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Lynch, W. G.

Publications and source records attributed to Lynch, W. G..

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Strong Evidence for N 9 and the Limits of Existence of Atomic Nuclei

The boundaries of the Chart of Nuclides contain exotic isotopes that possess extreme proton-to-neutron asymmetries. Here we report on strong evidence of 9 N, one of the most exotic proton-rich isotopes where more than one half of its constitute nucleons are unbound. With seven protons and two neutrons, this extremely proton-rich system would represent the first-known example of a ground-state five-proton emitter. Here, the invariant-mass spectrum of its decay products can be fit with two peaks whose energies are consistent with the theoretical predictions of an open-quantum-system approach, however we cannot rule out the possibility that only a single resonance-like peak is present in the spectrum.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Determination of energy-dependent neutron backgrounds using shadow bars

Understanding the neutron background is essential for determining the neutron yield from nuclear reactions. Here, the neutron backgrounds were determined for heavy-ion collision experiment using the shadow-bar method, where beams of 40,48 Ca at 56, 140 MeV/u impinged on targets of 58,64 Ni and 112,124 Sn. In the analysis presented here, brass shadow bars are placed in front of organic liquid scintillator neutron detectors to determine the energy-dependent neutron background fractions. The measurement of neutron spectra with and without shadow bars is important to determine the neutron background more accurately. The neutron background, along with its sources and systematic uncertainties, are explored with a focus on the impact of background models and their dependence on neutron energy.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Constraints from isoscaling on the source size in energetic heavy ion collisions

In the framework of the statistical multifragmentation model, the nuclear isoscaling analysis is extended to constrain the ratio between the sizes of the decaying sources formed in a collision between two heavy ions. It is found that the ratio between the probabilities of observing n fragments in each event, for each of the sources, follows a scaling law, similar to the traditional nuclear isoscaling. However, the corresponding slope is sensitive to the source sizes. This property is explained analytically using the grand-canonical ensemble. Furthermore, the extent to which our findings are affected by finite size effects and by the deexcitation of the hot primary fragments is investigated. The scaling turns out to be robust and weakly affected by effects implied by these two aspects. We also find that the Poisson distribution is a fairly good approximation to the above mentioned probabilities, associated with both the primordial fragments, produced at the breakup stage, and the final ones, found at the end of the fragment deexcitation process.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Multiplicity trigger detector for the S π RIT experiment

A multiplicity trigger detector (MTD) was developed for the SπRIT experiment that aims to probe the high- density symmetry energy via heavy-ion collisions (HICs). The MTD is designed to measure the charged-particle multiplicity in HICs to provide a trigger signal that can be used to select high-multiplicity events induced by central collisions. The MTD consists of two side-walls segmented into 30 plastic scintillation paddles, each equipped with a multi-pixel photon counter. A custom board with EASIROC front-end ASIC is used as readout electronics. A multiplicity logic signal is generated by an on-board FPGA that processes the discriminated signals from EASIROCs. The overall latency of the whole detector system for outputting the trigger is less than 100 ns, including 52 ns of electronics latency for processing the signals. During the measurement of 112 Sn + 124 Sn reactions at an incident energy of 270 MeV/nucleon, the minimum multiplicity threshold of the MTD was set to 4, where the overall trigger efficiency was obtained to be about 39 % for inclusive nuclear reactions. Furthermore, a simulation study with a numerical calculation of HICs found that the central collisions of impact parameters of less than 4 fm can be triggered with a high efficiency of more than 95 % by the experimental trigger condition.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Proton decay spectroscopy of S 28 and Cl 30

States in 28 S and 30 Cl have been studied using one- and two-proton decay spectroscopy. In the first spectrometer setting, states in 28 S were populated following one-neutron knockout from a fast 29 S beam. Three new states are observed in 28 S from one- and two-proton decay. For the two-proton case the nature of the decay was investigated and found to proceed via sequential two-proton emission. For the second setting, states in 30 Cl were populated via one-proton knockout from a fast 31 Ar beam. The decay energy of the ground and first excited state were measured, with the ground-state decay energy found to be in disagreement with a previous measurement. Here, the spin and parity of these two 30 Cl states were inferred from shell-model calculations.

