In recent years the improved methods of nuclear
spectroscopy have provided an increasing body of
information about the modes of disintegration of both
naturally occurring and artificially produced radio-elements.
This has led to the development of nuclear
models which are capable of interpreting the nuclear
data in terms of the properties of the nuclear structure
with some success. Spins and parities are
assigned to nuclear energy levels, and selection rules
have been formulated by which the observed decay
properties can be explained fairly consistently. The
properties of the nuclear levels can be established
from a variety of measurements. In ß- and γ -ray
spectroscopy these include the relative intensities
and high energy end-points of the partial components of
the ß-speetrum, determined by the method of Fermi
analysis from the continuous spectrum produced in the
(ß-decay of a parent nucleus, and the intensities,
lifetimes and multipole nature of subsequent γ-
transitions between higher and lower lying energy
levels in the daughter nucleus. These γ-transitions
give rise to internal conversion electrons which are
superimposed as mono-energetic lines on the continuous
ß-spectrum. The internal conversion electrons are
formed through the interaction of a γ-ray of energy
Eγ with an electron of the K, L, -shell of the
product nucleus. The energy Eß of the electrons
emitted from the shell is given by Eß = Eγ - Eₖ (or
Eₗ ), where Eₖ' (or Eₗ', ) is the binding
energy of the K, L, -shell electrons in the pro¬
duct atom. It is customary to speak of the conversion
of the γ-rays although it is now recognised that the
electron emission is a competitive decay process resulting
from the mutual interaction of the overlapping
nuclear and electronic wave functions. The relative
conversion efficiencies for γ-rays in the different
shells or sub-shells and the ratio of conversion electrons
to photon de-excitations (the conversion coefficients)
in an atom depend, along with their lifetimes,
on the energy and multipole nature of the radiation.
The absolute intensities of the conversion lines,
together with theoretically or experimentally determined
conversion coefficients, permit the total intensities
of y-transitions to be calculated relative to the
total number of ß-transitions. The energies and
intensities of the ß- and γ-transitions in conjunction
with γ-ray studies may then form the basis of a
complete disintegration scheme, while measurements of the
coincidence of ß- and γ-transitions may be made to
decide conclusively between possible level schemes.
The present investigations on the electron spectrum
of heavy radio-elements were undertaken with a
magnetic spectrometer and provide information on the
energies and intensities of ß-transitions and internally
converted γ-transitions. The spectrometer has
recently been equipped with a γ-ray detector which,
with the possibility of making ß-γ coincidence
measurements, will extend its capabilities in future
studies.
The spectrometer was designed by Richardson (1, 2)
and the performance has been investigated and described,
by Braid and Richardson (3). A description of the
spectrometer is given in Chapter 3 but those features
that distinguish it from conventional ß-particle
spectrometers will be mentioned here, together with
those properties that determine the type of radio-element
that can be most profitably investigated
