Radiation is energy that travels in the form of waves or high speed particles. There are different types of radiation, including alpha particles, beta particles, neutrons, gamma rays, and x-rays. These types of radiation have different properties and can penetrate and interact with matter differently. Some types, like alpha particles, can be easily stopped by thin layers of materials like paper or skin. Other types, like gamma rays and neutrons, are much more difficult to stop and require thick lead or concrete shielding to provide protection. So when it comes to the hardest radiation to stop from reaching you and affecting your body, neutrons and gamma rays top the list.
What Makes Neutrons and Gamma Rays So Penetrating?
Neutrons and gamma rays have very high energy levels and do not carry an electrical charge. This allows them to penetrate deeply into materials before interacting or being absorbed.
Neutrons
Neutrons are emitted from the nuclei of unstable atoms that undergo radioactive decay. They are uncharged particles and have a high kinetic energy, allowing them to collide with the nuclei of other atoms and impart that energy. This makes neutron radiation extremely penetrating. In fact, neutrons can pass through several feet of concrete or a few inches of lead before being absorbed. They are primarily absorbed by hydrogenous materials like water or plastic. Paraffin wax, containing lots of hydrogen atoms, makes a good neutron shield. The hydrogen nuclei slow down fast neutrons during collisions, eventually capturing them entirely. But it takes a thick layer to effectively stop neutrons.
Gamma Rays
Gamma rays are a highly energetic form of electromagnetic radiation produced by radioactive decay or other nuclear processes. Like X-rays, they have no mass or charge. But gamma rays have even higher frequencies and energy than X-rays, allowing them to travel extremely far through air and penetrate deeply into materials. Gamma rays are stopped by thick layers of dense, high atomic number materials like lead and depleted uranium. A few inches of lead or a few feet of concrete are needed to shield gamma ray sources. The heavy nuclei in these materials absorb the gamma photon energy. But it takes a lot of material to stop them.
Why Are Neutrons and Gamma Rays So Difficult to Stop?
There are a few key reasons why neutron and gamma ray radiation are the most difficult to shield against:
- High energy – Neutrons and gamma rays have very high kinetic energies, allowing them to impart substantial damage to materials as they pass through.
- No charge – Being electrically neutral, neutrons and gamma rays do not interact with orbital electrons and are not slowed by Coulomb forces. This allows deeper penetration before being absorbed.
- Low ionization – Compared to alpha and beta particles which cause high ionization along their path, neutrons and gammas undergo less interactions. Less energy is lost ionizing atoms, allowing them to travel farther.
- Secondary radiation – Interactions of neutrons and gammas can produce more penetrating radiation throughPair production and neutron activation. This increases exposure.
These factors make neutrons and gamma rays far more penetrating than other common radiation types. Thick shielding is required to provide protection. Even several feet of concrete or inches of lead will only attenuate the radiation, not completely absorb it. Proper shielding against neutrons and gamma rays requires strategic use of hydrogenous and high density materials respectively.
Everyday Sources of Neutrons and Gamma Rays
While neutrons and gamma rays require special radioactive sources or nuclear reactions to be produced, we are exposed to small amounts of these penetrating radiations in our everyday lives:
Neutrons
- Cosmic radiation – Neutrons are generated from collisions between cosmic rays and atoms in the upper atmosphere.
- Air travel – Exposure to cosmic radiation increases during flights at high altitudes.
- Nuclear reactors – Fission reactions in nuclear reactors emit neutron radiation which is moderated and absorbed by reactor shielding.
- Particle accelerators – Accelerators smash atoms together to produce neutron beams for research and medical purposes.
- Industrial sources – Neutron gauges and well logging tools contain americium-beryllium or californium sources.
Gamma Rays
- Natural background – Terrestrial gamma rays are emitted by radioactive isotopes in soil and building materials.
- Medical procedures – X-rays, CT scans, radiotherapy all involve exposure to ionizing radiation including gammas.
- Nuclear facilities – Gamma rays are produced by fission and from radioactivity in nuclear fuel and waste.
- Industrial sources – Gamma ray devices are used to scan cargo, gauge levels, and analyze materials.
- Security screening – X-ray backscatter technology emits low level gamma radiation.
While these sources involve much lower exposure levels than directly handling radioactive material, they illustrate how neutrons and gamma rays penetrate into our lives. Proper shielding and safe handling practices help limit radiation exposure.
Most Harmful Effects of Neutron and Gamma Radiation
Neutrons and gamma rays are the most biologically damaging forms of ionizing radiation due to their high energy and deep tissue penetration. The harmful effects primarily stem from:
Cell Damage and Death
The high energy neutrons and gammas deposit into cells can directly damage DNA strands. This can kill cells or cause mutations that lead to cancer. Rapidly dividing cells are most vulnerable.
Tissue Damage
The energy deposited causes ionization and molecular damage that kills or impairs tissue function. This can lead to burns, organ failure, and other acute radiation sickness effects.
Radiation Sickness
The gastrointestinal tract, bone marrow, and other sensitive tissues are damaged at high doses. This causes nausea, immune system suppression, weakness and can be fatal.
Cancer
DNA damage leads to increased cancer risk years after exposure, particularly leukemia and solid tumor cancers. The risk depends on the radiation dose.
Genetic Effects
Changes to reproductive cells can lead to inherited disorders in children conceived after one parent’s radiation exposure. This is most likely at very high doses.
Neutrons and gamma rays are therefore hazardous even at low doses if proper shielding or distance is not maintained. Exposure should always be kept as low as reasonably achievable.
Key Points on Neutron and Gamma Radiation
- Neutrons and gamma rays have very high energy levels that allow deep penetration into materials and human tissue.
- Thick shielding like lead, concrete, or water is required to absorb neutron and gamma radiation.
- Their high energy, lack of charge, and low ionization density make neutrons and gammas very difficult to stop.
- Neutrons and gammas damage tissue through direct cell damage and burns when highly exposed.
- Lower dose exposure increases lifetime cancer risk and can cause radiation sickness.
- Exposure should be minimized through shielding, distance, and limiting time spent around neutron and gamma sources.
Conclusion
In summary, neutrons and gamma rays represent the most penetrating and hazardous forms of radiation exposure. Their high energies allow them to pass through substantial shielding and damage human tissue at the cellular level. Sufficient shielding with hydrogenous and dense materials can reduce exposure, but neutrons and gammas are still difficult to completely stop. Care should be taken when handling sources of these types of radiation to limit dose and prevent acute and long term harm. Maintaining distance, minimizing time, and proper shielding help provide protection. While present in small amounts in nature and certain medical procedures, unnecessary exposure to neutrons and gamma rays should be avoided. Their ability to deeply penetrate the human body makes them the most concerning radiation types to shield against.