Dynamics of core-excited ammonia: disentangling fragmentation pathways by complementary spectroscopic methods

Fragmentation dynamics of core-excited isolated ammonia molecules is studied by two different and complementary experimental methods, high-resolution resonant Auger spectroscopy and electron energy-selected Auger electron–photoion coincidence spectroscopy (AEPICO). The combined use of these two techniques allows obtaining information on different dissociation patterns, in particular fragmentation before relaxation, often called ultrafast dissociation (UFD), and fragmentation after relaxation. The resonant Auger spectra contain the spectral signature of both molecular and fragment final states, and therefore can provide information on all events occurring during the core-hole lifetime, in particular fragmentation before relaxation. Coincidence measurements allow correlating Auger electrons with ionic fragments from the same molecule, and relating the ionic fragments to specific Auger final electronic states, and yield additional information on which final states are dissociative, and which ionic fragments can be produced in timescales either corresponding to the core-hole lifetime or longer. Furthermore, we show that by the combined use of two complementary experimental techniques we are able to identify more electronic states of the NH2+ fragment with respect to the single one already reported in the literature

Enhancing surface production of negative ions using nitrogen doped diamond in a deuterium plasma

The production of negative ions is of significant interest for applications including mass spectrometry, particle acceleration, material surface processing, and neutral beam injection for magnetic confinement fusion. Methods to improve the efficiency of the surface production of negative ions, without the use of low work function metals, are of interest for mitigating the complex engineering challenges these materials introduce. In this study we investigate the production of negative ions by doping diamond with nitrogen. Negatively biased ($-20$ V or $-130$ V), nitrogen doped micro-crystalline diamond films are introduced to a low pressure deuterium plasma (helicon source operated in capacitive mode, 2 Pa, 26 W) and negative ion energy distribution functions (NIEDFs) are measured via mass spectrometry with respect to the surface temperature (30$^{\circ}$C to 750$^{\circ}$C) and dopant concentration. The results suggest that nitrogen doping has little influence on the yield when the sample is biased at $-130$ V, but when a relatively small bias voltage of $-20$ V is applied the yield is increased by a factor of 2 above that of un-doped diamond when its temperature reaches 550$^{\circ}$C. The doping of diamond with nitrogen is a new method for controlling the surface production of negative ions, which continues to be of significant interest for a wide variety of practical applications

Etude de la production d'ions négatifs en surface dans un plasma H2 et D2 sans césium à basse pression

Cette thèse porte sur l’étude de la production de surface des ions négatifs (IN) pour des applications dans la fusion thermonucléaire. Ce travail a été réalisé à l'aide d'une source plasma PHISIS. Les IN formés en surface de l'échantillon sont collectés et analysés avec un spectromètre de masse (SM). La fonction de la distribution en énergie des ions négatifs FDEIN est mesurée. Dans cette thèse, une technique de polarisation DC pulsée est introduite pour permettre l'étude de la production d'IN en surface sur des échantillons isolants comme le diamant. Un modèle qui calcule le taux de changement de la variation de la tension sur une surface isolante polarisée en mode pulsé est développé. De façon surprenante, la production d’IN en surface sur un diamant dopé au bore ou non dopé est beaucoup plus élevée en mode pulsé qu'en mode continu. Il est traité également la production d’IN en surface dans les conditions de faible tension de polarisation. Le meilleur rendement d’IN mesuré à faible polarisation est obtenu avec du diamant dopé au bore (BDD) et il est 2 fois plus élevé que celui mesuré sur HOPG (high oriented pyrolitic graphite). L'analyse de la production d’IN en surface à différents polarisations pour différents matériaux a été effectuée afin de corréler l'évolution du rendement d’IN aux changements d'état de surface. Une étude approfondie de la production en surface d'IN a été réalisée sur la surface de Nanoporous 12 CaO. 7Al2O3 electride surface. L'influence des conditions expérimentalles sur le rendement en IN a été étudiée. Dans cette contribution, nous montrons que ce matériau pourrait potentiellement être utilisé dans les sources d'ions négatifs sans césiumThis thesis deals with negative ions (NI) surface production for applications in thermonuclear fusion. This work was conducted using a plasma source PHISIS. NI formed on a negatively biased sample surfaceare collected and analyzed with energy mass spectrometer (MS). Negative ion distribution function NIEDF is measured. A SIMION calculation was done to have a complete idea about MS transmission effect on the NIEDF. In the course of this thesis, a DC pulsed bias technique is introduced to enable the study of negative ion surface production on insulating samples as non-doped diamond layers. A model that calculate the rate of change of bias on insulator surface biased in pulsed mode is developed. Surprisingly, negative-ion surface production on boron-doped or non-doped diamond is much higher in pulsed mode than in continuous mode. This thesis deals also with negative ion surface production in low bias condition. The best NI yield measured at low bias is obtained with Boron doped diamond (BDD) ant it is 2 times higher than the one measured on HOPG (highly oriented pyrolytic graphite) surface. Analysis of NI surface production at different surface bias for different material were performed in order to correlate the NI yield evolution to the surface state changes.An extensive study of NI surface production was performed on Nanoporous 12CaO.7Al2O3 electride surface. The influence of surface temperature, bias and plasma exposure time on negative-ion yield was investigated. In this contribution, we show that the electride material has potentials to be used as a production surface in negative ion sources devoted to nuclear fusion applicatio

