A. Oed

High resolution axial ionization chamber for fission products

Abstract The construction of an ionization chamber with the electrical field parallel to the particle beam (axial chamber) is described. The energy resolution achieved for typical light and heavy mass fragments from the thermal neutron induced fission of 235 U is 385 keV and 510 keV, respectively.

A mass spectrometer for fission fragments based on time-of-flight and energy measurements

With the aim of determining masses of fission fragments by measuring velocities and kinetic energies, specially adapted time-of-flight detectors and ionization chambers were developed. The start and stop detectors for the time-of-flight sense the electrons emitted from a thin foil upon passage of fragments. The time resolution achieved is ⋍ 100 ps. The ionization chambers have the electric field arranged parallel to the particle trajectory, and with isobutane as the counting gas, the intrinsic energy resolution for fragments with m ⋍ 100 amu is typically 400 keV. The combination of both the time-of-flight and ionization chamber, to produce an energy-time-of-flight spectrometer, was tested with fragments from the 235U(n, f) reaction on an external thermal neutron beam at the ILL/Grenoble. In the light group of fission fragments, all masses are resolved individually with a mass resolving power m/δm = 170 for m = 95.

A new method to identify nuclear charges of fission fragments

Abstract For a mass and velocity selected beam of fission fragments, the elemental components of the beam have been determined by measuring the difference between the time the fragments enter an axial ionization chamber (with the electrical field lines parallel to the particle trajectory) and the time the anode pulse crosses a given level. The nuclear charge resolution achieved for typical fission fragments out of the light mass group in thermal neutron induced fission of 235U is Z/ΔZ = 43 for a nuclear charge Z = 39.

Precision measurements of mean kinetic energy release in thermal-neutron-induced fission of 233U, 235U and 239Pu

Abstract The values of the total kinetic energy (TKE) of fission fragments published until now show discrenancies up to several MeVs depending on the type of experiment. Therefore, a novel method was developed to get more reliable figures of high precision by avoiding systematic errors of earlier measurements. Moreover, the determination of primary fragment mass- and energy-distributions is feasible.

Cold deformed fission

Fragment mass and charge distributions have been taken for the fission reaction 235U(nth,f) both at very high and low fragment kinetic energies. At high kinetic energies cold fission, with virtually no excitation energy being left to the fragments, is by now well established. Rather surprisingly, the fragment characteristics at very low kinetic energies again point to a fragmentation process where at scission the nascent fragments, though heavily deformed, carry no intrinsic excitation. This limiting case of nuclear fission is called cold deformed fission.

Mass spectrometry of fission fragments by simultaneous energy and time-of-flight measurements

Abstract With the aim of determining masses of fission fragments by measuring velocities and kinetic energies, specially adapted time-of-flight detectors and ionization chambers were develpoed. The combination of both the time-of-flight spectrometer, was tested with fragments from the 235U(n, f) reaction. In the light group of fission fragments, all masses are resolved individually with a mass resolving power m/δm = 170 for m = 95. At high energies also the heavy masss are responsible. A possible nuclear-charge determination by the instrument is discussed.

Determination of the isobaric elemental yields in velocity selected fission products

Abstract An experimental technique is described which allows the elemental yields of a fission particle beam composed of several masses of equal velocity such as supplied by the spectrograph “Lohengrin” at the ILL, Grenoble, to be measured.

Features of microstrip proportional counters

The light emission of a microstrip-anode in noble gas mixture, with a gas amplification of 4(DOT)104, is 60 times higher than the light emission of NaI(Tl) scintillator.

Mass and energy distribution of fission fragments in 249Cf(nth, f)

Abstract The mass and energy distribution of fission fragments in 249Cf(nth, f) were determined by combining TOF and energy data of the fragments. The first results are discussed.

Bragg curves of fission fragments in gases

Abstract An unexpectedly high probability of collisions between the fission particles and the atoms in an ionization chamber along the entire particle track causes a strong fluctuation of the shapes of the Bragg curves. This fluctuation imposes an upper limit of the charge resolution δZ/Z which can be achieved.