1. Detecting Giant Monopole Resonances Peter Nguyen Advisors: Dr. Youngblood, Dr. Lui Texas A&M University Energy Loss Identifying The Particles Discovered in the late 1940s by bombarding nuclei with gamma rays Giant resonances is a collective motion of nucleons that occurs when the nucleus becomes excited Each mode has an associated multipole integer value L to represent the angular momentum transfer Classification – Isoscalar means the protons and neutrons move in phase and is denoted as ∆T = 0 – Isovector means the protons and neutrons do not move out of phase and is denoted by ∆T = 1 Giant Resonances Motivation Behind K nm It is a fundamental quantity describing the ground state properties of nuclear matter Uses – Supernova collapses – Neutron stars – Heavy-ion collisions – Determine the Nuclear Equation of State Measuring it – Deduce information from the frequency of the compression mode of the nucleus during ISGMR and ISGDR – Relate the compressibility to the centroid energy of the ISGMR Difficult to detect because Giant Quadrupole Resonance GQR hid the GMR except at small scattering angles Beam analysis system provides a very clean beam which can be used in the measurement Using a beam of specific MeV, the beam will collide target nucleus Detection of ISGMR MDM Spectrometer Stable Nuclei Excessive studies have been made on the stable nuclei by using alpha particles scattering Through inelastic scattering, information of ISGMR and ISGDR have been obtain from the stable nuclei ( 12 C - 208 Pb) Researcher are focusing more on unstable nuclei Unstable Nuclei Unstable nuclei cannot be placed in the target chamber because of its decaying nature. The nuclei will immediately decay into another element To study the unstable nuclei, an inverse reaction is needed, the unstable nuclei becomes the projectile Detector on the back of spectrometer combined with decay detector inside target chamber to measure the resonance of unstable nucleus Reaction- 28 Si( 6 Li, 6 Li) 28 Si* Inverse Reaction - 6 Li ( 28 Si, 28 Si*) 6 Li The detector is compose of a thick scintillator block, and vertical and horizontal thin strips that are 1 mm thick The particles will go through the vertical strip first and then the horizontal strip. This will determine the position of the outgoing particles The scintillator block measures the energy of the particles Scintillator – Sensitive to Energy Represented as a linear function – Fast Time Response Recovery time is short – Pulse Shape Discrimination Determining different particles A scintillator is a device that absorbs energy and emits light Several kinds of scintillating material exists including: organic, inorganic and plastic The particle hits the scintillator which excites the molecules in the scintillating material to emit light The photons released is then capture by a photomultiplier that is coupled to the scintillator via a light guide or directly attached Photomultiplier Using SRIM, a program that computes the energy associated with scintillator thickness, the energy loss after striking the scintillator is calculated and subtracted from the initial energy Light Output ISGMR is the “breathing” mode where the nucleons compress and expand causing the nucleus’ radius to fluctuate ISGMR can be related to the nucleus, denoted as K nm Isoscalar Giant Monopole Resonances (ISGMR) Decay Detector in Target Chamber The photomultiplier absorbs the emitted light and electrons are release via photoelectric effect at the photocathode The cathode, dynodes, and the anodes create a potential “ladder” that directs the electrons The electrons travel from the photocathode to the first dynode and excite more electrons in the dynode The excited electrons leave the dynode and travel to the next dynode to repeat the process At the anode all the electrons are collected and then amplify to create a readable current The target nuclei in the target will excite to a higher energy level α particles with different energy will separate by MDM spectrometer and focus on different position of the detector