20 ≤ A ≤ 38↗
DOE OSTI2022

Beam particle identification and tagging of incompletely stripped heavy beams with HEIST

A challenge preventing successful inverse kinematics measurements with heavy nuclei that are not fully stripped is identifying and tagging the beam particles. For this purpose, the HEavy ISotope Tagger (HEIST) has been developed. HEIST utilizes two micro-channel plate timing detectors to measure the time-of-flight, a multi-sampling ion chamber to measure energy loss, and a high-purity germanium detector to identify isomer decays and calibrate the isotope identification system. HEIST has successfully identified 198 Pb and other nearby nuclei at energies of about 75 MeV/A. In the experiment discussed, a typical cut containing 89% of all 198 Pb 80+ in the beam had a purity of 86%. We examine the issues of charge state contamination. Here, the observed charge state populations of these ions are presented and, using an adjusted beam energy, are well described by the charge state model GLOBAL.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

First Observation of the Four-Proton Unbound Nucleus 18 Mg

18 Mg was observed, for the first time, by the invariant-mass reconstruction of 14 O + 4p events. The ground-state decay energy and width are E T = 4.865(34) MeV and Γ = 115(100) keV, respectively. The observed momentum correlations between the five particles are consistent with two sequential steps of prompt 2p decay passing through the ground state of 16 Ne. The invariant-mass spectrum also provides evidence for an excited state at an excitation energy of 1.84(14) MeV, which is likely the first excited 2 + state. As this energy exceeds that for the 2 + state in 20 Mg, this observation provides an argument for the demise of the N = 8 shell closure in nuclei far from stability. Furthermore, in open systems this classical argument for shell strength is compromised by Thomas-Ehrman shifts.

6 ≤ A ≤ 19↗
DOE OSTI2021

Rapidity distributions of Z = 1 isotopes and the nuclear symmetry energy from Sn+Sn collisions with radioactive beams at 270 MeV/nucleon

The rapidity distributions of hydrogen isotopes emitted from central collisions of neutron-rich 132 Sn+ 124 Sn and neutron-deficient 108 Sn+ 112 Sn systems at 270 MeV/nucleon were investigated at RIKEN-RIBF. The data are compared with antisymmetrized molecular dynamics (AMD) calculations and the rapidity distributions can be reproduced after adjusting the in-medium nucleon-nucleon cross sections. The double ratios between the two reaction systems taken for the relative yields of deuteron to proton (d/p) and triton to proton (t/p) are further examined in the midrapidity domain, where the adjustments in the AMD calculations do not affect much on them. The d/p and t/p double ratios at midrapidity agree well with the ratio of the system neutron numbers and its squared value, respectively, and the rapidity dependence of these double ratios is consistent with a picture of partial mixing of colliding nuclei. By comparing with the AMD model which shows a strong symmetry energy dependence of the t/p double ratio, the experimental result in the midrapidity domain favors the calculation with a symmetry-energy slope parameter around L = 46 MeV rather than L = 108 MeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Reaction losses of charged particles in CsI(Tl) crystals

To efficiently detect energetic light charged particles, it is common to use arrays of energy-loss telescopes involving two or more layers of detection media. As the energy of the particles increases, thicker layers are usually needed. However, carrying out measurements with thick-telescopes may require corrections for the losses due to nuclear reactions induced by the incident particles on nuclei within the detector and for the scattering of incident particles out of the detector, without depositing their full energy in the active material. In this paper, we develop a method for measuring such corrections and determine the reaction and out-scattering losses for data measured with the silicon-CsI(Tl) telescopes of the newly developed HiRA10 array. Here, the extracted efficiencies are in good agreement with model predictions using the GEANT4 reaction loss algorithm for Z = 1 and Z = 2 isotopes. After correcting for the HiRA10 geometry, we obtain a general function that describes the loss of efficiency due to reaction losses in CsI(Tl) crystals as a function of range.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