Radioactive Decay - MCAT Chemical and Physical Foundations of Biological Systems
Card 1 of 133
The half-life of a particular isotope of radium is 1600 years. If a sample of this isotope originally has a mass of 120g, how long would it take the mass of this isotope to decrease to 15g?
The half-life of a particular isotope of radium is 1600 years. If a sample of this isotope originally has a mass of 120g, how long would it take the mass of this isotope to decrease to 15g?
Tap to reveal answer
First note that 15g is 1/8 of the original 120-gram mass, so all but 1/8 of these radium nuclei have decayed. By definition, ½ of the nuclei decay during one half-life. So the number of nuclei remaining after n half-lives is 
. In this case, three half-lives have elapsed since, 
. The answer is 3 * 1600 = 4800 years.
First note that 15g is 1/8 of the original 120-gram mass, so all but 1/8 of these radium nuclei have decayed. By definition, ½ of the nuclei decay during one half-life. So the number of nuclei remaining after n half-lives is
← Didn't Know|Knew It →
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
When a U-235 atom breaks down .
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
When a U-235 atom breaks down .
Tap to reveal answer
Like any system, energy is absorbed to break bonds and released when bonds are formed. Energy is absorbed to get U-235 to an unstable state. It then breaks apart, and new species form. These new species release more energy than was originally absorbed when they form their bonds, thus leading to a net release of energy from the system.
Like any system, energy is absorbed to break bonds and released when bonds are formed. Energy is absorbed to get U-235 to an unstable state. It then breaks apart, and new species form. These new species release more energy than was originally absorbed when they form their bonds, thus leading to a net release of energy from the system.
← Didn't Know|Knew It →
What is the product when 
undergoes an alpha decay?
What is the product when
Tap to reveal answer
Alpha decay is the loss of a helium atom from the original particle.
The number of protons is reduced by two, and the nuclear mass is reduced by four.
Alpha decay is the loss of a helium atom from the original particle.
The number of protons is reduced by two, and the nuclear mass is reduced by four.
← Didn't Know|Knew It →
Which type of nuclear decay is displayed below?
Which type of nuclear decay is displayed below?
Tap to reveal answer
Positron emission is when the nucleus ejects a positron, or positive equivalent of an electron. It is also known as 
decay.
Beta decay is when the nucleus ejects a beta particle (electron).
Alpha decay is when the nucleus ejects an alpha particle (helium nucleus).
Electron capture is when the nucleus caputres an electron from the inner most shell. This process converts a proton to a neutron.
Finally, gamma decay is when an excited nucleus emits gamma rays. Gamma rays have no mass or charge.
Positron emission is when the nucleus ejects a positron, or positive equivalent of an electron. It is also known as
Beta decay is when the nucleus ejects a beta particle (electron).
Alpha decay is when the nucleus ejects an alpha particle (helium nucleus).
Electron capture is when the nucleus caputres an electron from the inner most shell. This process converts a proton to a neutron.
Finally, gamma decay is when an excited nucleus emits gamma rays. Gamma rays have no mass or charge.
← Didn't Know|Knew It →
Which of the following best describes the missing component in the reaction above?
Which of the following best describes the missing component in the reaction above?
Tap to reveal answer
This is an example of beta decay because the atomic number increases (from 6 to 7). This means a neutron has decayed into a proton, which occurs by emitting an electron, 
.
This is an example of beta decay because the atomic number increases (from 6 to 7). This means a neutron has decayed into a proton, which occurs by emitting an electron,
← Didn't Know|Knew It →
Thorium, 
, emits an alpha particle as it decays. Which of the following nuclei emerges from the decay?
Thorium,
Tap to reveal answer
In alpha decay a helium nucleus, 
, is emitted. Since the total number of nucleons must be conserved, the atomic number of the parent nucleus must decrease by two, and the mass number must decrease by four. Here, the new atomic number is 90 - 2 = 88, and new mass number is 234 - 4 = 230.
In alpha decay a helium nucleus,
← Didn't Know|Knew It →
If gold, 
, emits a beta particle, what will be the resulting product?
If gold,
Tap to reveal answer
When a nucleus ejects a beta particle, the element is undergoing beta decay. The ejection of a beta particle is equivalent to the ejection of an electron. When gold ejects an electron, 
, the product will be 
.
