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Reaction rates in the Laboratory Example I: 14 N(p,  ) 15 O stable target  can be measured directly: slowest reaction in the CNO cycle  Controls duration.

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Presentation on theme: "Reaction rates in the Laboratory Example I: 14 N(p,  ) 15 O stable target  can be measured directly: slowest reaction in the CNO cycle  Controls duration."— Presentation transcript:

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

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

3 Events detected in experiment per second R det  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 00  -signature of resonance 6791 keV Direct gs capture ~7297 keV + E p Gamow window 0.1 GK: 91-97 keV 14 N(p,  ) level scheme

5 Gran Sasso Mountain scheme LUNA Laboratory Underground for Nuclear Astrophysics (Transparencies: F. Strieder http://www.jinaweb.org/events/tucson/Talk_Strieder.pdf) 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: Formicola et al. PLB 591 (2004) 61 Gamow Window New S(0)=1.7 +- 0.2 keVb (NACRE: 3.2 +- 0.8)

12 Resonance claim and TUNL disproof New Resonance ?

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: 21 Na(p,  ) 22 Mg problem: 21 Na is unstable (half-life 22.5 s) solution: radioactive beam experiment in inverse kinematics: 21Na + p  22Mg +  Accelerator I Accelerator 2 p beam thick 21Na production target ion source 21 Na beam hydrogen target  -detectors 22Mg products particle identification difficulty: beam intensity typically 10 7-11 1/s (compare with 100  A protons = 6x10 14 /s)  so far only succeeded in 2 cases: 13N(p,  ) at Louvain la Neuve and 21Na(p,  ) in TRIUMF (for capture reaction)

16

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18 DRAGON @ TRIUMF

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

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

21 H. Schatz NSCL Coupled Cyclotron Facility

22 Installation of D4 steel, Jul/2000

23 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 …

24 Focal plane: identify 33Ar S800 Spectrometer at NSCL: Plastic target Radioactive 34 Ar beam 84 MeV/u T 1/2 =844 ms (from 150 MeV/u 36 Ar) 33 Ar 34 Ar SEGA Ge array (18 Detectors) Beam blocker D. Bazin R. Clement A. Cole A. Gade T. Glasmacher B. Lynch W. Mueller H. Schatz B. Sherrill M. VanGoethem M. Wallace H. Schatz Setup People: d Plastic 34Ar 33Ar excited 34 Ar

25 SEGA Ge-array S800 Spectrometer

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

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