Identification of New Isotopes ¹²⁵Pd and ¹²⁶Pd Produced by In-Flight Fission of 345 MeV/nucleon ²³⁸U: First Results from the RIKEN RI Beam Factory

Abstract

A search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam has been carried out in the commissioning experiment of the next-generation in-flight radioactive isotope beam separator BigRIPS at the RI Beam Factory at the RIKEN Nishina Center. Two neutron-rich palladium isotopes 125 Pd and 126 Pd were observed for the first time, which demonstrates the great potential of the RIKEN RI beam factory. 2) at the RIKEN Nishina Center that promises to advance the study of exotic nuclei to a great extent. The new superconducting in-flight RI beam separator BigRIPS is a major experimental device at the RIBF for RI beam production based on the in-flight separation technique and for research with exotic nuclei.3,4) Thanks to its large acceptances, not only projectile fragmentation of various heavy-ion beams but also in-flight fission of fissile beams 5) can be efficiently used as a production reaction in the BigRIPS separator. Figure 1 shows a schematic layout of the BigRIPS separator along with the IRC and SRC cyclotrons 1) and the ZeroDegree spectrometer.3) The cyclotrons at the RIBF can accelerate all heavy ions up to approximately 400 MeV/nucleon, including very heavy elements such as uranium, with the goal of reaching an intensity of 1 pmA (6 Â 10 12 particles/s). 1)In-flight fission of fissile beams, such as a 238 U beam, is known as an excellent mechanism for producing a wide range of neutron-rich exotic nuclei far from stability. This was well demonstrated by experiments at GSI, in which more than a hundred new isotopes were identified in a single experiment.6,7) The BigRIPS separator has been designed with large acceptances, to take advantage of the high production cross sections of neutron-rich isotopes from these reactions. The full angular acceptances of 80 mrad (horizontal) and 100 mrad (vertical), and the full momentum acceptance of 6% allows efficient RI beam production with in-flight fission, in which fission fragments are produced with large spreads in both angle and momentum. Due to its large acceptance, the BigRIPS separator has an approximately 50% efficiency for the collection of these fission fragments.Another important feature of the BigRIPS separator is its two-stage structure, which allows delivery of tagged RI beams, or use as a two-stage separator. In the tagging mode, which may also be called a separator-spectrometer mode, the first stage is used to produce and separate RI beams with a wedge energy degrader, while the second works as a spectrometer to analyze and identify those RI beams. The momentum resolution of the second stage has been designed to be high enough to identify RI beams without measuring their total kinetic energies, even though they are produced in several charge states in our energy domain. In the two-stage LETTERS Ã

Shell Evolution towards Ni78 : Low-Lying States in Cu77Şahin1, Garrote2, Tsunoda3 et al. 2017Phys. Rev. Lett.347220View full textAdd to dashboardCite

“…In this Letter, we report on the first measurement of excited states in neutronrich 77 Cu by means of β-delayed γ-ray spectroscopy. An experimental campaign to study neutron-rich nuclei took place at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center [28,29]. The present data were collected during two separate beam times in which radioactive isotopes were produced via in-flight fission of 238 U projectiles with an incident energy of 345 A MeV on thick 9 Be targets.…”

New Isotopes and Proton Emitters–Crossing the Drip Line in the Vicinity ofSn100

“…The quest for new isotopes at the limits of nuclear binding is one of the major research lines in nuclear physics and in particular in RIKEN, where numerous experiments have been performed recently to test mass models and theoretical predictions of the drip lines. Different production mechanisms have been employed to these ends, for example, inflight fission of a 345A MeV 238 U and reactions with a 48 Ca beam [10][11][12] to synthesise neutron-rich isotopes, and projectile fragmentation of a 345A MeV 124 Xe beam [13] to produce nuclei at the proton drip line.…”

Isomers inPd128andPd126: Evidence for a Robust Shell Closure at the Neutron Magic Number 82 in Exotic Palladium Isotopes

“…Since the discovery of these isotopes at the RI Beam Factory (RIBF) facility at RIKEN [12,13], steady improvements in the intensity of uranium beams, in combination with a highly efficient -ray detection system, enable us to conduct detailed spectroscopic studies.…”