In a nuclear charge-exchange reaction, a proton (neutron) in the target is
exchanged with a neutron (proton) in the projectile. Therefore, the products (the ejectile and the residual) have proton and
neutron numbers that differ by 1 from the projectile and target.
For example, in the animation a triton (Hydrogen-3, which
contains 2 neutrons and 1 proton) interacts with a target of mass A having Z protons and N=A-Z neutrons. If after the collision
a Helium-3 nucleus (2 protons and 1 neutron) is detected, the residual must contain Z-1 protons and N+1 neutrons, but still
have a total mass A. By measuring the velocity of the outgoing ejectile (the Helium-3 in the example), we can determine how
much energy is transfered to the target nucleus. By measuring the chance of exciting a certain energy state as a function of the
angle of the ejectile, we can learn about its quantum properties.
Excitation energy of 24Na via the (t,3He) reaction
In the figure to the left, three excitation energy spectra are shown, all for 24Na excited the via
24Mg(t,3He) reaction. a) shows all events for which the angle of the outgoing triton is less than 4o. Several excited states can be identified.
Depending on the transfer of angular momentum (one of the relevant quantum numbers) in the reaction, some excited states will peak at forward angles, as shown in b), and others will become
more prominant at backward angles, as shown in c).
Charge-exchange reactions provide an important tool to learn about nuclear structure.
Such information is not only important for better understanding of the basic properties of nuclei, but also for a number of applications
relating to astrophysics and particle physics.
There are many different charge-exchange reactions, such as: (p,n) (n,p) (d,2He) (3He,t)
(t,3He) (7Li,7Be).
We're currently working with four of these reactions: (t,3He), (3He,t), (p,n), and
(7Li,7Be). For more information about specific experiments and their applications, see the sidebars
"Experimental Programs" and
"Research Applications."
