Competencies:

• Explain the concept of radioactivity with its properties to understand the safety precautions while working with radiations.

Scope:

The Nuclear Atom. (Scope: nuclear composition, protons and neutrons, proton number, nucleon number, nuclide notation).

Radioactivity (Scope: detection and properties of of α , β, γ radiation, characteristics of α, β, γ emission, random nature of radioactive emission and safety precautions of the radiations)

Objectives:

1. Describe the composition of nucleus, in terms of protons and neutron and represent radioactive elements using nuclide notation.

2. Explore the characteristics of α, β and γ particles and identify their emission using a simulation.

3. Mention the safety precautions one needs to consider while working with the radiations.

Number of Protons : This is the same as the atomic number (Z)

A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are jointly referred to as "nucleons" (particles present in atomic nuclei).

Number of electrons : For atoms, this will be the same as the atomic number. However ions are different, in that they have a charge. If the ion is positively charged, it means it has lost electrons(s). Consequently, the number of electrons will be calculated by subtracting the charge from the number of protons (atomic number – which never changes).

The electron is a subatomic particle, (denoted by the symbol e− or β−), whose electric charge is negative one elementary charge.

Number of Neutrons : The mass of an atom is given by the number of neutrons (mass – 1 amu) plus the number of protons (mass – 1 amu).

Consequently, the number of neutrons can be calculated by subtracting the atomic number (number of protons) from the mass number.

The neutron is a subatomic particle, symbol n or n⁰, which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one atomic mass unit, they are both referred to as nucleons

Nucleon Number: The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.

The mass number is different for each different isotope of a chemical element. This is not the same as the atomic number (Z) which denotes the number of protons in a nucleus, and thus uniquely identifies an element.

Hence, the difference between the mass number and the atomic number gives the number of neutrons (N) in a given nucleus: N=A−Z

Radioactivity

Radioactive decay occurs when an unstable atomic nucleus loses energy by emitting energy in the form of emitted particles or electromagnetic waves, called radiation. Isotopes are atoms of the same element (thereby having the same number of protons) which differ in the number of neutrons in their nucleus. Some isotopes of a given element are more unstable than others, causing a nuclear reaction which releases energy to achieve a more stable nuclear configuration. Such isotopes are radioactive, and are referred to as “radioisotopes.”

The radioactive decay products we will discuss here are alpha, beta, and gamma, ordered by their ability to penetrate matter. Alpha denotes the largest particle, and it penetrates the least.

• Alpha particles carry a positive charge, beta particles carry a negative charge, and gamma rays are neutral.

• An alpha particle is made up of two protons and two neutrons bound together.

• Beta particles are high energy electrons.

• Gamma rays are waves of electromagnetic energy, or photons.

Penetration power-Alpha particles can be completely stopped by a sheet of paper. Beta particles can be stopped by aluminum shielding. Gamma rays can only be reduced by much more substantial mass, such as a very thick layer of lead.

Terms

• alpha particle- A particle consisting of two protons and two neutrons bound together, identical to a helium nucleus.

• beta particle- A high energy electron released during beta decay.

• gamma ray- High-energy wave of electromagnetic energy.

• isotope- A variant of a particular chemical element, which shares the same number of protons as other atoms of the element, but differs in its number of neutrons.

• Transmutation: It is the act of a changing an atom into another type of atom.

• Alpha decay and beta decay are examples of transmutation

Alpha Decay:

Alpha decay is a nuclear decay process where an unstable nucleus changes to another element by shooting out a particle composed of two protons and two neutrons. This ejected particle is known as an alpha particle and is simply a helium nucleus. Alpha particles have a relatively large mass and a positive charge.

Uses:

Radioactive elements that undergo alpha decay are used in smoke detectors.

A new cancer treatment known as targeted alpha therapy or TAT uses alpha decay to kill cancer cells. Lead-212 is ingested and travels to the site of the tumor, then giving off alpha radiation which kills all the cells in the area.

Health Issue of alpha decay

The health effects of alpha particles vary with how the exposure takes place. If the alpha emitter is inhaled, swallowed, or absorbed into the blood stream there can be lasting biological damage. This damage increases a persons risk of cancer. Alpha radiation is known to cause lung cancer in humans if the alpha emitter is inhaled. The inhalation of radon, an alpha emitter, is one of the biggest sources of alpha decay related illness in humans.

Beta Decay

Beta decay is a nuclear decay process where an unstable nucleus transmutes and ejects particles to become more stable. There are two different types of beta decay - beta minus and beta plus. In both of these decays, a nucleon in the nucleus is transformed into a different type of nucleon, releasing particles in the process.

Beta Decay is the emission of a beta particle from the nucleus of an atom undergoing radioactive decay.

Beta decay occurs when a neutron turns into a proton and an electron.

Neutron .......>> Proton + Electron

As a result of beta decay, the nucleus has one fewer neutron, but one extra proton.

Therefore the atomic number, Z increases by 1 and the mass number, A stays the same.

When a beta particle is emitted, the unstable atom is changed into a more stable atom.

Uses:

Elements that have beta decay can have useful medical applications. Radionuclide therapy (RNT) or radiotherapy is a cancer treatment that uses beta decay.

Carbon dating relies on the properties of beta decay. To determine the approximate age of artifacts, wood, and animal remains the ratio of carbon-14 to carbon-12 in an object must be determined.

By looking at the ratio of carbon-14 to carbon-12, the approximate age of the artifact can be determined.

