Thick target neutron yields and angular distributions are essential for shielding calculations for ion beam accelerators. Most of such measurements available in the literature are for proton and ...alpha particle bombardments. In case of heavy ions, very few data are available in the energy region of 20
MeV
amu
−1 and below. We report here the neutron yield, double differential neutron yields and neutron dose equivalent values obtained from the double differential yields at 0° and 90° with respect to the beam for various heavy ions in the energy range of 3.5–7.0
MeV
amu
−1. Pulse shape discrimination was used to separate neutrons from gamma rays and time of flight technique was used for energy measurement. The double differential neutron yields were fitted using the moving source model and the nuclear temperature and source intensity are also determined. The neutron yield increases inversely with the mass of the projectile except in the case of
7Li where the yields are much lower than that obtained from
11B. This could be due to the structure of the loosely bound
7Li projectile. The neutron dose equivalent shows increasing trend with the decrease of the mass of the projectile.
External particle-induced X-ray emission Vijayan, V.; Choudhury, R. K.; Mallick, B. ...
Current science (Bangalore),
09/2003, Letnik:
85, Številka:
6
Journal Article
Recenzirano
Particle induced X-ray emission (PIXE) technique has been used for a variety of analytical applications with an MeV accelerator. Normally, for PIXE analysis, the sample is kept inside a high vacuum ...chamber for bombardment with the particle beam from the accelerator. In case of vacuum-incompatible biological and liquid specimens and for large archaeological objects, it is necessary to take the beam outside the chamber in order to carry out the analysis by the so-called external PIXE technique. In such a case, a number of technical issues such as isolation of accelerator vacuum, beam-charge integration for quantitative analysis, sample scanning and X-ray background suppression, etc. are to be addressed. Recently, at the Institute of Physics, Bhubaneswar, an external PIXE set-up has been installed at the 3 MV tandem pelletron accelerator. This note presents the various aspects of the external PIXE set-up along with some of the experimental results, which demonstrate the applicability of this method to different areas to which these studies can be extended.
Radiocarbon dating has found wide applications in many areas of science like archaeology, geology, oceanography, palaeoseismology and palaeoclimatology. As a tracer, radiocarbon has applications in ...biology and medicine. Radiocarbon dating using Accelerator Mass Spectrometry (AMS) provides several advantages over the conventional decay counting method. The first AMS facility in India for radiocarbon dating has become operational at the Institute of Physics, Bhubaneswar. This note describes the operational features of this facility and inter-laboratory comparison of data.
Nuclear fission process involves large scale shape changes of the nucleus, while it evolves from a nearly spherical configuration to two separated fission fragments. The dynamics of these shape ...changes in the nuclear many body system is governed by a strong interplay of the collective and single particle degrees of freedom. With the availability of heavy ion accelerators, there has been an impetus to study the nuclear dynamics through the investigations of nucleus-nucleus collisions involving fusion and fission process. From the various investigations carried out in the past years, it is now well recognized that there is large scale damping of collective modes in heavy ion induced fission reactions, which in other words implies that nuclear motion is highly viscous. In recent years, there have been many experimental observations in heavy ion induced fission reactions at medium bombarding energies, which suggest possible occurrence of various non-equilibrium modes of fission such as quasi-fission, fast fission and pre-equilibrium fission, where some of the internal degrees of freedom of the nucleus is not fully equilibrated. We have carried out extensive investigations on the fission fragment angular distributions at near barrier bombarding energies using heavy fissile targets. The measured fragment anisotropies when compared with the standard saddle point model (SSPM) calculations show that for projectile-target systems having zero or low ground state spins, the angular anisotropy exhibits a peak-like behaviour at the sub barrier energies, which cannot be explained by the SSPM calculations. For projectiles or targets with large ground state spins, the anomalous peaking gets washed out due to smearing of the K-distribution by the intrinsic entrance channel spins. Recently studies have been carried out on the spin distributions of fission fragments through the gamma ray multiplicity measurements. The fission fragments acquire spin mainly from two sources: (i) due to rigid rotation of the nascent fragments at scission and (ii) due to statistical excitation of the spin bearing collective modes in the fissioning nucleus. One of the collective modes — the tilting mode depends on the K quantum number and is responsible for the emission angle dependence of fragment spin. In our studies, we have shown conclusively that the collective statistical spin modes get strongly suppressed for high K values corresponding to large rotational frequencies along the fission axis. These results bring out the importance of the dynamical effects in the heavy ion induced fusion-fission reactions. The present article will review the work carried out on the above aspects in heavy ion fission reactions as well as on the fission time scales, and some of the recent studies on the mass-energy correlations of fission fragments at near-barrier bombarding energies.
Pulse shape discrimination (PSD) with totally depleted transmission type Si surface barrier detector in reverse mount has been investigated to identify fission fragments in the presence of elastic ...background in heavy ion-induced fission reactions by both numerical simulation and experimental studies. The PSD method is compared with the other conventional methods adopted to identify fission fragments with solid-state detectors such as ΔE–E telescope and single thin ΔE detector and the data for the10B +232Th fission reaction are presented. Results demonstrate the usefulness of a single transmission-type surface barrier detector for the identification of fission fragments and projectiles like heavy ions
A large area position-sensitive ionization chamber with a wide dynamic range has been developed to measure the mass, charge and energy of the heavy ions and the fission fragments produced in ...heavy-ion-induced reactions. The split anode geometry of the detector makes it suitable for both particle identification and energy measurements for heavy ions and fission fragments. The detector has been tested with α particles from
241Am–
239Pu source, fission fragments from
252Cf and the heavy-ion beams from the 14UD Mumbai Pelletron accelerator facility. Using this detector, measurements on mass and total kinetic energy distributions in heavy-ion-induced fusion–fission reactions have been carried out for a wide range of excitation energies. Results on deep inelastic collisions and mass–energy correlations on different systems using this detector setup are discussed.
In the recent past, there have been a number of new initiatives to improve the access to primary education in many developing countries. Such initiatives, which came from the public, private and ...non-governmental (NGO) sectors, have resulted in improved performance in various efficiency indicators. This paper reports results from a nationwide study in Bangladesh on the levels and changes in enrolment pattern of children at the primary level. The gross enrolment ratio has reached 107% and the net enrolment rate 77%. Gender gap has disappeared; in fact girls have surpassed boys! However, the increase in enrolment taking place is not at the desired speed; it is less than one percentage point per year. The government is still the major provider of primary education with two-thirds of all enrolments, but non-formal schools run by NGOs also have important contributions to the positive changes that are taking place in Bangladesh.
Fission-fragment angular distributions in reactions of {sup 10}B, {sup 12}C, {sup 16}O+{sup 232}Th and {sup 237}Np, and {sup 19}F+{sup 237}Np have been measured. While the measured anisotropies in B- ...and C-induced fission are found to be in agreement with the predictions of the standard Halpern-Strutinsky theory, they are anomalously large in the case of O- and F-induced fission. Such a discontinuous behavior in angular anisotropy with respect to the entrance-channel mass-to-charge asymmetry provides an experimental verification of the predictions of the preequilibrium fission model proposed earlier to explain the anomalous fragment angular distributions.
A new method is suggested for pattern recognition of particle tracks based on a combined approach of both artificial neural network (ANN) and principal component analysis (PCA). It is seen that in ...high multiplicity environment, neither the PCA nor the ANN method is satisfactory when used separately as a track classifier. Best performance is achieved when the data are preprocessed using PCA technique, before it is fed to the backpropagated neural network.
