P6 - Radioactivity

Question 1

What is an isotope?

Answer 1

Atoms of the same element with the same number of protons but different number of neutrons - they tend to be unstable and radioactive (they give out nuclear radiation and decay into other stable elements).

Question 2

What are the 3 types of radiation?

Answer 2

Alpha radiation:
-An unstable nucleus emits an alpha particle (2 protons and 2 neutrons) -> mass number decrease by 4 and atomic number decrease by 2

Beta radiation:
-If nucleus has too much neutrons, a beta particle (electron) is emitted and a neutron in the nucleus will turn to a proton. Atomic number increases (proton added) and mass number remains the same (1 proton gained and 1 neutron lost)

Gamma radiation:
- After spitting out beta or alpha particle, nucleus may need to rid of extra energy by emitting gamma rays. Nothing happens to the mass or proton number.

Question 3

Types of radiation and their penetration power:

Answer 3

Alpha radiation have low penetration: they can be stopped by paper as alpha particles are large colliding with atoms slowing them down.

Beta radiation have medium penetration: they can be stopped by thin aluminium as they are a smaller size than alpha particles so they can travel further without colliding with atoms

Gamma radiation have high penetration: they can be stopped by thick lead as they travel the furthest without hitting atoms.

Question 4

Types of radiation and their ionisation power:

Answer 4

Alpha radiation have high penetration: they are the largest therefore they can’t travel far without hitting atoms and knocking off electrons

Beta radiation have medium ionisation: are smaller than alpha particles so they can travel further before hitting atoms and knocking off electrons

Gamma radiation has low ionisation: Gamma rays are just energy therefore there is the lowest likelihood of hitting atoms and knocking off electrons.

Question 5

Nuclear equations - Alpha radiation

Answer 5

Nucleus emits alpha particles (2 protons and 2 neutrons) so mass number decreases by 4 and atomic number decreases by 2

Eg 266,88 Ra -> 222,86 Rn + 4,2α

Question 6

Nuclear equations - Beta radiation

Answer 6

Nucleus emits electron and a neutron becomes a proton therefore mass number the same (1 proton gained and 1 neutron lost). Atomic number increases as proton in atom increases by 1

EG 14,6 C -> 0,-1e- + 14,7 N

Question 7

Nuclear equations - Gamma radiation

Answer 7

The mass number and atomic number doesn’t change

EG 234,91Pa -> 234,91Pa + γ

Question 8

What happens when an electron absorbs an electromagnetic wave in an atom?

Answer 8

• An electron can move up shells when they gain energy (become excited) from absorbing an electromagnetic wave supplying them with enough energy to move up an energy shell
• The electron will move back to their original shell and all excess energy is released in doing so. The same amount of energy which was absorbed by the electron to move up energy level will be released when doing so.

Question 9

How do florescent lights work?

Answer 9

• Ultraviolet has a high frequency and when absorbed by electron it has enough energy to become excited and move up multiple energy levels
• When electrons moves back to its original shell it doesn’t go back in one step so it moves back energy level by energy level releasing little amounts of energy as it goes as visible light

Question 10

What is the absorption spectrum?

Answer 10

• Rainbow colored rectangle from red to violet with black lines
• > the black lines are the amount of energy the electron absorbed to move up energy levels

Question 11

What is the emission spectrum?

Answer 11

• Black rectangle with coloured lines

- > the coloured lines are the energy released from electron when returning to its original shell

Question 12

Activity equation?

Answer 12

Activity (*Bq) = Number of decays / time (s)

*Bq = Becquerels

Question 13

What is the experiment to measure decay?

Answer 13

The geiger muller experiment

• The geiger muller tube detects alpha, beta and gamma radiation as they hit it
• When they hit it the geiger muller tube beeps and allows us to count the decay per seconds (activity)

Question 14

What is half life?

Answer 14

The time taken for half the radioactive substance to decay to half.

Question 15

What does a long and short half life mean?

Answer 15

Long half life: activity falls slowly as most of the nuclei makes a long time to decay

Short half life: activity falls quickly as most of the nuclei decays in a short amount of time

Question 16

Half-life on a graph:

Answer 16

Y axis: Activity
X axis: Time (s, min or hr)

1) Halve the total activity and draw a line from there to the curved line. When it hits the line draw down and find the time.
2) The next half life is half the previous half-life’s activity and draw down to find the time

• To note: If the activity never reaches 0 then there is background radiation which shouldn’t be taken into consideration when working out half-life

Question 17

Some half life Questions:
Q1) The count rate of a substance is measured as 640 counts a minute. Two hours later it has fallen to 40 counts per minute. Find half life?

Q2) The half life of a substance is 60hr. Find the activity after 240hr, if it is originally 480 Bq?

Q3) A radioactive substance has half life of 15hrs. A tube contains 8mg of isotopes. What is the mass after

a) 15 hrs
b) 45 hrs

Answer 17

Q1) 640 -> 320 -> 160 -> 80 -> 40
4 half lives = 2 hours
1 Half life = 30 minutes

Q2) 480 -> 240-> 120-> 60-> 30->
1 half life = 60
4 half lives = 240
30 Bq at 240hr

Q3) 8mg -> 4mg -> 2mg -> 1mg
1 half life = 15hr
3 half lives = 45hr

15 hrs = 4mg
45hrs = 1mg

Question 18

Where does the background radiation formed -> percentages

Answer 18

37% = radon and thoron gas released from soil, rocks and building materials 
19% = gamma rays from rocks and soil 
17% = radiation from bodies 
14% = cosmic rays from space 
11.5% = medical industry 
0.5% = other (like travel)
0.5% = nuclear weapons 
0.4% = work related 
0.1% = from nuclear power industry

Question 19

What are the dangers of radioactivity?

