Experimental Nuclear Astrophysics Relevant to Supernovae Alex Murphy

Experimental Nuclear Astrophysics Relevant to Supernovae Alex Murphy http: //www. ph. ed. ac. uk/nuclear/ Alex Murphy 1/2 Day IOP meeting on Supernovae http: //hepwww. rl. ac. uk/ukdmc. html/ 1

Nuclear Astrophysics Interstellar gas Gravitational collapse Triple a HCNO Breakout rp-process r-process Explosive nucleosynthesis Rise in T and r Formation of stars pp-chains Thermonuclear runaway Nuclear Reactions Stellar stability pp-chains CNO cycles s-process Alex Murphy 1/2 Day IOP meeting on Supernovae 2

Nuclear Physics in Stars The rate at which reactions occur is determined by the overlap of thermal energy distribution and nuclear cross sections Thermal energy distribution n n For ions – use MB statistics Novae: up to 2 -3 x 108 K X-ray bursts: up to 2 -3 x 109 K Supernovae: up to 1010 K Relevant energies 10 ke. V - 10 Me. V Cross sections n Alex Murphy Typically below Coulomb barrier n Low cross sections n Resonant processes dominate n Low density of states n Indirect methods can be useful Need to know energies, spins, widths 1/2 Day IOP meeting on Supernovae 3

(E) Alex Murphy Coulomb barrier Astrophysical region Ecoul E, J, ℓtr, G EG E, J, ℓtr, G resonance E, J, ℓtr, G non-resonant E, J, ℓtr, G direct measurements What we do and how we do it LOG SCALE 1/2 Day IOP meeting on Supernovae 4

Focus of recent research… n n Explosive astrophysical environments n Novae, X-ray bursters, exotic scenarios Typically we have been concentrating on proton rich side, A<30 n This is largely for technical reasons (H)CNO cycles Breakout from CNO processing rp-processing… Alex Murphy 1/2 Day IOP meeting on Supernovae 5

Example of what we do… Novae n n n Masssive star (e. g. Red Giant) More massive star expands… Outer layers transferred to compact object n movie n 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 n Ejecta n n n Alex Murphy Elemental composition Gamma ray emission…? 1/2 Day IOP meeting on Supernovae 6

Gamma-ray production in Novae n n n Clayton & Hoyle Ap. J. 494 (1974) – direct observation of g-rays in novae ejecta Nucleus t Emission Nova type 13 N 862 s 511 ke. V CO ONe 18 F 158 m 511 ke. V CO ONe 7 Be 77 d 478 ke. V CO 22 Na 3. 75 yr 1275 ke. V ONe 26 Al 6 yr 1809 ke. V flux ONe Intensity of 1. 0 x 10 an observed g-ray would provide a strong constraint on novae modelling. Need to know the relevant reaction rates! 21 Na(p, g)22 Mg Alex Murphy INTEGRAL: launched Oct ’ 02 1/2 Day IOP meeting on Supernovae 7

Why is this reaction important? 24 Si Need to know (p, g) rate compared to bdecay rate Alex Murphy – 25 Si 26 Si 27 Si 28 Si 24 Al 25 Al 26 Al 27 Al 23 Mg 24 Mg 25 Mg 26 Mg rp Synthesis of 22 Na in ONe novae 20 Ne(p, g)21 Na(p, g)22 Mg(b+)22 Na § or 20 Ne(p, g)21 Na(b+)21 Ne(p, g)22 Na § 23 Al pr oc es s Example: Novae 22 Mg Mg. Al Cycle 20 Na 21 Na 22 Na 23 Na Ne. Na Cycle 18 Ne 19 Ne 20 Ne 17 F 18 F 19 F 21 Ne 1/2 Day IOP meeting on Supernovae 22 Ne 8

Experimental method Radiative capture and elastic scattering studies (p, g) (p, p) We use radioactive beam facilities such as those at TRIUMF and Louvain-la. Neuve DRAGON TUDA Alex Murphy 1/2 Day IOP meeting on Supernovae 9

Resonant elastic scattering TUDA Radioactive Beam 5 x 107 pps Target: 795 mg/cm 2 CH 2 foil LEDA surface ion source Si. C primary target 192 strips, energy, angle and time of flight from each Primary beam: 20 m. A, 500 Me. V, protons Alex Murphy 1/2 Day IOP meeting on Supernovae 10

