P7 Radioactivity

Question 1

Who discovered radioactivity?

Answer 1

Henri Becquerel in 1896.

He discovered it by observing an image on photographic film caused by uranium salts.

Question 2

What are the three main types of radiation emitted by radioactive substances?

Answer 2

• Alpha (α)
• Beta (β)
• Gamma (γ)

These types differ in their properties and penetrating abilities.

Question 3

What is a Geiger counter used for?

Answer 3

To detect radioactivity.

It consists of a Geiger-Müller tube connected to an electronic counter.

Question 4

What type of radiation is stopped by paper?

Answer 4

Alpha radiation (α).

Alpha particles are positively charged and relatively large.

Question 5

What type of radiation can pass through paper?

Answer 5

Beta radiation (β).

Beta particles are smaller and more penetrating than alpha particles.

Question 6

Which type of radiation is the most penetrating?

Answer 6

Gamma radiation (γ).

Gamma rays can pass through most materials and require dense substances for shielding.

Question 7

What happens to an unstable nucleus during radioactive decay?

Answer 7

It emits radiation and becomes more stable.

This process is random and cannot be predicted.

Question 8

What did Ernest Rutherford discover about the atom’s structure?

Answer 8

The atom has a positively charged nucleus containing protons and neutrons.

This was demonstrated through his experiments with alpha particles and thin metal foil.

Question 9

True or False: Radioactive decay can be influenced or predicted.

Answer 9

False.

Radioactive decay is a random event.

Question 10

What is meant by the term ‘decaying’ in the context of radioactivity?

Answer 10

When an unstable nucleus emits radiation.

Decay results in the nucleus becoming more stable.

Question 11

What is the significance of the Geiger counter clicking rapidly?

Answer 11

It indicates that the substance nearby is highly radioactive.

The frequency of clicks correlates with the level of radiation detected.

Question 12

Why do some radioactive substances emit radiation all the time?

Answer 12

Their nuclei are unstable and decay continuously.

This results in a constant emission of radiation until the nucleus stabilizes.

Question 13

what is a radioactive substance

Answer 13

A radioactive substance contains an unstable nuclei that becomes stable by emitting radiation

Question 14

what are the types of radiation given out from a radioactive substance

Answer 14

alpha, beta, gamma

Question 15

what is it called when a radioactive source emits radiation

Answer 15

radioactive decay

Question 16

Why was the plum pudding model of the atom rejected.

Answer 16

Because it couldn’t explain why some alpha particles were scarred through large angles.

Question 17

what conclusions were made about the atom from experimental evidence

Answer 17

that an atom has a small, positive,y charged nucleus where most of the atom’s mass is located.

Question 18

why was the nuclear model accepted

Answer 18

the nuclear model explained why some alpha particles scattered through large angles

Question 19

what is an isotope

Answer 19

an element with the same number of protons but different number of neutrons

Question 20

how does the nucleus of an atom change when it emits an alpha particle

Answer 20

when an unstable nucleus emits an alpha particle, its atomic number goes does by 2
its mass number goes down by 4
The mass and charge of nucleus are both reduced

Question 21

how does the nucleus of an atom change when. It emits a beta particle

Answer 21

• the atomic number of the nucleus goes up by one
• Its mass number is unchanged (because a neutron changes into a proton)
  -change of the nucleus is increases and the mass of the nucleus is unchanged.

Question 22

how do you represent the emission of an alpha particle from a nucleus.

Answer 22

represented by a helium nucleus which has 2 protons and 2 neutrons

add 2 to the atomic number
add 4 to the mass number

Question 23

how to represent the emmision of a beta particle from a nucleus

Answer 23

add 1 to the atomic number/represented as a electron

Question 24

how far can alpha radiation travel, what absorbs it and what’s the ionising power of it?

Answer 24

-alpha radiation has a race of a few centimetres in the air and is stopped by paper.
-It consists of particles, each composed of two protons and two neutrons
-It has the greatest ionising power.

Question 25

how far can beta radiation travel, what absorbs it and what’s its ionising power?

Answer 25

• beta radiation has a range of about 1 metre in the air
• its stopped by a thin sheet of metal.
• it’s less ionising than alpha radiation and more ionising than gamma radiation.
• consists of fast-moving electrons emitted from the nucleus .

Question 26

how far can gamma radiation travel, what absorbs it and what’s its ionising power.

Answer 26

• gamma radiation is stopped by thick lead
• it had an unlimited range in air
• it has lowest ionising power
• it consists of electromagnetic radiation

Question 27

why are alpha, beta and gamma radiation dangerous.

Answer 27

alpha beta and gamma radiation ionise substances as they pass through . Ionisation in a living cell can damage or kill the cell.

Question 28

What is meant by the half-life of a radioactive source?

Answer 28

• the average time it takes for the number of nuclei of the isotope in a sample to halve.
• for the count rate from the isotope in a sample to fall to half its initial value.

Question 29

what is meant by the count rate from a radioactive source?

Answer 29

the count rate of a Geiger counter caused by a radioactive source decreases as the activity of the source decreases.

Question 30

what happens to the count rate and the number of atoms from a radioactive isotope as it decays

Answer 30

the number of atoms of a radioactive isotope and the count rate both decreases by half every half life.

Question 31

how do you calculate count rates after a given number of half lives?

Answer 31

The count rate after x amount of lives = the initial count rate / 2^x

Question 32

what are radioactive isotopes are used for in medicine

Answer 32

radioactive isotopes are used for :
- medical imaging
- Treatments if cancer
- Tracers to monitor organs

Question 33

how to choose a radioactive isotope for a particular job

Answer 33

how useful a radioactive isotope is depends on:
-it’s half-life
-the type of radiation it gives out.

Question 34

what kind of half life should radiation have for medical imaging/tracing

Answer 34

For medical imaging with a radioactive isotope and for medical traces, the half-life shouldn’t be too long or too short.

Question 35

How do you use radioactivity to destroy cancer cells?

Answer 35

A gamma beam or a radioactive implant can destroy cancer cells in a tumor.