Radioactivity

What is the radius of the atom (approximately)?

The radius of an atom is approximately 1 x 10⁻¹⁰ m

What is the radius of the nucleus compared to the radius of an atom?

The radius of the nucleus is about 1/10000 smaller than the radius of an atom

Where is the majority of the mass in atom located?

The majority of mass of the atom is located in the nucleus

What is the mass and charge of a proton?

A protons has:
(Relative) mass: 1
Charge: 1

What is the mass and charge of a neutron?

A neutron has:
(Relative) mass: 1
Charge: 0

What is the mass and charge of an electron?

An electron has:
(Relative) mass: very small
Charge: -1

What subatomic particles are found in the nucleus?

The nucleus contains protons and neutrons

How are electrons arranged in an atom?

Electrons are arranged at different distances from the nucleus (different energy levels/shells)

What is the relationship between energy levels and the energy of electrons?

Electrons further away from the nucleus have a higher energy level (positive electron)

How can electrons in an atom move from one energy level to another?

★ To move from one energy level to another, electrons must gain/lose energy
✔︎ This is done by gaining or emitting electromagnetic radiation (e.g. light)

What do the numbers next to the elements mean?

Top number: relative mass
Bottom number: atomic number

What is the atomic number?

The atomic number is the amount of protons in an atom

How do we calculate the mass number of an atom?

The mass number is the sum of the number of protons and the number of of neutrons

Why do atoms have no overall charge?

★ Atoms contain an equal number of protons and electrons
➜ These charges cancel out
𐬽 An atom has no overall charge

What is an isotope?

★ Isotopes are atoms of the same element that:
★ Have the same number of protons
★ Have a different number of neutrons

What is an ion?

An ion is a charged atom as it has lost/gained electrons (it can't lose protons)

What were atoms first thought to be?

Atoms were thought to be tiny spheres that could not be divided.

What did the electron lead to?

The discovery of the electron lead to the plum pudding model

Who came up with the plum pudding model?

JJ Thomson

What is the plum pudding model?

The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.

Who came up with the nuclear model?

Ernest Rutherford came up with the nuclear model

What was the alpha scattering experiment?

★ The alpha scattering experiment saw (positively charged) alpha particles were fired at thin gold foil. ★The results from the experiment were recorded

What were the results of the alpha scattering experiment and what did they tell us?

★ The majority of α particles went straight through the gold foil
𐬽 An atom is mostly empty space
★ Some α particles were deflected (changed direction)
𐬽 The centre (nucleus) must be positively charged to repel the alpha particles
★ Some α particles bounced straight back
𐬽 The mass of the atom must be concentrated at the centre (nucleus)

What is the nuclear model?

The nuclear model states that:
★ Atoms are mostly empty space
★ Have a positive nucleus
★ Surrounded by negative electrons

What did scientist Niels Bohr suggest about the atom?

★ Niels Bohr suggested electrons orbit the nucleus at specific distances from the nucleus (energy levels)

When was the proton discovered?

The proton was discovered after Niels Bohr

Who discovered the neutron (relatively when)?

James Chadwick discovered the neutron around 20 years after the discovery of the atom

is radioactive decay a random process?

Yes, radioactive decay is a random process (you cannot predict when a nucleus will decay)

What is activity in physics?

The activity is the rate at which a source of unstable nuclei decay.

What is the unit of activity? What does it mean?

★ The unit of activity is the becquerel (Bq)
➜ This means 1 decay per second

How do we measure the activity of a radioactive source?

We can use a Geiger-Muller tube

What does a Geiger-Muller tube measure?

A Geiger-Muller tube measures the count-rate of a radioactive source
⚠︎︎ This is not the same as activity due to background radiation

What is an alpha (α) particle made of? What is it identical to?

★ An alpha (α) particle is made up of two neutrons and two protons
➜ This is the same as a helium (He) nucleus

What is a beta (β) particle?

A beta (β) particle is an electron which is ejected from the nucleus at a very high speed

How are beta (β) particles formed?

A beta (β) particle if formed inside a nucleus when a neutron changes into a proton and an electron

What are gamma (γ) rays?

Gamma rays are a type of electromagnetic radiation from the nucleus

What are the four (GCSE) types of radiation given by an unstable nucleus?

The four (GCSE) types of radiation given out by the nucleus are:
★ Alpha (α) particles
★ Beta (β) particles
★ Gamma (γ) rays
★ Neutrons (n) [not very often]

What type of radiation rarely happens?