Particle Identification Elastically scattered protons 1 H(20 Na, 1 H) beam is radioactive! alpha decays E (Me. V) 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 Time of Flight 20 Na Energy 20 Na 12 C(20 Na, 12 C) @ 32 Me. V on 795 mg/cm 2 CH 2, with 12. 65 mm Mylar Alex Murphy 1/2 Day IOP meeting on Supernovae 11

Data… Three resonances observed n n n Ex(21 Mg) = 4. 005 Me. V Ex(21 Mg) = 4. 26 Me. V Ex(21 Mg) = 4. 44 Me. V Alex Murphy Primary aim of the experiment. Tentative Jp = (1/2+) 3/2+ Previously only Ex known (no width, spin information) 5/2+ Previously unknown Jp = 3/2+ 1/2 Day IOP meeting on Supernovae 12

Radiative Capture n n n (p, g) or (a, g) 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 Alex Murphy 1/2 Day IOP meeting on Supernovae 13

Measurement of n n 21 Na(p, g)22 Mg 21 Na beam on hydrogen target Varied 21 Na beam energy in small steps so as to scan resonances Detected recoils in coincidence with prompt gammas Determined resonance strengths for seven states in 22 Mg between 200 and 1103 ke. V Alex Murphy 1/2 Day IOP meeting on Supernovae 14

Results – resonance strengths 22 Mg 21 Na 22 Mg recoils in DSSSD ER=740 ke. V Alex Murphy Yield curves for state at 206 ke. V (above) and at 821 ke. V (left) 1/2 Day IOP meeting on Supernovae 15

Results: Reaction rate Results: n The lowest measured state at 5. 714 Me. V (Ecm = 206 ke. V) dominates for all novae temperatures and up to about 1. 1 GK n Updated nova models showed that 22 Na production occurs earlier than previously thought while the envelope is still hot and dense enough for the 22 Na to be destroyed Ø Results explain the low abundance of 22 Na Alex Murphy 1/2 Day IOP meeting on Supernovae 16

What about observations…? g-ray emission from several close novae has been search for… Nova Her 1991 § 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) Alex Murphy 1/2 Day IOP meeting on Supernovae 17

Future directions: n Around the world, facilities are advancing… n ISAC-II (Canada), RIA (US), RIPS (Japan), Eurisol, REX-Isolde, SPIRAL-II, FAIR (Europe), n More intense beams, more exotic beams, heavier beams Opportunities for detector development n Now is the time to go after new physics! n Alex Murphy 1/2 Day IOP meeting on Supernovae 18

Future Directions An example relevant to type Ia supernovae Alex Murphy 1/2 Day IOP meeting on Supernovae 19

SN Ia n n n 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 LCDM n Non-standard SN Ia’s n Effects that can change luminosity (e. g. metalicity) SN 1991 D Alex Murphy 1/2 Day IOP meeting on Supernovae 20

Recent ‘atypical’ observations: n Recently, several atypical SNIa’s have been observed: n n n n SN 1987 G SN 1986 G SN 1990 N SN 1991 T SN 1991 bg SN 1999 by - fast decline from maximum anomalies in optical spectra 'largely deviated' from standard dimmer than usual, some H detected. very similar to SN 1991 bg 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. Alex Murphy 1/2 Day IOP meeting on Supernovae 21

Sub-Chandrasekhar mass models n The existence of sub-luminous SN Ia’s interpreted as less than 1. 4 M 56 Ni powering the light curve The Sub-Chandrasekhar mechanism: n A 0. 6 – 0. 8 M CO WD accretes He rich matter. n n n 98% 4 He, 1% 12 C, 0. 5% 14 N, 0. 5% 16 O Existence (but not the exact quantity) of 14 N critical – a product of pop-I burning Moderate accretion rate (~10 -8 M yr-1) He ignition at the CO/He interface. Competition between 14 N(e–, n)14 C(a, g)18 O (‘NCO’) & Triple-a Ignition of He may strongly depend on rate of 14 C(a, g)18 O Alex Murphy 1/2 Day IOP meeting on Supernovae 22

LOI XXXV An indirect study of the 14 C(a, g)18 O reaction n Alex Murphy Alison Laird Jordi Jose EEC Meeting, TRIUMF

Future Directions An example relevant to Core Collapse supernovae Alex Murphy 1/2 Day IOP meeting on Supernovae 24

