Plastic Cap Research Articles

Studies on the aeration improvement of inner bottle(1100ml) culture system during the mycelial culture of Pleurotus ostreatus

ABSTRACTS: The plastic culture bottle cap types and accumulated concentration of carbon dioxide, media humidity in the process of medium culture, chitin content and yield were observed in Pleurotus ostreatus 850ml bottle in Iksan, Jeollabuk-do, Korea, during 2011. The concentration of carbon dioxide in the process of medium culture was the highest after 8~9 days cultivation irrespective of cap sizes and types. The accumulated concentration of carbon dioxide in size cap of 29~41mm was 6.5~4.0% in the upper-under perforation hole of cap and 9.0~6.5% in the under perforation hole of cap. The upper-under 23~33mm perforation hole and under 29mm perforation hole of caps in the 850ml bottle were best condition for cultivation of mushroom and increased fruit body, 15.8~21.2% and 20%, respectively. However, the upper-under & under 41mm perforation hole of fruit body were decreased 60.7% and 23.6%, respectively. Also it was weak, lose vitality and the lower of biologically activity substance because the upper medium humidity was too dry. KEYWORDS : Carbon dioxide(CO

Remarks by Judith Kimerling

I would like to begin with some comments from the field about the application of forum non conveniens by the Aguinda v. Texaco court, and then discuss one of the affected groups, the Huaorani. I have worked in the affected region since 1989, and my research was the basis for the environmental allegations in the complaint, but I am not part of the plaintiffs' litigation team. I have written about the Aguinda litigation in New York, so I will cut to the chase: the application of the forum non conveniens doctrine to dismiss the case was colored by a series of detailed but questionable factual assumptions. Many facts were uncontested. But others are in dispute. One key area relates to control of the operations. While not determinative by itself of the legal issues, the factual issue of where decisions were made about the practices that caused the pollution underlying the claims, and who made them, was a material element of the decision to dismiss. The proposition, advocated by Texaco and accepted by the court, that Ecuadorians controlled the relevant decisions, that employees in the United States had virtually no role in designing or directing the operations, and that environmental practices were regulated by Ecuador, is a recurring theme. The court also distinguished Texaco from Texaco Petroleum, the subsidiary that operated in Ecuador (in a consortium with Ecuador's state oil company). That, and the portrait of the subsidiary as basically an Ecuadorian company far removed from the parent is dramatically different from the image of Texaco in Ecuador, and the impression there that the state had contracted with the U.S. company, Texaco. It is also at odds with the portrait cultivated by Texaco before it was sued, of a multinational industry leader that transferred world-class technology. Ecuador relied on Texaco as the operator of the fields to design, procure, and operate the infrastructure that turned Ecuador into an oil exporter. In its contract with the state, Texaco agreed to train Ecuadorian workers and turn over the operations to the state oil company. Texaco's international prestige and control of field operations gave it enormous power in the oil patch, which was compounded by systemic shortcomings in the rule of law. As for environmental law, there were boilerplate legal directives, but they were not implemented. So Texaco set its own standards, and there was virtually no environmental protection. Workers who were trained by Texaco were so unaware of the hazards of crude oil during the 1970s and 1980s that they put it on their heads to prevent balding. They sat in the sun or covered their hair with plastic caps overnight. To remove the crude, they washed their hair with diesel. Much has been written about the impacts of the operations, so in the interest of time I will just say that pollution and other impacts have made large areas of ancestral Huaorani lands uninhabitable to them. The damage is so serious and widespread that other companies have gone to great lengths to try to distinguish their operations--We're not like Texaco; we use international standards and best practices to protect the environment is a common refrain. The Aguinda court also made erroneous and unsupported findings about the history of litigation in Ecuador. The basic determination--that the case has nothing to do with the United States--is remarkable considering the reality of oil development. The Huaorani have lived in Amazonia since time immemorial. Their ancestral territory includes lands with infrastructure built by Texaco, and lands that were colonized by settlers who followed Texaco into Huaorani territory. When Texaco first struck oil (in 1967, near Huaorani lands), Ecuador's institutions had little influence in the Amazon. The Huaorani who lived in areas where Texaco wanted to operate were free and sovereign, living in voluntary isolation. The discovery of black gold made national integration of the Amazon and pacification of the Huaorani a national policy imperative. …

Adenoma detection with cap-assisted colonoscopy versus regular colonoscopy: a randomised controlled trial

ObjectiveConventional colonoscopy (CC) is considered the reference standard for detection of colorectal neoplasia, but it can still miss a substantial number of adenomas. The use of a transparent plastic cap...