Neutron (n) radiation isn't very common

How far can alpha (α) particles, beta (β) particles and gamma (γ) rays particles travel in air? What is their penetration?

Particles travelling in air before stopping + penetration:
★ Alpha (α) particles: 5cm (small)
★ Beta (β) particles: 15cm (quite)
★ Gamma (γ) rays: several meters (very)

What is required to stop alpha (α) particles, beta (β) particles and gamma (γ) rays?

To stop these sources of radiation:
★ Alpha (α) particles: A single sheet of paper
★ Beta (β) particles: A few mm of aluminium
★ Gamma (γ) rays/radiation: Several cm of lead

What is ionising power?

Ionising power is how easily electrons are knocked off atoms creating positive ions

What is the ionising power of alpha (α) particles, beta (β) particles and gamma (γ) rays?

Ionising power of radiation:
★ Alpha (α) particles: Very strongly ionising
★ Beta (β) particles: Quite strongly ionising
★ Gamma (γ) rays: Weakly ionising

What is the link between the size of particles and the ionising power?

★ The bigger the type of radiation, the less ionising power
✔︎ This is because there is less mass to interact with matter

What is penetration?

Penetration is how much material a source of radiation can get through

What happens to the mass and charge of an atom when it undergoes alpha (α) decay?

When an atom undergoes alpha (α) decay:
★ The mass number (of the atom) goes down by 4
★ The charge (of the atom) goes down by 4

What happens to the mass and charge of an atom when it undergoes beta (β) decay?

When an atom undergoes beta (β) decay:
★ The mass number (of the atom) stays the same
★ The charge (of the atom) goes by 1

What happens to the mass and charge of an atom when it undergoes gamma (γ) decay?

When an atom undergoes gamma decay, the mass and charge remain constan

How do we express alpha (α) and beta (β) particles in nuclear equations?

★ We can express alpha (α) particles as:
⁴₂ He or ⁴₂α
★ We can express beta (β) particles as:
⁰₋₁ e⁻ or ⁰₋₁β

What are the two definitions of half-life?

★ The half-life of a radioactive isotope is the time it takes for the
number of nuclei of the isotope in a sample to halve
OR
★ The time it takes for the count rate (or activity) from a sample containing the
isotope to fall to half its initial level.

What is nuclear fission [briefly]?

Nuclear fission is the splitting of a large and unstable nucleus (eg
uranium or plutonium).

Can nuclear fission happen spontaneously?

Spontaneous fission is rare. Usually, for fission to occur the
unstable nucleus must first absorb a neutron.

What happens in nuclear fission? [Steps]

1) A uranium nucleus receives a neutron and undergoes fission (splits)
2) ★ The nucleus splits into two smaller nuclei (of roughly equal size.) These are called daughter nuclei
★ It also emits 2 or 3 neutrons and gamma radiation
★ Energy is also released as part of the fission reaction. All of the fission products have kinetic energy
3) The neutrons can now be absorbed by more uranium nuclei and trigger fission again.
✔︎ This is called a chain reaction

How can controlled chain reaction be used?

A controlled chain reaction is used to release energy in a nuclear reactor

How is the explosion in a nuclear weapon caused?

The explosion in a nuclear weapon is case by an uncontrolled fission chain reaction

What is nuclear fusion?

★ In nuclear fusion, two light nuclei (e.g. hydrogen) are joined to form a heavier nucleus
★ Some of the mass of the nuclei can be converted into energy, which is released as radiation.

In what unit is radiation dose measured?

Radiation dose is measured in sieverts (Sv)

What is mSv?

mSv means millisievert (1/1000 of a Sv)

What are two forms of natural background radiation?

Two types of natural background radiation are:
★ Rocks
★ Cosmic rays (from space)

What are two forms of man-made background radiation?

Two types of man-made background radiation are:
★ Fallout from nuclear weapons testing
★ Fallout from nuclear accidents

How can your occupation and location affect the amount of background radiation you receive?

★ Location such as Cornwall receive more background radiation from rocks
★ Pilots receive more background radiation as they are high up in the atmosphere where they are more exposed to cosmic rays

Do radioactive isotopes have a small range of half-life values or a large range of half-life values

Radioactive isotopes have a very wide range of half-life values.

What is irradiation?

Irrigation is exposing an object to nuclear radiation (e.g. α,β,γ,n radiation)

What is a use of irradiation?

A use of irradiation is sterilisation; medical tools are irradiated to kill bacteria (when killing the bacteria via heating is not possible)

How is medical equipment, e.g. a syringe, sterilised using irradiation?

