CHAPTER NINE: NUCLEAR RADIATION Flashcards
Most naturally occurring isotopes of elements up to atomic number ____ have stable nuclei, which means that __________.
19; the forces of attraction and repulsion between the protons and neutrons are balanced.
Elements with atomic numbers ____ and higher usually have one or more isotopes that have unstable nuclei, which means that ____________.
20; too many or too few protons compared to the number of newborns, which means the forces between protons and neutrons are unbalanced.
What is RADIATION?
An unstable nucleus is RADIOACTIVE, which means that it spontaneously emits small particles of energy called RADIATION, to become more stable.
Radiation may take the form of particles such as alpha and beta particles, or pure energy such as gamma rays.
What is a RADIOISOTOPE?
An isotope that emits radiation.
For most types of radiation, there is a change in the number of ________ in the nucleus, which means that an atom is __________.
protons
converted into an atom of a different element.
Elements with atomic numbers of ____ or higher are produced artificially in the nuclear laboratories and consist only of ________ __________.
93
radioactive isotopes
Remember that the MASS number is equal to the number of __________ and _________ in the nucleus, and the ATOMIC number is equal to the number of ________.
Radioactive isotopes are identified by writing the ________ number after the element’s name or symbol.
protons and neutrons
protons
mass number
Example: iodine-131 OR I-131
TYPES OF RADIATION:
What is an ALPHA PARTICLE? It has a mass number of _____, an atomic number of ___, and a charge of _____.
What is the SYMBOL for an alpha particle?
An ALPHA PARTICLE is identical to a helium (He) nucleus, which has 2 protons and 2 neutrons.
It has a mass number of 4, an atomic number of 2, and a charge of 2+.
The symbol for an alpha particle is the Greek letter alpha OR the symbol of a helium nucleus except that the 2+ charge is omitted.
TYPES OF RADIATION:
What is a BETA PARTICLE?
What is its MASS number?
What is the symbol for a beta particle?
How is a beta particle formed?
Another type of radiation occurs when a radioisotope emits a BETA PARTICLE.
A beta particle is a high-energy electron, with a charge of 1- and, because its mass is so much less than the mass of a proton, it has a mass number of 0.
It is represented by the Greek letter beta OR by the symbol for the electron (e) including the mass number and the charge.
A beta particle forms when a neutron in an unstable nucleus changes to a proton and an electron.
TYPES OF RADIATION:
What is a POSITRON?
What is the symbol for a positron?
How is a positron produced?
A POSITRON has a positive (1+) charge with a mass number of 0, which makes it similar to a beta particle.
A positron is represented by the Greek symbol beta and a +. See page 321 for how the symbols for a beta particle and a positron are written.
A positron is produced by an unstable nucleus when a proton is transformed into a neutron and a positron.
What is ANTIMATTER?
A positron is an example of ANTIMATTER, a term physicists use to describe a particle that is the exact opposite of another particle, in this case, an electron.
What are GAMMA RAYS?
What is the symbol for a gamma ray?
When an electron and a positron collide, their minute masses are completely converted to energy in the form of GAMMA RAYS.
Gamma rays are high-energy radiation, released when an unstable nucleus undergoes a rearrangement of its particles to give a more stable, lower energy nucleus.
Gamma rays are often emitted along with other types of radiation.
A gamma ray is written as the Greek letter gamma (y). They are energy only, so zeros are used to show that a gamma ray has no mass or charge. See page 322
Types of radiation- see Table 9.2
page 322
When working with radioactive isotopes, we must use proper radiation protection, or ________, to prevent exposure.
Shielding
What are the dangers of being exposed to ALPHA PARTICLES and how can you protect yourself?
Alpha particles, which have the greatest mass and highest charge of the radiation particles, travel only a few centimeters in the air before they collide with air molecules, acquire electrons, and become helium atoms.
External sources of protection are provided by a piece of paper, lab coats and the skin.
If ingested or inhaled, alpha particles can cause serious internal damage because of the large mass and high charge.
What are the dangers of being exposed to BETA PARTICLES and how can you protect yourself?
Beta particles have a very small mass and move much faster and farther than alpha particles, traveling as much as several meters through the air. They can pass through paper and penetrate a far as 4-5 mm into body tissue.
External exposure to beta particles can burn the surface of the skin, but the are stopped before they reach the internal organs.
Heavy clothing such a lab coats and gloves are needed to protect the skin from beta particles.
What are the dangers of being exposed to GAMMA RAYS and how can you protect yourself?
Gamma rays travel great distances through the air and pass through many materials, including body tissues. Because gamma rays can penetrate so deeply, exposure to these rays is extremely hazardous. Only very dense shielding, such as lead or concrete, will stop them.
When working with radioactive materials, wear protective clothing and gloves and stand behind a shield. Long tongs may be used to pick up vials of radioactive material, keeping them away from the hands and body. See page 323, Table 9.3 for a summary of properties of ionizing radiation and shielding required.
