Natural Radioactivity

Properties of alpha rays

1. Alpha rays or alpha particles are the positively charged particles.
2. Alpha particles have the least penetration power. They cannot penetrate the skin but this does not mean that they are not dangerous.
3. Since they have a great ionization power, so if they get into the body they can cause serious damage. They have the ability of ionizing numerous atoms a short distance

Properties of beta rays

1. Beta particles are highly energetic electrons, which are released from inside of a nucleus.
2. They are negatively charged and have a negligible mass.
3. Beta particles have a greater penetration power than the alpha particles and can easily travel through the skin.
4. However, beta particles have less ionization power than the alpha particles but still they are dangerous and so their contact with the body must be avoided.

Properties of gamma rays

1. They have greatest power of penetration.
2. They are the least ionizing but most penetrating and it is extremely difficult to stop them from entering the body.
3. These rays carry huge amount of energy and can even travel through thin lead and thick concrete.

Geiger counter, with Geiger-Mueller (GM) tube or probe

A GM tube is a gas-filled device that, when a high voltage is applied, creates an electrical pulse when radiation interacts with the wall or gas in the tube. These pulses are converted to a reading on the instrument meter.

If the instrument has a speaker, the pulses also give an audible click. Common readout units are roentgens per hour (R/ hr), mill roentgens per hour (mR/hr), rem per hour (rem/hr), millirem per hour (mrem/hr), and counts per minute (cpm).

GM probes (e.g., "pancake" type) are most often used with handheld radiation survey instruments for contamination measurements. However, energy-compensated GM tubes may be employed for exposure measurements.

Alpha radiation is often used for field measurements where alpha-emitting radioactive materials need to be measured.

Spark counter

This consists of a fine metal gauze mounted about a millimetre away from a thin wire. A voltage is applied between the two so that sparking takes place between them - this usually requires some 4000 - 5000 V. The voltage is then reduced until sparking just stops.

Cloud chamber

The cloud chamber (Wilson chamber) is a particle detector used for detecting ionizing radiation.

Rare picture shows in a single shot the 4 particles that we can detect in a cloud chamber: proton, electron, muon (probably) and alpha. In its most basic form, a cloud chamber is a sealed environment containing a supersaturated vapor of water or alcohol.

Other devices used to detect radiation include

1. Photographic film
2. Bubble chamber
3. Gold-leaf electroscope

Half-life can be defined as the time taken for the number of nuclei in a radioactive material to halve.

OR

It the time taken for the count rate of a sample of radioactive material to fall to half of its starting level.

The half-life of a radioactive element

An exponential decay process can be described by any of the following three equivalent formulas:

$N(t) = N_0 \left(\frac{1}{2}\right)^{t/T_{1/2}}$

$N(t) = N_0 e^{-t/\tau}$

$N(t) = N_0 e^{-\lambda t}$

where

$N_0$ is the initial quantity of the substance that will decay (this quantity may be measured in grams, moles, number of atoms, etc).

$N(t)$ is the quantity that still remains and has not yet decayed after a time $t$.

$t_{1/2}$ is the half-life of the decaying quantity.

$\tau$ is a positive number called the mean lifetime of the decaying quantity.

$\lambda$ is a positive number called the decay constant of the decaying quantity

The three parameters $t_{1/2}$, $\tau$ and $\lambda$ are all directly related in the following.

$t_{1/2} = \frac{\ln(2)}{\lambda} = \tau \ln(2)$

Where

$\ln(2)$ is the natural logarithm of 2 (approximately 0.693).

By plugging in and manipulating these relationships, we get all of the following equivalent descriptions of exponential decay, in terms of the half-life:

$N(t) = N_0 \left(\frac{1}{2}\right)^{t/t_{1/2}} = N_0 \cdot 2^{-t/t_{1/2}}$

$= N_0 e^{-t \ln(2)/t_{1/2}}$

$N_0 e^{-t \ln(2)/t_{1/2}}$

$t_{1/2} = t / \log(N_0/N(t)) = t / (\log_2(N_0) - \log(N(t)))$

$= 1 / (\log_2 t(N_0) - \log_2 t(N(t))) = t \ln(2) / (\ln(N_0) - \ln(N(t)))$

Medical uses

Hospitals, doctors, and dentists use a variety of nuclear materials and procedures to diagnose, monitor, and treat a wide assortment of metabolic processes and medical conditions in humans.

The most common of these medical procedures involves the use of x-rays — a type of radiation that can pass through our skin. When x-rayed, our bones and other structures cast shadows because they are denser than our skin, and those shadows can be detected on photographic film. X-rays and other forms of radiation also have a variety of therapeutic uses.

Industrial uses

In irradiation, for instance, foods, medical equipment, and other substances are exposed to certain types of radiation (such as x-rays) to kill germs without harming the substance that is being disinfected and without making it radioactive.

Radiation is used to help remove toxic pollutants, such as exhaust gases from coal-fired power stations and industry. For example, electron beam radiation can remove dangerous Sulphur dioxides and nitrogen oxides from our environment.

The agricultural industry makes use of radiation to improve food production and packaging. Plant seeds, for example, have been exposed to radiation to bring about new and better types of plants.

Nuclear power plants

Electricity produced by nuclear fission — splitting the atom — is one of the greatest uses of radiation. As our country becomes a nation of electricity users, we need a reliable, abundant, clean, and affordable source of electricity. We depend on it to give us light, to help us groom and feed ourselves, to keep our homes and businesses running, and to power the many machines we use.

The purpose of a nuclear power plant is to boil water to produce steam to power a generator to produce electricity.

In agriculture

Radioisotopes are used to induce mutations in plants in order to develop superior varieties that are harder and more resistant to diseases.