RT203 - RADIOACTIVITY (BASICS)

No solving, just the basics

Radioactivity

• Process of losing energy to reach a stable state.

• This excited state can last for a few moments to billion of years and is measured in terms of half-lives.

• This lose of energy can be in form of pure energy, particles, or both.

• The nuclei of some nuclides are not stable

• They disintegrate or undergo nuclear transformation spontaneously and in random process

Radioactivity

is the emission of particles and energy in order to become stable.

Radioactivity Decay

results in emission of Alpha particles, beta particles and gamma rays.

Half-Life

the time required for a quantity of radioactivity to be reduced to one-half its original value.

1 Bq

• 1 per second

• the number of decaying nuclei per second

1 Cu

3.7 x 10^10 Bq

(1852-1908)

Henri Becquerel

Henri Becquerel

• Discover the radioactivity in 1896

1896

Henri Becquerel Disocovered Radioactivity in?

Henri Becquerel

• He noted that a piece of mineral containing uranium when placed over an exposed photographic plate just as if it has been exposed to light.

• The blackening of the photographic plate was due not to light but to a radiation being emitted by the uranium mineral.

photographic plate, radiation being emitted by the uranium mineral.

The blackening of the __________________ was due not to light but to a _____________________________.

(1867-1924)

Marie Curie

Pierre & Marie Curie

Discovered that polonium and radium also emit radiation.

Polonium & Radium

Pierre & Marie Curie discovered?

Artificial Radioactivity

• Radioactivity produced by man

• Irene Curie-Joliot produced the first radioactive product when they bombarded aluminum with alpha particles from polonium source to study the emitted neutrons and positrons.

Irene Curie-Joliot

Produced the first radioactive product when they bombarded aluminum with alpha particles from polonium source to study the emitted neutrons and positrons.

• Alpha Particles

• Beta Particles

• Gamma Rays

Radioactive elements emitted into 3 types of radiation

Alpha Particles

Fast moving helium nuclei; positive electrical charge

Beta Particles

Negative electrical charged electrons.

Gamma Rays

o Electromagnetic waves of very short wavelength and travelling within the speed of light.

o No charge at all.

Half-Life

the time in which a radioactive substance will lose half of its activity through disintegration.

Half-Life

The amount of time that is required to reduce the radioactivity to 1⁄2 of its present value.

• Physical Half-Life

• Biological Half-Life

• Effective Half-Life

3 Types of Half-Life:

3.83 Days

Half Life of:

Radon Gas

2.7 days

Half Life of:

Gold-198

Physical Half-Life

the average time required for the decay of half the atoms in a given amount of a radioactive substance.

Biologic Half-Life

the time in which a living tissue, organ, or individual eliminates, through biologic processes, half of a given amount of a substance that has been introduced into it.

Effective Half-Life

the half-life of a radioactive isotope in a biologic organism, resulting from the combination of radioactive decay and biologic elimination.

• Alpha Decay

• Beta Negative Decay

• Beta Positive Decay

• Gamma Ray Emission

• Electron Capture

Types of Decay:

Alpha Decay

Americium 241 – smoke detectors

Alpha Decay

If substances emitting alpha particles are ingested, inhaled, injected or introduced through the skin, then it could result in a measurable dose.

Alpha Decay

accompanied by gamma photon emission.

• Alexander Litvinenko's 2006 murder

• Polonium-210

Russian dissident ___________________________ by radiation poisoning is thought to have been carried out with _______________, an alpha emitter.

Alpha Decay

Russian dissident Alexander Litvinenko's 2006 murder by radiation poisoning is thought to have been carried out

with polonium-210, an alpha emitter.

• Beta Minus

• Beta Plus

2 types of Beta Decay:

Beta Minus

Interacts with neutron

Beta plus

Interacts with protons

Electron Capture

is a process in which a proton-rich nuclide absorbs an inner atomic electron (changing a nuclear proton to a neutron) and simultaneously emits a neutrino.

Radioactive Decay Law

• Julius Elster and Hans Geitel observed that the strength of a pure radioactive substance decrease exponentially.

• Radioactivity was found to be a property of the individual atoms, not of a substance as a whole.

• Statistical nature of disintegration was established.

• Random process

• Universal law that describes the statistical behavior of a large number of nuclides

Julius Elster & Hans Geitel

observed that the strength of a pure radioactive substance decrease exponentially.

• Curie (Ci)

• Becquerel (Bq)

• 1 Bq = 1 disintegration per second

• 1 Ci = 3.7x10^10 Bq

Unit of Radioactivity

A = present activity

Exponential Decay Law:

What is the meaning of (A) in the formula?
(A is same with N)

A0 = original activity

(Can also be Initial Activity)

Exponential Decay Law:

What is the meaning of (A0) in the formula?
(A0 is same with N0)

λ = disintegration constant / decay constant

(it’s not or, but over decay constant)

Exponential Decay Law:

What is the meaning of (λ) in the formula?

t = elapsed time

Exponential Decay Law:

What is the meaning of (t) in the formula?

t ½ = Half-Life

Exponential Decay Law:

What is the meaning of (t ½ ) in the formula?