P7: Radioactivity

Question 1

What is a radioactive substance?

Answer 1

A substance that contains nuclei that become stable by emitting radiation

Question 2

What are the three types of radiation that comes from radioactive substances?

Answer 2

• alpha
• bets
• gamma

Question 3

Why can’t you predict or influence when radioactive decay happens?

Answer 3

Because Radioactive decay is a random event

Question 4

Radioactive sources emmit?

Answer 4

• alpha radiation
• beta radiation
• gamma radiation

Question 5

Alpha radiation is stopped by___?

Answer 5

Paper

Question 6

Beta radiation goes through____

Answer 6

Paper

Question 7

Rutherford used ____ particles to probe inside atoms

Answer 7

Alpha

Question 8

What did Rutherford find from his experiment?

Answer 8

Some of the alpha particles were scattered through large angles(1/10000 more than 90 degrees

Question 9

What did Rutherford deduce from his results?

Answer 9

There is a positively charged nucleus at the centre of every atom

(Because alpha particles are positive and they rebounded)

Question 10

What was wrong with the plum pudding model?

Answer 10

It could not explain why some alpha particles were scattered through large angles

Question 11

Most of an atom’s mass is located in the _____

Answer 11

Nucleus

Question 12

What did the nuclear model correctly exlpain?

Answer 12

Why some alpha particles scattered through large angles

Question 13

What did Bohr’s model of the atom show?

Answer 13

Electrons in an atom orbit the nucleus as specific distances and have specific energy levels

• his model showed electrons could move to another orbit
• absorbing electromagnetic radiation-away from the neccleus
• emitting elecromagnetic radiation-move closer to the nucleus

Question 14

Who came up with the nuclear model

Answer 14

Rutherford

Question 15

What are isotopes!

Answer 15

Atoms of the same elemwnt with different numbers of nuetrons

Question 16

How can an unstable nucleus become more stable?

Answer 16

-emitting alpha or beta radiation

Or emitting a gamma ray

Question 17

An alpha particle is made out of what?

Answer 17

2 protons and 2 nuetrons

(Relative charge +2)

(Mass number:4’
(Atomic number:2)

Question 18

What is a beta particle?

Answer 18

An electron emitted by the nucleus, reltive charge =-1

Question 19

What is gamma radiation?

Answer 19

Electromagnetic radiation from the nucleus of an atom?

Question 20

Why does gamma radiation not change the number of protons or nuetrons in an atom?

Answer 20

It is uncharged and has no mass

Question 21

What is the activty of a radioactive substance?

Answer 21

Number of unstable atoms in the source that decay per second

Question 22

What does a Geiger do?

Answer 22

Monitors the activty of a radioactive substance

Question 23

What do you need for a Geiger to monitor the activity of a radioactive substance?

Answer 23

You need to measure the count rate

Question 24

What is the count rate proportional to?

Answer 24

The activity of the source as long as the distance between the tube and the source stays the same

Question 25

What is a half life?

Answer 25

The average time taken for the count rate to fall by half is always the same

Question 26

The half life of a radioactive substance is the average time it takes……………

Answer 26

For the number of nuclei of the isotope in a sample to halve

For the count rate in an isotope from a sample to fall to half its original value

Question 27

What is the count rate

Answer 27

Number of decays per second