Crescimento e aspectos sintomatológicos na aclimatização de Ipê-roxo

Este trabalho teve por objetivo avaliar a influência do tipo de vedação e substrato na pré-aclimatização e os aspectos sintomatológicos na aclimatização de Ipê-roxo. Para pré-aclimatização, plantas de Ipê-roxo obtidas in vitro por meio de cultura de embriões zigóticos foram inoculadas assepticamente em tubos de ensaio contendo diferentes tipos de vedação (algodão, tampa plástica + parafilme e tampa plástica) e diferentes substratos (ágar, vermiculita e Plantmax®) suplementados com meio de cultivo WPM acrescidos de 1 gL-1 de carvão ativado, 10 mgL-1 de ácido cítrico e 30 gL-1 de sacarose. Para a aclimatização, plantas de Ipê-roxo obtidas in vitro foram transplantadas para tubetes de 56 cm³; contendo vermiculita e Plantmax®na proporção 2:1, previamente autoclavado a 121ºC e 1 atm, por 20 minutos. Após o transplantio, as plantas foram irrigadas com diferentes concentrações do meio MS (25%, 50%, 75%, 100% e 150%), sendo utilizada como controle água destilada. Após 30 dias, foram verificados efeitos do tipo de vedação e substrato na pré-aclimatização. O algodão pode ser recomendado quando se utiliza Plantmax®ou vermiculita como substrato. Na aclimatização, verificou-se que as plantas quando irrigadas com água destilada e concentrações < 50% apresentaram sintomas de deficiência nutricional. Foram observados sintomas semelhantes com a utilização de MS em concentração igual ou superior a 100%. A concentração 75% do meio MS foi a mais eficiente na manutenção do vigor nutricional de mudas de Ipê-roxo em processo de aclimatização.

DEVELOPMENT OF IN VITRO PROPAGATION AND CONSERVATION PROTOCOLS OF THE NATIVE BRAZILIAN MANGABA TREE

DEVELOPMENT OF IN VITRO PROPAGATION AND CONSERVATION PROTOCOLS OF THE NATIVE BRAZILIAN MANGABA TREE

Pasteurization: A reliable method for preservation of nutrient in seawater samples for inter-laboratory and field applications

Following previous work, the production of reference material for nutrients in seawater, using pasteurization as a preservation method, was carried out seven times between 2006 and 2010 in the framework of inter-laboratory exercises. The preparation of samples from natural seawater allowed to become depleted in nutrients then spiked, bottled and pasteurized, is described. Five main nutrients are involved in this study: ammonium, nitrite, nitrate, phosphate and silicate. Bottles are in glass for the ammonium samples and in plastic for the other nutrients. Pasteurization was performed at 80 ± 3 °C for 2 h. Samples were controlled for homogeneity and stability at 3–5 month interval, before and after the period allocated for each exercise and a third time between 8 to 40 months storage. Homogeneity, not altered by sample aging, remains within a few nanomoles per litre for nitrite (< 1.4 μmol/L) and phosphate (< 3 μmol/L) and within a few tens of nanomoles per litre for ammonium (< 4.5 μmol/L), nitrate (< 35 μmol/L) and silicate (< 30 μmol/L). Except for ammonium, stability data are close to homogeneity data at the low level and within 0.3–0.5% at the high level. Ammonium shows a slight drift due to atmospheric contamination through the plastic cap, in the order of 0.1 μmol/L per year, which allows nevertheless an acceptable performance over an 1–2 month analytical delay. Except for ammonium, pasteurization does not produce detectable concentration changes, thus it can be applied to field samples for long term storage at ambient temperature.

Transcutaneous implant evacuation system: a new approach to continent stoma construction

Several attempts have been made to construct a mechanical continent stoma without success. A system based on a titanium implant has been developed in an animal model. Following evaluation of this device in animals, the transcutaneous implant evacuation system (TIES) has now been tested in humans. The implant consists of a titanium cylinder including a mesh and a plastic cap. This design allows the intestine and subcutaneous tissue to grow into the device. Four patients with inflammatory bowel disease underwent surgery. The indications for surgery were malfunctioning pouches or skin problems around the stoma. Following abdominal surgery, implantation of the device was made behind the external fascia with diversion of the ileum through the device to create a permanent stoma. Primary surgery was uncomplicated. Skin tissue growth into the implant was delayed in one case and one patient had impaired healing between intestine and the device. In these cases minor surgical correction was necessary. The tested cap design in the current device was inconvenient and needs to be further developed. No local infections occurred. This first clinical study of the TIES device has shown few device-related complications and no significant safety concerns. In our experience bridging of connective tissue between the intestine and skin is crucial for healing. Further development of the lid, the implant and the implantation method within clinical trials is necessary before the device can be introduced in general practice.

