Heyu Wu

A BGO detector array and its application in intermediate energy heavy ion experiments

A BGO crystal (Bi4Ge3O12) as the E detector of ΔE-E for identification of reaction products has been used for detecting the charged particles emitting from the 25 MeV/u 40Ar induced reaction. The responses of the BGO crystal to various light charged particles were measured. A close-packed hexagonal array consisting of thirteen ΔE-E telescopes (Si-BGO) has been developed to detect the light charged particles interfering with each other in intermediate-energy heavy-ion induced reactions. Some applications of this telescope array are also described.

Temperature and excitation energy of hot nuclei in the reaction of 40Ar+197Au at 25 MeV/nucleon

Abstract The coincidence measurements between heavy fission fragments and light charged particles with Z ⩽ 2 were carried out for the 40 Ar+ 197 Au reaction at 25 MeV/nucleon, to study the properties of hot nuclei in heavy ion induced reactions. The linear momentum transfers (LMTs) were deduced from the folding angle and the time-of-flight difference between two fission fragments of heavy residues. The relationship of the nuclear temperature (slope parameter of the energy spectrum) and the excitation energy was determined independently from the measurement of the kinetic energy spectra in the frames of the emitting sources and from the LMT analysis. Both the temperature and the excitation energy increase with decreasing impact parameter, which suggests that a plateau temperature of 5.5 MeV is reached at an excitation energy of 3.1 MeV/nucleon. The result was also compared with various statistical models that explain the plateau by the multifragmentation process, where the excitation energy is assumed to be stored in compression and expansion effects.

Breakup of 33.4 MeV/u 17N on a 9Be Target

Correlation measurements of neutrons and fragments have been performed in a reaction of 33.4 MeV/u 17N on a 9Be target. Energy spectra of n and nitrogen fragments were obtained at different angles. Based on the nuclear diffraction dissociation model, the measured energy spectra and the neutron angular distributions were reproduced quite well assuming that 17N was composed of 16N and n or 15N and 2n interacting with the nonlocal separable potential. The satisfactory agreement between the theoretical calculations and the experimental data shows that the contribution of Coulomb dissociation is negligible in the reaction concerned.

A BGO hodoscope for intermediate mass fragments

Abstract A BGO hodoscope was developed to detect intermediate mass fragments (IMF) emitted from the intermediate energy heavy ion collisions. It consists of 13 Δ E – E telescopes (Si–BGO). The responses of the BGO detector for charged particles and IMF were tested. The results indicate that charge resolution for helium, IMF and isotope resolution for hydrogen are achieved for this hodoscope. Some applications of this hodoscope are also described.

The 4-fold fission in 40Ar + 209Bi, 197Au and 159Tb reactions at 25 MeV/u

Abstract The paper presents the 4-fold fission or fragmentation of hot nuclei produced in 25 MeV/u 40 Ar + 209 Bi , 197Au and 159Tb reactions. The events with 4 massive fragments emitted with angles larger than 36 ° were detected by 8 PPACs with area of 25 × 20 cm2. The TKE, distributions of mass and velocity for the four fragments have been obtained.

Evidence for Different Fission Behavior of Hot Nuclei Formed in Central and Peripheral Collisions of 40Ar+209Bi Reaction at 25 MeV/u

Correlated fission fragments from the reaction of 25 MeV/u 40Ar+209Bi and their further correlation with α particles have been studied for peripheral and central collisions simultaneously. The excitation energy at scission deduced from postscission multiplicity is about 172.5 MeV. The fission timescale deduced from prescission multiplicity is about 4×10-21 s. Systematic analysis of the mass and energy distributions of fission fragments as a function of the initial temperature of hot fissioning nuclei reveals the existence of different fission behavior of hot nuclei formed in central and peripheral collisions. Experimental data demonstrate the change of fission behavior at T similar 4 MeV.

Which sort of particles was emitted earlier during decay of highly excited nuclei

Emission orders of light charged particles and Li fragments from highly excited fissioning nuclei in the reaction of40Ar +197Au atEbeam/A = 25 MeV have been studied by measuring difference velocity distributions of two correlated particles at small relative angles in coincidence with two fission fragments. By comparing the data with three-body trajectory calculations, it is found that high-velocity light particles (tritons and He particles) are emitted prior to high-velocity Li fragments but low-velocity light particles are emitted after low-velocity Li fragments. On the other hand, no preferential emission was observed among light particles, such as deuterons and tritons.