Re: Are their any harmful or negative uses of radioactive isotopes?

Parvathy,

There is the possibility of harmful events associated with all aspects of 
the use of radioactive materials. I am going to restrict myself to 
effects on humans for this discusion. The term radioactive means that the 
atom in question is unstable and will emit ionizing radiaton. This can be 
in the form of alpha particles (helium nuclei with two protons and two 
neutrons), beta particles (identical to a negatively charged electron), 
and gamma rays (high energy electromagnetic radiation). Those are the 
major types encountered. There are some rarer radioactive materials, or 
mixtures, that emit postitively charged electrons called positrons, and 
sources designed to emit neutrons--those are used for measurements of 
soil or cement density, and are in sealed units in those instruments.

The negative effects are caused by the ability of "ionizing radiation" to 
remove electrons from atoms (hence the name "ionizing") as they interact 
with matter. If the matter is the human body, electrons can be removed 
from atoms creating charged particles, or ions, and those can interact 
with biological molecules damaging them so that they cannot perform their 
normal functions. 

For an overview on this subject, I suggest you read a few of the articles 
found by entering "interaction of radiation with matter" and "biological 
effects of ionizing radiation" into a search engine. The university 
articles, and even the Wikipedia articles are good introductions to the 
mechanisms.

You will find that alpha particles are not a danger as long as they 
remain outside the body. They cannot penetrate the skin. Their danger is 
if they get inhaled or injected into the body. There, their energy is 
very disruptive to atoms over a short distance. The most common 
radioactime element to get into the body this was is radon, a radioactive 
inert gas, from the decay of naturally occurring Uranium and Thorium in 
the earth. This gas may be in water, cement, enter into basements from 
bedrock, or be in the air underground miners breathe. Long exposures to 
high levels of radon gas can cause lung cancer to develop after some 
years.

Industrially, in the 1920s through the 1940s radium uas painted onto 
dials and indicators (like hands on a watch) because it glowed in the 
dark. The painters (almost all women) used to tip the brushes with their 
tongue to get a very fine point for painting dial markings or indicators. 
Over the years (these painters were followed by health physicists the 
rest of their lives) many suffered from cancer caused by the radiation 
from the radium (a bone-seeking atom when in the body) which contained 
alpha, beta, and gamma radiation. You can find out about their stories by 
searching for "Radium Dial Painters History" if you are interested in 
further details.

Beta and Gamma radiation can affect the body from the outside because 
they have enough energy to get through the outer layer of the skin. Now, 
like any harmful agent, it is the dose that matters.

Beta particles being high energy electrons have ability to ionize atoms 
than gamma rays (which have a probability of passing through you without 
interacting). Beta particles are also worse when ingested because the 
damage is done inside the body. From the outside, plastic or aluminum are 
good for shielding persons working with them. Many radioisotopes used in 
research in a laboratory are beta emitters, and they are sefely handled 
with light shielding like 3/4 inch lucite. People have worked with beta 
emitting materials over long times, and with the basic shielding and 
hygiene have had no ill effects. However, large amounts of external beta 
radiation will cause skin burns from ionizing the layers of the skin just 
as Ultra-violet rays from the sun will do. 

Although more shielding is needed to work with gamma emitting 
radionuclides, lead is one of the shields used for gamma rays, again 
proper techniques, shielding, and hygiene will make the workplace safe. 
One of the industrial uses of large gamma emitting sources is 
radiography. Gamma rays are high energy X-rays, and can be used to take 
Gamma Radiographs of objects using photographic film. The source is in a 
lead shield. This unit is placed on a holder in the center of a large 
welded pipe--such as on an oil or gas pipeline. Film is placed on the 
outside of the pipe all around the weld. The radiographer can cause the 
source to be moved out of its shield on a wire that is welded to the 
source and unwinds from the back of the shield. The source is left out 
for the amount of time necessary to radiograph the welds to look for 
voids or other defects that could cause the weld to fail. After that time 
has passed (with all workers, including the radiographer, away from the 
source), the radiographer winds the source back into its shield. 
Sometimes the source gets stuck without going all the way into the 
shield. Radiographers have gotten burns and radiation exposures from 
those incidents. 

While excessive exposures are negative effects, we live in a sea of 
radiation all the time. This is the background radiation from the 
radioactive materials in the earth, cosmic radiation (more radiation at 
higher altitudes because the atmosphere didn't absorb as much), and 
medical uses of radiation (x-rays (including fancy scanning like full-
mouth scans at a dentist or CAT, computed axial tomagraphy), radiactive 
materials injected for tests or treatment. 

One thing to remember is that life on this planet has developed over a 
very long time. While life was first forming, the level of radiation from 
the planet, the background radiation at that time, was much greater than 
it is today. The radioactive materials in the earch today have ha;f-lives 
on the order of the age of the earth. All of those radioactive elements 
with half lives shorter than about one tenth the age of the earth have 
decayed away. If you look at a chart of the radioactive nuclides, you 
will see that radium and radon are very short lived with respect to the 
age of the earth--however, they are being continuously formed by the 
decay of uranium and thorium nuclides that are a long-lived as the age of 
the earth (you can find the math for this by searching "Radioactive 
Serics Decay" or "Uranium Decay Series". Absent large doses from medical 
or other non-natural radiation, we actually live in a lower background 
radiation that when life developed. 

I hope this answers your question about negative effects, and puts some 
of the natural radiation into perspective for you.