Health Issue of beta decay

If a beta source enters the body, it causes tissue damage and can increase the risk of cancer. Some beta emitters are distributed throughout the body - such as carbon-14 (which occurs naturally at levels that cause no harm to the human body)- while others accumulate in specific organs. An example of this would be iodine-131, which concentrates in the thyroid gland and increases the risk of thyroid cancer.

Supplementary Reading Material. (Need not copy this notes, just read once)

RADIATION HEALTH BASICS

What is the difference between alpha, beta, gamma and neutron radiation?

Gamma rays and beta particles make up most of the fallout radiation immediately after a nuclear explosion. Gamma rays are the immediate hazard to life. There are four major types of radiation.

Alpha particles:

Alpha particles cannot penetrate most matter. A piece of paper or the outer layers of skin is sufficient to stop alpha particles. Radioactive material that emits alpha particles (alpha emitters) can be very harmful when inhaled, swallowed, or absorbed into the blood stream through wounds.

Beta particles:

Beta particles can be stopped by a layer of clothing or by a few millimeters of a substance such as aluminum.

Beta particles are capable of penetrating the skin and causing radiation damage, such as skin burns.

As with alpha emitters, beta emitters are most hazardous when they are inhaled or swallowed or absorbed into the blood stream through wounds.

Gamma rays and X-rays:

Gamma rays and X-rays are penetrating. Several feet of concrete or a few inches of lead are required to stop them. Gamma rays are the reason why it is best to shelter in a basement or a centrally located room in a high rise.

Gamma rays and X-rays are a radiation hazard for the entire body. While gamma rays and X-rays can easily pass completely through the human body, some fraction of the energy will always be absorbed by body tissue.

Neutrons:

Neutrons are only a hazard close to and during the initial blast (within a few miles of ground zero). Neutrons are particles and are very penetrating. Several feet of concrete or another material rich in hydrogen (such as water) are required to stop them.

Neutrons are a radiation hazard for the entire body. Neutrons interact with tissues in the body and have the potential to cause damage.

What type of radiation is most harmful?

It depends on whether your exposure to radiation is internal or external. Alpha particles are the most harmful internal hazard as compared with gamma rays and beta particles. Radioactive materials that emit alpha and beta particles are most harmful when swallowed, inhaled, absorbed, or injected.

Gamma rays are the most harmful external hazard. Beta particles can partially penetrate skin, causing “beta burns”. Alpha particles cannot penetrate intact skin.

Gamma and x-rays can pass through a person damaging cells in their path.

Neutron radiation present during nuclear reactions, within a few miles of ground zero, is as penetrating as gamma rays.

What Happens When People Are Exposed to Radiation?

Radiation can affect the body in a number of ways, and the adverse health effects of exposure may not be apparent for many years. These adverse health effects can range from mild effects, such as skin reddening, to

serious effects such as cancer and death, depending on the amount of radiation absorbed by the body (the dose), the type of radiation, the route of exposure, and the length of time a person was exposed.

Exposure to above-normal levels of radiation can lead to fatigue, nausea and vomiting, and changes in the blood.

Exposure to very large does of radiation can lead to radiation sickness, with symptoms such as loss of appetite, hair loss, diarrhea, or even death within a few days or months. This is called Acute Radiation Syndrome (NYCDHMH, 2011).

Exposure to lower doses of radiation may lead to an increased risk of developing cancer or other adverse health effects later in life (USEPA, 2011).

What is Acute Radiation Syndrome/Sickness (ARS)?

You can only get Acute Radiation Syndrome (ARS) from short-term exposure to a large amount of radiation. ARS occurs when most of the body was exposed to high levels of radiation. The radiation must reach internal organs. ARS only occurs in extreme circumstances. Initial symptoms may begin from minutes to days after exposure. Symptoms include skin burns, nausea, and/or vomiting. These symptoms may come and go in the first few days. Symptoms may completely go away and the person may feel healthy. Additional symptoms can occur weeks and months after exposure: loss of appetite, fatigue, fever, nausea, vomiting, diarrhea, seizures, and/or a coma. People with ARS typically also have some skin damage. This damage can start to show within a few hours after exposure and can include swelling, itching, and redness of the skin (like a bad sunburn). There also can be hair loss (CDCb, 2011). This stage of serious illness can last for months. ARS can lead to death. Seek medical attention immediately if you think you are suffering from ARS.

Exercise:

A. Fill in the blanks:

1. An alpha particle is made up of ________ protons and 2 _________.

2. Atomic number of element is the number of _________ present in the nucleus of the element.

3. Beta decay occurs when a _________ turns into a proton and an electron.

4. The mass of an atom is given by the number of _______plus the number of ________

5. The act of a changing an atom into another type of atom is known as ___________

B. Write whether the following statement is TRUE or FALSE

1. α-particles have high ionizing power.

2. Alpha particles are deflected the most when made to pass through electric field.

3. Gamma rays are waves of electromagnetic energy, or photons.

4. Gamma rays have the least penetrating power compared to alpha and beta particles.

5. As a result of beta decay, the nucleus has one fewer neutron, but one extra proton.

C. Answer the following questions

1. An unstable uranium atom emits a neutron. How will its mass number and atomic number change?

2. You are working in a nuclear power plant. Mention at least two precautions that you must take to get rid of harmful effect of nuclear radiations.

3. What are the uses of alpha, beta and gamma decay?

4. Explain health issues due to alpha, beta and gamma decay.

5. Which among alpha, beta and gamma rays is more harmful. Explain the reason.