TYPES OF DECAY: 1. Alpha decay (α decay) ⢠Need short range ...
TYPES OF DECAY:
1. Alpha decay (α decay)
Helium nucleus ( 42𝐻𝑒)
Need short range nuclear forces to become stronger so it loses mass
2. Beta decay (β decay)
Emits a beta particle (electron) A neutron is changed into a proton
3. Positron decay (β+ decay)
Emits a positron (positively charged electron) A proton is converted to a neutron Positron collides with an electron to form gamma radiation o Positron is called antimatter because it annihilates an electron
4. Electron Capture
Electron combines with a proton to form a neutron Common among synthetic radionuclides Emits some x-rays as electrons fall down the shells to fill the gaps after their electrons have been captured
5. Neutron Emission
Simply emits a neutron Changes the mass
6. Gamma emission
No change in atomic number or mass High frequency radiation that often accompanies other forms of decay (usually alpha and beta emission)
Factors determining stability:
The size of the nucleus o Strong nuclear forces only work over small distances o Larger nucleus’ have more protons and greater electrostatic repulsion Neutron : Proton ratio
Example of a radioactive decay sequence
Above 82 protons, the electrostatic repulsions are too great
Neutron : Proton ratio
N:P ratio too high o Found on the left side of the zone of stability o Needs to: Gain protons (beta decay) Lose neutrons (neutron emission)
N:P ratio too low o Found on the right side of the zone of stability o Needs to: Gain neutrons (positron decay) Lose protons (electron capture)
Should be around 1:1 for stability
Radiation Why is radiation damaging?
Very high energy Causes the ionisation of matter (ejects an electron from an atom) Can pass through matter without ionising it Ionisation of a molecule requires just 10eV o Alpha radiation has 5MeV… In humans: o Radiation reacts with the body’s water o Leads to the formation of dangerous free radical
o Free radicals can cause genetic damage, cell break down, and loss of enzyme functions
Factors affecting the magnitude of damage:
Type of radiation o Alpha radiation – Only penetrates 40mm so won’t get past skin o Beta radiation – Penetration of 6-300mm (skin burns) o Gamma radiation – Penetrates 400m so will go straight through your body o X-ray (comparison) – Penetrates 200m
Length of exposure o Short term exposure Radiation poising High doses in short periods can cause acute cell damage and death o Long term exposure Radiation induced cancer Interrupts DNA and leads to cancer
Source of exposure o Internal exposure Ingestion or inhalation Alpha and Beta radiation is most dangerous like this as it cannot escape the body once inside o External exposure Alpha and Beta radiation cannot penetrate through air and skin Gamma radiation can penetrate skin and therefore is more dangerous
Exposure to radiation:
The Sievert (SR) measure the biological effect of radiation o Takes into account the type, energy and activity of the radiation We are exposed to radiation through o Radon We breath it into our lungs and it is completely unavoidable 40 o K Present naturally which we consume and come into contact with through bananas, beans and sunflower seeds
o Cosmic rays Neutrons coming down from the upper atmosphere o Man-made devices (x-rays, PET scans, mammogram)
1. Alpha decay (α decay)
Helium nucleus ( 42𝐻𝑒)
Need short range nuclear forces to become stronger so it loses mass
2. Beta decay (β decay)
Emits a beta particle (electron) A neutron is changed into a proton
3. Positron decay (β+ decay)
Emits a positron (positively charged electron) A proton is converted to a neutron Positron collides with an electron to form gamma radiation o Positron is called antimatter because it annihilates an electron
4. Electron Capture
Electron combines with a proton to form a neutron Common among synthetic radionuclides Emits some x-rays as electrons fall down the shells to fill the gaps after their electrons have been captured
5. Neutron Emission
Simply emits a neutron Changes the mass
6. Gamma emission
No change in atomic number or mass High frequency radiation that often accompanies other forms of decay (usually alpha and beta emission)
Factors determining stability:
The size of the nucleus o Strong nuclear forces only work over small distances o Larger nucleus’ have more protons and greater electrostatic repulsion Neutron : Proton ratio
Example of a radioactive decay sequence
Above 82 protons, the electrostatic repulsions are too great
Neutron : Proton ratio
N:P ratio too high o Found on the left side of the zone of stability o Needs to: Gain protons (beta decay) Lose neutrons (neutron emission)
N:P ratio too low o Found on the right side of the zone of stability o Needs to: Gain neutrons (positron decay) Lose protons (electron capture)
Should be around 1:1 for stability
Radiation Why is radiation damaging?
Very high energy Causes the ionisation of matter (ejects an electron from an atom) Can pass through matter without ionising it Ionisation of a molecule requires just 10eV o Alpha radiation has 5MeV… In humans: o Radiation reacts with the body’s water o Leads to the formation of dangerous free radical
o Free radicals can cause genetic damage, cell break down, and loss of enzyme functions
Factors affecting the magnitude of damage:
Type of radiation o Alpha radiation – Only penetrates 40mm so won’t get past skin o Beta radiation – Penetration of 6-300mm (skin burns) o Gamma radiation – Penetrates 400m so will go straight through your body o X-ray (comparison) – Penetrates 200m
Length of exposure o Short term exposure Radiation poising High doses in short periods can cause acute cell damage and death o Long term exposure Radiation induced cancer Interrupts DNA and leads to cancer
Source of exposure o Internal exposure Ingestion or inhalation Alpha and Beta radiation is most dangerous like this as it cannot escape the body once inside o External exposure Alpha and Beta radiation cannot penetrate through air and skin Gamma radiation can penetrate skin and therefore is more dangerous
Exposure to radiation:
The Sievert (SR) measure the biological effect of radiation o Takes into account the type, energy and activity of the radiation We are exposed to radiation through o Radon We breath it into our lungs and it is completely unavoidable 40 o K Present naturally which we consume and come into contact with through bananas, beans and sunflower seeds
o Cosmic rays Neutrons coming down from the upper atmosphere o Man-made devices (x-rays, PET scans, mammogram)