Do bites of kissing bugs cause unexplained allergies? Results from a survey in triatomine-exposed and unexposed areas in southern california.

BACKGROUND: The bite of Triatominae can cause cutaneous allergic reactions and even anaphylaxis. Since the early 1980s, no population-based surveys have been done in Southern California, and none was ever carried out in inland Los Angeles or Riverside Counties. OBJECTIVES: To measure the frequency of insect sightings, bites and allergic reactions in a suburban area of eastern Los Angeles County and along with rural and urban sites in Riverside County. METHODS: A door-to-door survey was done in triatomine exposed and unexposed areas. Logistic regression modeling was used for the analysis, and study participants were asked to collect insects. RESULTS: Out of the 221 study participants in the exposed areas, 46 (20%) knew about the presence of Triatominae in their neighborhood. Fifteen (7%) persons reported triatomine sightings in their house during the month preceding the interview. Also, 15 (7%) participants reported ever being bitten by a triatomine. Ten (5%) participants collected either a Triatoma protracta Uhler and/or Paratriatoma hirsuta Barber in and around their house. Twenty-nine (13%) persons in the rural Riverside County reported symptoms compatible with allergy to triatomine bites. This was 4 times higher than in the urban control area where only 4 (3%) of 115 persons reported these symptoms. The association between living in a triatomine-exposed area and self-reported symptoms suggestive of allergies increased slightly when adjusted for the participant's sex and the age of their house (adjusted odds ratio: 5.1, 95% confidence interval: 1.2 to 22.0). Reporting these symptoms was associated with seeing Triatominae in the neighborhood and having been bitten. CONCLUSION: Allergies to triatomine bites could be a significant problem in inland Southern California. Further investigations, a diagnostic test and better information of persons living in triatomine-exposed areas are needed

Negative-hydrogen-ion production from a nanoporous 12CaO ∙ 7Al 2 O 3 electride surface

International audienceA high production rate of negative hydrogen ion was observed from a nanoporous C12A7 electride surface immersed in hydrogen/deuterium low-pressure plasmas. The target was biased at 10-170 V negatively and the target surface was bombarded by H3 + ions from the plasma. The production rate was 1-2 orders higher than a clean molybdenum surface. The measured H-energy spectrum indicates that the major production mechanism is desorption by sputtering. This material has potential to be used as production surface of cesium-free negative ion sources for accelerators, heating beams in nuclear fusion, and surface modification for industrial applications

Characteristics of persons participating in a door-to-door survey in selected areas in Southern California, 2009.

<p>SD = standard deviation. Numbers may slightly differ from the total due to missing data. IQR = interquartile range.</p>*<p>including lizards, birds, rat, rabbits, reptiles, snake, chicken, hamster, tortoise, in addition to cats and dogs.</p

Logistic regression modeling of factors associated with self-reported symptoms typical for those to triatomine bites among persons participating in the survey (n = 336).

*<p>Adjusted for all variables shown.</p><p>Numbers may be slightly lower than the total due to missing data.</p

Comparison of persons with and without self-reported symptoms matching those typical for allergies to triatomine bites in triatomine-exposed areas (n = 221).

<p>Tally may be slightly lower than the total due to missing data.</p>†<p>rashes, red or itchy spots on the body, waking up at night or the morning feeling dizzy, sick, having swollen eyes or difficulties breathing.</p

Main outcomes by triatomine-exposed and -unexposed area (n = 336).

<p>Numbers may be small than the total due to missing data. Triatomine exposed areas were surveyed in summer, triatomine unexposed in winter, which may contribute to the observed differences.</p><p>n.a. =  not applicable, since persons in the control region were not asked to collect insects.</p>*<p>Comparing exposed versus non exposed populations.</p>†<p>rashes, red or itchy spots on the body,</p>#<p>waking up at night or the morning feeling dizzy, sick, having swollen eyes or difficulties breathing.</p>§<p>Only one specimen per insect species listed per study participant.</p