Physics - Atoms & Radioactivity

State what happens when electrons move to a higher orbit. (1)

The atom has absorbed electromagnetic radiation.

State what happens when electrons move to a lower orbit. (1)

The atom has emitted electromagnetic radiation.

What could happen if an electron gains enough energy? (2)

● Can leave the atom

● To form a positive ion

How does activity affect the rate of decay? (2)

● A sample with high activity

● Has a fast rate of decay

Name the 4 forms of decay. (4)

● Alpha (a helium nucleus)

● Beta Minus (electron)

● Gamma (electromagnetic radiation)

● Neutrons

What does alpha decay cause? (4)

● Mass of nucleus decreases

● Charge of nucleus decreases

What does beta decay cause? (4)

● Mass of nucleus stays unchanged

● Charge of the nucleus increases

What does gamma decay cause? (2)

● Does not cause the mass or charge to change

Explain what a short half-life means. (3)

● Less of a long-term risk

● Does not remain strongly radioactive

● As it quickly dies down

Explain what a long half-life means. (3)

● Source is weakly radioactive for a long period of time

● Will not need to be replenished

● Weak activity will mean it won’t be harmful to anyone

What element is used in smoke alarms and what is its half-life? (2)

● Americium

● 432 years

Why is americium used in smoke alarms? (3)

● It is an alpha emitter

● It doesn’t reach far

● As it is weakly penetrating

How to smoke alarms respond to the presence of smoke? (2)

● The amount of alpha particles in the surrounding air drops

● This causes the alarm to sound

Compare contamination and irradiation. (6)

● Contamination lasts for a long period of time

● The source of radiation is transferred to an object

● E.g. radioactive dust settling on your skin

● Irradiation lasts for a short period of time

● The source emits radiation, but doesn’t make it radioactive

● E.g medical items are irradiated sometimes to kill bacteria on its surface

Why do scientific reports published need to be peer reviewed? (3)

● If initial studies got measurements wrong

● Safety levels based on the study

● May cause people to die

Name 4 types of background radiation. (4)

● Cosmic rays

● Radiation from underground rocks

● Nuclear fallout

● Medical rays

Name 2 uses of radiation. (2)

● Tracers

● Chemotherapy

Explain the uses of technetium in medicine. (6)

● Medical tracer

● Half-life of 6 hours

● Decays into a safe isotope that can be excreted by the body

● It is injected/swallowed

● Gamma emitter

● Can pass through the body tissue without being absorbed

Explain how chemotherapy works. (5)

● Gamma emitters emit gamma rays

● Cancer cells absorb the energy of the gamma rays and die

● It is used to control any other unwanted tissue too

● Surrounding healthy cells will also be irradiated

● This can cause side effects

Explain what nuclear fission is and give two examples. (3)

● Splitting of a large and unstable nucleus

● Uranium and plutonium

How does nuclear fission usually occur? (2)

● The unstable nucleus

● Must first absorb a neutron

Explain the process of nuclear fission. (6)

● The unstable nuclei absorbs a neutron

● And splits into two smaller nuclei

● Emits 2 or 3 neutrons and gamma rays

● The neutron may collide with another radioactive nucleus

● Energy is released by the fission reaction

● This causes a chain reaction

Why do neutrons need to be fully absorbed before it splits? (2)

● It needs a little extra energy before it can split

● So it can release lots of energy

Explain the consequences of an uncontrolled chain reaction. (3)

● It will increase at an exponential rate

● This happens in a nuclear weapon

● As the nuclei and the neutrons both have kinetic energy

Explain what nuclear fusion is and what it does in the process. (4)

● Two small nuclei fuse to form a heavier nucleus

● Releases a lot of energy

● The sum of the masses of the nuclei is more than the mass of the heavier nucleus

● Some of the mass is converted into energy

Give an example of a natural fusion reactor. (1)

The Sun

Explain why an alpha particle might go a different way than another. (2)

Alpha particles and the nucleus are both positive

So they repel each other

Explain why the path of an alpha particle closer to the centre of the nucleus is more tightly curved than the path of one not as close. (2)

The closer particle repels with a stronger force

As it’s more closer to the nucleus

Explain how the Bohr model of the atom is different from the nuclear model of the atom. (1)

The Bohr model electrons orbit at specific distances

Describe the process of nuclear fission in a Uranium fuelled reactor. (4)

A uranium nucleus absorbs a neutron

And splits into two/three smaller nuclei

Two/three neutrons are released

The nuclei also emits gamma rays

Describe the purpose of the following parts of a nuclear reactor. (2)

Control rods, Moderator

Absorbs excess neutrons

Slows down the neutrons (for easy absorption)

Describe the difference between irradiation and radioactive contamination. (2)

Irradiation is when something is only exposed to radiation

Contamination is the unwanted presence of radioactive nuclei on a person/object

Polonium-209 has a half-life of 125 years.

Polonium-210 has a half-life of 138 days.

Explain how the activity of polonium-209 compares with the activity of polonium-210 in this sample. (2)

Polonium-209 has lower activity 

And a longer half-life

What is meant by the ‘random nature of radioactive decay’? (1)

Cannot predict when the nucleus will decay next