An overview of the S1105 experiment at TRIUMF. 1 Martin Jones The University of Liverpool Email: [email protected].

An overview of the S1105 experiment at TRIUMF.

1

Martin JonesThe University of Liverpool

Email: [email protected]

Overview.

Martin Jones – Tigress experiment December 2008.2

• The physics behind the experiment.

• The experiment.

• Detector setup.

• Schedule of experiment.

• Summary.

The Physics behind the experiment.

Martin Jones – Tigress experiment December 2008.3

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).

The Physics behind the experiment.

Martin Jones – Tigress experiment December 2008.4

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 2008.5

• 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

The Silicon detectors.

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The Germanium detectors.

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• 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.

Experimental setup.

Martin Jones – Tigress experiment December 2008.8

TIGRESSdetector array

TIGRESSdetector array

21Na beam

E

TIGRESSdetector at 0°

EMylar

Bambino target chamber

21Na

Experiment schedule.

Martin Jones – Tigress experiment December 2008.9

• 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.

Experiment schedule.

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• 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”.

A further experiment.

Martin Jones – Tigress experiment December 2008.11

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.

A further experiment.

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S1151 15O schematic illustration

Collimator

16O beam

E

TIGRESSdetector at 0°

E

Implanted 3He Au

Vacuum chamber

88Y

• 50MeV beam from ISAC-II• 15um Au foil implanted with ~ 6 x 1017 3He atoms.• Foil thick enough to stop recoiling 15O ions but thin enough to allow transmission of lighter particles.

To summarise.

Martin Jones – Tigress experiment December 2008.13

• 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.