Application to Polymers

Mallon, Peter E.

doi:10.1142/9789812775610_0010

Cited by 50 publications

(18 citation statements)

References 69 publications

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“…From this table we observe that in human skin the o-Ps intensity (I 3 ) is about 13-15% and the o-Ps lifetime (τ 3 ) is between 1.9 to 2.0 ns. These data are similar to polymeric materials [7]. Also Comparing the values of I 3 and τ 3 between the sample pair with and without cancer from the same patient we find both o-Ps I 3 and τ 3 in this experiment under wet condition are consistent with the slow positron beam data at the skin depth > 5 keV (or 1 µm) [6].…”

Section: Introductionsupporting

confidence: 85%

“…The long lifetime (τ 3 ) is assigned to ortho-Ps (o-Ps, a triplet state) with intensity (I 3 ). τ 3 is used to calculate the mean radius (R) of free volume (fv) and along with I 3 , to estimate the relative fractional free volume (ffv) in the skin according to the established method in polymeric research [7]. PAL data were also analyzed into a continuous lifetime distribution using the MELT program.…”

Section: Introductionmentioning

confidence: 99%

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Applications of positron annihilation to dermatology and skin cancer

Liu

Chen

Chakka

et al. 2007

Phys. Status Solidi (c)

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Positronium annihilation lifetime experiments have been performed to investigate the interaction between skin cancer and positronium for human skin samples. Positronium annihilation lifetime is found to be shorter and intensity is found to be less for the samples with basal cell carcinoma and squamous cell carcinoma than the normal skin samples. These results indicate a reduction of free volume in the molecular level for the skin with cancer with respect to the skin without cancer. Positron annihilation spectroscopy may be potentially developed as a new noninvasive and external method for dermatology clinics, early detection of cancer, and nano-PET technology in the future. However, the sun's UV-radiation can cause skin damage including wrinkles, lowered immunity against infection, aging skin disorders, and also lead to cancer [2]. The possible mechanisms for UV skin damage are collagen breakdown, the formation of free radicals, interfering with DNA repair, and inhibiting the immune system. The current method to diagnose skin cancer uses an invasive biopsy which is surgically excised from human body for pathological analysis [3]. This is a destructive technique which can cause a scar in the skin. Therefore, to develop a non-invasive and external technique to detect skin diseases is becoming one of most significant research areas for dermatology and skin cancer.Currently, one of the most practical methods in detecting cancer is Positron Emission Tomography (PET), which uses nuclear medicine containing positron emitters to generate positron annihilation radiation inside human body and then utilizes the gamma energy imaging technology to detect tumors [4]. However, PET is mainly for internal use and the detection focuses on the size (in mm) of tumor. The important information about molecular interaction between positron and cancer has not been investigated in current PET technique. Positron annihilation spectroscopy (PAS) has been recently developed to determine defects at a size in the order of 0.1-2 nm in polymeric materials [5] since the positronium (Ps, a bound atom consisting of a positron and an electron) was found to preferentially exist in free volumes.Recently we discovered that in a variable energy positron beam experiment the positron annihilation rate is significant lower for skin samples with cancer cells of basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) comparing with the skin without cancer cells [6]. However, those beam experiments were performed under high vacuum condition and the skin samples were dried. A more realistic measurement for skin system is for the skin in the presence of water molecules. In this paper we report

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Section: Introductionsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Applications of positron annihilation to dermatology and skin cancer

Liu

Chen

Chakka

et al. 2007

Phys. Status Solidi (c)

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“…Among the available techniques, positron annihilation lifetime spectroscopy (PALS) has become popular, since it is a relatively simple way to probe the properties of free-volume holes in a nondestructive way [Mallon, 2003;Dlubek et al, 2004]. The technique is based on the fact that when positrons are injected into a material under investigation, some may form an unstable electron-positron complex, termed positronium (Ps), which becomes trapped in low-electron-density regions of the host matrix (i.e., holes).…”

Section: Introductionmentioning

confidence: 99%

Morphology of Free‐Volume Holes in Amorphous Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Consolati

Quasso

2010

Polymer Physics

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“…The obtained DBES spectrum was expressed as the S parameter, which is defined as a ratio of integrated counts near 0.511 MeV at the central part to the total counts. The S parameter has been employed to indicate the relative free-volume quantity in polymeric materials since it is mainly derived from para-Positronium (p-Ps, the singlet positronium) annihilation in molecular systems (Jean et al, 1997;Mallon, 2003). The energy resolution of the solid detector was 1.5 keV at 0.511 MeV.…”

Section: Methodsmentioning

confidence: 99%

“…Recently, PAS has been successfully developed (Jean, 1990(Jean, , 1993Mallon, 2003) to measure the free volume in polymeric materials at a size on the order of 0.1-2 nm. The selectivity of detecting those sub-to nanometer defects in complicated polymeric systems is magnified by the fact that the positronium (Ps) is preferentially localized in the free volume (Jean, 1996;Jean et al, 2003).…”

Section: Introductionmentioning

confidence: 99%