108 research outputs found
A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures
The 18F(p,alpha) reaction was recognized as one of the most important for
gamma ray astronomy in novae as it governs the early 511 keV emission. However,
its rate remains largely uncertain at nova temperatures. A direct measurement
of the cross section over the full range of nova energies is impossible because
of its vanishing value at low energy and of the short 18F lifetime. Therefore,
in order to better constrain this reaction rate, we have performed an indirect
experiment taking advantage of the availability of a high purity and intense
radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the
first results of the data analysis and discuss the consequences.Comment: Contribution to the Classical Novae Explosions conference, Sitges,
Spain, 20-24 May 2002, 5 pages, 3 figure
New ecological options for the management of horticultural crop pests in Sudano-Sahelian agroecosystems of west Africa
The agroecological approach to agroecosystem management relies on two
pillars: vegetational diversification and soil biological activity enhancement. Although
crop pests and their natural enemies may be diversely affected by measures derived
from these principles, those generally result in increased agroecosystem resilience visĂ -
vis both aerial and soil pests. Earlier studies by ICRISAT and CIRAD and their
partners in West Africa showed the potential of the implementation of these principles
for the management of some major pests of both staple food and horticultural crops,
and their limitations for others, notably in the water-saving and income-generating
systems mixing cereals, legumes, and high-value crops currently promoted in the
Sudano-Sahelian zones, such as the drip irrigation-based African Market Garden
(AMG) and the water harvesting-based Bio-Reclamation of Degraded Lands (BDL)
systems. Pigeon-pea showed potential for trap-cropping tomato fruit worm (TFW) on
okra, while Andropogon grass was dismissed for such management of stem-borer on
pearl millet, and mixed results were obtained with castor bean and other potential
trap crops for panicle-feeding bug management on sorghum. The results presented
highlight the potential for mobilizing either aerial or soil-bound biological processes
for managing fruit flies (FF), the main pest of grafted jujube tree, and leaf worm, the
main pest of the Moringa tree, for sustainable production of these two major crops (in
BDL and AMG systems, respectively), without having to rely on synthetic pesticide
sprays. Studies on the social acceptability of the proposed management options (e.g.,
pigeon-pea in okra-based BDL) are also underway. The potential of the Jatropha
shrub grown as a live-fence around these systems, either for its top-down effects or via
the use of its extracts in an assisted push-pull strategy, is discussed. These studies on
targeted pathosystems serve the dual purpose of finding solutions to local problems
and contribute more globally to the design of pest resilient agrosystems
New ecological options for the management of horticultural crop pests in Sudano-Sahelian agroecosystems of west Africa
The agroecological approach to agroecosystem management relies on two
pillars: vegetational diversification and soil biological activity enhancement. Although
crop pests and their natural enemies may be diversely affected by measures derived
from these principles, those generally result in increased agroecosystem resilience visĂ -
vis both aerial and soil pests. Earlier studies by ICRISAT and CIRAD and their
partners in West Africa showed the potential of the implementation of these principles
for the management of some major pests of both staple food and horticultural crops,
and their limitations for others, notably in the water-saving and income-generating
systems mixing cereals, legumes, and high-value crops currently promoted in the
Sudano-Sahelian zones, such as the drip irrigation-based African Market Garden
(AMG) and the water harvesting-based Bio-Reclamation of Degraded Lands (BDL)
systems. Pigeon-pea showed potential for trap-cropping tomato fruit worm (TFW) on
okra, while Andropogon grass was dismissed for such management of stem-borer on
pearl millet, and mixed results were obtained with castor bean and other potential
trap crops for panicle-feeding bug management on sorghum. The results presented
highlight the potential for mobilizing either aerial or soil-bound biological processes
for managing fruit flies (FF), the main pest of grafted jujube tree, and leaf worm, the
main pest of the Moringa tree, for sustainable production of these two major crops (in
BDL and AMG systems, respectively), without having to rely on synthetic pesticide
sprays. Studies on the social acceptability of the proposed management options (e.g.,
pigeon-pea in okra-based BDL) are also underway. The potential of the Jatropha
shrub grown as a live-fence around these systems, either for its top-down effects or via
the use of its extracts in an assisted push-pull strategy, is discussed. These studies on
targeted pathosystems serve the dual purpose of finding solutions to local problems
and contribute more globally to the design of pest resilient agrosystems
Indirect study of 19Ne states near the 18F+p threshold
The early E < 511 keV gamma-ray emission from novae depends critically on the
18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O
reaction is still largely uncertain due to the unknown strengths of low-lying
proton resonances near the 18F+p threshold which play an important role in the
nova temperature regime. We report here our last results concerning the study
of the d(18F,p)19F(alpha)15N transfer reaction. We show in particular that
these two low-lying resonances cannot be neglected. These results are then used
to perform a careful study of the remaining uncertainties associated to the
18F(p,a)15O and 18F(p,g)19Ne reaction rates.Comment: 18 pages, 8 figures. Accepted in Nuclear Physics
D(18F,pa)15N reaction applied to nova gamma-ray emission
The 18F(p,alpha)15O reaction is recognized to be one of the most important
reactions for nova gamma-ray astronomy as it governs the early E <= 511keV
gamma emission. However in the nova temperature regime, its rate remains
largely uncertain due to unknown low-energy resonance strengths. We report here
the measurement of the D(18F,p)19F(alpha)15N one-nucleon transfer reaction,
induced by a 14 MeV 18F radioactive beam impinging on a CD2 target; outgoing
protons and 15N (or alpha-particles) were detected in coincidence in two
silicon strip detectors. A DWBA analysis of the data resulted in new limits to
the contribution of low-energy resonances to the rate of the 18F(p,alpha)15O
reaction.Comment: Rapid Communication to appear in Phys. Rev. C., 4 pages and 4 figure
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