13 research outputs found
Direct and compound-nucleus reaction mechanisms in the Be-7+Ni-58 system at near-barrier energies
The energy and angular distributions of He-3 and He-4 ions produced in
the Be-7 + Ni-58 reaction at a bombarding energy of 22 MeV have been
measured for the first time. The yield of the heavier helium isotope was
four to five times more abundant than that of its lighter counterpart,
ruling out the possibility that in this energy range the Be-7 reaction
dynamics is dominated by the exclusive breakup process Be-7 -> He-3 +
He-4 (S-alpha = 1.586 MeV). Extensive kinematic and theoretical
calculations suggest that the He-3 ions mostly originate from the
He-4-stripping process and the He-4 production is mainly triggered by
the fusion-evaporation channel. The role played by the breakup,
He-3-stripping, 1n-stripping, and 1n-pickup processes is also discussed
Reaction dynamics studies for the system Be-7+Ni-58
The study of reactions induced by exotic weakly bound nuclei at energies
around the Coulomb barrier had attracted a large interest in the last
decade, since the features of these nuclei can deeply affect the
reaction dynamics. The discrimination between different reaction
mechanisms is, in general, a rather difficult task. It can be achieved
by using detector arrays covering high solid angle and with high
granularity that allow to measure the reaction products and, possibly,
coincidences between them, as, for example, recently done for stable
weakly bound nuclei [1, 2]. We investigated the collision of the
weakly bound nucleus Be-7 on a Ni-58 target at the beam energy of 1.1
times the Coulomb barrier, measuring the elastic scattering angular
distribution and the energy and angular distributions of He-3 and He-4.
The Be-7 radioactive ion beam was produced by the facility EXOTIC at
INFN-LNL with an energy of 22 MeV and an intensity of similar to 3x10(5)
pps. Results showed that the He-4 yeld is about 4 times larger than He-3
yield, suggesting that reaction mechanisms other than the break-up
mostly produce the He isotopes. Theoretical calculations for transfer
channels and compound nucleus reactions suggest that complete fusion
accounts for (41 +/- 5%) of the total reaction cross section extracted
from optical model analysis of the elastic scattering data, and that
He-3 and He-4 stripping are the most populated reaction channels among
direct processes. Eventually estimation of incomplete fusion
contributions to the He-3,He-4 production cross sections was performed
through semi-classical calculations with the code PLATYPUS [3]
Transfer vs. Breakup in the interaction of the Be-7 Radioactive Ion Beam with a Ni-58 target at Coulomb barrier energies
We measured for the first time Be-7 elastically scattered nuclei as well
as He-3,He-4 reaction products from a Ni-58 target at 22.3 MeV beam
energy. The data were analyzed within the optical model formalism to
extract the total reaction cross section. Extensive kinematical,
Distorted Wave Born Approximation (DWBA) and Continuum Discretized
Coupled Channel (CDCC) calculations were performed to investigate the
He-3,He-4 originating mechanisms and the interplay between different
reaction channels
The first coronal mass ejection observed in both visible-light and UV H I Ly-alpha channels of the Metis coronagraph on board Solar Orbiter
Context. The Metis coronagraph on board Solar Orbiter offers a new view
of coronal mass ejections (CMEs), observing them for the first time with
simultaneous images acquired with a broad-band filter in the
visible-light interval and with a narrow-band filter around the H I
Ly-alpha line at 121.567 nm, the so-called Metis UV channel.
Aims. We show the first Metis observations of a CME, obtained on 16 and
17 January 2021. The event was also observed by the EUI/FSI imager on
board Solar Orbiter, as well as by other space-based coronagraphs, such
as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here with
Metis data.
Methods. Different images are analysed here to reconstruct the 3D
orientation of the expanding CME flux rope using the graduated
cylindrical shell model. This also allows us to identify the possible
location of the source region. Measurements of the CME kinematics allow
us to quantify the expected Doppler dimming in the Ly-alpha channel.
Results. Observations show that most CME features seen in the
visible-light images are also seen in the Ly-alpha images, although some
features in the latter channel appear more structured than their
visible-light counterparts. We estimated the expansion velocity of this
event to be below 140 km s(-1). Hence, these observations can be
understood by assuming that Doppler dimming effects do not strongly
reduce the Ly-alpha emission from the CME. These velocities are
comparable with or smaller than the radial velocities inferred from the
same data in a similar coronal structure on the east side of the Sun.
