Structure Of Atoms + Nucleur Radiation Flashcards
How big are atoms?
Very small - radius is about 1 x 10 to the power of -10 meters.
What is the basic structure of an atom
Positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.
How big is the radius of the nucleus
Less then 1/10,000 of an atom. Most of the mass is concentrated in the nucleus.
How are electrons arranged
At different distances from the nucleus - diff energy levels. It may change with the absorption of EM radiation - move further from the nucleus or by the emission of EM radiation - move closer.
Is an atom which two are equal?
Electrons and protons are equal
What do all atoms of a particular element have?
The same number of protons. These are also known as the atomic number.
Mass number
The total number of protons and neutrons
Isotopes
Atoms of the same element which have the same number of protons but a different number of neutrons.
Do the number of neutrons affect the charge or mass of an atom?
It doesn’t affect the charge, only the mass because neutrons have no charge but do have a mass.
How were protons discovered?
Experiment led to the idea that the positive charge if any nucleus could be subdivided into a whole number of particles, each particle having the same amount of positive charge.
What is radioactive decay?
Some atomic nuclei are unstable. These nucleus gives out radiation as it changes to become more stable. This is a random process.
Activity
The rate at which a source of unstable nuclei decays. Measured in becquerel.
What is the count rate?
The number of decays recorded each second by a detector - Geiger muller tube
Alpha particle
2 neutrons and 2 protons - same as the helium nucleus
Low penetration - stopped by sheet of paper - large size
Strongly ionizing - can knock out electrons from atoms - turning them into ions quite effectively
Beta particle
A high speed electron ejected from the nucleus as a neutron turns into a proton. Carry single - charge.
Moderately ionizing and have greater penetrating power then alpha
Can travel several meters in the air - aluminum 5mm thick.
Gamma ray
Electromagnetic radiation from the nucleus. No mass, no charge - can penetrate through materials much more effectively.
Lowest ionizing power but can travel longest distances.
To stop - thick sheets of dense concrete/materials.
The nuclear radiation emitted may be:
Gamma ray
Alpha particle
Beta particle
A neutron
What can alpha radiation be used for?
Smoke detectors - high ionizing ability - ionize particles creating a detectable electric current. Large size - interact with matter. Smoke interrupts flow of ions, current drop - detector senses.
Beta particles usage
Material thickness measurements. Have moderate penetration depth and ionizing power. Absorb by predictable rates of diff materials, allowing for precise thickness measurements.
Gamma ray use
Medical tracers - injected in body and flow through blood where radiation can be detected externally do follow progress. Penetrated tissues and exit buy without being absorbed as much. Low ionizing - reduces risk of damage to healthy tissues
Why would the count rate be less then the activity of gamma radiation ?
Because only dime of the radiation passes into GM tube is detected - gamma is weakly ionizing
Why would people stand far away from experiments using gamma radiation ?
To reduce amount of radiation received because radiation can lead to a mutation and increase risk of cancer.
