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Reaction rates in the Laboratory

Reaction rates in the Laboratory. Example I: 14 N(p, g ) 15 O. slowest reaction in the CNO cycle Controls duration of hydrogen burning Determines main sequence turnoff – glob. cluster ages. stable target  can be measured directly:. g -ray detectors. Accelerator. vacuum beam line.

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Reaction rates in the Laboratory

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  1. Reaction rates in the Laboratory Example I:14N(p,g)15O • slowest reaction in the CNO cycle • Controls duration of hydrogen burning • Determines main sequence turnoff – glob. cluster ages • stable target  can be measured directly: g-ray detectors Accelerator vacuum beam line Faraday cup to collect charge Proton beam N-target • but cross sections are extremely low: •  Measure as low an energy as possible – then extrapolate to Gamow window

  2. Calculating experimental event rates and yields beam of particles hits target at rest area A j,v thickness d assume thin target (unattenuated beam intensity throughout target) Reaction rate (per target nucleus): Total reaction rate (reactions per second) with nT: number density of target nucleiI=jA : beam number current (number of particles per second hitting the target) note: dnTis number of target nuclei per cm2. Often the target thickness is specified in these terms.

  3. Events detected in experiment per second Rdet e is the detection efficiency and can accounts for: • detector efficiency (fraction of particles hitting a detector that produce a signal that is registered) • solid angle limitations • absorption losses in materials • energy losses that cause particles energies to slide below a detection threshold • …

  4. 14N(p,g) level scheme Gamow window0.1 GK: 91-97 keV g-signature of resonance6791 keV g0 Direct gs capture~7297 keV + Ep

  5. LUNALaboratory Underground for Nuclear Astrophysics(Transparencies: F. Strieder http://www.jinaweb.org/events/tucson/Talk_Strieder.pdf) Gran Sasso Mountain scheme 1:1 Mio cosmic ray suppression

  6. Spectra: above and under ground

  7. Beschleuniger bild

  8. Setup picture

  9. Spectrum overall

  10. Spectrum blowup

  11. Results: GamowWindow Formicola et al. PLB 591 (2004) 61 New S(0)=1.7 +- 0.2 keVb (NACRE: 3.2 +- 0.8)

  12. New Resonance ? Resonance claim and TUNL disproof

  13. Effect that speculative resonance would have had

  14. Example II: 21Na(p,g)22Mg problem: 21Na is unstable (half-life 22.5 s) solution: radioactive beam experiment in inverse kinematics: 21Na + p  22Mg + g thick 21Na production target hydrogen target 22Mg products Accelerator I Accelerator 2 p beam 21Na beam g-detectors ionsource particleidentification difficulty: beam intensity typically 107-11 1/s (compare with 100 mA protons = 6x1014/s)  so far only succeeded in 2 cases: 13N(p,g) at Louvain la Neuve and 21Na(p,g) in TRIUMF (for capture reaction)

  15. DRAGON @ TRIUMF

  16. Results Result for 206 keV resonance: S. Bishop et al. Phys. Rev. Lett. 90 (2003) 2501

  17. Example III: 32Cl(p,g)33Ar Shell model calculations Herndl et al. Phys. Rev. C 52(1995)1078  proton width strongly energy dependent rate strongly resonance energy dependent

  18. H. Schatz NSCL Coupled Cyclotron Facility

  19. Installation of D4 steel, Jul/2000

  20. Fast radioactive beams at the NSCL: • low beam intensities • Impure, mixed beams • high energies (80-100 MeV per nucleon) (astrophysical rates at 1-2 MeV per nucleon)  great for indirect techniques • Coulomb breakup • Transfer reactions • Decay studies • …

  21. H. Schatz Setup Focal plane:identify 33Ar S800 Spectrometer at NSCL: 34Ar Beamblocker 33Ar 33Arexcited 34Ar d Plastic People: Plastictarget 34Ar D. Bazin R. Clement A. Cole A. Gade T. Glasmacher B. Lynch W. Mueller H. Schatz B. Sherrill M. VanGoethem M. Wallace Radioactive 34Ar beam84 MeV/u T1/2=844 ms(from 150 MeV/u 36Ar) SEGAGe array(18 Detectors)

  22. S800 Spectrometer SEGA Ge-array

  23. H. Schatz with experimental data shell model only x 3 uncertainty x10000 uncertainty New 32Cl(p,g)33Ar rate – Clement et al. PRL 92 (2004) 2502 Doppler corrected g-rays in coincidence with 33Ar in S800 focal plane: g-rays from predicted 3.97 MeV state stellar reaction rate reaction rate (cm3/s/mole) 33Ar level energies measured: 3819(4) keV (150 keV below SM) 3456(6) keV (104 keV below SM) temperature (GK) Typical X-ray burst temperatures

  24. NSCL ReA3 Fast beams Gas cell

  25. Science with CCF reaccelerated beams and p-process … Rates in pps >108 direct (p,g) 107-8 106-7 direct (p,a) or (a,p)transfer 105-6 104-5 (p,p), some transfer 102-4 Up to here: For indirect measurements: many For direct measurements: some important rates • Capabilities: • sufficient beam intensities for many important measurements • all beams available once system commissioned • probably very good beam purity • none of the measurements identified can be performed at another facility as of now

  26. Overview of the FRIB Layout

  27. ReA12 and Experimental Areas • A full suite of experimental equipment will be available for fast, stopped and reaccelerated beams • New equipment • Stopped beam area (LASERS) • ISLA Recoil Separator • Solenoid spectrometer • Active Target TPC

  28. Science with reaccelerated beams at FRIB Direct measurementsfor many (a,g) reactions in p-process Rates in pps 10>10 109-10 108-9 107-8 All reaction rates can beindirectly measuredincluding 72Kr waiting point 106-7 105-6 104-5 102-4 most reaction rates up to ~Sr can bedirectly measured All reaction rates up to ~Ti can be directly measured  Very strong nuclear astrophysics science case

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