Browsing by Author "Triambak, Smarajit"

Now showing 1 - 9 of 9
  • Thumbnail Image
    Item
    Analysis and simulations to obtain the weak magnetism term in ²²Na beta decay
    (University of the Western Cape, 2016) Phuthu, Lutendo; Triambak, Smarajit
    The study of ²²Na beta decay offers an opportunity to test the Standard Model of Particle Physics via measurements of the β−γ angular correlation. A previous measurement of this correlation yielded a non-zero value, indicating the need for a higher-order matrix element to the decay, beyond the allowed V − A approximation. On assuming the Conserved Vector Current (CVC) hypothesis for weak interactions and using the magnetic dipole M1 width of the analog 2+ state in ²²Na, one obtains an unexpectedly large 'second-class' form factor for 22Na β decay that is in disagreement with the Standard Model prediction. This thesis describes an analysis of data obtained from a previous ²¹Ne(p, γ) experiment to obtain the M1 width of the 2+ state of interest in ²²Na. This work aims to use the M1 width and the independently measured of the β − γ angular correlation to obtain a higher-order Standard-Model-allowed weak magnetism form factor for the decay, in an attempt to explain the observed anomaly mentioned above.
  • Thumbnail Image
    Item
    Characterisation of the first 1/2+ excited state in 9B and isospin symmetry breaking studies in A = 9 nuclei
    (University of the Western Cape, 2019) Mukwevho, Ndinannyi Justice; Triambak, Smarajit
    The 9Be - 9B isospin doublet carries fundamental significance for both nuclear structure and nuclear astrophysics studies. The first excited 1/2+ state in 9Be is already well established. However, its isobaric analogue 1/2+ state in 9B has not been unambigously determined yet. Theoretically, two popular descriptions of the 9Bnucleus either use a cluster model with two unbound alpha particles held together by a covalent proton or using the shell model, as a 8Be core + proton in the sd shell. An experimental determination of the excitation energy of the first 1/2+ state in 9B will provide valuable information in validating the theoretical model that adequately describes such light unbound nuclei. Further, it will also provide a robust test of mirror (isospin) symmetry violations via measurements of mirror energy differences in the doublet. Although there have been several experimental attempts to characterize the first 1/2+ state in 9B several discrepancies still exist in reported values of the excitation energies. This thesis describes an experiment performed at iThemba LABS using the 9Be(3He,t)9B reaction to address the above issue. As a byproduct, the thesis also describes an additional determination of the excitation energy of the second J-pi = 1/2+, T = 3/2 state in 9B from the same experiment. This was performed in order to resolve a discrepancy related to the excitation energy of this state. The consequence of this measurement related to Isobaric Multiplet Mass Equation (IMME) for the excited T = 3/2, A = 9 quartet is discussed briefly.
  • Thumbnail Image
    Item
    The design and simulation of a new experimental set up to measure nuclear level lifetimes
    (University of the Western Cape, 2016) Singh, Bhivek; Triambak, Smarajit; Orce, Nico
    Measurements of nuclear level lifetimes are an important aspect of experimental nuclear physics. Such measurements determine transition matrix elements for nuclear structure research and also provide the widths of relevant excited states in nuclei that are of astrophysical interest. In the latter, the measured widths are used to obtain reaction rates in main sequence stars such as the Sun and in binary-star systems where the accretion of material from one star to another provides an opportunity to study extreme stellar environments such as novae and x-ray bursts. This thesis work describes the design and simulation of a new experimental set up at iThemba LABS that will allow for highprecision femtosecond-level lifetime measurements of nuclear states using the Doppler Shift Attenuation Method (DSAM). We use the Solid Edge computer-aided design (CAD) software to design a new scattering chamber with a cooled target ladder specifically for such measurements using inverse-kinematic transfer reactions with ion implanted targets. The light charged ejectiles from the reaction will be detected with a ΔE - E silicon telescope, while Doppler shifted rays will be registered using a high-purity and 100% efficient germanium (HPGe) detector. We also describe preliminary Monte Carlo simulation codes that are being developed in a relativistically invariant framework to optimize the experimental set up and to obtain predicted lineshapes of γ rays from several astrophysically relevant states in nuclei using this experimental set up.
  • Thumbnail Image
    Item
    E2/M1 mixing in the Jπ= 5/2+ to 3/2+ transition in 21Na and its relation to the 20Ne(p,y ) stellar reaction rate
    (University of the Western Cape, 2022) Gopal, Sumeera; Triambak, Smarajit
    In the above, M is the total mass of the molecular cloud, R is its radius, k is Boltzmann's constant, G is the gravitational constant, T is the cloud temperature, m is the mean molecular weight, and is the cloud molecular density. Interstellar clouds typically have densities of about 100 atoms cm􀀀3 and T ' 100 K. The Jeans criterion is only met when the mass of the cloud is greater than 2 104 M [5] (where M denotes one solar mass). The genesis of stars is initiated through such condensation of gas clouds in interstellar space. The gravitational collapse to a high central density results in the formation of a protostar. The internal heat that is generated is radiated away from the center, which is relatively hotter than the surface.
