ENERGY #3: Nuclear B

ENERGY #3: Nuclear B

Multiple Choice

When we study Nuclear Energy we also study NUCLEAR DECAY. Nuclear Decay involves a change in the _______________ of the atom. Energy is released.

• nucleus

• energy shells

• electrons

• protons only

Types of Nuclear Decay

• Alpha

• Beta

• Positron Emission

• Electron capture

• Gamma

• Spontaneous Fission

Alpha Decay

This occurs when a large, unstable nucleus releases 2 protons and 2 electrons (a He atom). A new, lighter element also results. Notice the proton number of the daughter decreases by 2 and the mass number decreases by 4.

*this is what type of radiation is used in smoke alarms. Because the alpha particle is easily stopped by skin and paper, this is NOT as dangerous unless it is ingested or enters the body in which case it can damage tissue and DNA

Multiple Choice

If Rn-222 isotope undergoes alpha decay, what will be the new element?

• Po-218

• Po-84

• Po-86

• Rn-218

The answer to the previous slide is Po-218.

to figure it out, notice that the mass # (A)decreases by 4 and the proton # (Z) decreases by 2. This is valid for all alpha decay examples

Beta Decay

In Beta Decay an unstable nucleus undergoes a change where within the nucleus a neutron changes into an electron and a proton.

As a result, the daughter element has a proton number increase of 1, and the mass number does NOT change.

Beta particles are more penetrating than alpha particles, but are less damaging to living tissue and DNA because the ionizations they produce are more widely spaced. Skin, clothes or aluminum can stop them.

Multiple Choice

An unstable isotope of Tl-210 undergoes beta decay. What is the new isotope?

• Pb-210

• Pb-211

• Tl- 211

• Tl-209

The answer to the previous slide shows that Tl-210 becomes Pb-210.

This is because the nucleus GAINED a proton and so the atomic # (proton number or Z) increased by 1.......the mass # (A) stays the same because although it lost a neutron it gained a proton.

Positron Emission

A proton in the nucleus breaks down. It leaves behind a neutron and emits a "positron" (an electron with a positive charge).

The mass# (A) of the daughter element stays the same but the atomic # (Z) is reduced by one.

Multiple Choice

An unstable isotope of K-37 undergoes positron emission. What will the products be?

• Ar-37 and a positron

• K-38 and a positron

• Ar-38 and a positron

• K-36 and a positron

The answer to the previous question is Ar-37

The daughter element has a decrease in atomic # only.

Beta Decay

Notice Beta minus is what we call "beta decay" and that Beta plus is what we call "Positron emission"

Study the pictures so you can differentiate

Electron Capture

Notice the beta particle (- electron) is on the reactant side of the equation. This means that an atom absorbed an electron. The electron is taken into the nucleus and merges with a proton resulting in a neutron.

As such, the daughter element has an atomic #(Z) that is reduced by 1 but the mass # (A) stays the same

Multiple Choice

If At-218 undergoes electron capture, what will the daughter element be?

• Po-218

• At-217

• Bi-218

• Bi-217

The answer to the previous slide is Po-218

Gamma Decay

In gamma decay, the parent element is 'excited'. The only thing that occurs is that the excited parent element releases a burst of energy in the form of a gamma ray. There is no change to the atomic # or the mass #.

Gamma rays are a radiation hazard for the entire body. They can easily penetrate barriers - Gamma rays have so much penetrating power that several inches of a dense material like lead, or even a few feet of concrete may be required to stop them. Gamma rays can pass completely through the human body; as they pass through, they can cause ionizations that damage tissue and DNA.

Multiple Choice

If an excited atom of Iodine, isotope 125 underwent gamma decay, what would be the products?

• I-125 and a gamma ray

• I-124 and a gamma ray

• Ra

• He

The answer to the previous slide is I-125 and a gamma ray (photon)

In gamma radiation, the parent element is 'excited' and has unstable energy. The energy (gamma photon) is released. No change in atomic # or mass # occurs.

Spontaneous Fission

This occurs when a neutron strikes a heavy nucleus. The nucleus breaks into daughter nuclei and in the process releases neutrons and energy (in the picture the energy is quantified as 200 MeV). The Law of Conservation still applies- protons, and neutrons must equal on both sides of the nuclear equation

Multiple Choice

Uranium-235 undergoes spontaneous fission when a neutron slowly is absorbed into its nucleus. What are the products?

• Ba-139 + Kr-94 + 3 neutrons

• Ba-138 + Kr-94 + 2 neutrons

• I have no idea

• never happened

The answer to the previous slide is shown to the right.

Notice that on the reactant slide the 'incoming' neutron is not displayed**** but you must count it. Therefore, add 1+235= 236 for a mass # on the reactant side. On the product side--> 90+143+3 = 236

"DECAY CHAIN"

Sometimes, elements go through many types of decay until they are "stable".

An atom can experience more than ONE type of decay (alpha plus gamma, for example

NOT ALL elements are radioactive OR undergo nuclear decay

• Elements that are heavier than an atomic# of 84 and above are naturally radioactive

• Other isotopes can be radioactive

Multiple Choice

IF 500 atoms of an isotope "A" underwent ONE half-life of decay, how many atoms of "A" would remain?

• 250

• 50

• 500

• 125

Multiple Choice

What % of the original radioactive element would be left after 3 half-lives?

• 12.5 %

• 25%

• 50%

• 6.25%

Multiple Choice

How much of the NEW daughter element would be present after 2 half-lives?

• 75%

• 50%

• 25%

• 100%