Nuclear Decay 72-73 Flashcards

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1
Q

What are isotopes?

A

Atoms with the same number of protons but different numbers of neutrons are called isotopes.

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2
Q

Why is it easy for a nucleus to become unstable?

A

The nucleus is under the influence of the strong nuclear force holding it together and the electromagnetic force pushing the protons apart. It’s a very delicate balance.

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3
Q

When will a nucleus becomes unstable?

A

A nucleus will be unstable if it has:

1) Too many neutrons
2) Too few neutrons
3) Too many nucleons altogether, ie it’s too heavy.
4) Too much energy.

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4
Q

What is a stability graph?

Roughly sketch the line of stability on the graph. Make sure the axes are clearly shown.

A

You can get a stability graph by plotting Z (atomic number) against N (number of neutrons.).

The line of stability is found by plotting N against Z for stable nuclei.

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5
Q

When a heavy nuclei decays what is emitted and how many protons/neutrons does the nuclei loose?

A

Heavy nuclei release alpha emission.

The proton number decreases by two, and the nucleon number decreases by four. (because alpha has a mass of 4.)

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6
Q

Why does alpha emission only happen in very heavy atoms?

How heavy do the atoms need to be to decay?

A

Alpha emission only happens in very heavy atoms ( with more than 82 protons.), like uranium and radium.

The nuclei of these atoms are too massive to be stable.

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7
Q

Write the equation for uranium(u) decaying to thorium(Th)

A
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8
Q

What is beta-minus decay?

A

It is the emission of an electron from the nucleus along with an antineutrino.

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9
Q

What does beta decay occur?

A

Beta decay happens in isotopes that are “ neutron rich” (have more neutrons than protons.)

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10
Q

What happens to the structure of the nucleus during beta-plus emission(in terms of protons/neutrons)?

A

A proton gets changed into a neutron. The proton number increases by one, and then nucleon number stays the same.

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11
Q

When does gamma emission occur from a nuclei?

A

A nucleus with excess energy is said to be excited, this energy can be lost by emitting a gamma ray. This often happens after an alpha or beta decay.

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12
Q

How is the nucleus changed after a gamma emission?

A

During gamma emission, there is no change to the nuclear constituents - the nucleus just looses excess energy.

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13
Q

In every nuclear reaction what is consereved?

A

In every nuclear reaction energy, momentum, proton number/ charge and nucleon number must be conserved.

The nucleon numbers must balance.

The proton numbers must balance.

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14
Q

Explain why the mass of an alpha particle is less than the individual masses of two protons and two neutrons.

A

The difference in mass is called the mass defect. Mass doesn’t have to be conserved because of Einstain’s equation: E = mc2.

This says that mass and energy are equivalent. The energy released when the nucleons bonded together accounts for the missing mass - so the energy released is the same as the magnitude of the mass defect x c2.

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