New Era of Resonance Reaction Studies
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NUCLEI Experiment
New Era of Resonance Reaction Studies V. Z. Goldberg1)* and G. V. Rogachev1), 2) Received Deсember 25, 2019; revised Deсember 25, 2019; accepted Deсember 25, 2019
Abstract—The article presents a review of resonance reaction studies made by TTIK method. DOI: 10.1134/S1063778820040110
1. INTRODUCTION The 20th century left us with remarkable examples of the experimental studies of resonance reactions like investigation of narrow analog states. The excitation energy of these states of a relatively simple structure can be predicted with precision of few tens of keV using the Coulomb difference between the analog states in different nuclei. However, investigation of analog states at high excitation energies surrounded by much more complicated compound nucleus states was an important challenge for the experimentalists. Some analog states at high excitation energy still cannot decay according to the isospin conservation law. Therefore, they are extremely narrow in spite of many open decays by nucleons. For instance, the width of the lowest T = 3/2 state in 13 N at the excitation energy of 15.06 MeV is just 0.86 keV. The total width and partial widths for this state were obtained in resonance reactions with energy resolution of few hundreds of eV [1]. At the same 80th, one of the authors (V.Z.G.) of this article was interested in the α-cluster structure of atomic nuclei and considered an idea to study resonances in the interaction of α particles with light nuclei. The excitation energies of the cluster states could not be predicted with a good precision needed for the classical approach of the few-keV steps in excitation functions provided by electrostatic accelerators. A team at the Kurchatov Institute [2] used an approach (probably also prompted by the fact that tandems were rare in the former Soviet Union) which was drastically different from classical way of resonance reactions studies. The new approach uses a cyclotron beam, Inverse Kinematics and a Thick Target (TTIK). In the TTIK technique, the incoming ions enter a scattering chamber through a thin entrance
window and slowed in a target gas (helium, methane, hydrogen). The light recoils, originally α particles from helium gas, are detected from a scattering event (Fig. 1). These recoils emerge from the interaction with the beam ions and hit a Si detector array located at forward angles, while the beam ions are stopped in the gas, as α particles have smaller energy losses than the scattered ions. The TTIK approach provides a continuous excitation function as a result of the slowing down of the beam. While the TTIK method cannot compete with a classical approach in terms of energy resolution, the possibility of observing excitation functions at and close to 180◦ , where the resonance scattering dominates over the potential scattering, enables one to obtain more reliable information on many states with widths over 1 keV. An additional advantage of the TTIK method is that the laboratory energy of the α particles corresponding to the low energies and bac
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