An overview of the S1105 experiment at TRIUMF.

1. An overview of the S1105experiment at TRIUMF. Martin Jones The University of Liverpool Email: mj@ns.ph.liv.ac.uk

2. Overview. • The physics behind the experiment. • The experiment. • Detector setup. • Schedule of experiment. • Summary. Martin Jones – Tigress experiment December 2008.

3. The Physics behind the experiment. nuclear resonance - the resonance absorption of a gamma ray by a nucleus identical to the nucleus that emitted the gamma ray. • 18Ne(α,p) reaction one of two key reactions thought to determine breakout conditions from the hot-CNO cycles [2] into rp-process in X-ray bursters. • This particular reaction has been measured directly by Bradfield-Smith et al [1] and Groombridge et al [2] who report strong resonances in the range of 1.7-2.9MeV [2]. • Further study by Sinha et al [3] show the reaction cross section of the latter to be 50 times less. • This work called into question. • Further studies required to understand with more accuracy these resonance states. [1] W. Bradfield-Smith et al., Phys. Rev. C 59, 3402 (1999). [2] D. Groombridge et al., Phys. Rev. C 66, 055802 (2002). [3] S. Sinha et al., ANL Physics Division Annual Report 04/22, section a.3 (2004). Martin Jones – Tigress experiment December 2008.

4. The Physics behind the experiment. Details on the hot CNO cycle can be found in; D. Groombridge et al (2002). Or in more detail in: Evolution of starts and stellar populations by Maurizio Salaris and Santi Cassisi. Martin Jones – Tigress experiment December 2008.

5. The experiment • Main aim to identify resonances with significant inelastic branches, particularly to the 333keV state in 21Na. • 3.1 - 3.5MeV/u 21Na beams accelerated by ISAC-II • Mylar targets (Argonne – C8H10O4). Multiple thicknesses. • Inelastic and elastic protons detected by dE and E CD Silicon detectors. • dE  150um. E  1000um • Foils fitted in front of Silicon detectors to absorb scattered 12C ions from target. • Thicker targets first to cover all resonances. • Later use thinner targets to focus on specific resonances. 21Na (p, p’ gamma) 21Na Martin Jones – Tigress experiment December 2008.

6. The Silicon detectors. Martin Jones – Tigress experiment December 2008.

7. The Germanium detectors. • Tigress modules are being used for distinguishing the inelastic scattering events by detecting the coincident gamma ray. (333keV). • There is a need to distinguish the 333keV gamma ray from random coincidences with the 350keV gamma ray from the mirror level in 21Ne. This is a populated 5% branch from beta decay of 21Na beam and also from background reactions on the target. Martin Jones – Tigress experiment December 2008.

8. Experimental setup. TIGRESS detector array 21Na Bambino target chamber E TIGRESS detector at 0° 21Na beam Mylar E TIGRESS detector array Martin Jones – Tigress experiment December 2008.

9. Experiment schedule. • 4th/5th December  calibration/background runs/stable beam measurements. • 5th/6th December  3.5MeV/u beam 660ug/cm2 target online analysis. • 7th/8th December  beam change, 3.327MeV/u 660ug/cm2 target online. • PROBLEMS with leakage current on Silicon S2 detector continuously rising from 1.5uA stabilising at 14.5uA. HV bias shutdown at 20uA. • TEMPORARY RESPONSE  change HV to 100uA bias shutdown. No longer monitor the leakage current. • Detector still performed as usual – leakage current investigation. • Checked for radiation damage from spectra – nothing. • SUSPISCION – electrons released from Al foil and target are accumulating on the surface and not active area of the detector. Once electrons disperse the detector acts as normal. Martin Jones – Tigress experiment December 2008.

10. Experiment schedule. • 9th/11th December  Beam energy alterations ranging from 2.85  3.35MeV/u using 660ug/cm2 target looking for specific resonances. • 11th/12th December  Beam energy moved up to 3.35MeV/u with 209ug/cm2 target for final shift. • Dave Jenkins – “ comprehensive results on first look from online analysis, we’ll see what happens when we get the data back to York”. Martin Jones – Tigress experiment December 2008.

11. A further experiment. S1151 15O • Experiment aimed to measure the lifetime of 6.791MeV state in 15O • Heavy ions bombard 3He – implanted foils and excited states are populated via one nucleon transfer reactions. • Gamma recoils are stopped in the target foil while the lighter particles traverse the foil and are detected by the Silicon detectors. • Tigress detector used at 0⁰ to beam-line to measure Doppler shifted de-excited gammas emitted by the recoil as it slows in the target foil. Martin Jones – Tigress experiment December 2008.

12. A further experiment. S1151 15O schematic illustration Collimator Vacuum chamber 88Y E TIGRESS detector at 0° 16O beam Implanted 3He Au E • 50MeV beam from ISAC-II • 15um Au foil implanted with ~ 6 x 10173He atoms. • Foil thick enough to stop recoiling 15O ions but thin enough to allow transmission of lighter particles. Martin Jones – Tigress experiment December 2008.

13. To summarise. • Physics theory. • Experiment and experimental setup. • Detectors. • Shift scheduling. • Overall the experiment was deemed a success after last summers cancellation. • Further analysis being done at York by Adam Tuff and Andrew Robinson. Martin Jones – Tigress experiment December 2008.