Impact parameter selected nuclear temperatures of hot nuclei from excited state populations for 40Ar+197 Au reactions at E/A=25MeV

Nuclear temperatures extracted from excited state populations were measured as a function of linear momentum transfer (LMT) for ⁴⁰Ar+¹⁹⁷ Au reactions at 25MeV/nucleon. The emission temperatures increased slightly with increasing linear momentum transfer or decreasing impact parameter. Taking into account the corrections of detection efficiency and sequential feeding from higher-lying states, a temperature of T ≈ 4MeV was deduced for central collisions. For peripheral collisions the extracted temperatures increased with the energy of the particles.     

Breakup temperature of target spectators in 197Au + 197Au collisions at E/A = 1000 MeV

Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction ¹⁹⁷Au + ¹⁹⁷Au at 1000 MeV per nucleon. Pairs of ^3,4He and ^6,7Li isotopes and pairs of ^3,4He and H isotopes (p, d and d, t) yield consistent temperatures after feeding corrections, based on the quantum statistical model, are applied. The temperatures rise with decreasing impact parameter from 4 MeV for peripheral to about 10 MeV for the most central collisions. The good agreement with the breakup temperatures measured previously for projectile spectators at an incident energy of 600 MeV per nucleon confirms the universality established for the spectator decayat relativistic bombarding energies. The measured temperatures also agree with the breakup temperatures predicted by the statistical multifragmentation model. For these calculations a relation between the initial excitation energy and mass was derived which gives good simultaneous agreement for the fragment charge correlations. The energy spectra of light charged particles, measured at τ_lab = 150°, exhibit Maxwellian shapes with inverse slope parameters much higher than the breakup temperatures. The statistical multifragmentation model, because Coulomb repulsion and sequential decay processes are included, yields light-particle spectra with inverse slope parameters higher than the breakup temperatures but considerably below the measured values. The systematic behavior of the differences suggests that they are caused by light-charged-particle emission prior to the final breakup stage.     

Two-particle correlation functions at small relative momenta for 14N induced reactions on 197Au at E/A = 35 MeV

Two-particle correlation functions at small relative momenta were measured for light particles (p, d, t, α) emitted in ¹⁴N induced reactions on ¹⁹⁷Au at E/A = 35 MeV. Energy dependent emission source radii are extracted with final-state interaction techniques.     

Light particle emission in fusion-like 14N + 197Au collisions at E/A = 35 MeV

Single- and two-particle inclusive cross sections for light nuclei (p, d, t, ^3,4He, ^6–9Li, ^7,8,10Be) were measured for ¹⁴N induced reactions on ¹⁹⁷Au at E/A = 35 MeV. At forward angles, θ ≈ 20°, quasi-elastic peripheral reactions and more violent fusion-like collisions were discriminated by measuring the folding angle between two coincident fission fragments resulting from the decay of the heavy reaction residue. More pronounced correlation functions, but very similar emission temperatures are observed for fusion-like collisions as compared to peripheral collisions.     

35MeV/u 40Ar+197Au反应中热核的统计发射研究

利用硅半导体+CsI(T1)闪烁体望远镜测量35MeV/u ⁴⁰Ar+¹⁹⁷Au中发射的轻带电粒子,用能谱斜率方法和双同位素产额比方法提取了核温度参量.研究了热核发射过程中的统计发射规律.     

External Coulomb distortion of proton-deuteron final-state interactions for induced reactions on Au at E/A = 35 MeV

Correlations between coincident protons and deuterons were measured for induced reactions on Au at E/A = 35 MeV. Because of their different mass-to-charge ratios, protons and deuterons experience different accelerations in the Coulomb field of the heavy target residue. Correlations measured at small relative momenta are, therefore, influenced not only by the interaction between the coincident particles but also by this external field. The modification of the p−d correlation function by this field suggests that emission occurs close to the surface of the target residue.     

