Na

or 20Ne(p,)21Na(+)21Ne(p,)22Na

rp – p

roce

ss

rp – p

roce

ss

20Ne

21Na

22Mg

23Al

24Si

19Ne

20Na

22Ne

23Na

24Mg

25Al

26Si

21Ne

22Na

23Mg

24Al

25Si

25Mg

26Al

27Si

26Mg

27Al

28Si

19F18F17F

NeNa CycleNeNa Cycle

MgAl CycleMgAl Cycle

18Ne

22Na

Need to know (p,) rate compared to b-decay rate


Experimental method

TUDA

DRAGON

Radiative capture and elastic scattering studies

(p,) (p,p)

We use radioactive beam facilities such as those at TRIUMF and Louvain-la-

Neuve


192 strips, energy, angle and time of flight from each

Resonant elastic scattering

Primary beam: 20 A, 500 MeV, protons

SiC primary target

surface ion surface ion sourcesource

Radioactive Beam 5x107 pps

TUDA

LEDA

Target: 795 g/cm2 CH2 foil


Energy

Tim

e o

f Fl

ight

E (MeV) B.R.

5.701 0.0016

5.272 0.036

4.894 0.193

4.683 0.087

4.438 2.94

3.801 0.25

3.210 0.03

2.148 16.4

20Na beam is radioactive! alpha decays

Elastically scattered protons1H(20Na,1H)

12C(20Na,12C)

20Na @ 32 MeV on 795 g/cm2 CH2, with 12.65 m Mylar

Particle Identification


Data…

Three resonances observed Ex(21Mg) = 4.005MeV Primary aim of the experiment. Tentative J= (1/2+) 3/2+

Ex(21Mg) = 4.26 MeV Previously only Ex known (no width, spin information) 5/2+

Ex(21Mg) = 4.44 MeV Previously unknown J= 3/2+


Radiative Capture

(p,) or (,) Use a Recoil mass separator +

a gamma-ray array E.g. DRAGON: Detector of

Recoils And Gammas of Nuclear Reactions

Windowless gas target End detectors – silicon strip

detector or ion chamber


Measurement of 21Na(p,)22Mg

21Na beam on hydrogen target Varied 21Na beam energy in small steps

so as to scan resonances Detected recoils in coincidence with

prompt gammas Determined resonance strengths for

seven states in 22Mg between 200 and 1103 keV


Results – resonance strengths

Yield curves for state at206 keV (above) and at821 keV (left)

22Mg recoils in DSSSD ER=740 keV

22Mg21Na


Results: Reaction rate

Results: The lowest measured state at 5.714

MeV (Ecm = 206 keV) dominates for all novae temperatures and up to about 1.1 GK

Updated nova models showed that 22Na production occurs earlier than previously thought while the envelope is still hot and dense enough for the 22Na to be destroyed

Results explain the low abundance of 22Na


What about observations…?

CGRO/COMPTEL – So far no detection; upper limits only. But… consistent with current theory incorporating new reaction rate data. Expectation…

INTEGRAL should see signal from nova < 1.1 kpc away (~1 ONe nova per 5 yrs)

-ray emission from several close novae has been search for…

Nova Her 1991


Future directions:

Around the world, facilities are advancing… ISAC-II (Canada), RIA (US), RIPS (Japan),

Eurisol, REX-Isolde, SPIRAL-II, FAIR (Europe), More intense beams, more exotic beams, heavier beams Opportunities for detector development

Now is the time to go after new physics!


Future Directions

An example relevant to type Ia supernovae


SN Ia

Scatter in brightness <0.3 mags, even without extinction correction (which is usually quite small). Over 90% have very reproducible light curves.

Thus very useful as a standard candle

Especially important in light of CDM Non-standard SN Ia’s Effects that can change luminosity

(e.g. metalicity)

SN1991 D


Recent ‘atypical’ observations:

Recently, several atypical SNIa’s have been observed: SN 1987G - fast decline from maximum SN 1986G - anomalies in optical spectra SN 1990N - anomalies in optical spectra SN 1991T - 'largely deviated' from standard SN1991bg - dimmer than usual, some H detected. SN1999by - very similar to SN1991bg

These differences suggest that maybe there really are two progenitor types...

