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Physics P2 > 6 Radioactivity > Flashcards

6 Radioactivity Flashcards

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1
Q

What does a radioactive substance contain?

A

an unstable nuclei that becomes stable after emitting radiation

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2
Q

What are the three main types of radiation from radioactive substances?

A
  • alpha
  • beta
  • gamma
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3
Q

What is radioactive decay known as?

A

a random event

we cannot predict it or influence when it will happen

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4
Q

What can measure background radiation and where does it come from?

A

a Geiger counter…

  • in the environment (e.g. in the air or the ground or in building materials)
  • from space (cosmic rays)
  • from devices such as x-ray tubes
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5
Q

What was the ‘plum pudding model’?

A

some scientists thought that an atom was like a plum pudding with:

  • the positively charged matter in the atom evenly spread out
  • electrons buried inside
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6
Q

What was the set up of Ernest Rutherford’s radioactivity investigation?

A
  • used a gold leaf (1 layer of gold atoms) and passed alpha particles through it
  • known as scattering experiment to see if the alpha particles would bounce back
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7
Q

What did Ernest Rutherford find in his investigation?

A
  • most of the alpha particles passed straight through the metal foil
  • the number of alpha particles deflected per minute decreased as the angle of deflection increased
  • about 1 in 10 000 alpha particles were deflected by more than 90degrees
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8
Q

What did Rutherford deduce from his scattering experiment results?

A

he knew that alpha particles are positively charged so he deduced that there is a nucleus at the centre of every atom that is…

  • positively charged because it repels alpha particles (like charges attract/unlike charges repel)
  • much smaller than the atom because most alpha particles pass through without deflection
  • where most of the mass of the atom is located
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9
Q

Why did Rutherford’s nuclear model of the atom become accepted?

A
  • it agreed exactly with the measurements made in the experiment (found the diameter of the nucleus was about 100 000 times smaller than atom)
  • it explained radioactivity in terms of changes that happen to an unstable nucleus when it emits radiation
  • predicted the existence of the neutron which was later discovered
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10
Q

Why was the plum pudding model abandoned?

A

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

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11
Q

What is the atomic (proton) number?

A
  • the number of protons in the nucleus

- symbol: Z

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12
Q

What are isotopes?

A
  • atoms of the same element with different numbers of neutrons
  • (same proton number, different neutron number)
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13
Q

What is the mass number?

A
  • the number of protons and neutrons in a nucleus

- symbol: A

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14
Q

What is radioactive decay?

A

when an unstable nucleus becomes more stable by emitting an alpha or beta particle or by emitting gamma radiation

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15
Q

What does an alpha particle consist of?

A

2 protons
2 neutrons
+2 relative charge
( a helium nucleus)

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16
Q

What happens when an unstable nucleus emits an alpha particle?

A
  • atomic number goes down by 2 and mass number by 4
  • equation:
    A A-4 4
    Z X –> Z-2 Y + 2 alpha particle
17
Q

What does a beta particle consist of?

A 
an electron (high speed)
(emitted by nucleus with too many neutrons compared to protons- a neutron in the nucleus changes into a proton and a beta particle which is instantly emitted at high speed from the nucleus)
18
Q

What happens when an unstable nucleus emits a beta particle?

A
  • atomic number of nucleus goes up by 1 but its mass number stays the same (because neutron changes into proton)
  • equation:
    A A 0
    Z X –> Z+1 Y + -1 beta particle
19
Q

How is gamma radiation emitted by some unstable nuclei?

A

(high energy EM wave)

  • after an alpha or beta particle has been emitted
  • gamma radiation is uncharged and has no mass
  • does not change the number of protons or neutrons in a nucleus
20
Q

What is the penetration power of alpha particle radiation?

A
  • can be absorbed by a thin sheet of paper

- has a range of around 5 cm in air

21
Q

What is the penetration of beta particle radiation?

A
  • can be absorbed by an aluminium sheet about 5 mm thick and a lead sheet about 2-3 mm thick
  • has a range of around 1 m in air
22
Q

What is the penetration power of gamma radiation?

A
  • can be absorbed by a thick lead sheet about several cm thick and concrete more than 1 m thick
  • has an unlimited range in air
23
Q

What can be used to separate a beam of alpha, beta and gamma radiation?

A

a magnetic or electric field

shows properties as the charges influence it…

24
Q

What is ionisation?

A

when atoms become charged because they lose or gain electrons

25
Q

Which radiation types can ionise and how strongly?

A

They ionise substances they pass through which in living cells can damage or kill them…

  • alpha: yes, very strongly
  • beta: yes, weaker
  • gamma: yes, very weakly
26
Q

What is the half-life of a radioactive isotope?

A

the average time it takes:

  • for the number of nuclei of the isotope in a sample (and therefore the mass of parent atoms) to halve
  • for the count rate of the isotope in a sample to fall to half its initial value
27
Q

What is the activity of a radioactive source?

A

the number of atoms/nuclei that decay per second

28
Q

What can we use the Geiger counter for?

A
  • to monitor the activity of a radioactive sample

- can measure a count rate

29
Q

What does the use we can make of a radioactive isotope depend on?

A
  • its half life

- the type of radiation it gives out

30
Q

Give an example of how a radioactive substance can be useful for monitoring?

A

Kidney monitoring (radioactive iodine water substance goes into kidney- if functioning reading will go up then down where it flows straight through, if blocked then reading on detector stays up)

31
Q

What makes a radioactive substance good at monitoring?

A
  • if it has a long enough half-life but will then decay and be gone
  • if it emits gamma radiation as it can be detected outside the body
  • if it decays into a stable product
32
Q

What are the 2 types of radioactive dating?

A
  • carbon dating: used to find the age of organic material (half-life around 5600 years)
  • uranium dating: used to find age of igneous rocks (half-life around 4500 million years)
33
Q

What do we need for a radioactive dating sample?

A

a radioactive isotope that is present in the sample which has the same half life as the age of the sample

Physics P2 (7 decks)

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