Excitation functions of191+193Ir,197Au(6Li,xn+yp) compound nuclear reactions at ELi=48–156 MeV

Excitation functions of the compound nuclear reactions^191+193Ir,¹⁹⁷Au(⁶Li,xn+yp) forx =3–13 andy=0–2 have been investigated by means of in-beamγ-ray spectroscopy at the 156 MeV⁶Li beam of the Karlsruhe Isochronous Cyclotron. The beam energy has been varied in the range of 48 to 156 MeV in steps of about 10 MeV by Be-absorber foils in the external beam line. Absolute cross sections have been determined by normalizing the measuredγ-ray intensities to the production cross sections ofK- X-rays in the target. The experimental excitation functions are discussed on the basis of predictions of the preequilibrium (hybrid) model. While in most cases the theoretical calculations fairly well reproduce energy position and shapes of the curves, strong discrepancies in the absolute scale of the cross sections are observed. The theoretical predictions overestimate the (⁶Li,xn) cross sections by a factor of about 6. Conspicuous anomalies have been detected when comparing the (⁶Li, xn+1(2)p) reactions with (⁶Li,xn) reactions. The reactions with emission of one or two protons are considerably enhanced. The discrepancies and anomalies observed are tentatively explained by the influence of direct reaction channels as the⁶Li break-up, which experimentally proved to be the dominant contribution to the total reaction cross section. The enhancement of the reactions with emission of protons may be a consequence of transfer reactions into highly excited states combined with compound nucleus formation thus implying a cluster effect in preequilibrium emission process.     

Investigation of the 40Ar + 197Au, 238U systems at 44 MeV/u

We have measured the angular correlation between two fragments emitted in the reactions Ar + Au and Ar + U at 44 MeV/u at GANIL. The aim was to investigate the amount of initial linear momentum transferred from the projectile to a fissioning nucleus. It turned out that this amount is much smaller than can be extrapolated from previous experiments. Furthermore, the probability of forming a fissioning nucleus is very small.     

Inclusive fragment production in84Kr +197Au atE/A=35 MeV

Inclusive cross sections of intermediate mass fragments from the reaction⁸⁴Kr+¹⁹⁷Au atE/A=35 MeV were measured over the range 8°≦Θ _lab≦70° with a low detection threshold. A moving-source parameterization was used to fit the double-differential cross sections. The integrated cross section for fragment production exceeds the total reaction cross section thus indicating a large probability for multi-fragment processes. The deduced large temperature parameters can be explained by assuming emission from a rotating source. From the comparison to reactions with¹²C and⁴⁰Ar projectiles at E/A=30 MeV a systematics of inclusive fragment production as a function of the projectile mass is obtained.     

Nuclear collective flow and charged-pion emission in Ne-nucleus collisions at E/A = 800 MeV

Triple-differential cross sections of charged pions were measured for collisions of Ne projectiles at E/A = 800 MeV with NaF, Nb, and Pb targets. The reaction plane was estimated event by event from the light-baryon momentum distribution. For heavy targets, preferential emission of charged pions away from the interaction zone towards the projectile side was observed in the transverse direction. Such a preferential emission, which is not predicted by cascade calculations, may be attributed to a stronger pion absorption by the heavier spectator remnant.     

The correlation functions and emission time scales for light particles and light fragments in 40Ar+197Au reactions at 25 MeV/nucleon

Two-particle correlation functions were measured for the emission of protons, deuterons, tritons, α, and lithium fragment at small relative momenta in ⁴⁰Ar-induced reactions on ¹⁹⁷Au at 25 MeV/nucleon. Based on three-body trajectory calculations the emission time scales for the particles were extracted from p-d, d-d, t-t, and lithium-lithium correlation functions. The mean emission time was found to decrease with increasing sum of the kinetic energies of the particle in a correlated pairs, indicating the emission of more energetic particles at earlier stages of the reaction than at later stages. The time scale for the emission of lithium fragments emission suggests that sequential binary disassembly occurs in ⁴⁰Ar+¹⁹⁷Au reaction at MeV/nucleon. Mean emission temperature of 3.5_−0.8^+1.3 and 3.6±0.4 MeV were also extracted from the relative populations of the excited and ground states of the respective emitted nuclides ⁸Be and ⁴He.     

Peripheral collisions in the 84Kr + 92,98Mo,natAg and 197Au reactions at 22 MeV/u

Peripheral reactions induced on ⁹²Mo,⁹⁸Mo, ^natAg and ¹⁹⁷Au targets by 22 MeV per nucleon krypton beam were studied. Fragments observed with velocities close to the beam velocity can be interpreted as coming from a quasi-fragmentation of the projectile. The isotopic distributions measured for the fragments produced with the Kr projectile reflect some influence of the composite system. Thus it seems that projectile fragmentation is not the only mechanism involved in these reactions and that the mean field interaction still plays an important role at this energy.