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Dr Mohammed Alkhorayef


Visiting Senior Fellow

Academic and research departments

Department of Physics.

My publications

Publications

Niki Bardi, Izabela Jurewicz, AK King, Mohammed Alkhorayef, David Bradley, Alan Dalton (2017)X-ray irradiation-induced structural changes on Single Wall Carbon Nanotubes, In: Radiation Physics and Chemistry140pp. 34-37 Elsevier

Dosimetry devices based on Carbon Nanotubes are a promising new technology. In particular using devices based on single wall carbon nanotubes may offer a tissue equivalent response with the possibility for device miniaturisation, high scale manufacturing and low cost. An important precursor to device fabrication requires a quantitative study of the effects of X-ray radiation on the physical and chemical properties of the individual nanotubes. In this study, we concentrate on the effects of relatively low doses, 20 cGy and 45 cGy, respectively. We use a range of characterization techniques including scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy to quantify the effects of the radiation dose on inherent properties of the nanotubes. Specifically we find that the radiation exposure results in a reduction in the sp2 nature of the nanotube bond structure. Moreover, our analysis indicates that the exposure results in nanotubes that have an increased defect density which ultimately effects the electrical properties of the nanotubes.

A Alanazi, M Alkhorayef, K Alzimami, I Jurewicz, N Abuhadi, A Dalton, DA Bradley (2016)Carbon nanotubes buckypaper radiation studies for medical physics applications., In: Appl Radiat Isot

Graphite ion chambers and semiconductor diode detectors have been used to make measurements in phantoms but these active devices represent a clear disadvantage when considered for in vivo dosimetry. In such circumstance, dosimeters with atomic number similar to human tissue are needed. Carbon nanotubes have properties that potentially meet the demand, requiring low voltage in active devices and an atomic number similar to adipose tissue. In this study, single-wall carbon nanotubes (SWCNTs) buckypaper has been used to measure the beta particle dose deposited from a strontium-90 source, the medium displaying thermoluminescence at potentially useful sensitivity. As an example, the samples show a clear response for a dose of 2Gy. This finding suggests that carbon nanotubes can be used as a passive dosimeter specifically for the high levels of radiation exposures used in radiation therapy. Furthermore, the finding points towards further potential applications such as for space radiation measurements, not least because the medium satisfies a demand for light but strong materials of minimal capacitance.

David Bradley, A S Siti Shafiqah, Z Siti Rozaila, S N Sabtu, S F Abdul Sani, A H Alanazi, Shakardokht Jafari, G Amouzad Mahdiraji, F R Mahamd Adikan, M J Maah, Andrew Nisbet, N Tamchek, H A Abdul Rashid, M Alkhorayef, K Alzimami (2016)Developments in production of silica-based thermoluminescence dosimeters, In: Radiation Physics and Chemistry137pp. 37-44 http://www.elsevier.com/

This work addresses purpose-made thermoluminescence dosimeters (TLD) based on doped silica fibres and sol–gel nanoparticles, produced via Modified Chemical Vapour Deposition (MCVD) and wet chemistry techniques respectively. These seek to improve upon the versatility offered by conventional phosphor-based TLD forms such as that of doped LiF. Fabrication and irradiation-dependent factors are seen to produce defects of differing origin, influencing the luminescence of the media. In coming to a close, we illustrate the utility of Ge-doped silica media for ionizing radiation dosimetry, first showing results from gamma-irradiated Ag-decorated nanoparticles, in the particular instance pointing to an extended dynamic range of dose. For the fibres, at radiotherapy dose levels, we show high spatial resolution (0.1 mm) depth-dose results for proton irradiations. For novel microstructured fibres (photonic crystal fibres, PCFs) we show first results from a study of undisturbed and technologically modified naturally occurring radioactivity environments, measuring doses of some 10 s of μGy over a period of several months.

S.F. Abdul Sani, R Hammond, Shakardokht Jafari, N Wahab, G Amouzad Mahdiraji, A S Siti Shafiqah, H A Abdul Rashid, M J Maah, H Aldousari, Mohammed Alkhorayef, M Alzimami, David Bradley (2016)Measurement of a wide-range of X-ray doses using specialty doped silica fibres, In: Radiation Physics and Chemistry137pp. 49-55 http://www.elsevier.com/

Using six types of tailor-made doped optical fibres, we carry out thermoluminescent (TL) studies of X-rays, investigating the TL yield for doses from 20 mGy through to 50 Gy. Dosimetric parameters were investigated for nominal 8 wt% Ge doped fibres that in two cases were co-doped, using B in one case and Br in the other. A comparative measurement of surface analysis has also been made for non-annealed and annealed capillary fibres, use being made of X-ray Photoelectron Spectroscopy (XPS) analysis. Comparison was made with the conventional TL phosphor LiF in the form of the proprietary product TLD-100, including dose response and glow curves investigated for X-rays generated at 60 kVp over a dose range from 2 cGy to 50 Gy. The energy response of the fibres was also performed for X-rays generated at peak accelerating potentials of 80 kVp, 140 kVp, 250 kVp and 6 MV photons for an absorbed dose of 2 Gy. Present results show the samples to be suitable for use as TL dosimeters, with good linearity of response and a simple glow curve (simple trap) distribution. It has been established that the TL performance of an irradiated fibre is not only influenced by radiation parameters such as energy, dose-rate and total dose but also the type of fibre.

R Garriga, Izabela Jurewicz, S Seyedin, Niki Bardi, Styliani Totti, B Matta‐ Domjan, Eirini Velliou, Mohammed Alkhorayef, VL Cebolla, JM Razal, Alan Dalton, E Muñoz (2017)Multifunctional, Biocompatible and pH-Responsive Carbon Nanotube- and Graphene Oxide/Tectomer Hybrid Composites and Coatings, In: Nanoscale9pp. 7791-7804 Royal Society of Chemistry

Here we present a route for non‐covalent functionalization of carboxylated multi‐wall carbon nanotubes and graphene oxide with novel two‐dimensional peptide assemblies. We show that self‐assembled amino‐terminated biantennary and tetraantennary oligoglycine peptides (referred to as tectomers) effectively coat carboxylated multi‐walled carbon nanotubes and also strongly interact with graphene oxide due to electrostatic interactions and hydrogen bonding as the driving force, respectively. The resulting hybrids can be made into free‐standing conducting composites or applied in the form of thin, pH‐switchable bioadhesive coatings onto graphene oxide fibers. Monitoring of cell viability of pancreatic cell lines, seeded on those CNT hybrids, show that they can be used as two‐ and three‐dimensional scaffolds to tissue engineer tumour models for studying ex vivo the tumour development and response to treatment. This highly versatile method in producing pH‐responsive hybrids and coatings offers an attractive platform for a variety of biomedical applications and for the development of functional materials such as smart textiles, sensors and bioelectronic devices.

E Abuelhia, K Alzimami, M Alkhorayef, Z Podolyak, NM Spyrou (2008)Measurement of coincidence timing resolution of scintillation detectors compared to semiconductor detectors to image three-photon positron annihilation, In: JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY278(3)pp. 767-771 SPRINGER