Isotopes&radioactive decay

Question 1

Isotopes

Answer 1

Nuclei that have the same number of protons but different number of neutrons

∴ same number of electrons

Question 2

When do stable nuclei have equal numbers of protons and neutrons?

Answer 2

When Z is small

Question 3

When do stable nuclides have more neutrons than protons

Answer 3

As Z gets larger

Question 4

Radioactivity

Answer 4

The disintegration of the nucleus by emitting particles and energy to attain stability

Question 5

Charateristics of radioactivity

Answer 5

Random: can’t be predicted
Spontaneous: not affected by external factors

Question 6

In a magnetic field, the α particle deflects towards?

Answer 6

South

Question 7

In a magnetic field, the β particle deflects towards?

Answer 7

North

Question 8

What is produced in alpha decay?

Answer 8

Ph1. New element with 4 less nucleons and 2 less protons
2. α particle
3. Photon( γ)

Question 9

What is produced in a beta minus decay?

Answer 9

1. New element(same mass no. and 1 more proton
2. Electron
3. Electron anti-neutrino

Because a neutron turns into a proton!

Question 10

What is produced in a beta plus decay?

Answer 10

1. New element(same mass no. , 1 less proton)
2. Positron
3. Neutrino

Because a proton turns into a neutron!

Question 11

Law of radioactivity

Answer 11

The rate of decay is proportional to the number of nuclei that have not decayed yet

ΔN/t ∝ N

N = number of nuclei that haven’t decayed

Question 12

Half life

Answer 12

time taken for half the number of radioactive particles to decay

Question 13

Are gamma rays affected by electric or magnetic fields?

Answer 13

No

Question 14

What is a decay series?

Answer 14

the set of decays that take place until a nucleus becomes stable

Question 15

What is the probability of a nucleus decaying in any one of its half lives?

Answer 15

50%

Question 16

Probability of nucleus having decayed by its second half life

Answer 16

75%

1. Decays in 1st: 0.5
2. OR Decays in 2nd: 0.5 * 0.5 = 0.25

0.5+0.25=0.75

Question 17

What are the four fundamental forces

Answer 17

1. Electromagnetic interaction
2. Weak nuclear interaction
3. Strong nuclear interaction
4. Gravitational interaction

Question 18

Electromagnetic interaction

Answer 18

• acts on any particle with charge
• force given by Coulomb’s law
• infinite range

Question 19

Weak nuclear interactions

Answer 19

• acts on protons, neutrons, electrons and neutrinos to bring about beta decay
• Very short range

Question 20

Strong nuclear interaction

Answer 20

• mainly attractive force between protons and neutrons to kepe them bound in nucleus
• Short range

Question 21

Gravitational interaction

Answer 21

• attractive force between masses
• infinite range

Irrelevant;atomic particles have very small mass