PHYSICS ASSIGNME

NTRADIOACTIVITY

NAME : NOOR ANIS NABILA BT. HAMZAHCLASS : 5 FARABI

TEACHER’S NAME : EN.MOHD RADZI

NUCLEUS OF AN ATOM

The composition of the nucleus of an atomMatter is made up of very small particles called atom. Each atom has a very small and very dense core called nucleus.Most of the mass of atom is contained in the nucleus. The electrons move in orbits around the nucleus. A nucleus consists of number of proton and neutrons. Proton and neutrons also known as nucleons. A proton has a unit of positive charges. A neutron is an uncharged particles of about the same mass of the proton. An atom is neutral because it contains an equal number of negatively charged electrons. So the net charged is zero.

The proton number (Z)The proton number is defined as the number of protons in the nucleus. The number of electrons is equal to the number of protons. An element is identified by its proton number.

Nucleon number(A)Nucleon number is defined as the total number of protons and neutrons in a nucleus.

Number of neutrons(N) = A-Z

Nuclide and its notation

A nuclide is a type of atom whose nuclei have specific numbers of protons and neutrons (both are called nucleons). Therefore, nuclides are composite particles of nucleons.

According to the standard model, up and down quarks are the basic components of nucleons. Thus, nuclides can also be considered composite particles of quarks

The term isotopes is often used to mean nuclides, because a nuclide is usually an isotope of an element. Strictly speaking, isotopes are atoms with the same number of protons but different number of neutrons in their nuclei.

Notation for a nuclide

The notation for a nuclide with mass number A and atomic number Z is representd by a symbol of its element E.

Notation of a nuclide AEZ

For example

235U92

Stable and Unstable Nuclides There are stable and radioactive nuclides. Stable nuclides exist for an indefinite period of time, and they are the constituents of ordinary material. Unstable nuclides emit subatomic particles, with 4a, b, g, n, p being the most common. Few undergo nuclear fission. However, unstable nuclides with long half-lives are also present in nature.

Stable nuclides are not radioactive. They remain unchanged for an indefinite period.

Unstable nuclides are radioactive, and they emit alpha, beta, gamma, or proton and they eventually convert to stable nuclides.

The study of nuclides is an experimental and observatory science. It involves data gathering, classification, organization, observation, and theorization about nature.

Isotope

Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes. For example, the most common isotope of hydrogen has no neutrons at all; there's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons.

Hydrogen Deuterium Tritium

As a result of their having different numbers of neutrons, an element's isotopes differ in mass. Atomic mass has very little bearing on chemical reactions; therefore the chemical reactions of an element's different isotopes are almost identical.

The physical properties of atoms, however, do depend on mass. This enables isotopes to be separated from one another by methods such as diffusion and fractional distillation.

Isotopes of an element contain the same number of proton and the same number of electron. So isotopes have the same chemical properties. However they have different physical properties because their mass is different. Some isotopes exist naturally and some of them can also be made artificially.

RADIOACTIVE DACAY

Radioactivity

An unstable nucleus spontaneously emits particles and energy in a process known as radioactive decay. The term radioactivity refers to the particles emitted. When enough particles and energy have been emitted to create a new, stable nucleus radioactivity ceases.

Radioactive emissions

Alpha Radiation

Alpha rays have the least penetrating power, move at a slower velocity than the other types, and are deflected slightly by a magnetic field in a direction that indicates a positive charge.

Beta Radiation

Beta rays are more penetrating than alpha rays, move at a very high speed, and are deflected considerably by a magnetic field in a direction that indicates a negative charge

Gamma Radiation

Gamma rays have very great penetrating power and are not affected at all by a magnetic field. They move at the speed of light and have a very short wavelength (or high frequency); thus they are a type of electromagnetic radiation

Radioactive decay

Alpha Decay

The reason alpha decay occurs is because the nucleus has too many protons which cause excessive repulsion. In an attempt to reduce the repulsion, a Helium nucleus is emitted. The way it works is that the Helium nuclei are in constant collision with the walls of the nucleus and because of its energy and mass, there exists a nonzero probability of transmission. That is, an alpha particle (Helium nucleus) will tunnel out of the nucleus. Here is an example of alpha emission with americium-241:

Alpha Decay of Americium-241 to Neptunium-237. Adapted from Alpha Decay.