Core Collapse Supernovae n n There is consensus on the basic mechanism n And yet even the best simulations still don’t explode! Extremely complex n Need a good diagnostic SN 1987 A 44 Ti! n n n M 1 – The Crab Produced in vicinity of mass cut Sensitive diagnostic of models Gamma-ray observable nuclide Alex Murphy 1/2 Day IOP meeting on Supernovae 25

Core Collapse Massive star (>10– 12 M ) n Stellar evolution onion-skin-like structure n At maximum of BE/A, thermal support lost Core collapses n After core-bounce, shock wave passes through Si layer above core n Dissociation back to n, p, and a n …Nuclear statistical equilibrium… n …Alpha-rich freeze out n Dominant site for 44 Ti production n Key reactions to be studied* 40 Ca(a, g) 44 Ti(a, p) EPSRC Grant 45 V(p, g) n Triple a n n Alex Murphy * (The et al Ap. J 504 (1998) 500) 1/2 Day IOP meeting on Supernovae 26

44 Ti production as a diagnostic Amount ejected sensitively depends on location of the ‘mass cut’ n Material that ‘falls back’ is not available for detection 44 Ti yield a sensitive diagnostic of n the explosion mechanism n Thus, VERY useful for models to make comparisons against n What’s more, it’s (relatively) easily observed n Gamma-Ray observation n 1. 157 Me. V n INTEGRAL & other missions n Meteoritic data 44 Ca in n Enrichment of type X presolar grains Alex Murphy 1/2 Day IOP meeting on Supernovae Wilson. (1985) Timmes et al. (1996) 27

Pretty pictures… Integral A grain from the Murchison Meteorite GLAST Alex Murphy 1/2 Day IOP meeting on Supernovae 28

Summary n n Alex Murphy 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! 1/2 Day IOP meeting on Supernovae 29

The End Thank you Alex Murphy 1/2 Day IOP meeting on Supernovae 30

n Alex Murphy Spare slides 1/2 Day IOP meeting on Supernovae 31

Latest development… n n Proposed research requires: 44 Ti and 45 V beams n Low energy n 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 n Potential users: n Nuclear Medicine n Geophysics n Astrophysics n … Could bleed these ions into a non-RNB ion source and re-accelerate them n LLN? Triumf? Other? n Proposal in to EU FP 7 programme Alex Murphy 1/2 Day IOP meeting on Supernovae 32

Typical set-up (from 20 Na(p, p) expt) 9. 55 or 12. 40 mm Mylar High sensitivity Faraday cup 5. 65 or 9. 65 mm Mylar roton il p Reco 795 mg/cm 2 CH 2 20 Na LEDA • 1. 25 Me. V/u • 1. 60 Me. V/u 5 19. Alex Murphy LEDA cm 5 60. cm 4. 6 o < qlab < 31. 2 o 3. 50 < Ex (21 Mg) < 4. 64 Me. V 1/2 Day IOP meeting on Supernovae 33

Astrophysical significance: Ne. Mg Novae n Temperatures achieved are too low for breakout n n Ne. Na and Mg. Al cycles thought to provide necessary energy production. Ne. Na cycle: n n n Alex Murphy First stage is 20 Ne(p, g)21 Na. 20 Ne come from? n Where does the b-decay of 20 Na feeds 20 Ne. Rate of 20 Na(p, g) compared to the b+ decay of 20 Na (448 ms) determines abundance of 20 Ne 21 Mg 22 Mg 23 Mg 20 Na 21 Na 22 Na 23 Na 19 Ne 20 Ne 21 Ne Ne. Na cycle 1/2 Day IOP meeting on Supernovae 34

Observations Nuclear Astrophysics An understanding of the cosmos Modelling … Alex Murphy 1/2 Day IOP meeting on Supernovae 35

Novae and X-ray Bursters… Binary systems! n n n n 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 Ø Alex Murphy Radioactive nuclei important 1/2 Day IOP meeting on Supernovae 36

Novae n n n n White dwarf with companion star Temperatures of up to 3 x 108 K Time: 100 -1000 s 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 n n Alex Murphy Elemental composition Gamma ray emission…? Nova Herculis 1934: AAT 1/2 Day IOP meeting on Supernovae 37