Conclusions. The first observations by Metis of a CME demonstrate the
capability of the instrument to provide valuable and novel information
on the structure and dynamics of these coronal events. Considering also
its diagnostics capabilities regarding the conditions of the ambient
corona, Metis promises to significantly advance our knowledge of such
phenomena
First light observations of the solar wind in the outer corona with the Metis coronagraph
In this work, we present an investigation of the wind in the solar
corona that has been initiated by observations of the resonantly
scattered ultraviolet emission of the coronal plasma obtained with
UVCS-SOHO, designed to measure the wind outflow speed by applying
Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS
spectroscopic observations that were performed during solar activity
cycle 23 by simultaneously imaging the polarized visible light and the H
I Lyman-alpha corona in order to obtain high spatial and temporal
resolution maps of the outward velocity of the continuously expanding
solar atmosphere. The Metis observations, taken on May 15, 2020, provide
the first H I Lyman-alpha images of the extended corona and the first
instantaneous map of the speed of the coronal plasma outflows during the
minimum of solar activity and allow us to identify the layer where the
slow wind flow is observed. The polarized visible light (580-640 nm) and
the ultraviolet H I Ly alpha (121.6 nm) coronal emissions, obtained with
the two Metis channels, were combined in order to measure the dimming of
the UV emission relative to a static corona. This effect is caused by
the outward motion of the coronal plasma along the direction of
incidence of the chromospheric photons on the coronal neutral hydrogen.
The plasma outflow velocity was then derived as a function of the
measured Doppler dimming. The static corona UV emission was simulated on
the basis of the plasma electron density inferred from the polarized
visible light. This study leads to the identification, in the velocity
maps of the solar corona, of the high-density layer about +/- 10 degrees
wide, centered on the extension of a quiet equatorial streamer present
at the east limb - the coronal origin of the heliospheric current sheet
- where the slowest wind flows at about 160 +/- 18 km s(-1) from 4
R-circle dot to 6 R-circle dot. Beyond the boundaries of the
high-density layer, the wind velocity rapidly increases, marking the
transition between slow and fast wind in the corona
Relationship between method of anastomosis and anastomotic failure after right hemicolectomy and ileo-caecal resection: an international snapshot audit
Aim The anastomosis technique used following right-sided colonic
resection is widely variable and may affect patient outcome. This study
aimed to assess the association between leak and anastomosis technique
(stapled vs handsewn).
Method This was a prospective, multicentre, international audit
including patients undergoing elective or emergency right hemicolectomy
or ileo-caecal resection operations over a 2-month period in early 2015.
The primary outcome measure was the presence of anastomotic leak within
30 days of surgery, determined using a prespecified definition. Mixed
effects logistic regression models were used to assess the association
between leak and anastomosis method, adjusting for patient, disease and
operative cofactors, with centre included as a random-effect variable.
Results This study included 3208 patients, of whom 78.4\% (n = 2515)
underwent surgery for malignancy and 11.7\% (n = 375) underwent surgery
for Crohn's disease. An anastomosis was performed in 94.8\% (n = 3041)
of patients, which was handsewn in 38.9\% (n = 1183) and stapled in
61.1\% (n = 1858). Patients undergoing hand-sewn anastomosis were more
likely to be emergency admissions (20.5\% handsewn vs 12.9\% stapled)
and to undergo open surgery (54.7\% handsewn vs 36.6\% stapled). The
overall anastomotic leak rate was 8.1\% (245/3041), which was similar
following handsewn (7.4\%) and stapled (8.5\%) techniques (P = 0.3).
After adjustment for cofactors, the odds of a leak were higher for
stapled anastomosis (adjusted OR = 1.43; 95\% CI: 1.04-1.95; P = 0.03).
Conclusion Despite being used in lower-risk patients, stapled
anastomosis was associated with an increased anastomotic leak rate in
this observational study. Further research is needed to define patient
groups in whom a stapled anastomosis is safe
Beta decay of 101Sn
\u3b2 decay of the very neutron-deficient isotope 101Sn was studied at the GSI on-line mass separator using silicon detectors for recording charged particles and germanium detectors for \u3b3-ray spectroscopy. Based on the \u3b2-delayed proton data the production cross-section of 101Sn in the 50Cr + 58Ni fusion-evaporation reaction was determined to be about 60nb. The half-life of 101Sn was measured to be 1.9(3)s. For the first time \u3b2-delayed \u3b3-rays of 101Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065keV transitions in 101In. The results for the 101Sn decay as well as those from previous work on the 103Sn decay are discussed by comparing them to predictions obtained from shell model calculations employing a new interaction in the 88Sr to 132Sn model space
Coupling a CLOVER detector array with the PRISMA magnetic spectrometer
Following the commissioning of the PRISMA large-acceptance spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), an international nuclear-structure collaboration has started to develop a large -ray setup to be installed in the target position of the spectrometer. The array is based on the EUROBALL composite CLOVER detectors. In this contribution the CLOVER detector array is described and its expected performance figures discussed. This new setup, by using the high-intensity heavy-ion beams provided by the LNL ALPI linac, will push the study of nuclear structure towards moderately neutron-rich nuclei by means of quasi-elastic and deep inelastic reactions