CERN@school: demonstrating physics with the Timepix detector

Abstract

This article shows how the Timepix hybrid silicon pixel detector, developed by the Medipix2 Collaboration, can be used by students and teachers alike to demonstrate some key aspects of any well-rounded physics curriculum with CERN@school. After an overview of the programme, the detector’s capabilities for measuring and visualising ionising radiation are examined. The classification of clusters – groups of adjacent pixels – is discussed with respect to identifying the different types of particles. Three demonstration experiments – background radiation measurements, radiation profiles and the attenuation of radiation – are described; these can used as part of lessons or as inspiration for independent research projects. Results for exemplar data-sets are presented for reference, as well as details of ongoing research projects inspired by these experiments. Interested readers are encouraged to join the CERN@school Collaboration and so contribute to achieving the programme’s aim of inspiring the next generation of scientists and engineers.

Keywords:

• science education
• student-led research
• CERN
• silicon pixel detectors
• space radiation environment
• LUCID
• GridPP
• grid computing

Acknowledgements

The authors are grateful for the continued support and guidance of M. Campbell and J.A. Alozy (the Medipix2 Collaboration), D. Cooke, E. Brownbill and S. Wokes (SSTL), C. Harvey (formerly of SEPnet), N. Hollingworth and E. Cunningham (STFC), G. Williams (Institute of Physics), J.P. Eastwood (Imperial College London), C. J. Walker (Queen Mary University of London/GridPP), S. Skipsey (Uni. Glasgow/GridPP), J. Martyniak (Imperial College London/GridPP), J.R. Wilson and S.L. Lloyd (Queen Mary University of London), H. Pollard (The Ogden Trust), I. Holmes (Kettering Buccleuch Academy) and L. Pinsky (NASA/Uni. of Houston). Allpix was developed by J. Idarraga, M. Benoit and S. Arfaoui, and the LUCID Timepix detector calibration was carried out at IEAP, CTU in Prague by J. Jakubek et al.

Notes

No potential conflict of interest was reported by the authors.

1 Now the UK Space Agency.

2 http://www.particlecamera.com.

3 It is possible to use other types of sensor elements with the Timepix ASIC, but this is beyond the scope of this article.

4 http://medipix.web.cern.ch.

5 11,810 is the maximum value determined by the shift register, returned when the pixel is saturated.

6 Please contact Jablotron directly via http://www.particlecamera.com for up-to-date pricing information.

7 It is worth noting that qualitative features may also be used to classify clusters in cases where it is not possible to devise a suitably robust computational algorithm. Such an approach is adopted in the Galaxy Zoo citizen science research programme [21], where volunteers are invited en masse to classify images of galaxies by eye. This has the added benefit of allowing objects that fall outside of a given classification scheme to be flagged for further study. This approach to Timepix cluster classification will feature in future work.

8 While it is possible to define variables based on the pixel count values, these are not considered here, as the experiments described do not require energy measurements.

9 Energy measurements require a calibration data-set to have been obtained with the detector used to make the measurement. If such a data-set is unavailable, a useful measurement may be still be made with the said detector; the energy information may be extracted later once the calibration data-set has been obtained.

10 Threshold Equalisation (TEQ) is a procedure that may be performed on the Mk1 units to establish the deviation from a mean lower threshold (THL) value required for each of the 65,536 pixels. This is not required for the MX-10 units. See [3] for further details.

11 That is, File output is ticked in the Pixelman Device Control panel, and Single file is unticked.

12 Properties relating to the counts recorded by the detector are not discussed here as the detector used in this experiment had not been calibrated at the time of writing.

13 The fitted values of $\widehat{\mathit{\mu }}$ and ${\widehat{B}}_0$ produce a Pearson’s ${\mathit{\chi }}^2$ value of 0.0120 (7 d.o.f), satisfying the null hypothesis of a straight line fit at the 5% significance level.

Additional information

Funding

This work was supported by a Science in Society Large Award [ref. ST/J000256/1] from the UK Science and Technology Facilities Council (STFC) and a Special Award from the Royal Commission for the Exhibition of 1851. Summer student placements were supported by the South East Physics Network (SEPnet), STFC and the Institute of Physics (IOP).