Radioactivity

Radioactivity

Samiul EhsanComputer Science & Engineering

Radioactivity

▪ Radioactivity also known as radioactive decay is a process in which unstable atomic nucleus loses energy by emitting radiation.

▪ Radiation is released in form of particles or electromagnetic waves.

▪ The rate of radioactive decay is described in half-lives.

▪ The main source of radiation in Earth is sun. Radiation is going through everywhere and all the time.

Pioneers in Radioactivity

Roentgen:

Discoverer of X-rays

1895

Becquerel:

Discoverer of

Radioactivity 1896

The Curies:

Discoverers of Radium

and Polonium

1900-1908

Rutherford:

Discoverer Alpha and Beta rays

1897

Type of Radioactivity

By the end of the 1800s, it was known that certain isotopes emit penetrating rays. Three types of radiation were known:

1)Alpha particles (a)

2)Beta particles (b)

3)Gamma-rays (g)

Particle

Mass

Charge

Gamma (g) 0 0

Beta (b) ~0.5 -1

Alpha (a) ~3752 +2

Alpha Particles (a)

Radium

R226

88 protons138 neutrons

Radon

Rn222

This is theatomic weight, whichis the number ofprotons plus neutrons


+ nnp

p

a (4He)2 protons2 neutrons

The alpha-particle (a) is a Helium nucleus. It’s the same as the element Helium, with the electrons

stripped off ! A sheet of paper or human skin can stop Alpha Particles. These are only hazardous to human health if they are

inhaled.

Beta Particles (b)

CarbonC14

6 protons8 neutrons

NitrogenN14

7 protons7 neutrons

+ e-

electron(beta-particle)

We see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus. In symbolic notation, the following process occurred:

n p + e ( + n )

Beta Particles (b)

They can travel a few feet in air but can usually be stopped by clothing or a few centimeters of wood.

They are considered hazardous mainly if ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough.

Unstable Neutron decays into a proton.

Gamma particles (g)

In much the same way that electrons in atoms can be in an excited state, so can a nucleus.

A gamma is a high energy light particle. It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum.

NeonNe20


(in excited state)


(lowest energy state)

+

gamma

NeonNe20

Gamma particles (g)

Occurs when an unstable nucleus emits electromagnetic radiation. The radiation has no mass, and so its emission does not change the element.

They penetrate matter easily and are best stopped by

water or thick layers of lead or concrete.

Gamma radiation is hazardous to people inside and outside of the body.

Gamma rays have the lowest ionizing power, but the highest penetrating power.

Half-Life

The “half-life” (h) is the time it takes for half the atoms of a radioactive substance to decay.

For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after:

10,000 (50%)

5,000 (25%)

2,500 (12.5%)

1 hour (one lifetime) ?

2 hours (two lifetimes) ?

3 hours (three lifetimes) ?

Time #atomsremaining

% of atomsremaining

Lifetime(t)

The “lifetime” of a particle is an alternate definition ofthe rate of decay.

The lifetime of a free neutron is 14.7 minutes. If there were 1000 free neutrons in a box, after 14.7

minutes some number of them will have decayed. The number remaining after some time is given by the

radioactive decay law-

/0

tN N e N0 = starting number of particlest = particle’s lifetime

Its value is 2.718

Lifetime

Not all particles have the same lifetime. Uranium-238 has a lifetime of about 4.5 billion (4.5x109) years ! Some subatomic particles have lifetimes that are less than 1x10-12 sec ! Given a batch of unstable particles, we cannotsay which one will decay. The process of decay is statistical. That is, we can only talk about either,

1) the lifetime of a radioactive substance*, or2) the “probability” that a given particle will decay.

Uses of radiation

• Radioactive tracers are used to locate tumors, to study the functioning of a particular organ, or to monitor the flow of blood. Such as iodine-131 is used for thyroid problems.

• used to treat cancer may involve the use of implanted radioactive isotopes such as gold-198 or iridium-192.

• Radioactive particles often used to measure the thickness of metal goods.

• Radio isotopes often used for smoke alarms.• Nuclear fission is used to generate Electricity.• The age of fossil or rock or anything can be determined by

radio isotopes suck as carbon-14. though it can measure only 50,000years.

Geiger Muller Counter

• Is used to detect radiation

• original operating principle was discovered in 1908 in early radiation research.

• However, there are limitations in measuring high radiation rates.

Thank You

Education

Radioactivity