When a nucleus ejects a beta particle, the element is undergoing beta decay. The ejection of a beta particle is equivalent to the ejection of an electron. When gold ejects an electron,
← Didn't Know|Knew It →
If an atom of potassium undergoes a positron emission, what will be the daughter nucleus?
If an atom of potassium undergoes a positron emission, what will be the daughter nucleus?
Tap to reveal answer
An emission of a positron is also known to be 
decay. A positron emission can be viewed as a positron being ejected; therefore, when potassium undergoes a positron emission, the daughter nucleus will be argon (Ar) with the weight of 39.
To understand how the daughter nucleus was determined, create a positron emission reaction with potassium.
An emission of a positron is also known to be
To understand how the daughter nucleus was determined, create a positron emission reaction with potassium.
← Didn't Know|Knew It →
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
Nuclear reactions, such as the one described above with uranium, emit energy in the form of radiation. A scientist is considering three different forms of radiation to generate power. Which of the following types of radiation is highest in energy?
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
Nuclear reactions, such as the one described above with uranium, emit energy in the form of radiation. A scientist is considering three different forms of radiation to generate power. Which of the following types of radiation is highest in energy?
Tap to reveal answer
Gamma radiation is a highly energetic form of radiation, and is the type of radiation emitted when antimatter and matter annhilate each other upon contact.
Gamma radiation is a highly energetic form of radiation, and is the type of radiation emitted when antimatter and matter annhilate each other upon contact.
← Didn't Know|Knew It →
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
Xe-135 has a half life of around 9.2 hours. A reaction generated 70g of Xe-135, as measured by a scientist on a Friday afternoon. If he returned 46 hours later to study the sample, how much would remain?
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
Xe-135 has a half life of around 9.2 hours. A reaction generated 70g of Xe-135, as measured by a scientist on a Friday afternoon. If he returned 46 hours later to study the sample, how much would remain?
Tap to reveal answer
The scientist allowed the substance to sit for a duration that was equal to five of its half life. The original sample decayed from 70g, to 35g, to 17.5g, to 8.75g, to 4.35g, to ~2 g.
n is equal to the number of half lives that have passed. For us, n is equal to 5.
The scientist allowed the substance to sit for a duration that was equal to five of its half life. The original sample decayed from 70g, to 35g, to 17.5g, to 8.75g, to 4.35g, to ~2 g.
n is equal to the number of half lives that have passed. For us, n is equal to 5.
← Didn't Know|Knew It →
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist is studying a nuclear reaction similar to the one in the passage. He finds that the atomic mass of the reactant does not change, but its atomic number decreases by one. This type of nuclear reaction is best described as .
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist is studying a nuclear reaction similar to the one in the passage. He finds that the atomic mass of the reactant does not change, but its atomic number decreases by one. This type of nuclear reaction is best described as .
Tap to reveal answer
If the atomic number decreases by one, but the atomic mass is unchanged, the reactant must be converting one proton to a neutron. The resulting byproduct is a positron.
Notice that the positron on the right is released upon the rectant's conversion. This type of emission is known as positron emission.
If the atomic number decreases by one, but the atomic mass is unchanged, the reactant must be converting one proton to a neutron. The resulting byproduct is a positron.
Notice that the positron on the right is released upon the rectant's conversion. This type of emission is known as positron emission.
← Didn't Know|Knew It →
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist is studying a nuclear reaction similar to the one described in the passage. He realizes that the product atom has a mass number four less than the reactant, and an atomic number two less than the reactant. What is true of this type of radiation?
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist is studying a nuclear reaction similar to the one described in the passage. He realizes that the product atom has a mass number four less than the reactant, and an atomic number two less than the reactant. What is true of this type of radiation?
Tap to reveal answer
This is an example of alpha radiation, which is the emission of a helium nucleus, 
, thus explaining the loss of two protons and four mass units from the original species. Because this is a nucleus, it can interact with other atoms in the environment to generate ionic species. This is in contrast to non-ionizing radiation, such as infrared or radio waves.
This is an example of alpha radiation, which is the emission of a helium nucleus,
← Didn't Know|Knew It →
Which of the following choices incorrectly represents a radioactive decay process?
