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RADIOACTIVITY METHODINTRODUCTION



• In the last twenty-years a property of certain elements has become of great

economic importance.

• This property is known as

“RADIOACTIVITY”



DISCOVERY OF

RADIOACTIVITY



DISCOVERY BY BEQUEREL

• Original discovery of radioactivity was made by Henry Becquerel in1896,shortly after Roentgendiscovered X-rays in 1895

• Becquerel found that Uranium andits salts emit “Radiations" which:

• Pass through materialsopaque to ordinary light.

• Affect photographic films ina manner similar to X-rays.



DISCOVERY BY MADAM CURIE

• Madam Curie whileinvestigating minerals of uranium ,extracted two new elements:

»POLONIUM»RADIUM

These elements weremuch more activethan uranium thus was important.



• Twenty naturally occurring have been found to beradioactive…

BUT….

• Uranium (U), Thorium (Th) and an isotope of Potassium (K) are of importance in exploration.

• Rubidium is also very useful in determining agesof rocks.

• The rest are either so rare or so weakly radioactivity to be of no significance in Appliedgeophysics.

IMPORTANT RADIOACTIVEELEMENTS



PRINCIPLE OFRADIOACTIVITY



“ An unstable atomic nucleus breaks apart,and converts into another atom with

emission of certain radiations”

Lets discuss this concept in detail………



ATOM:

• The atom is a basic unit of matter thatconsists of a dense, central nucleussurrounded by a cloud of negatively

charged electrons.



ELECTRON

• The electron is a subatomicparticle carrying a negative electric charge.

• It has no known components or

substructure. Therefore, the electron isgenerally believed to be an elementary particle .



• The antiparticle of the electron is calledthe positron.

• The positron is identical to the electronexcept that it carries opposite charge.

• When an electron collides with a positron,

it produces a pair (or more) of gammaray photons.



CONSTITUENTS OF THENUCLEUS



WHAT IS A NUCLEUS?

• The nucleus is the very dense region consistingof nucleons i.e. protonsand neutrons at the center of

an atom.• Almost all of the mass in an

atom is made up from theprotons and neutrons in thenucleus, with a very smallcontribution fromthe orbiting electrons.



PROTONS:

• The proton is a subatomic particle with apositive electric charge of 1 elementary charge.

• One or more protons are present in

the nucleus of each atom , along with neutrons.



• The proton is also stable by itself.

• Free protons are emitted directly in somerare types of radioactive decay, and resultfrom the decay of free neutrons from otherradioactivity.

• They soon pick up an electron and become neutral hydrogen, which may thenreact chemically.



NEUTRONS

• The neutron is a subatomic particle withno net electric charge and a mass slightly larger than that of a proton.



• While bound neutrons in stable nuclei arestable.

• Free neutrons are unstable they undergo beta decay with a mean lifetime of justunder 15 minutes (885.7±0.8 s).

• Free neutrons are produced in nuclearfission and fusion.



ISOTOPES

• Isotopes are atoms of aparticular element must contain the samenumber of protons but may have a distinct

number of neutrons which differs from atom toatom, without changing the designation of theatom as a particular element.



STABLE ISOTOPES

• “Stable isotopes arechemical isotopes that may or may not be radioactive, but if radioactive, have half

lives too long to be measured.”

• Of the 80 elements with one or morestable isotopes, twenty-six have only a

single stable isotope, and are thustermed monoisotopic



UNSTABLE ISOTOPES

• Unstable isotopes are atoms thatdisintegrate at predictable and measurablerates to form other isotopes by emitting a

nuclear electron or a helium nucleus andradiation. These isotopes continue todecay until they reach stability.



The stable isotopes are shown ingreen, while unstable isotopesare shown in yellow.

The red line shows where thenumberof protons is equal to thenumber of neutrons.



• Examples of unstable isotopes: abound andinclude such infamous elements as

Uranium-238, Plutonium-239, Carbon-14,and Phosphorus-32.

• Over time these elements emit alpha, beta, or gamma particles to become wholly different elements and/or elements with alower energy state.



RADIOACTIVE DECAY

• There are three main types of radioactivedecay:

– Alpha decay

– Beta decay

– Gamma decay



ALPHA DECAY

• The reason alpha decay occurs is because the nucleus hastoo many protons which cause excessive repulsion.

• In an attempt to reduce the repulsion, a Helium nucleusis emitted.

• The way it works is that the Helium nuclei are inconstant collision with the walls of the nucleus and because of its energy and mass .

• There exists a nonzero probability of transmission. Thatis, an alpha particle (Helium nucleus) will tunnel out of the nucleus. :



• Here is an example of alpha emission withamericium-241

Alpha Decay of Americium-241 toNeptunium-237



BETA DECAY

• Beta decay occurs when the neutron toproton ratio is too great in the nucleus andcauses instability.

• In basic beta decay, a neutron is turnedinto a proton and an electron.

• The electron is then emitted.



• Here's a diagram of beta decay withhydrogen-3:

Beta Decay of Carbon-11 to Boron-11



GAMMA DECAY

• Gamma decay occurs because the

nucleus is at too high energy.• The nucleus falls down to a lower energy

state and, in the process, emits a high

energy photon known as a gamma particle.



• Here's a diagram of gamma decay withhelium-3:

Gamma Decay of Helium-3



RADIOACTIVE PROPERTIES

OF ROCKS



PENETRATING PROPERTIES AND

DETECTION OF RADIOACTIVEELEMENTS

• The radioactive emissions have different



• The radioactive emissions have differentpenetrating properties:

• Alpha particles

– are effectively stopped by sheet of paper

– can travel no more than few centimeters.

• Beta particles

– are stopped by a few millimeter of aluminum.

– can travel only few decimeters.

• Gamma rays

– are stopped only by few centimeters of lead.

– Can travel several hundreds of meters.



DETECTION

• Alpha particles cannot be detected by radiometric surveying.

• Beta particles are detected only in groundsurveying.

• Gamma rays are detected in airbornesurveying…



UNIT

• The unit used for activity of radioactivespecimen is curie named after discovererof radium Madam Curie.

• Standard unit of gamma radiations isroentgen.

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