ANALYZING RADIOACTIVE DECAY (Radioactivity-Nuclear)

Radioactivity-Nuclear

Radioactive Detectors

Cloud Chamber
A cloud chamber is used to show the path of ionizing radiation. The tracks of the radioactive emission are formed in the same way as the condensation trails behind a high-flying aero plane when the air in the sky is cold and damp enough. Different tracks are formed for each radioactive emission.

Tracks of radioactive emissions

Geiger-Muller Tube
A Geiger-Muller tube (GM tube) is a very versatile, sensitive and useful detector of radiation. It operates at a voltage of about 450 V. Radiation enters the GM tube through the mica window and ionizes the argon gas. A pulse of current is produced. This pulse of current is counted by a scalar or a rate meter. The scalar gives the number of counts over a certain period of time. The rate meter gives the count rate in counts per second or counts per minute. The GM tube can detect alpha particles, beta particles and gamma rays.

Photographic Film
A photographic film found in badges worn by the staff at radiation laboratories is developed at the end of every month. The degree of darkening of the photographic film indicates the amount of radiation received.

Spark Counter
A spark counter uses the ionizing effect of radiation. A high voltage is applied between the gauze and a wire below the gauze, and adjusted until it is just below the voltage required to produce sparks. When a radioactive source is brought near, the radiation ionizes the air between the gauze and the wire, and sparks are produced. Spark counters are suitable for detecting alpha particles.

Characteristics of radioactive emissions

There are three kinds of radioactive emissions
• Alpha particles
• Beta particles
• Gamma rays

Penetrating powers of radioactive emissions

Alpha decay
An alpha particle is emitted. The proton number is reduced by two and the nucleon number is reduced by four. These particles are positively charged.

Beta decay
A beta particle is emitted. The proton number is increased by one and the nucleon number is unchanged. These particles are negatively charged.

Gama decay

A gamma ray proton is emitted. The proton number and nucleon number are unchanged. This particle does not carry any charge.

The effect of an electric field on the radioactive emissions



The effect of a magnetic field on the radioactive emissions


Radioactivity-Nuclear

RADIOACTIVITY

Radioactivity-Nuclear

Radioactivity

The year 2006 was observed as the 100th anniversary of the discovery of radioactivity. During these years, the untiring work and research of scientists have resulted in a wide range of uses for radioactivity, all the benefit of mankind..

Radioactivity is the spontaneous disintegration of an unstable nucleus accompanied by the emission of energetic particles or protons.

Understanding the nucleus of an atom

Nucleus



Gieger-Marsden Experiment

In 1906, Rutherford noticed that many alpha particles could pass through a very thin sheet of mica as if the mica was not there. Two of his assistants, Geiger and Marsden, investigated the scattering of alpha particles by thin gold foils as shown in figure above. They found that most of the alpha particles passed through the gold foil with little or no deflection. However, to their amazement, a very small but significant number of alpha particles bounced back from the gold foil.

Rutherford proposed in 1911, a nuclear model of the atom as shown in Figure below, the atom has a very small dense core called the nucleus. All the positively charged particles and most of the mass of the atom are contained in the nucleus. The electrons move in orbits around the nucleus.

Rutherford-Model

Nucleons
The particles in a nucleus are called nucleons. There are two types of nucleons, protons and neutrons. A proton is a positively charged particle. It carries a charge of +e, where e = 1.6 x 10 power of -19 C.

The number of protons in a nucleus is known as the proton number, Z.

The nucleon number, A gives the total number of protons and neutrons in a nucleus. It is also known as the mass number.
The number of neutrons in a nucleus is A+Z.

Nuclide notation
Nuclide is a type of nucleus with a particular proton and nucleon number.

Isotopes
The nuclide is used to specify an atom or a nucleus with a particular proton-neutron combination. The number of protons in each atom of a particular element should be the same. However in some cases, the neutron numbers maybe different. Isotopes are atoms of an element which have the same proton number but different nucleon numbers.

Radioactivity-Nuclear