Decaymechanisms

Examquestion

Radioisotopes

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An alpha particle is really four particleswhich are ejected from the nucleusof an unstable atom.

An alpha particle is two protons andtwo neutrons.

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What happens when atoms of emit alpha particles?

Notice that it is impossible to predict which atoms will decay but we can seethat the rate ofdecay slows down with time.

We will now lookdeeper inside the atom to see what is happening to the nucleus.

23793 Np

This is a model to simulate how ALPHA particles are emitted from a radioactive isotope of NEPTUNIUM.

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The nucleus

loses 2 protonsand 2 neutrons which we call an alpha particle

Taking a closer look inside the NEPTUNIUM atom

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Before After

Np Pa237

93 91 +Neptunium Palladium alpha

+

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Fill in the missing numbersto complete the equation

Before After

Np Pa237

93

233

91 +4

2

Neptunium Palladium alpha

+

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answers

A beta particle is simply a fast movingelectron.

This particle is also ejected fromthe nucleus of an unstable atom but the way this happens is more complicated thanalpha emission.

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What happens when atoms emit beta particles?

Notice that it is impossible to predict whichatoms will decay but we can seethat the rateof decay slowsdown with time.

233Pa91

We will now lookdeeper inside the atom to see what is happening to the nucleus.

This is a model to simulate how BETA particles are emitted from a radioactive isotope of PALLADIUM.

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emits a betaparticle whena neutronchanges intoa proton andan electron

Taking a closer look inside the PALLADIUM atom

The nucleus

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Before After

Pa U233

91 +0

-1

Palladium Uranium Beta

B

+

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Fill in the missing numbersto balance the equation

Before After

Pa U233

91

233

92+

0

-1

Palladium Uranium Beta

B

+

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answers

Gamma rays are really electromagneticrays which are given out by the nucleusof unstable atoms. You will not need to know how this affectsthe nucleus of an unstable atom.

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145

144

143

142

141

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137

13687 88 89 90 91 92 93 94

Number ofneutrons

Number ofprotons

X

Np237

Pa233

U233

Th229

Neptunium-237 ( Np)is a radioactive element.The graph shows the numbers of neutrons andprotons in the nuclei ofthe elements formed when Np decays.

237

237

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144

143

142

141

140

139

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137

13687 88 89 90 91 92 93 94

Number ofneutrons

Number of protons

X

Np237

Pa233

U233

Th229

(a)Use the periodic tableto identify element X.

(b) Why are Pa and U considered to be different elements?

233

233

(c) What type of radiationis released when Npdecays to form Pa?

237

233

(d) What change takes placein the nucleus when Pachanges into U?

233

233

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145

144

143

142

141

140

139

138

137

13687 88 89 90 91 92 93 94

Number ofneutrons

Number ofprotons

X

Np237

Pa233

U233

Th229

(a)Use the periodic tableto identify element X.

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145

144

143

142

141

140

139

138

137

13687 88 89 90 91 92 93 94

Number ofneutrons

Number ofprotons

X

Np237

Pa233

U233

Th229

(b) Why are Pa and U considered to be different elements?

233

233

Pa has 91 protons

U has 92 protons

Different protonnumber meansdifferent element.

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145

144

143

142

141

140

139

138

137

13687 88 89 90 91 92 93 94

Number ofneutrons

Number ofprotons

Np237

Pa233

(c) What type of radiationis released when Npdecays to form Pa?

237

233

The nucleus of Neptuniumhas lost 2 neutrons

and 2 protons.

Alpha particle

NeptuniumnucleusPa nucleus

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145

144

143

142

141

140

139

138

137

13687 88 89 90 91 92 93 94

Number ofneutrons

Number ofprotons

Np237

Pa233

U233

(d) What change takes placein the nucleus when Pachanges into U?233

233

The neutron number decreases by one

but the proton numberincreases by one

A neutron changes into a proton andan electron

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An isotope is an atom which has the same number of protons but a different number of neutrons

The underlined phrases score the marks---so learn this definition off by heart

XA

Z

C12

6 H1

1 Li7

3

Symbolof theelement

Nucleonnumber

Protonnumber

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You should know what an isotope is

What a radio-isotope is and

give some examples.

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H H H

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Write in the missing numbers(the bottom one is the number of protons)(the top one is the protons and neutrons)

H1

1 H2

1 H3

1

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answers

He He

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He4

2 He3

2

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answers

C12

6 C14

6

Now lets have a closer look at thenuclei of these isotopes.

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C CN

Carbon-12 is stable but Carbon-14 is unstable (a radio-isotope). Carbon-14 emits a beta particle and decays to become nitrogen

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Count the particlesin these nuclei afterthe beta particle is emitted and fill in thenumbers

C12

6

14

7 N

Carbon-12 is stable but Carbon-14 is unstable (a radio-isotope). Carbon-14 emits a beta particle and decays to become nitrogen

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answers

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