B. Kolb

A time-of-flight spectrometer using short heavy ion pulses

Abstract A time-of-flight spectrometer consisting of a rebuncher (START signal) and selected surface barrier detectors (STOP signal) has been tested at the Heidelberg post-accelerator. Using the reaction 32 S + 27 Al in an incident energy range of E Lab = 140−320 MeV a time resolution of Δt ∼ 70 ps was routinely achieved. This resulted in a mass resolution for medium-heavy reaction products ( m ≲ 60 u) of Δm ≲ 0.5 u.

Complete and incomplete fusion in 19F+40Ca and 32S+27Al

Abstract Velocity distributions and excitation functions of fusionlike evaporation residues (ER) were measured for 41–216 MeV 19 F + 40 Ca and 142–393 MeV 32 S + 27 Al . The ER cross sections for 19 F + 40 Ca exceed those of 32 S + 27 Al by up to 44%, mainly due to an earlier onset of incomplete fusion of about 3.7 MeV/nucleon above the interaction barrier in 19 F + 40 Ca , compared to 5.6–7.7 MeV/nucleon in 32 S + 27 Al .

The Heidelberg 3MV-CW Heavy Ion Postaccelerator Section Using Independently Phased Spiral Resonators

The Heidelberg 3MV heavy ion postaccelerator section based on independently phased normal conducting spiral resonators working at 108 MHz is described. The design veloctity of the spiral resonators is ß = 0.10. The peak voltage drop is 0.37 MV at 20 kW CW input power (0.74 MV at 80 kW, duty factor 0.25) corresponding to a peak accelerating field of 1.7MV/m (3,4MV/m) averaged over the external length of the resonator. Using a synchronous phase of ¿S = -20° gives a maximum effective voltage of 0.35 MV (0.7 MV). The resonators are stacked in modules of four with one external quadrupole doublet. The total effective voltage of this first test section of the Heidelberg postaccelerator under construction is 3 MV-CW (6 MV d. f. 0,25) providing ion energies up to 6 MeV/ nucleon at mass A=40. The postaccelerator will be integrated into the existing experimental area. Beam matching to the longitudinal acceptance of the postaccelerator is done by a separate spiral resonator as rebuncher. The high quality of the tandem beam with respect to longitudinal and transverse phase space is maintained in the designed postaccelerator.

Complete and incomplete fusion in 19 F + 40 Ca and 32 S + 27 Al

Abstract Velocity distributions and excitation functions of fusionlike evaporation residues (ER) were measured for 41–216 MeV 19 F + 40 Ca and 142–393 MeV 32 S + 27 Al . The ER cross sections for 19 F + 40 Ca exceed those of 32 S + 27 Al by up to 44%, mainly due to an earlier onset of incomplete fusion of about 3.7 MeV/nucleon above the interaction barrier in 19 F + 40 Ca , compared to 5.6–7.7 MeV/nucleon in 32 S + 27 Al .

A new position measurement for ionization chambers

Abstract A new method has been applied for measuring the second position coordinate of particles detected in an ionization chamber. The position is determined by geometrically dividing the charge on the first ΔE anode. The resolution obtained was 0.3 mm. The energy, energy loss, and time resolution of the time-of-flight spectrometer (ionization chamber plus parallel plate avalanche counter) were δE/E=0.3%, δ ΔE/ΔE = 3%, Δt = 150 ps for 142 MeV 32 S ions .

The Heidelberg Heavy Ion Postaccelerator

The Heidelberg Heavy Ion Postaccelerator, a linear accelerator booster for the upgraded MP-Tandem is operational in its extended version since end of 1979. Yielding 9.7 MV in CW and 18.5 MV in pulsed mode (duty factor 0.25) it has considerably increased the mass and energy range of heavy ions for Nuclear Physics experiments at Heidelberg. The high flexibility of the booster is guaranteed by using 32 independently phased spiral resonators allowing operation of the machine in the mass range of A=10 to A=100 with almost constant accelerating voltage; although even ions as heavy as 197Au have been successfully postaccelerated. Typical examples of postaccele-rated beams are: 164 MeV 12C, 332 MeV 32S, 476 MeV 79Br, 511 MeV 127J and 640 MeV 197Au. Longitudinal and transversal beam quality are tandem like with ¿r < 2¿ mm mrad and ¿l < 3.2¿ MeV .deg., the debunched energy resolution being well below 10-3. The overall availability of the postaccelerator together with the MP-Tandem was 83% of the scheduled user beam time in 1980.