1) The medical equipment is placed inside a plastic wrapper
✔︎ This is to prevent bacteria from entering
2) Place the object near a radioactive isotope that emits γ (gamma) radiation
⚠︎︎ This is inside a lead shield to protect workers from the radiation
3) Withdraw the internal lead shield to allow γ (gamma) radiation to irradiate the object
✔︎ The γ (gamma) radiation kills any bacteria present

Do irradiated objects become radioactive?

No, the irradiated object does not become radioactive

Why do irradiated objects not become radioactive?

★ Irradiated objects do not become radioactive
✔︎ This is because the irradiated object comes in contact with the radiation
⚠︎︎ But not the radioactive isotope itself

What does ionising radiation increase the risk of?

Ionising radiation can increase the risk of cancer

How can we use shielding to mitigate the risk from irradiation? [In normal cases]

Ways to use shielding to mitigate the risk from irradiation:
★ We can wear gloves to prevent against the less ionising α (alpha) radiation
★ However, for β (beta) and γ (gamma) radiation, a lead apron may be required to reduce the radiation
★ For more extreme cases, these may be required:
★ Lead walls
★ Lead-glass screen

How can we use shielding to mitigate the risk from irradiation? [In MORE EXTREME cases]

For more extreme cases, these may be required to reduce the risk of irradiation:
★ Lead walls
★ Lead-glass screen

How can monitoring reduce risk from radiation?

★ Using a radiation monitor, we can measure how much radiation someone receives
★ If someone has received too much radiation…
➜ We can stop them from using radioactive isotopes

What is radioactive contamination?

Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials

How is radioactive contamination hazardous?

★ Radioactive contamination is hazardous as the radioactive atoms decay and emit ionising radiation
⚠︎︎ With radioactive contamination, you have source on you or in you
⚠︎︎ You could get a large dose of radiation

How dangerous is α radiation when it comes to radioactive contamination?

α radiation and radioactive contamination:
⚠︎︎ α radiation is strongly ionising
✔︎ Easily stopped by dead cells on the skin surface
⚠︎︎ α emitters can be dangerous if:
★ Inhaled
★ Swallowed

When can α emitters be especially dangerous?

α emitters are especially dangerous when:
★ Inhaled
★ Swallowed

How dangerous is β radiation when it comes to radioactive contamination?

β radiation and radioactive contamination:
★ Quite ionising
★ Can penetrate skin into the body

How dangerous is γ radiation when it comes to radioactive contamination?

γ radiation and radioactive contamination:
★ Weakly ionising
⚠︎︎ Can penetrate your body
✔︎ Likely to pass straight through

What is peer review?

Peer review is when:
★ Studies are published
★ And then shared with other scientists
✔︎ This is very important when it comes to radiation

How can nuclear radiation be used for someone who has problems with their thyroid glad?

If a patient has a problem with their thyroid gland:
★ They should drink a solution of radioactive iodine ¹²³I
✔︎ Radioactive iodine ¹²³I emits γ radiation which passes out of the bound and can be detected
★ If the scan shows that the thyroid has absorbed too much or too little iodine, the doctor can use this information to diagnose the patient's decision

What can bone scans detect?

Bone scans (which use γ radiation) could be used for:
★ Used to visualise damage caused by arthritis
★ To detect tumours

What issues are there with exploring internal organs using a tracer?

Issues with exploring internal organs using a tracer:
★ The tracer must emit radiation that can pass out of the body and be detected
𐬽✔︎ β or γ radiation is used
𐬽⚠︎︎ α radiation is not used
★ The tracer must nor be strongly ionising
✔︎ This is to minimise damage to body tissue
✔︎ This again means γ radiation is ideal
★ The tacer must not decay into another radioactive isotope
★ The tracer must have a short half-life
⚠︎︎ If it didn't
➜ It would continue to decay in the body for a long time
➜ Cause significant damage to body tissues

What is radiotherapy?

Radiotherapy is when certain cancers can be destroyed using ionising radiation

How does radiotherapy work?

In radiotherapy, γ rays pass into the body ad destroy the tumour

What is a disadvantage of radiotherapy?

A disadvantages of radiotherapy is that healthy tissue may also be damaged as the radiation passes through the body

What is an example of the radiation source being placed inside the body in radiotherapy?

A patient can have radioactive rods inserted inside his body to treat prostrate cancer

What is the benefit of the radiation source being inside your body in radiotherapy?

★ The benefit of the radiation source being inside your body is:
★ The radiation is targeted very precisely to the tumour
➜ There is less damage to healthy tissue