Physics and Engineering of Radiation Detection

48 Chapter 1. Properties and Sources of Radiation

Laser Ion Accelerators

Unlike conventional particle accelerators, laser ion accelerators are relatively small
sized devices that are used to accelerate ions at high energies using powerful lasers.
This new technique is capable of accelerating ions at very high energies in a very
short time and distance. In order to accelerate protons at severalMeV,ahighly
intense laser (> 1019 W/cm^2 ) with ultra-short pulses is focused on a solid or gaseous
target. This results in a collimated beam of high energy protons, which can be used,
for example to destroy cancerous tissues.
A lot of research is currently underway to study the feasibility of these devices
for cancer therapy and it is hoped that soon they will be an integral part of oncology
clinics and hospitals.

Radioactive Sources of Protons

Table 1.6.4: Common proton emitters and their half lives.

Element Isotope T 1 / 2

Indium^10953 I 103 μs

Cesium^11355 Cs 17 μs

Thulium^14769 mTm 360 μs

Lutetium^15171 Lu 120 ms

Tantalum^15773 Ta 300 ms

Rhenium^16175 Re 370 μs

Bismuth^18583 mBi 44 μs

There are no naturally occurring proton emitting isotopes suitable for use in
laboratory. However, it is possible to produce such radioisotopes with the help of
nuclear reactions, where a target material is bombarded by high energy particles.
This process excites the nuclei of the target material and makes them unstable.
The excited nuclei decay be proton, neutron,α-particle, and photon emissions. The
types of particles emitted actually depend on the target material and the projectile
energy. Table 1.6.4 lists a few of the many proton emitting isotopes that have been
discovered so far.

1.6.E Neutrons

Neutrons were the last of the basic atomic constituents to be discovered mainly
because of their almost identical mass to protons and no electrical charge. A British