Endoscopic full-thickness resection in the colon by using a clip-and-cut technique: an animal study

Although endoscopic resection techniques have been established for definitive therapy of mucosal neoplasia, complete histopathological assessment or resection of subepithelial lesions is not reliably possible. To overcome these limitations, a novel endoscopic full-thickness resection (EFTR) and closure technique was developed. Animal survival study. Eight female domestic pigs. Two-centimeter artificial distal colonic lesions were created endoscopically. EFTR of the lesions was attempted using a prototype device, which consists of a large transparent plastic cap with a preloaded snare and a modified over-the-scope clip. After the procedure, half of the animals were killed after 7 days, and the other half after 28 days. Complete resection (all markings included in the specimen), technical success, complication rates, and wound healing on follow-up autopsy and histology. EFTR of healthy colonic tissue was possible in all cases; 2 additional clips had to be placed for complete closure in 1 case. In 1 animal, the preloaded closure failed, and the animal was prematurely killed. All other animals had an uneventful postoperative course. Necropsy and histopathological evaluation demonstrated well-healed resection sites with no evidence of intra-abdominal infection or inadvertent organ inclusion. Animal model, resection of healthy tissue. This novel device allows for reliable full-thickness resection and closure of 2-cm specimens of the colonic wall in a single procedure as well as reliable wound healing of EFTR defects.

Retention of Implant-Supported Overdenture With Bar/Clip and Stud Attachment Designs

The degree of retention for overdenture attachments depends on design, location, and alignment of supporting dental implants and the type of attachments. The aim of this study was to evaluate the retention of an implant-supported overdenture with different attachment designs. An overdenture was made on an edentulous mandibular model with 2 ITI implants (4.1 × 10 mm) in the symphyseal region. Five specimens of 8 attachment designs with corresponding abutments and superstructures were used: ITI regular Dolder bar with 1 metal clip, ITI regular Dolder bar with cantilever and 3 metal clips, Hader bar with 1 plastic clip, Hader bar with cantilever and 3 plastic clips, Sphero block abutment with Rhein plastic caps (green, white, and pink), and retentive anchor with ITI elliptical matrix. The attachments' housings were interchangeable and fixed into the overdenture through nut and screw. The overdenture attachments were subjected to 8 consecutive pulls on a universal testing machine with a crosshead speed of 50.8 mm/min in the vertical and posteroanterior directions. Analysis of variance and Duncan tests were used to determine differences between mean retention values (α = .05). The highest average value retention was recorded for the ITI Dolder bar with cantilever and 3 metal clips in both the vertical and posteroanterior directions, respectively (P < .05). The Rhein pink caps had the lowest retention in the posteroanterior direction (P < .05). Retention decreased over the course of consecutive pulls for all attachments in both directions. The type, number, and placement of attachments affect the retention of implant-supported mandibular overdentures.

Experimental Research on Using Heat Shrinkable Material to Protect Prestressed Anchor

nchor is the key component for force transmission of prestressed structure. It is difficult for the current sealing technology of anchor to ensure the normal performance of strand. And it will directly affect the bearing capacity and durability of the whole prestressed structure. The advanced method abroad smears anti-corrosion grease at the end of anchor, and then covers it with plastic cap. Based on the national patent: the method of using heat shrinkable material to protect prestressed anchor(patent number: ZL200710304303.2), some experiments of using heat shrinkable material to protect anchor are carried out, such as the construction technology verification, the electrical insulation and the sealing experiment, and anti-stripping experiment. The results show that the method of using heat shrinkable material to protect anchor has the advantages of simple and reliable construction technology, short construction period, low cost, good electrical insulation, high sealing property and anti-stripping strength. This method can protect the anchor of prestressed system very well, and has wide application value.