Answer 19

-> Can cause ionisation (especially alpha radiation) knocking off electrons and forming ions

Lower doses: radiation damages cells by causing mutations in DNA causing uncontrollable cell division (cancer)
Higher doses: kill living cells entirely and cause radiation sickness

Question 20

Radiation dangers from different places:

Answer 20

OUTSIDE THE BODY
Beta and gamma radiation are most dangerous due to there high penetration power to enter body

INSIDE BODY:
Alpha radiation is most dangerous as it has high ionisation power meaning it can knock off electrons due to large size

Question 21

What is irradiation?

Answer 21

• Occurs when an object is exposed to a source of radiation outside the object.
• > it can be shielded or moving object away prevents irradiation

Question 22

Likeliness of irradiation:

Answer 22

• If gamma irradiation: a higher likeliness as there is a higher range it can reach
• If alpha irradiation: lower likeliness as it has a shorter range than gamma radiation.

Question 23

What is contamination:

Answer 23

Occurs when radiative substance is in or on the object

-> It cannot be shielded or blocked as substance is in contact with the object and is hard to remove all contamination

Question 24

Likeliness of contamination:

Answer 24

• If substance is a solid: there is no contamination risk as long as the substance doesn’t touch the object
• If substance is a gas, there is high contamination risk as it can move

Question 25

Half life and radioactive danger?

Answer 25

Shorter half lives are safer

Longer half lives are more dangerous

Question 26

Medical uses of radiation?

Answer 26

-Tracers: (short half life gamma ray emitters) are injected or swallowed to see how organs work or how things move in the body

Short half life: Relatively short half life to be as safe as possible so radiation disappears quickly but enough to be detected

Gamma rays: due to high penetration power they can penetrate out the body to be detected by gamma detectors

Question 27

Cancer treatments with radiation?

Answer 27

RADIOTHERAPY:

• To treat cancer externally
  1) Gamma rays concentrated on the tumor
  2) The beam - producing gamma rays- is rotated around patient with tumor at centre, minimising damaging to living cells
  3) Treatment taken in intervals to allow living cells to repair and grow

BRACHYTHERAPY:

• To treat cancer internally:
  1) Implants containing beta particles are placed inside tumor.
  2) Beta particles damage the tumor cells but have a short enough range not to damage living cells
  3) Alpha emitters can be injected in as they have high ionisation power and short range causing lots of damage to tumor

Question 28

What is nuclear fission:

Answer 28

When an unstable nucleus splits into two releasing lots of energy

Question 29

What 2 ways can nuclear fission occur:

Answer 29

1) Spontaneously

2) By absorbing a slow moving neutron causing it to become unstable and split

Question 30

How does nuclear fission of Uranium work?

Answer 30

1) When.a slow moving neutron is absorbed by the uranium the nucleus becomes unstable and splits
2) The uranium-235 nucleus splits to krypton-89, barium-144, 3 neutrons and gamma rays (if there is excess energy)
3) The 3 neutrons can be absorbed by other Uranium nuclei causing fission and a chain reaction

Question 31

Advantages and disadvantages of nuclear power?

Answer 31

ADV

1) It doesn’t release CO2 emissions - no global warming contribution
2) It is extremely reliable -> there are lots of uranium - 235 and it produces lots of energy

DIS

1) Nuclear power stations contain highly dangerous radioactive materials which can cause disastre if released
2) Decommission of nuclear power stations take very long and very expensive
3) Generates large amounts of radioactive waste which must be stored away for thousands of years

Question 32

How does nuclear power stations produce electricity?

Answer 32

IN THE REACTOR CORE

1) Fissionable atoms like Uranium -235 are present and once one neutron is absorbed a chain reaction occurs
2) Moderator: is water and it keeps fission occurring as the 3 neutron emitted in each fission reaction have a lot of energy (they are too fast) therefore the neutrons collide with the H20 molecules slowing them down allowing fission to occur
3) Control rods: they allow us to control number of fission reactions occurring (if control rods lowered they stop neutrons from reach other nuclei slowing it down and vice versa for raising control rods)
4) Surrounded by thick lead to prevent escape of gamma radiation - which can be stopped by lead

IN THE HEAT EXCHANGER

1) The hot water (from energy from fission in reactor core) runs in tube through container of water in heat exchange
2) This transfers energy to the water in heat exchange producing steam as it boils
3) The steam travels up pipe and spins a turbine converting heat energy into electrical energy

IN THE PUMP
1) Pump helps supply heat exchange with constant supply of water as the water in heat exchanger changes state to steam

Question 33

What is nuclear fusion?

Answer 33

Two smaller nuclei joining together to form a larger nuclei

Question 34

Why does nuclear fusion release more energy than nuclear fission?

Answer 34

• Due to the difference in mass from before fusion and after fusion
• Before nuclear fusion the nuclei will always have more mass than after so the extra mass is converted into energy released as gamma radiation

Question 35

How does nuclear fusion of 2 Hydrogen work?

Answer 35

Two hydrogen nuclei combine to form He (Helium) releasing energy as well
(this occurs in the sun)

Question 36

Advantages and disadvantages of nuclear fusion?

Answer 36

ADV
1) It doesn’t create radioactive waste
2) There is plenty of hydrogen available for fusion
3) Produces more energy than fission
DIS
1) Requires extremely high temperatures and pressures and a very strong magnetic field

Question 37

Carbon isotope percentage in every living organism?

Answer 37

Carbon - 14 (10%)

Carbon - 12 (90%)

Over time the carbon -14 will decay to carbon - 12. We can use this to find age of organisms like trees.