Beta Decay

Beta decay occurs when the neutron to proton ratio is too great in the nucleus and causes instability. In basic beta decay, a neutron is turned into a proton and an electron. The electron is then emitted. Here's a diagram of beta decay with hydrogen-3:

Alpha Decay of Hydrogen-3 to Helium-3. Adapted from Stability of Nuclei.

Gamma Decay

Gamma decay occurs because the nucleus is at too high an 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 with helium-3:

Gamma Decay of Helium-3

Example of use equations to represent changes in the compositions of the nucleus when particles are emitted

Half lifeHalf-life is the period of time it takes for a substance undergoing decay to decrease by half. The name originally was used to describe a characteristic of unstable atoms (radioactive decay), but may apply to any quantity which follows a set-rate decay. The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.

The only thing which can alter the half-life is direct nuclear interaction with a particle from outside, e.g., a high energy collision in an accelerator.

Determine half life from a decay curve

Once an atom has decayed, it is no longer that type of atom.  (The carbon atom that decays is no longer a carbon atom.)   If we start with a certain number of atoms - say 100 million of them, then after a certain period we will notice that the number of atoms remaining is decreasing. The number remaining depends on how stable the atom is (or isn't)!  We end up with a graph which curves down towards zero.

Decay graph

This remarkable graph halves in equal time intervals called HALF-LIVES (T1/2).

Example of solve problems involving half lives

PROBLEM; Strontium - 90 has a half-life of 28.1 years. A sample has an initial activity of 400 MBq . What will be the activity after 92 years?

Solution;

   

From the graph, about 38 MBq. OR (not on syllabus )

Using the formula, let No = 400MBq , T1/2 = 28.1 years , t = 92 years.

Using    N =     N0                             t/T

1/2                          2

]=     400       292/28.1

=     400        23.274  

=   400      =   41.3 MBq       9.67

The formula is more precise than the graph and gives the activity at 41.3 MBq.

Greater precision could be gained using the graph if, say, the graph was recalibrated for after two half lives, starting at 100 MBq, then looking up a time of (93 - 56.2 ) years. One could do this because the SHAPE of the graph does NOT change despite starting point or calibration in half-life.  

RADIOISOTOPES

Many of the chemical elements have a number of isotopes. The isotopes of an element have the same number of protons in their atoms (atomic number) but different masses due to different numbers of neutrons. In an atom in the neutral state, the number of external electrons also equals the atomic number. These electrons determine the chemistry of the atom. The atomic mass is the sum of the protons and neutrons. There are 82 stable elements and about 275 stable isotopes of these elements.When a combination of neutrons and protons, which does not already exist in nature, is produced artificially, the atom will be unstable and is called a radioactive isotope or radioisotope. There are also a number of unstable natural isotopes arising from the decay of primordial uranium and thorium.Overall there are some 3800 radioisotopes. At present there are up to 200 radioisotopes used on a regular basis, and most must be produced artificially

Example of radioisotopesIodine--123

Carbon--11Phosphorous--32Iodine--131Thallium--201Gallium--67Chromium—51

The nucleus of a radioactive isotope spontaneously decomposes, emitting a particle (such as a proton, neutron, alpha particle, etc...) and electromagnetic radiation (such as gamma rays). Because of the loss of nuclear particles, the element in question can turn into a new element.

Consider the example of carbon-14, which is radioactive and undergoes radioactive decay and changes from carbon-14 to nitrogen-14, while emitting an electron and an anti-neutrino.

Applications of radioisotopes

Stable isotopes are tools used by researchers worldwide in the diagnosis of disease, to understand metabolic pathways in humans, and to answer fundamental questions in nature. They help researchers find answers by allowing them to look at a problem in a new way, from a different perspective. They help to better understand a process, trace a compound from a particular source, measure the concentration of a chemical in a sample, or measure the rate of a related process. Stable isotopes already play an important role in research today and will become even more important to research in the future.