Radioactivity

Question 1

What are Isotopes?

Answer 1

• same atoms with different mass number
• different mass because of the different amount of neutrons in the atom’s nucleus
• chemically they are identical as the electron shells are unaffected by the number of neutrons

Question 2

Explain the unstable nuclei

Answer 2

• The ratio of protons to neutrons affects the stability of a nucleus
• Nuclei with too many, or too few neutrons are unstable
• The nuclei of unstable elements spontaneously disintegrate this is called radioactivity
• The unstable nucleus that disintegrates is radioactive

Question 3

What is radioactivity?

Answer 3

• The process by which unstable atomic nuclei lose energy by emitting radiation
• Occurs because some atoms have too many protons or neutrons, making them unstable
• In order for them to reach a more stable state, they have to release energy in the form of particles or electromagnetic waves

Question 4

Which elements have a stable / unstable nuclei

Answer 4

Elements with atomic number <83 have one or more stable isotopes
The isotopes of all elements above atomic number 83 have unstable nuclei - they are radioactive

Question 5

What is a nuclear reaction?

Answer 5

• A reaction that changes the nucleus of an atom is called a nuclear reaction
• It is different to a chemical reaction, as new elements are formed (rearrangement in nucleus), not just new combinations of existing elements

Question 6

How does the disintegration of the nucleus emit?

Answer 6

• alpha particles
• beta particles (electrons, positrons)
• Gamma rays

Question 7

What is nuclear transmutation?

Answer 7

• Nuclear transmutation is the conversion of one nuclide into another, which can occur by the radioactive decay of a nucleus or the reaction of a nucleus with another particle
• The new nucleus (daughter) that remains may be radioactive or stable

Question 8

What are alpha particles?

Answer 8

• symbol a
• has 2 protons, 2 neutrons
• fast moving (5% speed of light)
• high energy
• relatively heavy
• loses energy quickly
• positive charge
• stopped by a piece of paper
• can travel 2.5 cm in the air

Question 9

What is alpha decay?

Answer 9

• When an unstable nucleus emits an alpha particle it undergoes alpha decay
• The nucleus emits an alpha particle, reducing its atomic number by 2 and its mass number by 4
• The resulting new nucleus is an isotope of a different element

Question 10

What are Beta particles?

Answer 10

• Fast moving electrons or positrons (counterpart of electrons)
• Symbol β
• very fast
• very light
• stopped by 0.1 mm of lead
• can travel about 4.5 cm in air
• penetrate skin 17 mm
• can be positively or negatively charged

Question 11

What is beta decay?

Answer 11

• If negative, (emission of electron)
• A neutron is transformed into a proton by emitting an electron
• Increases the atomic number by 1
• Transforms the element into a different one
• If positive, (emission of positron)
• A proton in the nucleus is converted into a neutron by emitting a positron
• Atomic number decreases by one
• Transforms the element into a different one

Question 12

What are Gamma rays?

Answer 12

• symbol y
• most penetrating form - electromagnetic radiation
• highest frequency and shortest wavelength in the electromagnetic spectrum - ionising
• Produced when the nucleus of an atom is in an excited state and then releases energy, becoming more stable
• When a nucleus emits an alpha or beta particle, the daughter nucleus is often left in an excited state, and it can then jump down to a lower energy state by emitting a gamma ray
• Require dense materials like lead or several centimetres of concrete to block them

Question 13

What is gamma decay?

Answer 13

• The nucleus releases energy in the form of gamma rays without changing the number of protons or neutrons
• Often occurs after other types of decay as the nucleus moves to a lower energy state