He rich accretion on to sub-Chandrasekhar mass CO WDs may be responsible for the <10% of SNIa’s that have ‘peculiar’ light curves.


Sub-Chandrasekhar mass models

The existence of sub-luminous SN Ia’s interpreted as less than 1.4 M 56Ni powering the light curve

The Sub-Chandrasekhar mechanism: A 0.6 – 0.8 M CO WD accretes He rich matter.

98% 4He, 1% 12C, 0.5% 14N, 0.5% 16O Existence (but not the exact quantity) of 14N critical – a product of pop-I burning

Moderate accretion rate (~10-8 M yr-1) He ignition at the CO/He interface.

Competition between 14N(e–,)14C()18O (‘NCO’) & Triple- Ignition of He may strongly depend on rate of 14C()18O

Alex MurphyAlex Murphy

An indirect study of the 14C()18O reaction

EEC Meeting, TRIUMF

Alison LairdAlison Laird

Jordi JoseJordi Jose

LOI XXXV


Future Directions

An example relevant to Core Collapse supernovae


Core Collapse Supernovae

There is consensus on the basic mechanism And yet even the best simulations still

don’t explode! Extremely complex

Need a good diagnostic

Produced in vicinity of mass cut Sensitive diagnostic of models Gamma-ray observable nuclide

SN1987A

M1 – The Crab44Ti!


Core Collapse

Massive star (>10–12 M) Stellar evolution onion-skin-like structure At maximum of BE/A, thermal support lost Core collapses After core-bounce, shock wave passes through Si layer above core Dissociation back to n, p, and …Nuclear statistical equilibrium… …Alpha-rich freeze out Dominant site for 44Ti production Key reactions to be studied*

40Ca() 44Ti() 44Ti(,p) 45V(p,) Triple

* (The et al ApJ 504 (1998) 500)

EPSRC Grant


44Ti production as a diagnostic

Amount ejected sensitively depends on location of the ‘mass cut’

Material that ‘falls back’ is not available for detection

44Ti yield a sensitive diagnostic of the explosion mechanism

Thus, VERY useful for models to make comparisons against

What’s more, it’s (relatively) easily observed

Gamma-Ray observation 1.157 MeV INTEGRAL & other

missions Meteoritic data

Enrichment of 44Ca in type X presolar grains Timmes et al. (1996)

Wilson. (1985)


Pretty pictures…

A grain from the Murchison Meteorite

Integral

GLAST


Summary

Nuclear reactions are the power behind most astrophysical phenomena

Astrophysical models require accurate nuclear physics inputs

New facilities (and upgrades) mean we can now start looking at reactions important in new environments

Nuclear Astrophysicists need good guidance!


The End

Thank you


Spare slides


Latest development…

Proposed research requires: Low energy 44Ti and 45V beams Refractory elements are hard to extract from ‘standard’ ion sources

A new approach…Exotic Radionuclides from Irradiated MAterials for Science and Technology

PSI is looking at reducing the amount of radioactive waste it has produced Potential users:

Nuclear Medicine Geophysics Astrophysics …

Could bleed these ions into a non-RNB ion source and re-accelerate them LLN? Triumf? Other? Proposal in to EU FP7 programme


LEDA

LEDA

795g/cm2 CH2

• 1.25 MeV/u• 1.60 MeV/u

High sensitivity Faraday cup

Recoil proton

9.55 or 12.40 m Mylar

5.65 or 9.65 m Mylar

19.5 cm 60.5 cm 4.6o < lab < 31.2o

Typical set-up (from 20Na(p,p) expt)

20Na

3.50 < Ex (21Mg) < 4.64 MeV


Astrophysical significance: NeMg Novae

Temperatures achieved are too low for breakout

NeNa and MgAl cycles thought to provide necessary energy production.

NeNa cycle: First stage is 20Ne(p,)21Na.