Which of the following choices incorrectly represents a radioactive decay process?
Tap to reveal answer
In general, there are three types of radioactive decay.
Alpha decay: An atomic nucleus emits a helium nucleus, composed of two protons and two neutrons. The net result is mass reduction of four (from the two neutrons and two protons) and an atomic number reduction of two (from the loss of two protons).
Beta decay: An atomic nucleus emits an electron, while a neutron splits into a proton, an electron, and anti-electron neutrino. The net result is an increase in atomic number (due to the added proton). Note, the atomic mass remains constant because although a neutron is lost, a proton is formed.
Possitron emmision: An atomic nucleus emits an anti-electron neutrino and electron, after a proton splits into a neutron. The net result is an decrease in atomic number (due to the tranformed proton). Note, the atomic mass remains constant because although a proton is lost, a neutron is formed.
Gamma Decay: The energy level of atomic nucleus drops, without losing protons or neutrons.
Each one of these decay processes are reflected individually in the answer choices, other than the decay process of 
. No such decay process emitting hydrogen atoms exists.
In general, there are three types of radioactive decay.
Alpha decay: An atomic nucleus emits a helium nucleus, composed of two protons and two neutrons. The net result is mass reduction of four (from the two neutrons and two protons) and an atomic number reduction of two (from the loss of two protons).
Beta decay: An atomic nucleus emits an electron, while a neutron splits into a proton, an electron, and anti-electron neutrino. The net result is an increase in atomic number (due to the added proton). Note, the atomic mass remains constant because although a neutron is lost, a proton is formed.
Possitron emmision: An atomic nucleus emits an anti-electron neutrino and electron, after a proton splits into a neutron. The net result is an decrease in atomic number (due to the tranformed proton). Note, the atomic mass remains constant because although a proton is lost, a neutron is formed.
Gamma Decay: The energy level of atomic nucleus drops, without losing protons or neutrons.
Each one of these decay processes are reflected individually in the answer choices, other than the decay process of
← Didn't Know|Knew It →
Which of the following types of radioactive decay alters the mass number?
Which of the following types of radioactive decay alters the mass number?
Tap to reveal answer
The mass number is the total number of nucleons (protons and neutrons) in an atom's nucleus. An atom that undergoes alpha decay will lose a helium nucleus. This decreases its mass number by four. All other forms of radioactive decay listed alter the atomic number of the atom, but not the mass number.
Beta emission involves the conversion of a neutron to a proton and an electron, but only expels the electron.
Electron capture involves the conversion of a proton and an electron into a neutron.
Positron emission involves the conversion of a proton to a neutron and a "positron," or positively charged electron.
The mass number is the total number of nucleons (protons and neutrons) in an atom's nucleus. An atom that undergoes alpha decay will lose a helium nucleus. This decreases its mass number by four. All other forms of radioactive decay listed alter the atomic number of the atom, but not the mass number.
Beta emission involves the conversion of a neutron to a proton and an electron, but only expels the electron.
Electron capture involves the conversion of a proton and an electron into a neutron.
Positron emission involves the conversion of a proton to a neutron and a "positron," or positively charged electron.
← Didn't Know|Knew It →
What is the daughter particle produced from 
-decay, followed by a single round of 
-decay, of 
?
What is the daughter particle produced from
Tap to reveal answer
Start with the parent particle, 
. Alpha decay will result in the loss of a helium nucleus: two protons and two neutrons.
Remember that a change in proton number must be associated with a change in elemental identity, changing gadolinium to samarium.
Next, the particle will undergo beta-decay. In this process, a neutron is converted to a proton and an electron. The result is no net change in mass, but an increase in proton number and the release of an electron.
The final result is a europium atom.
Start with the parent particle,
Remember that a change in proton number must be associated with a change in elemental identity, changing gadolinium to samarium.
Next, the particle will undergo beta-decay. In this process, a neutron is converted to a proton and an electron. The result is no net change in mass, but an increase in proton number and the release of an electron.
The final result is a europium atom.
← Didn't Know|Knew It →
An isotope of uranium initially contains 92 protons and 146 neutrons. This isotope then undergoes two alpha decays, one beta (
) particle decay, and two gamma decays. How many neutrons does the resulting nucleus contain?