Everyday Fingers

This article presents an overview of the artificial X-Finger created by Didrick. These surgical steel fingers can move, flex, and grasp, just like the wearer’s original fingers. The device is composed of stainless steel, with a plastic cap that sits on the tip of the finger and another bit of plastic that sits at the flange. This is covered with a thermoplastic cosmetic skin that is soft and resists tearing. Each finger contains 23 moving parts, though depending on the complexity of the case—such as whether the wearer retains a residual finger or not—it could contain more. For those without residual fingers, a wire runs into the webbing between the fingers to receive open and flex impulses. The device is attached to the wrist and fitted over the hand and the residual fingers. For those who have lost four fingers, the device allows the movement of the palm to control all the artificial fingers.

Seismic Behavior of Soil-Pile-Structure Interaction in Liquefiable Soils: Parametric Study

Nonlinearity of the soil medium plays a very important role on the seismic behavior of soil-pile-structure interaction. The problem of soil-pile-structure interaction is further complicated when the piles are embedded in liquefiable soil medium. A finite-element code was developed in MATLAB to model three-dimensional soil-pile-structure systems. Frequency dependent Kelvin elements (spring and dashpots) were used to model the radiation boundary conditions. A work-hardening plastic cap model was used for constitutive modeling of the soil medium. The pore pressure generation for liquefaction was incorporated by a two-parameter volume change model reported in the literature. In this paper, a 2×2 pile group in liquefiable soil is considered and a parametric study is conducted to investigate its seismic behavior. The effects of loading intensity and stiffness of the soil on the seismic behaviour of the soil-pile system are investigated, considering nonlinearity and liquefaction of the soil medium for a wide ran...

A New Method for Short-Term Rearing of Citrus Psyllids (Hemiptera: Pysllidae) and for Collecting their Honeydew Excretions

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an eco nomically important pest of citrus in the United States, Asia and other parts of the world, as a vec tor of huanglongbing (HLB) or citrus greening, which is considered one of the world's most seri ous diseases of citrus (Gottwald 2010). Addition ally, large populations of ACP can damage plants directly through feeding and excretion activities; ACP feeds on citrus phloem tissues and produces copious amounts of honeydew excretions (Brian sky & Rogers 2007). ACP adults can feed on ma ture citrus leaves, but nymphs must have young tender flush to survive. For biological and patho gen-vector relation studies on ACP (e.g., Wen ninger & Hall 2007; Pelz-Stelinski et al. 2010) rearing of single or small groups of psyllid nymphs or adults on whole citrus plants takes considerable space, time and other resources. Here, we describe a new, simpler method for short-term rearing of ACP using detached mature citrus leaves for adults and detached young ter minal shoots for nymphs (Fig. 1). ACP adults and nymphs were reared singly or in small groups (5-10 per tube) in clear plastic (polypropylene) 50-ml conical centrifuge tubes (3 cm wide and 11.5 cm long; Fisher Scientific, Pitts burg, PA). Young psyllid adults (approximately 1 wk-old) were reared on detached, mature, me dium-size leaves of sweet orange (Citrus sinensis (L.) Osbeck var Ridge Pineapple). Leaf sizes used for adults ranged between 3-4 cm in width and 6-8 cm in length with petioles about 2-3 cm long. The petioles of these leaves were cut diagonally with a sharp razor blade, and each inserted in a small (0.3 or 0.5 mL) microfuge tube filled with water or a piece of moistened cotton wool (Figs. 1A and IE). A piece of Parafilm membrane was wrapped around the top of this tube and the petiole to keep insects from drowning or contact with water. The detached leaf and microfuge tube were then inserted into the rearing tube, and the psyllid adults were added to the latter. The rearing tube was covered with a screw cap that had been finely perforated by a hot needle for ventilation. For better ventilation, how ever, wider holes can be cut in the plastic cap and a piece of fine mesh screen placed under the screw cap to prevent escape of the psyllids. The tubes were kept in an environmental chamber at 25°C and 14 h light per day. The clear plastic wall of the rearing tubes al lowed close observation and photography of the enclosed psyllids during their various activities either by the naked eye or through a stereomicro scope with minimal disturbance (Figs. IB-IE). For example, adults were observed feeding for long periods in their normal feeding posture (Fig. IB) mainly on the midrib or other veins on either side of the detached leaves. They were also observed excreting honeydew droplets regularly (Fig. IE), and occasionally laying eggs (Fig. IB in set), although they normally prefer younger leaves for laying eggs (Brlansky & Rogers 2007). Survival of young adults under the above condi tions on detached mature leaves, that were changed to fresh ones weekly, was 89, 80 and 75% after 2, 3, and 4 weeks, respectively (n = 130 adults). It was later observed, however, that ma ture leaves can stay fresh in the rearing tubes at least for 2 weeks.

