Studies have concluded that streams emit CO2, which indicates that natural sources of Greenhouse Gases can contribute to climate changefeedback. Why this is of interest is to be able to make reliable climate models. These studies are however debated, since there are differentmethods to measure CO2 evasion from streams which conclude that different hydrological and chemical factors are affecting the gas exchange themost. It is based on an upside-down-placed chamber in the streams, containing a sensor which is able to directly measure the partial pressure ofCO2 (pCO2) in streams. An advantage with this method is that it is built on cheap equipment and therefore can be afforded to cover a bigcatchment with differing hydrological factors. The aim for the thesis is to evaluate the usefulness of this new method by running several statisticalanalyses on the collected data and also by comparing the trend from the statistical results to other methods statistical trends of pCO2. What can beconcluded by this study is that discharge affects the pCO2 in streams and it often appears with a negative correlation. Also, diurnal patterns ofpCO2 seem to appear, with a peak before lunch and minimum levels in the afternoon, which could indicate that pCO2 are dependent onphotosynthesis/respiration and/or temperature. These conclusions are of interest to understand how C acts in freshwater and respond to the climatechange. The study has to be extended with investigation of how more factors affect pCO2 and also some improvement for the method, before itcan be fully used. / Forskning har visat att små skogsbäckar släpper ut CO2 och på så sätt bidrar de till naturliga utsläpp av växthusgaser ochklimatförändringar. Studiernas resultat är dock debatterade då de till att börja med används olika metoder för att dra dessa slutsatser,vilka pekar på både olika kvantiter av CO2 utsläpp och också på olika påverkan från hydrologiska och kemiska faktorer. På grund avdetta har en alldeles ny metod utvecklats. Den grundar sig på en uppochnervänd kammare placerad i vatten som med hjälp av eninbyggd sensor fångar upp och mäter partialtrycket CO2 (pCO2) i vattnet. En fördel är att den är byggd av enkelt material til l lågt pris,vilket gör att metoden kan användas på många platser samtidigt, då man har råd med ett stort antal kammare. Målet för avhandlingenär att utvärdera nyttan av denna nya metod genom att köra flera statistiska analyser på de insamlade uppgifterna och även genom attjämföra utvecklingen från statistiska resultaten till andra metoder statistiska trender av pCO2. Studien kan visa att vattenhastighetenpåverkar pCO2 från bäckarna, och korrelationens struktur är betydande på vattennivån i bäcken. Man kan även dra slutsatser om attdet finns en dygnsrytm i hur CO2 släpps ut från bäckar med högsta utsläpp under förmiddagen och lägsta på eftermiddagen. Dettaskulle kunna bero på att CO2 utsläpp beror på fotosyntes/respiration och/eller temperaturskillnader. Dessa slutsatser är väldigtintressanta för att bygga på kunskapen om hur kolemissioner från sötvatten påverkas av klimatförändringarna. Om man utökar studienmed fler möjliga variabler för att studera hur andra miljöfaktorer påverkas pCO2 och modifiera metoden och datainsamlandet något såkan detta vara en metod värd att fortsätta användas.

A heavily filtered fast neutron irradiation system (FNIS) was developed for a variety of applications, including the study of long-term health effects of fast neutrons by evaluating the biological mechanisms of damage in cultured cells and living animals such as rats or mice. This irradiation system includes an exposure cave made with a lead-bismuth alloy, a cave positioning system, a gamma and neutron monitoring system, a sample transfer system, and interchangeable filters. This system was installed in the irradiation cell of the Texas A&M University Nuclear Science Center Reactor (NSCR). By increasing the thickness of the lead-bismuth alloy, the neutron spectra were shifted into lower energies by the scattering interactions of fast neutrons with the alloy. It is possible, therefore, by changing the alloy thickness, to produce distinctly different dose weighted neutron spectra inside the exposure cave of the FNIS. The calculated neutron spectra showed close agreement with the results of activation foil measurements, unfolded by SAND-II close to the cell window. However, there was a considerable less agreement for locations far away from the cell window. Even though the magnitude of values such as neutron flux and tissue kerma rates in air differed, the weighted average neutron energies showed close agreement between the MCNP and SAND-II since the normalized neutron spectra were in a good agreement each other. A paired ion chamber system was constructed, one with a tissue equivalent plastic (A-150) and propane gas for total dose monitoring, and another with graphite and argon for photon dose monitoring. Using the pair of detectors, the neutron to gamma ratio can be inferred. With the 20 cm-thick FNIS, the absorbed dose rates of neutrons measured with the paired ion chamber method and calculated with the SAND-II results were 13.7 ?? 0.02 Gy/min and 15.5 Gy/min, respectively. The absorbed dose rate of photons and the gamma contribution to total dose were 6.7??10-1 ?? 1.3??10-1 Gy/min and 4.7%, respectively. However, the estimated gamma contribution to total dose varied between 3.6 % to 6.6 % as the assumed neutron sensitivity to the graphite detector was changed from 0.01 to 0.03.

Aquatic plants or macrophytes are known as conduits of Methane (CH4), Carbon dioxide (CO2) and Nitrous oxide (N2O) which contribute to the total fluxes of the Greenhouse gases emissions from lakes. Recent studies emphasized that the knowledge on plant mediated emissions calls for more systematic and comparative data especially in the areas of spatial and temporal variability. In this study I measured diel (24 hour) and diurnal(  daily hours only) plant mediated fluxes during four sampling sessions using chamber method from a  Swedish lake in summer 2012. The measurements were conducted on two macrophyte population patterns of mixed plant communities and Equisetum fluviatile (specie-specific) community. CH4 emissions were higher in darker hours and there were no diel correlation between CH4 fluxes and average diel temperature. CH4 fluxes varied between 0.42 mmol m-2d-1 and 2.3 mmol m-2d-1. The CO2 fluxes had negative fluxes in day and positive during the day which was logical due to macrophyte respiration and photosynthesis mechanisms. Occasional daily positive fluxes were seen (only) during the rainy hours and there were no correlation between temperature and diel CO2 fluxes. The total net CO2 exchange was 2.8mmol m-2d-1 indicating that there was more CO2 release in the littoral zone of that lake. N2O fluxes did not show any clear diel or monthly pattern and the fluxes ranged between positive and negative numbers. The N2O fluxes did not exceed 2µmol m-2 d-1 with the total average flux of 0.8µmol m-2 d-1.

Recently, the Oak Ridge National Laboratory (ORNL) successfully encapsulated a new generation of medical grade Cf-252 sources having intensities and size comparable to that of the widely used high-dose-rate (HDR) Ir-192 brachytherapy sources. Advent of the new sources, therefore, marked a new era for Cf-252-based neutron brachytherapy (NBT). As part of source calibration and characterization process, a study has been conducted at Georgia Tech lately on determining the neutron and gamma dose rates in water surrounding the new Cf-252 source. A Lucite-walled water phantom was built for this study. The neutron and gamma dose rates were determined both by ion chamber measurements and by Monte Carlo code MCNP. The results show that the measured neutron absorbed dose rates were approximately 25% lower than that predicted by MCNP for all dose positions in water, suggesting that the Cf-252 content of the new source is actually 25% lower than the ORNL's estimate. The measured gamma absorbed dose rates in water, on the contrary, are higher than that predicted by MCNP. The differences between the measured and MCNP-predicted gamma doses are not uniform for all dose positions; they are most pronounced (~a factor of two) at the distance of 1 cm, and fall to approximately 30% at distances 2 cm and beyond. These results suggest that the spectrum of gamma rays emitted from the new Cf-252 source may contain significantly more low-energy gamma rays than the previously published spectrum used in MCNP.