40 research outputs found
Identification and rejection of scattered neutrons in AGATA
Gamma rays and neutrons, emitted following spontaneous fission of 252Cf, were
measured in an AGATA experiment performed at INFN Laboratori Nazionali di
Legnaro in Italy. The setup consisted of four AGATA triple cluster detectors
(12 36-fold segmented high-purity germanium crystals), placed at a distance of
50 cm from the source, and 16 HELENA BaF2 detectors. The aim of the experiment
was to study the interaction of neutrons in the segmented high-purity germanium
detectors of AGATA and to investigate the possibility to discriminate neutrons
and gamma rays with the gamma-ray tracking technique. The BaF2 detectors were
used for a time-of-flight measurement, which gave an independent discrimination
of neutrons and gamma rays and which was used to optimise the gamma-ray
tracking-based neutron rejection methods. It was found that standard gamma-ray
tracking, without any additional neutron rejection features, eliminates
effectively most of the interaction points due to recoiling Ge nuclei after
elastic scattering of neutrons. Standard tracking rejects also a significant
amount of the events due to inelastic scattering of neutrons in the germanium
crystals. Further enhancements of the neutron rejection was obtained by setting
conditions on the following quantities, which were evaluated for each event by
the tracking algorithm: energy of the first and second interaction point,
difference in the calculated incoming direction of the gamma ray,
figure-of-merit value. The experimental results of tracking with neutron
rejection agree rather well with Geant4 simulations
Discrimination of gamma rays due to inelastic neutron scattering in AGATA
Possibilities of discriminating neutrons and gamma rays in the AGATA
gamma-ray tracking spectrometer have been investigated with the aim of reducing
the background due to inelastic scattering of neutrons in the high-purity
germanium crystals. This background may become a serious problem especially in
experiments with neutron-rich radioactive ion beams. Simulations using the
Geant4 toolkit and a tracking program based on the forward tracking algorithm
were carried out by emitting neutrons and gamma rays from the center of AGATA.
Three different methods were developed and tested in order to find
'fingerprints' of the neutron interaction points in the detectors. In a
simulation with simultaneous emission of six neutrons with energies in the
range 1-5 MeV and ten gamma rays with energies between 150 and 1450 keV, the
peak-to-background ratio at a gamma-ray energy of 1.0 MeV was improved by a
factor of 2.4 after neutron rejection with a reduction of the photopeak
efficiency at 1.0 MeV of only a factor of 1.25.Comment: Accepted for publication in Nuclear Instruments and Methods in
Physics Research, A, 26 May 2009; 13 pages, 5 tables, 12 figure
Compressional-mode resonances in the molybdenum isotopes: Emergence of softness in open-shell nuclei near A=90
"Why are the tin isotopes soft?" has remained, for the past decade, an open
problem in nuclear structure physics: models which reproduce the isoscalar
giant monopole resonance (ISGMR) in the "doubly-closed shell" nuclei, Zr
and Pb, overestimate the ISGMR energies of the open-shell tin and
cadmium nuclei, by as much as 1 MeV. In an effort to shed some light onto this
problem, we present results of detailed studies of the ISGMR in the molybdenum
nuclei, with the goal of elucidating where--and how--the softness manifests
itself between Zr and the cadmium and tin isotopes. The experiment was
conducted using the Mo() reaction at
MeV. A comparison of the results with relativistic,
self-consistent Random-Phase Approximation calculations indicates that the
ISGMR response begins to show softness in the molybdenum isotopes beginning
with .Comment: Accepted for publication to Physics Letters
Search for Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes
Classical novae are thermonuclear explosions in stellar binary systems, and
important sources of Al and Na. While gamma rays from the decay
of the former radioisotope have been observed throughout the Galaxy, Na
remains untraceable. The half-life of Na (2.6 yr) would allow the
observation of its 1.275 MeV gamma-ray line from a cosmic source. However, the
prediction of such an observation requires good knowledge of the nuclear
reactions involved in the production and destruction of this nucleus. The
Na()Mg reaction remains the only source of large
uncertainty about the amount of Na ejected. Its rate is dominated by a
single resonance on the short-lived state at 7785.0(7) keV in Mg. In the
present work, a combined analysis of particle-particle correlations and
velocity-difference profiles is proposed to measure femtosecond nuclear
lifetimes. The application of this novel method to the study of the Mg
states, combining magnetic and highly-segmented tracking gamma-ray