670 Adenoma Detection With Cap-Assisted Colonoscopy Versus Regular Colonoscopy: A Randomized Controlled Trial

Colonoscopy is widely accepted as the gold standard for detection of colorectal neoplasia, but it is also known to be an imperfect test. Adenoma detection miss-rates were reported in tandem colonoscopy studies to be as high as 22% for all size adenomas. Performing colonoscopy with a transparent plastic cap attached to the tip of the colonoscope (cap-assisted colonoscopy) may enhance adenoma detection due to improved visualization of the mucosal surface.

Plastic Pollution at a Sea Turtle Conservation Area in NE Brazil: Contrasting Developed and Undeveloped Beaches

Sea turtles are highly susceptible to plastic ingestion and entanglement. Beach debris were surveyed along the most important sea turtle nesting beaches in Brazil (Costa dos Coqueiros, Bahia State). No significant differences among developed and undeveloped beaches were observed in terms of total number of items. Local sources (tourism activities) represented 70% of debris on developed beaches, where cigarette butts, straws, paper fragments, soft plastic fragments, and food packaging were the most abundant items. Non-local sources (domestic and fishing activities) accounted for about 70% of debris on undeveloped beaches, where the most abundant items were rigid plastic fragments, ropes, soft plastic fragments, caps, and polystyrene. The projected surface area of beach debris did not vary among developed and undeveloped beaches. Overseas containers accounted for about 25% of regional plastic pollution, implying that international pollution prevention agreements are not being respected off the Brazilian coast.

Portrait of a Vincy Artist: Caroline “booops” Sardine

Nothing of him but doth changeInto something rich and strange.-Shakespeare, The TempestCAROLINE BOOOPS SARDINE WAS, as she says, one uv the very few children uv European-Creole blud 'born and bred' in St Vincent and the Grenadines [population 100,000] - BLACK was di culah uv my x-istance.1 Thirty-two years later, booops still lives in her parents' house on the outskirts of Kingstown, a stone's throw from the nearby coffee plantation house, Grand View, now a small hotel run by her parents. The family home on its small hill overlooking the bay she describes as a tabernacle, with its connotations of enclosure, protection and consecration. Its sacred contents are things old, all things weathered, all things broken.2This description is the key to Caroline's transformation into booops, an artist with a remarkable vision; a lower-case persona whose thoughts in Sycorax video-style nation language are graffiti-ed across large canvases and inscribed on assemblages. The house she grew up in is itself an assemblage of old things, a family history told in piles of accumulated clutter, juxtaposed with natural incursions in the shape of birds' nests or creepers. The views framed by the windows - of exclusive Young Island and Dove Island with its giant white cross marking a rich man's grave - are a feature of her imagery. I first saw her work when, wandering into Grand View for a drink, I found myself in the bar confronted by a six-foot-high naked woman bleeding from the vagina. I hadn't met booops then, and could not imagine how these uncompromising canvases had come to rest in the tranquil surroundings of a boutique hotel. I was shocked and puzzled by the violence done to dismembered or wounded female bodies with graffiti-like slogans scrawled across them (Figures I, 2). The disturbingly personal iconography of the paintings gestured towards something autobiographical, some painful experience which had driven the artist to represent it over and over again. What, for example, could explain the preoccupation with blood in the paintings - red tears seeping from eyes as well as menstrual blood gushing from the vagina, red footprints, bloodied hands? (See Figure 3.) At the same time the paintings were large, bold of line and vibrantly colourful, not austere at all. I sensed conflicted experience and a complex vision, and was driven to find out more.Since then, I have seen booops's work in many contexts - in her small studio in a converted garage; in galleries in Barbados and Jamaica; in the little craft shop she ran for a while and on the walls of offices in Kingstown, as well as those of private collectors in Barbados where she first went to study art. It takes the form of paintings, embroidered hangings, collage and box-like assemblages of found objects and cheap, throwaway materials like hardboard, plastic and metal bottle caps. When you see a booops piece you know it's hers not only because of obsessively recurring themes of violence and abuse, with their attendant motifs of dismembered body parts (hearts, overgrown feet, watchful eyes, blood), but by its combination of naivety of line, bold colour and distinctive iconography which demands to be decoded. For example, the small house on a small island surrounded by sea, the sheltering roof under a sunburst sun, the cross on a hill seen from a window (Figures 6, 7), are icons of safety and refuge which can also take the form of a box, a reliquary or a shrine enclosing precious personal totems. But the childlike sun beaming on a place of innocence belies the rupture which is the subject of the work. The sheltering space is also a kumbla, an ambivalent image of protection perpetually under threat.What happened to booops to bring about such a disturbing vision of a small-island society? The first and most obvious rupture was leaving home to study fine art at Barbados Community College in 1996; then at the Edna Manley College of the Visual and Performing Arts in Jamaica where she gained a diploma in painting in 1998; and finally leaving for London to gain an MA in painting at the Royal Academy of Art in 2000. …