Some recent measurements… p(20 Na, p) Indirect study of 20 Na(p, g)21 Mg reaction X-ray bursters: a crucial link in the rp-process Novae: affects Ne. Na cycle. p( 21 Na, p) Indirect study of 21 Na(p, g)22 Mg reaction Novae: Potential for satellite gamma ray observations p( 11 C, p) Indirect study of 11 C(p, g)12 N reaction High mass stars/Novae: 18 Ne(a, p) Direct study. Breakout from HCNO cycle: Catalyst for rp-process? Alex Murphy 1/2 Day IOP meeting on Supernovae 38

20 Na(p, p)20 Na Motivation Better knowledge of the level structure of 21 Mg is needed… n Astrophysics n n Nucleosynthesis and energy generation n X-ray bursts n Novae n Reaction rates dominated by resonant contributions Nuclear Physics n Proton-rich nuclei far from stability, Large level shifts, Comparison of reaction mechanisms, Shell model studies The Experiment Resonant elastic scattering: 20 Na(p, p)20 Na (inverse kinematics, using TUDA at TRIUMF) Alex Murphy 1/2 Day IOP meeting on Supernovae 39

Astrophysical significance: X-ray Bursters n T ~ 4 x 108 K n n n Energy generation by HCNO cycles Waiting points at 14 O, 15 O and 18 Ne isotopes T 6 x 108 K n n (a, p) and (p, g) rates overtake b+ decays Reaction flow dominated by 15 O(a, g)19 Ne(p, g)20 Na(p, g)21 Na… ‘Breakout’ into rp-process begins Triggers subsequent explosion 18 Ne 17 F 18 F 15 O 16 O 17 O 13 N 14 N 15 N 12 C 13 C 14 O Alex Murphy 14 O 15 O 21 Mg 22 Mg 23 Mg 20 Na 21 Na 22 Na 18 Ne 19 Ne 17 F 18 F 16 O 17 O 1/2 Day IOP meeting on Supernovae 40

The run: Successful experiment ran at TRIUMF n n 5 days of stable 20 Ne calibration beams 7 days of radioactive 20 Na beams: up to 5 x 107 pps. Thick target method: Scan through region of excitation in 21 Mg to look for resonances Detect proton recoils n Expect Rutherford + resonances (+ interference). n Resonance depends on Ex, Gp, J, and ltr n Two–body kinematics n For a selected angle energy of detected protons reflect the energy the reaction occurred at. n Hence, proton energy spectrum is just an excitation function. Alex Murphy 1/2 Day IOP meeting on Supernovae 41

Calibrations etc Standard triple alpha source Alex Murphy Pulser walk-through… 1/2 Day IOP meeting on Supernovae 42

Analysis of proton data n Gate on protons… n Project out energy spectrum… n Subtract alpha background… n R-matrix analysis… General formalism – Lane & Thomas n Inverse level matrix approach n n n Alex Murphy 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, … 1/2 Day IOP meeting on Supernovae 43

X-ray Bursters… n n Similar environment to novae, but replace white dwarf with a neutron star. Much deeper gravitational potential n n n Hotter, denser, faster n Less accreted material/smaller surface area lower luminosity than novae 9 n Temperatures up to ~2 -3 x 10 K Time: 1 -10 s to lift degeneracy and eject layer X-ray burster in NGC 6624: HST Ejecta? n little net ejecta due to gravitational field HEAO light curve of X-ray burst MXB 1728 -34 Alex Murphy 1/2 Day IOP meeting on Supernovae 44

Simulations n Helium burning at base of He layer Occurs around r=106 g/cc 14 N(e–, n)14 C(a, g)18 O (‘NCO’) & Triple-a n Competition between Nucleosynthesis (extended network codes : Goriely et al. A & A 388 2002) n Possible site for generating p-process nuclides. n Expanding outward shock wave T 9=2 – 3 n Material ejected n Mo and Ru isotopes produced 44 Ti (contrary to standard SN 1 a) n Such explosions produce n n Ignition of He may strongly depend on rate of 14 C(a, g)18 O See also: Hoflich, Khokhlov & Wheeler [1995], Goriely, Jose, Hernanz, Rayet and Arnould [2002] Alex Murphy 1/2 Day IOP meeting on Supernovae 45

