An overview of the S1105 experiment at TRIUMF. 1 Martin Jones The University of Liverpool

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

The Physics behind the experiment. Martin Jones – Tigress experiment December nuclear resonance - the resonance absorption of a gamma ray by a nucleus identical to the nucleus that emitted the gamma ray. 18 Ne( 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 MeV [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, (2002). [3] S. Sinha et al., ANL Physics Division Annual Report 04/22, section a.3 (2004).

The Physics behind the experiment. Martin Jones – Tigress experiment December 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.

The experiment Martin Jones – Tigress experiment December Main aim to identify resonances with significant inelastic branches, particularly to the 333keV state in 21 Na MeV/u 21 Na beams accelerated by ISAC-II Mylar targets (Argonne – C 8 H 10 O 4 ). 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 12 C ions from target. Thicker targets first to cover all resonances. Later use thinner targets to focus on specific resonances. 21Na (p, p’ gamma) 21Na

The Silicon detectors. Martin Jones – Tigress experiment December

The Germanium detectors. Martin Jones – Tigress experiment December 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 21 Ne. This is a populated 5% branch from beta decay of 21 Na beam and also from background reactions on the target.

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

Experiment schedule. Martin Jones – Tigress experiment December th /5 th December  calibration/background runs/stable beam measurements. 5 th /6 th December  3.5MeV/u beam 660ug/cm 2 target online analysis. 7 th /8 th December  beam change, 3.327MeV/u 660ug/cm 2 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.

Experiment schedule. Martin Jones – Tigress experiment December th /11 th December  Beam energy alterations ranging from 2.85  3.35MeV/u using 660ug/cm 2 target looking for specific resonances. 11 th /12 th December  Beam energy moved up to 3.35MeV/u with 209ug/cm 2 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”.

A further experiment. Martin Jones – Tigress experiment December S O Experiment aimed to measure the lifetime of 6.791MeV state in 15 O 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 0 ⁰ to beam-line to measure Doppler shifted de-excited gammas emitted by the recoil as it slows in the target foil.

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

To summarise. Martin Jones – Tigress experiment December 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.