spectrometers, places strong limits on the amount of Na produced in
novae, explains its non-observation to date in gamma rays (flux < 2.5x
ph/(cms)), and constrains its detectability with future space-borne
observatories.Comment: 18 pages, 3 figures, 1 tabl
Milne problem for non-absorbing medium with extremely anisotropic scattering kernel in the case of specular and diffuse reflecting boundaries
WOS:000423107300010The Milne problem is studied in one speed neutron transport theory using the linearly anisotropic scattering kernel which combines forward and backward scatterings (extremely anisotropic scattering) for a non-absorbing medium with specular and diffuse reflection boundary conditions. In order to calculate the extrapolated endpoint for the Milne problem, Legendre polynomial approximation (P-N method) is applied and numerical results are tabulated for selected cases as a function of different degrees of anisotropic scattering. Finally, some results are discussed and compared with the existing results in literature
Compression coated ornidazole tablets for colon specific drug delivery: Development, in vitro evaluation and optimisation by artificial neural network
The objective of the present study is to develop, evaluate and optimize colon targeted tablets of ornidazole. For this aim, the core tablets containing ornidazole were compression coated with different polymer mixtures and subjected to quality control studies. Thereafter, swelling, erosion and dissolution studies were performed under conditions mimicking mouth to colon transit. The results of in vitro studies showed that all of the compression coated tablet formulations prevented the drug release in mimicking conditions of stomach and small intestine. On the other hand, only the tablets that were compression coated with pectin and ethyl cellulose (EC) mixtures provided high ratio of drug release (up to 96%) during 24 h in colonic medium. Thereafter, the release kinetics of all formulations were investigated according to zero order kinetic model and the highest r2 value (0.967) was found to belong the formulation compression coated with 80% pectin and 20% EC N10 mixture. Finally, the large amount of in vitro experimental data obtained in this study was evaluated with artificial neural network (ANN) programme to optimize the best-fit formulation. The results obtained from ANN studies were similar with in vitro evaluation results but they were more accurate. According to ANN evaluation, tablets compression coated with 79.024% pectin and 20.976% EC N10 mixture was found to be the most likely formulation to provide targeting ornidazole for local action in the colon. © 2015, Colegio de Farmaceuticos de la Provincia de Buenos Aires. All rights reserved
Modified F N solution of the neutron transport equation for the Milne problem with FBIS kernel
The solution of the Milne problem is studied by one-speed neutron transport equation in plane geometry with İnönü’s scattering kernel, which is known as a linear combination of the forward, backward and isotropic scattering kernel (FBIS kernel). The solution of the neutron transport equation with İnönü’s scattering kernel can be written in terms of the solution of the neutron transport equation for isotropic scattering case. The extrapolation distance is calculated with modified FN (or HN) method. The numerical values of the extrapolation distance are obtained depending on the secondary neutron numbers and anisotropy coefficients and compared with the available data in the literature values
Nanovesicles for tumor-targeted drug delivery
Cancer is one of the most important burdens for the health systems worldwide due to cancer-related deaths associated with late diagnosis and treatment toxicities. Diagnosis of cancer plays a critical role in reducing cancer death rates as it facilitates early prognosis and treatment. Current cancer treatment mainly includes the resection of tumor tissue, radiation treatment, and pharmaceutical treatment. Although various techniques, methods, and drugs are clinically used in cancer diagnosis and treatment, they are inadequate for early diagnosis and effective treatment. Therefore, several studies regarding cancer-targeted nanosized drug delivery systems and theranostic approach are performed. Nanovesicular systems, one of the most important types of drug delivery systems, are formulated for the effective delivery and controlled release of active compounds such as drugs, genes, phytocompounds, and imaging agents. In this chapter, different types of nanovesicles are reviewed after providing information about conventional cancer imaging and treatment. Furthermore, targeting mechanisms of nanovesicles for cancer are explained. Finally, some studies performed to develop the nanovesicles as the imaging, treatment, or theranostic system for cancer are summarized. © 2022 Elsevier Inc. All rights reserved