N. R. Yoder

The Indiana silicon sphere 4π charged-particle detector array

A low threshold charged particle detector array for the study of fragmentation processes in light-ion-induced reactions has been constructed and successfully implemented at the IUCF and Saturne II accelerators. The array consists of 162-triple-element detector telescopes mounted in a spherical geometry and covering 74% of 4π in solid angle. Telescope elements are composed of (1) an axial-field gas ionization chamber operated with C3F8 gas; (2) a 0.5 mm thick passivated silicon detector, and (3) a 2.8 cm thick CsI(Tl) scintillation crystal with photodiode readout. Discrete element identification is obtained for ejectiles up to Z ∼ 16 over the dynamic range 0.7 ≤ EA ≤ 95 MeV/nucleon. Isotopes are also distinguished for H, He, Li and Be ejectiles with 8 ≲ EA ≲ 95 MeV. Custom-designed electronics are employed for bias supplies and linear signal processing. Data are acquired via a CAMAC/VME/Ethernet system.

Evaporation residue as a dominant exit channel at high thermal energies in 3He + Ag reactions

Abstract In the reaction 3 He (1.8 GeV) + nat Ag , events are observed with a heavy fragment (HF), A≥10 , in coincidence with charged particles detected over 70% of 4π solid angle. Calorimetric measurements show high thermal excitation energies of the target primary fragment: 6–8 MeV per nucleon for HF mass ≳45 . For these excitation energies, the probability for having an evaporative residue is shown to be unexpectedly high when compared with current multifragmentation models. This result is interpreted as linked to the use of light ion projectiles at relatively low incident energy.

MULTIFRAGMENTATION : THERMAL VS. DYNAMIC EFFECTS

Reactions of 1.8 – 4.8 GeV 3He, 5.0 – 9.2 GeV/c π− and 6.0 – 14.6 GeV/c protons with natAg and 197Au targets have been studied with the ISiS 4π detector array. From reconstructed events, excitation-energy distributions have been determined and combined with a 2,3H3,4He isotope-ratio thermometer to study the heating curve for the thermal-like component of these reactions. Dynamic effects also manifest themselves in the data, as evidenced by deposition-energy saturation above ∼5 GeV, IMF emission during expansion, and sideways peaking of the IMF angular distributions for beam energies Eb ≥ 10 GeV.

Saturation of deposition energy in relativisitic 3He-induced reactions

Abstract The 4π detector ISiS has been used to measure light-charged particles and intermediate-mass fragments emitted in the 1.8–4.8 GeV 3 He + nat Ag , 197Au reactions. Ejectile multiplicity and total event energy distributions scale systematically with projectile energy and target mass, except for the natAg target at 3.6 and 4.8 GeV. For this system, a saturation in deposition energy is indicated by the data, suggesting the upper projectile energy for stopping has been reached. Comparison of the experimental distributions with intranuclear cascade predictions shows qualitative agreement.

A 4 π charged-particle detector array for light-ion-induced nuclear fragmentation studies☆☆☆

Abstract Operating characteristics of the Indiana Silicon Sphere 4 π detector array are outlined. The detector geometry is spherical, with 90 telescopes in the forward hemisphere and 72 at backward angles, covering a total solid angle of 74% of 4π. Each telescope consists of a simple gas-ion chamber, operated with C3F8 gas, followed by a 0.5 mm thick ion-implanted silicon detector and a 28 mm CsI(Tl) crystal, readout by a photodiode. Custom-built bias supplies and NIM preamp/shaper modules were used in conjunction with commercial CFD, TDC and ADC CAMAC units.

Probing the nuclear EOS with GeV light-ion beams

Abstract The first 4π studies of identified light-charged-particles and IMFs emitted in the p, π − + 197 Au reactions above 5 GeV/c are reported. Multiplicity and angular distributions show little sensitivity to either bombarding energy or projectile type. Excitation energy distributions obtained from data for the 4.8 GeV 3 He + 197 Au reaction yield values up to E ∗ ≲ 1500 MeV and E ∗ A residue ≲ 10 MeV/nucleon . Analysis of large-angle, IMF-IMF correlations for this same system suggests that multifragmentation is a fast, time-dependent process.

Multifragmentation with GeV light-ion beams

Multifragmentation studies with GeV light-ion beams indicate that for the most violent collisions, complex fragments are emitted during expansion of the hot source, followed by near simultaneous breakup of the system near ρ/ρ 0 ∼ 1/3. The results are compared with hybrid INC/EES and INC/SMM models. Preliminary data for the 8 GeV/c π − and preactions on 197 Au show enhanced deposition energy for the antiproton beam.