Nuclear Instruments最新文献

A method has been developed to permit the simultaneous use of two targets with a pulsed linear electron accelerator. A magnet is arranged to deflect the beam onto one or the other target, and this magnet is electronically switched on or off in the interval between the beam pulses. A“ccount-down” circuit is used to select which pulses shall be directed to each target.

A 90° electromagnetic isotope separator with a beam radius of 100 cm is described. Using an acceleration voltage of 50 kV, ion currents of up to a few hundred μA can be handled. The ion current and resolving power can be varied within wide limits by adjusting the position of the lens system during operation. Two types of magnetic ion sources have been used to prepare targets for nuclear reaction studies and samples for beta- and gamma-ray spectroscopy.

The fast ionization chamber, 60 l in volume, filled with argon at 10 atm, is described. The pulse shapes are calculated assuming the ionization: (a) confined to an infinitesimal volume of the chamber, (b) distributed along a straight line parallel to the axis of the chamber, (c) distributed along a straight line passing through the axis of the chamber and perpendicular to it, (d) distributed along a straight line perpendicular to the axis of the chamber and not passing through it, (e) distributed throughout the volume of the chamber.

A comparison is made between the theoretical pulse shapes and the experimental ones.

An apparatus has been constructed to measure the velocities of both members of a fission-fragment pair. A zero-time signal is obtained at the expense of about one per cent of the fragment energy by detecting delta rays ejected by the fragment from a thin plastic foil placed near the source. The fragment times of flight are converted to pulse heights for analysis. An overall time resolution of 3.5 mμsec is obtained. A third variable, e.g. gamma-ray energy or prompt neutron time of flight, may also be recorded, the three pulse heights being punched consecutively on paper tape. Three-dimensional analysis is therefore possible but in practice sorting is done taking two variables at a time.

The scintillation response of europium activated crystals of Li⁶I to neutrons in the energy range 1–14MeV has been investigated with the crystals maintained at various temperatures. The pulse-height spectrum from mono-energetic neutrons incident on a crystal at room temperature demonstrates a poorly defined and broad fast-neutron peak. Upon cooling the crystal, the fast-neutron peak becomes sharper and assumes a nearly Gaussian shape at temperatures below about — 140° C. This behaviour is attributed to an increased scintillation efficiency of LiI(Eu) to alpha particles at low temperatures. Pulse-height spectra from crystals at the liquid nitrogen point are presented for neutrons from the D(d,n)He³, T(d,n)He⁴, and Be⁹(d,n)B¹⁰ reactions, a Po-Be source, and U²³⁵ fission. The principal features of Li⁶I(Eu) as a fast-neutron spectrometer are a relatively high detection efficiency (≈0.1%) and moderate resolution.

The authors built an apparatus for processing nuclear emulsions. Its functioning is shown by describing the processing of an Agfa K2 emulsion of 200 μ thickness.

The first part of this publication deals with the limitations of the discharge current, extraction of ions and focusing of large ion current beams. Three types of ion sources are described and their data are given.

The second part^†† deals with detailed investigation of the characteristics of the discharge of the Penning type. For this purpose a special ion source was build which allowed for the exchange of all inner parts.