1.2-STABLE AND UNSTABLE NUCLEI

Question 1

What does a stable isotope have?

Answer 1

nuclei that does not disintegrate, so there must be a force holding them together

Question 2

What is the force holding the protons + neutrons together in the nuclei called?

Answer 2

strong nuclear force

Question 3

What force does the strong nuclear force balance out?

Answer 3

It overcomes the electrostatic force of repulsion between the protons in the nucleus and keeps the protons and neutrons together

Question 4

What is the range of the strong nuclear force?

Answer 4

no more than about 3-4 femtometres (fm)

Question 5

What do 1 fm equal to in m?

Answer 5

1 fm = 10^(-15)m

Question 6

What is the range of the strong nuclear force about the same as?

Answer 6

diameter of a small nucleus

Question 7

What is the range of the electrostatic force between two charged particles like?

Answer 7

has an infinite range (although it decreases as the range increases)

Question 8

How does the strong nuclear force effect protons and neutrons?

Answer 8

it has the same effect between two protons as it does between two neutrons or a proton and neutron

Question 9

From what range is the strong nuclear force an attractive for?

Answer 9

from 3-4 fm down to about 0.5 fm

Question 10

What happens to the strong nuclear force when the separation is smaller than 3-4 fm to 0.5fm?

Answer 10

it is repulsive force that acts to prevent neutrons and protons being pushed into each other

Question 11

What do naturally occurring radioactive isotopes release?

Answer 11

3 different types of radiation:

alpha, beta, gamma

Question 12

Which force has the larger range?

Answer 12

electrimagetic

Question 13

What does alpha radiation consist of?

Answer 13

alpha particles which each comprise two protons and neutrons

Question 14

What is the proton number and mass number of an alpha particle?

Answer 14

proton number - 2

mass number - 4

Question 15

What happens to the numbers of an unstable nucleus of an element X when it emits an alpha particle?

Answer 15

its nucleon number decreases by 4 and its atomic number decreases by 2

Question 16

What happens as a result of the alpha particle being emitted? (element)

Answer 16

the product nucleus belongs to a different element Y

Question 17

How do you detect alpha radiation?

Answer 17

Tracks left by alpha alpha particles are seen in a cloud chamber.
Geiger counter of spark counters detect the ionising radiation - see the count rate drop if you slowly move it away from the source.

Question 18

What does beta radiation consist of?

Answer 18

fast-moving electrons with electron antineutrino’s

Question 19

What is the charge and mass of a beta particle like?

Answer 19

its charge is equal and opposite to that of the proton

its mass is much smaller than the proton’s mass

Question 20

Why does an unstable nucleus of an element X emit a beta particle?

Answer 20

Nucleus is isotope is neutron rich.

The neutron in the nucleus changes into a proton.

Question 21

What else is emitted with the beta particle?

Answer 21

an antiparticle with no charge, called an antineutrino

Question 22

What happens in Beta radiation?

What numbers increase / stay the same?

Answer 22

One of the neutrons from the nucleus is changed into a proton. The beta particle is created and is emitted instantly

Proton number increases by 1, Nucleon number stays the same

Antineutrino particle is released

Question 23

What does the antineutrino carry?

Answer 23

Some energy and momentum

Question 24

What do neutrinos have / not have and why?

Answer 24

Needed to conserve energy

Neutral charge, zero / almost zero mass, carries momentum and energy

Question 25

How does the beta particle being emitted affect the element X?

Answer 25

atomic number decreases by 1 but the nucleon number stays the same

Question 26

What happens to the product nucleus after beta particle being emitted?

Answer 26

belongs to a different element W

Question 27

What type of nuclei undergo beta decay?

Answer 27

nuclei that have too many neutrons

Question 28

What is gamma radiation?

Answer 28

electromagnetic radiation emitted by an unstable nucleus

Question 29

What can gamma radiation pass through?

Answer 29

thick metal plates

Question 30

What is the charge and mass like of gamma radiation?

Answer 30

no mass and no charge

Question 31

What type of nucleus emits gamma radiation and what is it followed by?

Answer 31

emitted by a nucleus with too much energy, following an alpha or beta emission

Question 32

What was found when the energy spectrum of beta particles was first measured?

Answer 32

beta particles were released with kinetic energy up to a maximum that depended on the isotope

Question 33

What did scientists think happened after they found out beta particles were released with K.E. up to a maximum that depends on the isotope ?

Answer 33

either energy was not conserved in the change or some of it was carried away by mystery particles

Question 34

What did scientists think happened after they found out beta particles were released with K.E. up to a maximum that depends on the isotope ?

Answer 34

either energy was not conserved in the change or some of it was carried away by mystery particles

Question 35

What were the mystery particles called that carried some charge away?

Answer 35

neutrinos and antineutrinos

Question 36

How were antineutrinos detected over 20 years later?

Answer 36

as a result of their interaction with cadmium nuclei in a large tank of water

Question 37

Where was the large tank of water where antineutrinos were discovered installed?

Answer 37

next to a nuclear reactor as a controllable source of these very elusive particles