  • Thumbnail Image
    Item
    Nuclear structure studies in the A=136 region using transfer reactions
    (University of the Western Cape, 2018) Rebeiro, Bernadette M.; Triambak, Smarajit
    This thesis describes research work undertaken to study neutron pairing correlations in 136Ba via the 138Ba(p, t) pair transfer reaction and to perform high-precision spectroscopy of low-lying states in 136Cs using the 138Ba(d, ) reaction. The aim of this project was to provide useful spectroscopic information relevant for matrix element calculations of 136Xe neutrinoless double beta decay. This work is relevant because neutrinoless double beta decays are standard-model-forbidden lepton number violating processes, which if observed, would establish the Majorana nature of the neutrinos and also determine the absolute mass scale of the light Majorana neutrinos. Our experiments show a signi cant fragmentation of the two-neutron transfer (p, t) strength to excited 0+ states in 136Ba, which could signi cantly affect future matrix element calculations. Additionally we obtain information on 65 new states in 136Cs observed in this work. It is anticipated that these new information will play a vital role in improving the precision of calculated matrix elements for 136Xe double beta decays.
  • Thumbnail Image
    Item
    Plausible explanation for the third COVID-19 wave in India and its implications
    (KeAi Communications, 2023) Triambak, Smarajit; Mahapatra, Durga Prasad; Barik, Niranjan
    Recently some of us used a random-walk Monte Carlo simulation approach to study the spread of COVID-19. The calculations were reasonably successful in describing secondary and tertiary waves of infection, in countries such as the USA, India, South Africa and Serbia. However, they failed to predict the observed third wave for India. In this work we present a more complete set of simulations for India, that take into consideration two aspects that were not incorporated previously. These include the stochastic movement of an erstwhile protected fraction of the population, and the reinfection of some recovered individuals because of their exposure to a new variant of the SARS-CoV-2 virus. The extended simulations now show the third COVID-19 wave for India that was missing in the earlier calculations. They also suggest an additional fourth wave, which was indeed observed during approximately the same time period as the model prediction.
  • Thumbnail Image
    Item
    Spectroscopy of proton unbound states in 32Cl
    (University of the Western Cape, 2019) Kamil, Mohamed; Triambak, Smarajit
    This project aimed to investigate proton unbound states in 32Cl using the 32S(3He; t) charge-exchange reaction. This research is relevant both in the context of nuclear structure and astrophysics. Excited states in 32Cl up to Ex 6 MeV were produced using a 50 MeV 3He++ beam from the K200 separated sector cyclotron at iThemba LABS. The triton ejectiles were mass analysed and detected at the focal plane of the K600 magnetic spectrometer. An additional segmented silicon detector array called CAKE was used to detect the unbound protons from states in 32Cl in conjunction with the tritons. In this work we looked for potential sources of isospin admixture that could explain the apparent violation of the Isobaric Multiplet Mass Equation (IMME) for the A = 32, T = 2 quintet. We also investigated the possibility of determining the 31S(p; ) reaction rate indirectly, via measurements of the partial proton widths of unbound states in 32Cl.
  • Thumbnail Image
    Item
    Study of low-lying proton unbound states in 24Al using the 24Mg(3He; t)24Al reaction.
    (University of the Western Cape, 2022) Vyfers, E. C.; Triambak, Smarajit
    This MSc project entails a study of astrophysically relevant states in 24Al, that are important for a better understanding of the 23Mg(p, )24Al nuclear reaction rate in classical novae. This is a crucial breakout reaction that links the NeNa and MgAl cycles and o ers an understanding of the nucleosynthesis of elements between Neon and Aluminium. In this work the K = 600 magnetic spectrometer at iThemba LABS was used together with a silicon detector array to measure proton branching ratios for the relevant states in 24Al using the 24Mg(3He,t) charge-exchange reaction. Our experiment yields the rst direct measurement of the relative proton branching ratios from these states. We used our measured observables and theoretical estimates of partial gamma widths of unbound states in 24Al, to indirectly determine the total 23Mg(p, ) reaction rate at nova temperatures.
  • Thumbnail Image
    Item
    A study of neutron pairing correlations using the 136Ba(p, t) reaction
    (University of Western Cape, 2020) Jespere Calderone, Nzobadila Ondze; Triambak, Smarajit
    Observation of neutrinoless double beta decay (0 ) is currently the only means by which one could establish the Majorana nature of neutrinos. Additionally, such an observation would determine the absolute neutrino mass scale. However, this requires that the matrix element for a given 0 decay process is accurately calculated. The objective of this project is to provide useful nuclear structure information that aim to improve future theoretical calculations for the nuclear matrix element (NME) of 136Xe 0 decay to 136Ba. We studied neutron pairing correlations in 134Ba using the 136Ba(p; t) reaction to stringently test the Bardeen-Cooper-Schrie er (BCS) approximation in the A = 136 mass region. This is because many theoretical calculations of the NME's for 0 decay are performed using the quasiparticle random phase approximation (QRPA), which uses the BCS approximation to describe the ground states of the even-even parent and daughter nuclei. Our results show a signi cant fragmentation of the neutron-pair transfer to excited 0+ states, implying a breakdown of the BCS approximation in this mass region.