Where does the 20Ne come from? -decay of 20Na feeds 20Ne. Rate of 20Na(p,) compared to the +

decay of 20Na (448ms) determines abundance of 20Ne

20Ne19Ne

21Na 22Na20Na

23Mg21Mg 22Mg

23Na

NeNa cycleNeNa cycle21Ne


An understanding of the cosmos

Observations

Modelling

Nuclear Astrophysics

…


Novae and X-ray Bursters…

Binary systems! Compact, evolved star (white dwarf or

neutron star) orbiting a massive star (e.g. Red Giant)

More massive star expands… Outer layers transferred to compact

object Layer of H builds up on top of evolved

material (e.g. C/O/…) Slow accretion rate leads to degeneracy Conditions for a thermonuclear

runaway High temperatures and short timescales

Radioactive nuclei important


Novae

White dwarf with companion star Temperatures of up to 3 x 108K Time: 100-1000s to eject layer Light curve increases to max in hours

but can take decades to decline Absolute magnitude can increase by

up to 11 magnitudes Can be recurrent Ejecta

Elemental composition Gamma ray emission…?

Nova Herculis 1934: AAT


Some recent measurements…

p(20Na,p) Indirect study of 20Na(p,)21Mg reaction

X-ray bursters: a crucial link in the rp-process

Novae: affects NeNa cycle.

p( 21Na,p) Indirect study of 21Na(p,)22Mg reaction

Novae: Potential for satellite gamma ray observations

p( 11C,p) Indirect study of 11C(p,)12N reaction

High mass stars/Novae:

18Ne(,p) Direct study.

Breakout from HCNO cycle: Catalyst for rp-process?


20Na(p,p)20Na Motivation

Better knowledge of the level structure of 21Mg is needed… Astrophysics

Nucleosynthesis and energy generation X-ray bursts Novae Reaction rates dominated by resonant contributions

Nuclear Physics Proton-rich nuclei far from stability, Large level shifts, Comparison of reaction

mechanisms, Shell model studies

The Experiment

Resonant elastic scattering: 20Na(p,p)20Na (inverse kinematics, using TUDA at TRIUMF)


Astrophysical significance: X-ray Bursters

T ~ 4 x 108K Energy generation by HCNO

cycles Waiting points at 14O, 15O and

18Ne isotopes

12C 13C

13N 14N

15O 16O

17F 18F

18Ne

15N

17O14O

15O 16O

17F 18F

18Ne

17O14O 15O 16O

17F 18F

18Ne 19Ne

21Na 22Na20Na

23Mg21Mg 22Mg

17O14O

T 6 x 108K (,p) and (p,) rates overtake decays Reaction flow dominated by

15O(,)19Ne(p,)20Na(p,)21Na… ‘Breakout’ into rp-process begins Triggers subsequent explosion


The run:

Successful experiment ran at TRIUMF 5 days of stable 20Ne calibration beams 7 days of radioactive 20Na beams: up to 5x107 pps.

Thick target method: Scan through region of excitation in 21Mg to look for resonances

Detect proton recoils Expect Rutherford + resonances (+ interference). Resonance depends on Ex, p, J, and ltr

Two–body kinematics For a selected angle energy of detected protons reflect the

energy the reaction occurred at. Hence, proton energy spectrum is just an excitation function.


Calibrations etc

Standard triple alpha source Pulser walk-through…


Analysis of proton data

Gate on protons…

Project out energy spectrum…

Subtract alpha background…

R-matrix analysis…General formalism – Lane & Thomas Inverse level matrix approach Based on earlier coding separately developed by

Lothar Buchman and by Dick Azuma Present version courtesy of C. Ruiz. ½ integer spin, multi-channel, non-zero ltr, …


X-ray Bursters…

Similar environment to novae, but replace white dwarf with a neutron star.

Much deeper gravitational potential Hotter, denser, faster

Less accreted material/smaller surface area lower luminosity than novae

Temperatures up to ~2-3 x 109K Time: 1-10s to lift degeneracy and eject

layer Ejecta?

little net ejecta due to gravitational field

X-ray burster in NGC 6624: HST

HEAO light curve of X-ray burst MXB 1728-34


Simulations

Helium burning at base of He layer Occurs around =106g/cc Competition between 14N(e–,)14C()18O (‘NCO’) & Triple-

Nucleosynthesis (extended network codes : Goriely et al. A & A 388 2002) Possible site for generating p-process nuclides.