An isotope of uranium initially contains 92 protons and 146 neutrons. This isotope then undergoes two alpha decays, one beta (
Tap to reveal answer
To solve this question, you must be familiar with each type of radioactive decay.
Alpha decay emits two protons and two neutrons: 
.
Beta particle decay emits an electron, which has been converted from a neutron: 
.
Gamma decay is purely electromagnetic, with no attached particles: 
.
We start with uranium: 
.
The number of neutrons will be equal to the total mass number, minus the number of protons.
There will be 141 neutrons in the final product nucleus.
To solve this question, you must be familiar with each type of radioactive decay.
Alpha decay emits two protons and two neutrons:
Beta particle decay emits an electron, which has been converted from a neutron:
Gamma decay is purely electromagnetic, with no attached particles:
We start with uranium:
The number of neutrons will be equal to the total mass number, minus the number of protons.
There will be 141 neutrons in the final product nucleus.
← Didn't Know|Knew It →
What is the decay constant of krypton-96, if half of a sample decays to rubidium-96 in 
?
What is the decay constant of krypton-96, if half of a sample decays to rubidium-96 in
Tap to reveal answer
The general equation for exponential decay is:
represents the initial amount of the compound, 
is the decay constant, and 
is the time.
If half of the initial amount of krypton has decayed after 
, we can set up the equation as a proportion:
To get the variable out from the exponent, take the natural log of both sides.
The general equation for exponential decay is:
If half of the initial amount of krypton has decayed after
To get the variable out from the exponent, take the natural log of both sides.
← Didn't Know|Knew It →
The activity of a radioactive element is 
. After 
, the activity is 
. What is the half-life of this element?
The activity of a radioactive element is
Tap to reveal answer
Radioactive elements spontaneously release particles. The half life is determined by the amount of time it takes half of a sample to release particles, thereby decreasing in mass and radioactive activity.
The formula for radioactive decay is:
We can solve for the half life by using the formula. We are given the initial and final activity values and the time period. Use these to solve for the half life.
Radioactive elements spontaneously release particles. The half life is determined by the amount of time it takes half of a sample to release particles, thereby decreasing in mass and radioactive activity.
The formula for radioactive decay is:
We can solve for the half life by using the formula. We are given the initial and final activity values and the time period. Use these to solve for the half life.
← Didn't Know|Knew It →
A sample of radioactive material decays from 64 atoms to 4 atoms in 6 hours. What is the half-life of this substance?
A sample of radioactive material decays from 64 atoms to 4 atoms in 6 hours. What is the half-life of this substance?
Tap to reveal answer
The half-life is the time it takes to reduce a sample by one-half of the original quantity. The substance would have to go through four half-life cycles to go from 64 atoms to 4 atoms.
If the total time for four cycles is 6 hours, then the half life is:
The half-life is the time it takes to reduce a sample by one-half of the original quantity. The substance would have to go through four half-life cycles to go from 64 atoms to 4 atoms.
If the total time for four cycles is 6 hours, then the half life is:
← Didn't Know|Knew It →
Which of the following types of radioactive decay alters the mass number?
Which of the following types of radioactive decay alters the mass number?
Tap to reveal answer
The mass number is the total number of nucleons (protons and neutrons) in an atom's nucleus. An atom that undergoes alpha decay will lose a helium nucleus. This decreases its mass number by four. All other forms of radioactive decay listed alter the atomic number of the atom, but not the mass number.
Beta emission involves the conversion of a neutron to a proton and an electron, but only expels the electron.
Electron capture involves the conversion of a proton and an electron into a neutron.
Positron emission involves the conversion of a proton to a neutron and a "positron," or positively charged electron.
The mass number is the total number of nucleons (protons and neutrons) in an atom's nucleus. An atom that undergoes alpha decay will lose a helium nucleus. This decreases its mass number by four. All other forms of radioactive decay listed alter the atomic number of the atom, but not the mass number.
Beta emission involves the conversion of a neutron to a proton and an electron, but only expels the electron.
Electron capture involves the conversion of a proton and an electron into a neutron.
Positron emission involves the conversion of a proton to a neutron and a "positron," or positively charged electron.
← Didn't Know|Knew It →