Search results for "nucleus"
showing 10 items of 1803 documents
Coherent, semicoherent and incoherent pion production in heavy-ion reactions
1996
Abstract Two types of coherent pion production in heavy-ion collisions are studied and calculations are performed for 12C against 12C collisions. The first one, doubly coherent production, produces a pion in one nucleus leaving it in its ground state, while the second nucleus is excited to the 1+, T = 1 state. The second process, semicoherent production, also leaves in its ground state the nucleus where the pion is produced while the second one is broken. The cross sections for forward pions are compared to the standard incoherent production process. We observe that at energies below 130 MeV/A the semicoherent process dominates the cross section for forward pion angles while at large energi…
Role of in-medium hadrons in photon–nucleus reactions: shadowing and dilepton spectrum
2003
We study the effect of in-medium hadronic properties in photon nucleus interactions in the context of shadowing as well as the dilepton spectrum for incident photon energies in the range 1.1- 3 GeV. A reasonable agreement with the experimental data for shadowing is obtained in a scenario of downward spectral shift of the hadrons. We show that distinguishable features for in-medium changes of the hadronic properties can be observed experimentally through the dilepton spectrum by judicious choice of target nuclei and incident energy of photons.
Coherent γ-production in (p,p′) reactions in nuclei in the Δ resonance region
1998
Abstract We study the process of coherent photon production in nuclei induced by the (p,p′) reaction around the Δ excitation region. The cross sections are about 200 times smaller than the corresponding ones for coherent pion production but within measurable range with present machines. The cross section selects the transverse part of the NN→NΔ transition, while coherent pion production selects the longitudinal one. The reactions are complementary and show different aspects of Δh propagation through the nucleus which are discussed here.
Production of exotic hypernuclei from excited nuclear systems
2012
We show that within a hybrid two-stage approach one can explain novel experimental data on the production of hypernuclei emitted from projectile residues in relativistic ion collisions. This reaction proceeds via formation of intermediate moderately excited hypernuclear systems, which decay into conventional nuclei and hyperfragments afterward. With a similar reaction mechanism one can also obtain weakly bound exotic hypernuclei (such as $\ensuremath{\Lambda}n$ and H-dibaryons), which may not be easily accessible in other processes.
Dependence of the C12(γ→,pd) reaction on photon linear polarisation
2007
Abstract The sensitivity of the C 12 ( γ → , pd ) reaction to photon linear polarisation has been determined at MAMI, giving the first measurement of the reaction for a nucleus heavier than 3He. Photon asymmetries and cross sections were measured for E γ = 170 to 350 MeV. For E γ below the Δ resonance, reactions leaving the residual 9Be near its ground state show a positive asymmetry of up to 0.3, similar to that observed for 3He suggesting a similar reaction mechanism for the two nuclei.
Isomeric state in the doubly odd196At nucleus
2000
An excited isomeric state has been identified in the 196At nucleus using the recoil decay tagging technique. This is the first identification of an excited state in this neutron-deficient odd-odd nucleus. Several tentative prompt γ-rays have also been correlated with 196At α-decay, although it has not been possible to assign them to specific energy levels in 196At. The mean lifetime of the isomeric state has been measured as τ = 11±2 µs. The new level is compared with similar low-lying states in neighbouring nuclei and is de-excited by an E2 γ-ray transition, the large hindrance of which is not expected.
DIRECT PRODUCTION OF PIONIC ATOMS FROM RADIATIVE TRAPPING OF PIONS IN FLIGHT
1992
Abstract The reaction π−A→(πb−A)γ with Tπ=10−30 MeV producing a π− bound in the nucleus is studied to see its viability as an instrument to produce deeply bound pionic atoms in nuclei. We obtain cross sections of the order of tens of μb/ (sr MeV) for the production of the 1s and 2p states of 208Pb and negligible background from radiative pion capture and the other sources. The negligible background expected in the present reaction is unique among all other reactions so far proposed. The cross sections obtained are three orders of magnitude bigger than those in the best electromagnetic reactions previously proposed. The small background, the large cross sections and the present available flu…
Beta-decay of 56Cu
1998
Beta-decay studies of proton-rich isotopes near the doubly closed-shell nucleus 56Ni are of interest as (i) nuclei with a few nucleons outside a doubly-magic core are expected to represent comparatively simple configurations and thus be useful for testing nuclear shell-model predictions, and (ii) the large decay-energy window guarantees that a sizeable fraction of the strength of the allowed β-decay can be reached by the experiment. Moreover, nuclear structure properties of proton-rich N ~ Z isotopes are of astrophysical interest, e.g., concerning the EC cooling of supernovae and the astrophysical rp-process.
Many-body approach to low-energy pion-nucleus scattering
1993
Abstract We have extrapolated for low-energy pions ( T π = 0–50 MeV) the results for the pion-nucleus optical potential previously developed for pionic atoms. The evaluation is done using microscopic many-body techniques which allow us to separate the different contributions to the imaginary part of the potential and relate them to the different reaction channels: quasielastic and absorption. Elastic differential, reaction, absorption and quasielastic cross sections are evaluated for different nuclei and energies and contrasted with experiments. The agreement with data for the different channels, energies and nuclei is rather good with some isolated discrepancies.
A heavy-ion identification system for the detection of rare events
1990
Abstract A large area detection system is described which consists of twelve low-pressure multi-wire proportional counters and is used in the search for exotic super-massive nuclei. The experiments are based on Rutherford backscattering of heavy ions, preferably 208Pb or 238U, from various target samples. The measured parameters of a detected particle are its time-of-flight, scattering angle, and specific ionization. From this information the mass of the target nucleus can be inferred. The present experimental sensitivity for the detection of exotic nuclei with at least twice the mass of the projectile is about 10−12 relative to the number of nucleons.