D. J. Fields

Limitations on linear momentum transfer in 14N induced reactions on 238U at EA=15, 20, 25 and 30MeV☆

Abstract Linear momentum transfer distributions have been dermimined for 14 N induced reactions on 238 U by measuring the folding angle between two coincident fission fragments. The data follow the systematic trends previously established for alpha conjugate projectile nuclei. Over the range of energies investigated, the most probable linear momentum transfer has not reached a limiting value. Extrapolation of the present results indicates that complete fusion should cease to be a relevant reaction mechanism above incident energies of E A =40−45 MeV

Emission of complex nuclei in 12C induced reactions at EA = 15 and 30 MeV☆

Abstract Cross sections for emission of complex nuclei (Z ≈ 3–20) with energies close to the exit channel Coulomb barrier increase by more than one order of magnitude for 12C induced reactions on Au between the incident energies of E A = 15 and 30 MeV. For reactions on Ag at E A = 30 MeV , the element yields exhibit a characteristic power law dependence. Simple statistical calculations reproduce the qualitative trends of the element yields.

Non-equilibrium versus equilibrium emission of complex fragments emitted in 14N induced reactions on Ag and Au at EA=20–50 MeV☆

Excitation functions have been measured for Z=3–12 fragments emitted in 14N+Ag and 14N+Au collisions and energies EA=20–50 MeV. With increasing bombarding energy, non-equilibriumemission processes grow in importance, dominating the fragment cross section at EA=50 MeV.

Nuclear temperature measurements and feeding from particle unbound states

Abstract Inclusive fragment cross sections and cross sections of coincident γ -ray transitions from the decay of 8 Li, 7 Be, 10 B, 12 B and 13 C fragments were measured for 32 S induced reactions on Ag at 715 MeV. These measurements are compared to quantum statistical model calculations which include sequential feeding from particle unbounds states of heavier fragments. When the uncertainties in the sequential feeding calculations are taken into account, although the measured γ -ray fractions are consistent with temperature, T ⪖ 4 MeV; the calculations demonstrate that the investigated γ -ray transitions cannot be used to determine the temperature of highly excited systems.

Azimuthal correlations between light particles emitted in 12O induced reactions on 12C and 197Au at 400 MeV

Abstract Azimuthal correlations between light particles emitted to polar angles of 40 and 70 degrees with respect to the beam axis were measured for 16 O induced reactions on 12 C and 197 Au at 400 MeV. Coincident light particles are preferentially emitted in a plane which contains the beam axis. For reactions on 12 C, coincident light particles are preferentially emitted to opposite sides of the beam axis. These correlations may be understood in terms of the phase constraints imposed by momentum conservation on systems with finite number of nucleons. For reactions on 197 Au, on the other hand, preferential emission of coincident deuterons and tritons to the same of the beam axis may be caused by the shadowing of preequilibrium particles by the adjacent cold spectator nuclear matter.

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

Abstract Single- and two-particle inclusive cross sections for light nuclei (p, d, t, 3,4 He, 6–9 Li, 7,8,10 Be) were measured for 14 N induced reactions on 197 Au 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.

Nuclear fragmentation and sequential decay

Abstract The effect of the sequential decay of excited primary fragments on final distributions in nuclear fragmentation reactions is studied. Particle decays of primary fragments, which are emitted with equilibrium populations of known states, can account for characteristic structures in the measured mass distributions. They also alter the relative populations of excited states, as implied by recent measurements.

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

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

Energy dependence of source radii and emission temperatures for 14N induced reactions at EA = 35 MeV

Abstract Correlations between coincident alpha particles and deuterons emitted in 14 N induced reactions on 197 Au at E A = 35 MeV are measured. Source radii ( r 0 ≈ 3−4 fm) and emission temperatures ( T ≈ 9−3 MeV) are extracted and shown to depend on the kinetic energy of the emitted particles.

Dependence of two-particle correlation functions on linear momentum transfer to a composite system

Abstract Light particle correlations at small relative momenta were measured in coincidence with two fission fragments for 14N induced reactions on 197Au at E/A = 35 MeV. The selection of large linear momentum transfers to the heavy reaction residue leads to a strong suppression of the beam velocity component of the light particle spectra and to enhanced maxima in the p-p and α-d correlation functions.