1 / 26

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.

sydnee-barron
Download Presentation

Reaction rates in the Laboratory

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 N-target Proton beam • 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. Age of oldest globular clusters Increases by 0.7-1 Gyr with new data (mainly reevaluation of subthreshold resonance influence)

  15. 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)

  16. DRAGON @ TRIUMF

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

  18. 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

  19. H. Schatz NSCL Coupled Cyclotron Facility

  20. Installation of D4 steel, Jul/2000

  21. 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 • …

  22. 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)

  23. S800 Spectrometer SEGA Ge-array

  24. 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

More Related