Size of Nuclei
T&R Figure 12.2
R = ro A1/3
Shell model for Nuclei
From E. Segre
“Nuclei and Particles”
3-D Harmonic
Square well
Trends in Nuclear Stability
T&R Figure 12.5
See also Nudat2 at:
Trends in Nuclear Stability
T&R Fig. 12.6
Types of Radiation
•Alpha (a):
•4He nucleus; very easy to stop (paper, dead skin etc.)
•Beta (b)
•Electrons or positions, relatively easy to stop
•Gamma (g)
•High-energy photons (of nuclear origin)
•High-energy photons (of atomic origin)
•Auger Electrons
•Neutron (n)
Types of Radiation
Alpha Decay
T&R Fig. 12.11
Lecture 23
Potential Barrier: Alpha decay
The deeper the “bound” state is below the top of the barrier, the lower will be
the kinetic energy of the alpha particle once it gets out, and the slower will be
the rate of tunneling (and hence the longer the half-life). Figures from Rohlf
“Modern Physics from a to Zo”.
Beta Radiation Decay
Beta Radiation DecayNeutrinos
The energy of the b particle
(electron or positron) is not
fixed, this led Pauli to suggest
that another unobserved
(unobservable?) particle must
also be involved in the decay.
The “neutrino” was the name
given by Fermi a few years
later after he developed a
theory for the above curve
(and after Chadwick
discovered the neutron).
About 10 of the CALM
respondents last night did not
quote this as the reason for
the energy distribution in beta
Typical Decay scheme
Most alpha, beta, EC, n, fission
etc. decay (but not all, 210Po for
example) leave the daughter
nucleus in an excited state, and a
gamma ray is (eventually)
produced to take the daughter to
its ground state.
Typical Decay scheme II
Nuclei can decrease their
proton number by one in
three ways, positron
emission (the most common)
Electron capture (much
more rarely; see next slide),
or proton emission (very
Electron Capture
An alternative to positron emission (in which a proton
converts to a neutron within the nucleus by emitting a
positively charged particle) is “electron capture” in which
an atomic electron is absorbed by the nucleus (also
converting the proton to a neutron). This event will most
likely take place when the energy available in the decay
is less than that needed to create a positron.
•What kind of electron would most likely be involved?
• What signatures might you expect from such an event?
•Examples: 7Be, 37Ar, 41Ca, 49V, 51Cr, 53Mn, 57Co, 58Ni