Expanding outward shock wave T9=2 – 3 Material ejected Mo and Ru isotopes produced Such explosions produce 44Ti (contrary to standard SN1a)

Ignition of He may strongly depend on rate of 14C()18O

See also: Hoflich, Khokhlov & Wheeler [1995], Goriely, Jose, Hernanz, Rayet and Arnould [2002]


The 14C() reaction rate: Effect

This reaction rate is undetermined, with an uncertainty factor 100

Model ‘A’ – Standard reaction rate Model ‘B’ – Standard reaction rate x 100 Model ‘C’ – Standard reaction rate 100

Model B

• Shorter accretion duration

• Less mass accreted

• Less 56Ni in explosion

• Ignition density =1.77x106 g/cc

Less violent explosion

• Peak (at base of He layer) T9 = 2.77

Model c

• Longer accretion duration

• More mass accreted

• More 56Ni in explosion

• Ignition density =3.92x106 g/cc

More violent explosion

• Peak T9 (at base of He layer) = 3.22



Direct capture

3– state at 177 keV

Current knowledge of reaction rate

Reaction rate See Buchmann, D’Auria & McCorquodale (1998),

Funck & Langanke (1989), Görres et al. (1992) Direct capture component (T<3x107 K) 177 keV resonant component remains undetermined.

Dominates rate 0.03 < T9 < 0.2 State of interest:

Er=177 keV (6.404 MeV in 18O), J=3– No direct measurements No spectroscopic factor Not calculated in theoretical studies

(e.g. Descouvemont & Baye 1985) Proximity to -threshold

Resonance strength determined by small branching ratio (~10-10)

Indirect methods must be used 6Li(14C,d)18O,12C(14C,8Be)18O, 7Li(14C,t)18O… Funck & Langanke (1989)


14C()18O Experimental details

Experimental issues Can 14C be separated from 14N? 5x107 pps for 1 week not likely to be a

radiological safety hazard Rate of FC <1000 Bq:range ~3 cm (in

air) 6Li(14C,d)18O – kinematics drive 2H from

different states very close together. Would require very thin (10g/cm2) targets Target contamination (C/O/F)

12C(14C,8Be)18O Identify 8Be from 2 alphas Erel=92 keV Coulomb Barrier…


Spectroscopic factor

Compare angular distribution to reaction model to get spectroscopic factor.

Alpha transfer below Coulomb barrier Need spectroscopic factor measured in transfer reaction

Must be careful of model uncertainties FRESCO, ZAFRA Calibration reaction? Compound nucleus contribution

HF & Angular distribution…


Summary

There are several reasons to believe that He rich accretion on to sub-Chandrasekhar mass CO WD SN occur.

They are astrophysically very interesting They are ‘consistent’ with sub-luminous SNIa Proposed as a site for p-processing

Evolution is likely to depend on the currently unknown reaction rate of 14C()18O

Direct measurement unfeasible Indirect methods:

14C(6Li,d), 14C(12C,8Be) Need to develop a 14C beam


Example: Type Ia Supernovae

For dark energy


Kinematics12C(14C,8Be)18O 6Li(14C,d)18O

cm vs

Lab

Elab vs Lab


States in 18O

14C+

6.227

18O

6.4043–

6.198

6.880

7117

1–

6.3512–

4+

1–

0.177

State populated strongly in (t,p): tot~0.4 mb (Cobern et al. PRC 23 (1981) 2387)Somewhat weaker in (7li,p)(d,p), (t,), (6Li,d), ES: little strength

Gamma decay to multiple states.


Proposed research

Take advantage of unique future ISAC beams 44Ti(,p)47V – direct measurement

Gas/implanted target Trilis, CSB LEDA/CD Not measured before at astrophysical energies - extrapolation of previous results suggests

it’s eminently feasible (@ 10^7 pps). 45V(p,p)45V – resonant elastic scattering

Knowledge of 46Cr, precursor to 45V(p,)46Cr Trilis, CSB CH2 target LEDA/CD Unmeasured. SM/TES suggests ‘feasible’ (@ 10^7 pps).

45V(p,)46Cr Trilis, CSB DRAGON Use (p,p) as guide.

Coordinated approach


UK Grant application

A request has been made to EPSRC specifically focussed on this work

Request was for 33 months of PDRA salary + Travel Panel met 27/7/05 …funded! Advertising now Deadline 16/09/05 Can start 1/11/05

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Alex Murphy