Possible contribution of low-l waves to the deep inelastic collisions of 32S with 27Al

Abstract The deep inelastic reactions of 32S with 27A1 have been studied at incident energies of 152.6 and 175 MeV by measuring inclusive fragment distributions, fragment-fragment and fragment-light particle coincidences. The observed Q-value distributions of the primary deep inelastic process range down to large negative Q-values as predicted by time-dependent Hartree-Fock calculations in the presence of low partial waves. No distinct low-l window for deep inelastic reactions can, however, be inferred from the data.

Application of a Spiral Resonator for Bunching Picosecond Heavy-Ion Pulses

A normal conducting spiral resonator (design ßo = vo/c = 0.06) with a maximum effective voltage of 0.33 MV at 20 kW CW input power has been used to bunch 156 MeV 58Ni and 96 MeV 32S ions. For an injected DC beam of 32S13+ of 96 MeV a pulse width of ¿tFWHM = 70ps was measured behind a drift length of 3.4 m. Phase locked to the 6.78/13.56 MHz nanosecond beam pulsing system of the MP tandem, pulse widths in the range of 200ps were obtained. In this case the pulse spacing is 147.5 ns with a background to pulse ratio of about 10-5. This spiral resonator is a standard section of the Heidelberg postaccelerator. It will also be used to match the pulsed heavy-ion beam to the postaccelerator over the whole mass range of interest A = 12-80. Furthermore it is installed in a normal beam line for heavy-ion time-of-flight experiments allowing a mass resolution of A < 1 for relatively heavy reaction products.

Evaporation residues from the fusion of 32S on 27Al at E = 142–227 MeV

Abstract The evaporation residues from the reaction 32 S on 27 Al were measured at 142, 153, 175, 187 and 227 MeV incident sulphur energies, using a time-of-flight spectrometer. The measured fusion-evaporation residue excitation function shows a maximum around E lab = 170 MeV, which corresponds to a limiting angular momentum of 43 ħ. Several possible mechanisms were investigated as being responsible for this limitation. It was found that both fission and entrance channel effects could be the limiting factors for the fusion-evaporation cross section at high energies.

Heavy Ion Acceleration at the Heidelberg Tandem Postaccelerator Combination

At the MPI für Kernphysik the range of heavy ions available with energy higher than 5 MeV/N has been extended to masses of about A=100 by combining the upgraded 13 MV MP-Tandem with a normal conducting RF-linac consisting of 32 independently phased spiral resonators. A first part of the linac of 10 resonators had already been operated between 1977 and 1979 with maximum effective voltages of 3.3 MV (CW) and 5.5 MV (pulse mode). After completion the extended booster now yields 9.7 MV in CW mode and 18.5 MV in pulse mode (duty factor 0.25). The high flexibility of the booster guaranteed by the independent phasing principle allows operation of the machine in the mass range of A=10 to A=100 with nearly constant acceleration voltage and with almost negligible set up times due to the flexible computer control. The maximum energies obtained so far are for some ions: 164 MeV 12C, 332 MeV 32S, 337 MeV 35Cl, 476 MeV 79Br and 511 MeV 127J. The tandemlike beam quality of the Tandem Booster combination (radial emittance < 2 II mm mrad, energy resolution < 10-3 (with debuncher)) and the available beam pulse width of less than 100 ps are an important contribution to the heavy ion nuclear and atomic physics experiments at MPI since March 1980. The overall availability of the postaccelerator together with the MP Tandem was above 80% of the scheduled user beam time.