Physics projects for Y3 and Y4 students

Project description

Radiation dose dependent Infrared Photoluminescence of Feldspar

(supervisor: Matt Gunn)

Nature of project: experimental, instrumental

Available to students on full-time physics degree schemes or joint students.

Project description and methodology

When materials are subjected to ionising radiation, electrons are excited from the ground state to higher energy levels. In the majority of cases the electron returns rapidly to the ground state and releases the excess energy as a photon of light. However, in some materials, some of the excited electrons are “trapped” in higher energy states and are unable to return to the ground state on their own. These “trapped” states can be stable for very long periods of time – potentially hundreds of thousands of years. If these electrons are excited out of the trapped states with either thermal energy or an optical photon, then they are able to return to the ground state with the emission of a photon – these processes are known as Thermo-Luminescence (TL) and Optically Stimulated Luminessence(OSL). The amount of light emitted is dependent on the number of trapped electrons which is proportional to the radiation dose received. Both TL and OSL are therefore used in radiation dosimetry but both processes empty the trapped states and so the dose can only be read out once.

In the last few years it has been discovered that when stimulated with infrared light, the trapped electrons can be excited but still return to the trapped state with the emission of a longer infrared wavelength – a process known as Infra-Red Photo-Luminessence (IRPL). IRPL does not reset the signal and so can be read out repeatedly, this offers numerous advantages when compared to OSL such as improved signal to noise ratio continuous dose monitoring.

An imaging IRPL reader has been developed at Aberystwyth University to enable to the measurement of the IRPL signal. This will be used to investigate the IRPL signal from feldspar samples dosed with ionizing radiation to “calibrate” the samples for use as a radiation dosimeter.

While this is an experimental project, there is plenty of archive data available should lab access become unavailable during the year.

A successful project will develop beyond the above in one/some of the following directions:
As this field is relatively new there is scope for significant novelty and for the investigations to proceed in a number of directions. Presently the major challenges for IRLP measurements are related to the signal to background ratio and the rejection of the excitation light from the detector. Some possible avenues for research could include: Investigation of different IRPL excitation wavelengths, investigation of different IRPL detection filter combinations, Investigations of the clean-up of the excitation laser(s). Investigations can also be carried out into the relationship between the signal and dose / dose rate, the bleaching (de-trapping) of the electrons giving rise to the signal etc.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: As this field is relatively new there are a number of alternative directions the investigation could take including: optimization of the apparatus to improve the signal to noise ratio, investigation of the IRPL signal response to excitation wavelength etc.

Please speak to Matt Gunn (mmg) if you consider doing this project.

Initial literature for students:

  1. Prasad, A.K., Poolton, N.R., Kook, M. and Jain, M., 2017. Optical dating in a new light: A direct, non-destructive probe of trapped electrons. Scientific reports, 7(1), p.12097.
  2. Kook, M., Kumar, R., Murray, A.S., Thomsen, K.J. and Jain, M., 2018. Instrumentation for the non-destructive optical measurement of trapped electrons in feldspar. Radiation Measurements, 120, pp.247-252.
  3. Kumar, R., Kook, M., Murray, A.S. and Jain, M., 2018. Towards direct measurement of electrons in metastable states in K-feldspar: Do infrared-photoluminescence and radioluminescence probe the same trap?. Radiation Measurements, 120, pp.7-13.

Novelty, degree of difficulty and amount of assistance required

This project offers the potential for a lot of novelty but will be challenging and require a thorough and methodical experimental technique and data analysis. Training will be required in the use of the equipment and assistance may be required for some aspects of the experimental investigations.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Project outlineend of November
Initial measurements and analysisend of February
Instrument build and advanced experimentsmid-March
Complete measurements and data analysisEaster

Students taking this project will have to submit a full risk assessment form