The 14 C(a, g) reaction rate: Effect This reaction rate is undetermined, with an uncertainty factor 100 n n n 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 56 Ni in explosion • Less 6 • Ignition density r=1. 77 x 10 g/cc Less violent explosion • Peak (at base of He layer) T 9 = 2. 77 Alex Murphy Model c • Longer accretion duration • More mass accreted 56 Ni in explosion • More 6 • Ignition density r=3. 92 x 10 g/cc More violent explosion • Peak T 9 (at base of He layer) = 3. 22 1/2 Day IOP meeting on Supernovae 46

Alex Murphy 1/2 Day IOP meeting on Supernovae 47

Current knowledge of reaction rate n Reaction rate n n n § re tu t cap c e r i D State of interest: § § § See Buchmann, D’Auria & Mc. Corquodale (1998), Funck & Langanke (1989), Görres et al. (1992) Direct capture component (T<3 x 107 K) 177 ke. V resonant component remains undetermined. n Dominates rate 0. 03 < T 9 < 0. 2 Er=177 ke. V (6. 404 Me. V in 18 O), Jp=3– No direct measurements No spectroscopic factor Not calculated in theoretical studies (e. g. Descouvemont & Baye 1985) Proximity to a-threshold § Resonance strength determined by Ga § small branching ratio (~10 -10) 3– state at 177 ke. V Indirect methods must be used Alex Murphy 6 Li(14 C, d)18 O, 12 C(14 C, 8 Be)18 O, 7 Li(14 C, t)18 O… 1/2 Day IOP meeting on Supernovae Funck & Langanke (1989) 48

14 C(a, g)18 O Experimental details Experimental issues § § Can 14 C be separated from 14 N? 5 x 107 pps for 1 week not likely to be a radiological safety hazard n § 6 Li(14 C, d)18 O – kinematics drive 2 H from different states very close together. n n § Rate of FC <1000 Bq: b range ~3 cm (in air) Would require very thin (10 mg/cm 2) targets Target contamination (C/O/F) 12 C(14 C, 8 Be)18 O § Identify 8 Be from 2 alphas Erel=92 ke. V § Coulomb Barrier… Alex Murphy 1/2 Day IOP meeting on Supernovae 49

Spectroscopic factor Compare angular distribution to reaction model to get spectroscopic factor. n Alpha transfer below Coulomb barrier n Need spectroscopic factor measured in transfer reaction Ga n Must be careful of model uncertainties n FRESCO, ZAFRA n Calibration reaction? n Compound nucleus contribution n HF & Angular distribution… Alex Murphy 1/2 Day IOP meeting on Supernovae 50

Summary n n There are several reasons to believe that He rich accretion on to sub-Chandrasekhar mass CO WD SN occur. They are astrophysically very interesting n n n 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 14 C(a, g)18 O n n Direct measurement unfeasible Indirect methods: 14 C(6 Li, d), 14 C(12 C, 8 Be) n n Alex Murphy Need to develop a 14 C beam 1/2 Day IOP meeting on Supernovae 51

Example: Type Ia Supernovae n Alex Murphy For dark energy 1/2 Day IOP meeting on Supernovae 52

Kinematics 12 C(14 C, 8 Be)18 O 6 Li(14 C, d)18 O qcm vs q. Lab Elab vs q. Lab Alex Murphy 1/2 Day IOP meeting on Supernovae 53

States in 18 O State populated strongly in (t, p): tot~0. 4 mb (Cobern et al. PRC 23 (1981) 2387) Somewhat weaker in (7 li, p) (d, p), (t, a), (6 Li, d), ES: little strength Gamma decay to multiple states. 0. 177 6. 227 14 C+a Alex Murphy 1– 7117 4+ 6. 880 3– 2– 6. 404 6. 351 1– 6. 198 18 O 1/2 Day IOP meeting on Supernovae 54

Proposed research Take advantage of unique future ISAC beams n 44 Ti(a, p)47 V n n n n n – resonant elastic scattering Knowledge of 46 Cr, precursor to 45 V(p, g)46 Cr Trilis, CSB CH 2 target LEDA/CD Unmeasured. SM/TES suggests ‘feasible’ (@ 10^7 pps). 45 V(p, g)46 Cr n n n Alex Murphy 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). 45 V(p, p)45 V n – direct measurement Coordinated approach Trilis, CSB DRAGON Use (p, p) as guide. 1/2 Day IOP meeting on Supernovae 55

UK Grant application n A request has been made to EPSRC n n n n Alex Murphy 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 1/2 Day IOP meeting on Supernovae 56