The Atomic Nucleus

Review…the nucleus

The nucleus is composed of particles called nucleons..__ & __

Neutrons and protons have the same mass, with ___ being slightly greater.

Neutrons have nearly 2000 times the mass of

_____.

protons and neutrons

neutrons

electrons

Review…the atomThe mass of an atom is

almost equal to the mass of the _____ alone

Nucleons are bound together by an attractive nuclear force called the ____ force

The positively charged protons in the nucleus hold the negatively charged electrons in their ____

nucleus

strong

orbits

Review…the atom

The number of ___ in the nucleus determines the chemical properties of the atom

The # of protons determines the # of ____ that orbit the atom

The # of ___ has no direct effect on the # of electrons

protons

Review…the atomThe principal role of the

neutrons in the nucleus is to act as a sort of ____ to hold the nucleus together

The electrical force acts as a ____ force between protons

The atom needs a certain balance of neutrons and protons for ___

cement

repulsive

stability

The symbol was created in 1946 UC- Berkeley to represent “activity

coming out of a atom”

What is Radioactivity?

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.

There are numerous types of radioactive decay. The general idea:

An unstable nucleus releases energy to become more stable

Radioactive Decay

Radioactive Decay

A neutron is very unstable. A lone neutron will spontaneously decay into a proton + an electron.

If you have a lot of neutrons, within 11 minutes ½ of them will have decayed

Particles that decay are said to be radioactive

A lone neutron is radioactive

All the elements heavier than Bismuth (At # All the elements heavier than Bismuth (At # 83)83)

Their atoms emit 3 things…alpha, beta Their atoms emit 3 things…alpha, beta particlesparticles and gamma and gamma raysrays

Which is more penetrating?Which is more penetrating?

Radioactive Isotope

Iodine-131, a beta emitter, is taken as sodium iodide in drinking water. Almost all of it will find its way to the thyroid

IsotopesIsotopes

They are atoms of the same element that have different numbers of neutrons.

Radioactive Half-life

Radioactive Half-Life

The half-life of an element is the time it takes for half of the material you started with to decay Remember, it doesn’t matter how much you start with. After 1 half-life, half of it will have decayed.

Each element decays into a new elementC14 decays into N14 while U238 decays into

Pb206 (lead), etcThe half-life of each element is constant. It’s

like a clock keeping perfect time

Half-life

Half-life

Half-life

Half-lifeHalf-life

“How much of this element remains after 4 half-lives?

Just remember that at the endof one half-life, 50% of theelement will remain. Find 50%on the vertical axis, Follow theblue line over to the red curveand drop straight down to findthe answer:

Carbon DatingCarbon Dating

The radioactivity of once living things decreases at a predictable rate

Uranium DatingUranium Dating

The dating of older, non-living things (like rocks) is accomplished by radioactive minerals, such as Uranium. Uranium decays very slowly.

Rocks on Earth have been dated to 3.7 bil yrs oldRocks on Moon dated to 4.2 bil yrs old

The Earth has been dated to 4.6 bil yrs old

Review…whew!

https://archive.org/details/NASARealWorldMath_WhatIsRadioactiveDecay_HD

http://en.wikipedia.org/wiki/Barium_swallow

Radiation Penetrating PowerRadiation Penetrating Power

Three Common Types of Radioactive Emissions - Penetrability

Alpha particles may be completely stopped by a sheet of paper, beta particles by aluminum shielding. Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead.

Radiation Penetrating PowerRadiation Penetrating Power

http://www.passmyexams.co.uk/GCSE/physics/penetrating-properties-of-radiation.html

Radiation and You (and me)!

http://people.chem.duke.edu/~jds/cruise_chem/nuclear/exposure.html

Is there radon in your home?

Sources of Radioactivity

Primordial - from before the creation of the Earth

Cosmogenic - formed as a result of cosmic ray interactions

Human produced - enhanced or formed due to human actions (minor amounts compared to natural)

Radiation Exposure to Americans

Review

Name three of the science pioneers in the study of Radioactivity.?

Why does a nucleus decay?Order these emissions from least to greatest

penetrability: Gamma, Alpha, Beta.What is the greatest source of exposure to

radioactivity in our everyday lives?

Nuclear Fusion - Energy released when two light nuclei combine or fuse

•However, a large amount of energy is required to start a fusion reaction:

o Need this energy to overcome ________ forces of protons.o Extremely high temperatures can provide start-up energy.

repulsion

More energy in fusing hydrogen that fission of uranium