Influence of flask sealing and activated charcoal on the morphogenesis and leaf anatomy of Annona glabra (Annonaceae) cultured in vitro

This study evaluated the effects of the type of tube closure and the use of activated charcoal in the morphogenesis and leaf anatomy of Annona glabra (Annonaceae). Nodal segments of A. glabra were inoculated in WPM medium supplemented with 30 g l-1 sucrose and five concentrations of activated charcoal (0, 1, 2, 3 and 4 g l-1). During in vitro culture, nodal segments were kept in test tubes closed in one of three ways: plastic cap sealed with PVC wrap, plastic cap without a PVC wrap and cotton plug. The results showed that the shoots obtained in tubes closed with a plastic cap without a PVC wrap or sealed with a cotton plug had increased growth compared to those obtained in tubes sealed with a plastic cap and a PVC wrap. The presence of activated charcoal caused a reduction of leaf abscission and influenced the anatomical development of the shoots in the tubes sealed with a cotton plug and sealed with a plastic cap without a PVC wrap. The highest means for leaf tissue thickness were obtained from the shoots kept in closed tubes with a plastic lid and a PVC wrap in the absence of activated charcoal.

Cuerpos extraños alojados en las vías aérea y digestiva. Diagnóstico y tratamiento

Introduction. Foreign body aspiration is one of the most common accidents in childhood morbidity and mortality. 3,9 This problem is caused, among other reasons by children’s curiosity, by immaturity of the swallowing mechanism and by anatomical narrowing of the pathway where most of the foreign bodies become. 4,5,22 Material and methods. This report describes the types of objects lodged in the airway and in the digestive tract; the time and the method of extraction, treated at the Hospital for Children in Toluca, from January 2008 to April 2009. It is a cross-sectional, retrospective and descriptive study. 82 patients who underwent laryngoscopy, bronchoscopy or panendoscopy, of foreign bodies lodged in either airway or digestive tract. Patients’ average age was two years; male sex predominated with 47 patients (57%), 35 female patients (43%). Procedures performed: laryngoscopy in 54 patients (67%), bronchoscopy, 19 (23%) and panendoscopy 9 (10%). Most procedures were done in an average time of 5 to 10 minutes. Results. The following objects were found: coins (65.8%); peanuts (7.3%); metal disk, fish bone, plastic cap (3.6%), metal cross, apple seed, grain corn (2.4%), crayon and pine branch (1.2%). A high percentage of foreign bodies were coins in the esophagus removed by direct laryngoscopy in a procedure lasting between 2 and 10 minutes. The only complication was glottic edema secondary to manipulation in one patient. Conclusion. The importance of a prompt removal of foreign bodies is the priority of maintaining an open airway, given its closeness to the digestive tract.

The Cost of Learning From Our Mistakes

The Cost of Learning From Our Mistakes

Impact of oxygen on the accuracy and precision of normoxic polymer gel dosimeters

Diffusion of oxygen in normoxic polymer gel dosimeters was studied. Gel samples in glass tubes were exposed to oxygen for different periods and then irradiated. Oxygen inhibited polymerization at the surface and polymerization occurred at larger depths. However the interface between these two regions revealed a local increase of polymerization. R2 values in these distinct regions are analyzed in terms of the concentration of oxygen and of antioxidant. Perhaps counter-intuitively, a small concentration of oxygen increases the sensitivity of the gel by consuming antioxidant molecules. The presence of antioxidant molecules is shown to cause a decrease of sensitivity, presumably through interactions with water free radicals and/or polymer radicals. Mixing and filling procedures as well as oxygen penetration from plastic caps or walls of gel containers are potential sources of oxygen-related discrepancies in normoxic polymer gel dosimeters. This effect may cause dosimetric inaccuracies of up to 60%.