The greater the distance from the radioactive source, the _______ the intensity of radiation you receive.
By doubling your distance from the radiation source, the intensity of radiation ____ to ________.
lower
drops to 1/4 of its previous value
What is RADIOACTIVE DECAY?
How is this process written?
An arrow between the atomic symbols indicates that this is a ________ equation.
A nucleus spontaneously breaks down by emitting radiation.
This process can be written using the atomic symbols of the original radioactive nucleus, the new nucleus and the radiation emitted.
nuclear equation. See page 324 for the equation.
In a nuclear equation, the mass numbers and the atomic numbers must _________ so the number of protons and neutrons are _______________.
However, in a nuclear equation, there is often a change in the number of _______, which gives a different _______.
balance; equal on both sides
protons, element
What is ALPHA DECAY?
An unstable nucleus undergoes alpha decay by emitting an alpha particle.
Because an alpha particle consists of 2 protons and 2 neutrons, the mass number decreases by 4 and the atomic number decreases by 2.
What is BETA DECAY?
The formation of a beta particle is the result of the breakdown of a neutron into a proton and an electron (beta particle). Because the proton remains in the nucleus, the number of protons increases by one, while the number of neutrons decreases by one.
In a nuclear equation for beta decay, the mass number of the radioactive nucleus and the mass number of the ne nucleus are the same.
However, the atomic number of the new nucleus increases by one, indicating a change of one element into another.
What is a POSITRON EMISSION?
In a positron emission, a proton in an unstable nucleus is converted to a neutron and a positron. The neutron remains in the nucleus, but the positron is emitted from the nucleus.
In a nuclear equation for positron emission, the mass number of the radioactive nucleus and the mass number of the new nucleus are the same.
However, the atomic number of the new nucleus decreases by one, indicating a change of one element into another.
What is GAMMA EMISSION?
In radiology, one of the most commonly used gamma emitters is _______.
By emitting energy in the form of gamma rays, the unstable nucleus becomes ___ ____.
Pure gamma emitters are rare, although some gamma radiation accompanies most alpha and beta radiation.
technetium (Tc)- the unstable isotope decays quickly and it is written as the metastable (m) isotope: technetium-99m
more stable
The changes in the nucleus for alpha, beta, positron and gamma radiation- Figure 9.2
page 329
What is TRANSMUTATION?
Many radioisotopes are produced in small amounts by converting stable, nonradioactive isotopes into radioactive ones in a process called TRANSMUTATION.
A stable nucleus is bombarded by high-speed particles such as alpha particles, protons, neutrons and small nuclei. When one of these particles is absorbed, the nucleus becomes a radioactive isotope.
All elements that have an atomic number greater than ____ have been produced by ________.
how many of these elements occur naturally?
92; bombardment
none occur naturally
NOTE: see page 330 about writing an isotope produced by bombardment and producing radioactive isotopes
One of the most common instruments for detecting beta and gamma radiation is the _______ ________. Describe it.
Geiger counter
It consists of a metal tube filled with a gas such as argon. When radiation enters a window on the end of the tube, argon atoms form ions, which produce an electrical current.
Each burst of current is amplified to give a click and a reading on a meter.
See page 331 for equation
Radiation is measured in several different ways. We can measure the _______ of a radioactive sample or determine the impact of radiation on ________ _________.
activity
biological tissue
How do we measure the ACTIVITY of a radioactive sample?
What was the original unit of activity?
What is the SI unit of radiation activity?
It is measured in terms of the number of nuclear disintegrations per second.
Original- the CURIE (Ci)- defined as the number of disintegrations that occur in one second for 1 gram of radium, which is equal to 3.7 x 10^10 disintegrations per second.
SI- the BECQUEREL (Bq), which is one disintegration per second.
What is the RAD?
RADIATION ABSORBED DOSE- a unit that measures the amount of radiation absorbed by a gram of material such as body tissue.
What is the SI unit for ABSORBED DOSE?
the GRAY (Gy), which is defined as the joules of energy absorbed by 1 kilogram of body tissue.
The gray is equal to 100 rad.
What is the REM?
RADIATION EQUIVALENT IN HUMANS
It measures the biological effects of different kinds of radiation.
How do we determine the EQUIVALENT DOSE or rem dose?
Often the measurement for an EQUIVALENT DOSE is in __________.
The SI unit is the _________, which is equal to ____ rem.
The absorbed dose (rad) is multiplied by a factor that adjusts for biological damage caused by a particular form of radiation.
For beta and gamma radiation, the factor is 1, so the biological damage in rems is the same as the absorbed radiation (rad).
For high-energy protons and neutrons, the factor is about 10.For alpha particles it is 20
Biological damage (rem)= absorbed dose (rad) x factor
The measurement for an EQUIVALENT DOSE is in MILLIREMS (mrem). The SI unit is the SIEVERT (Sv), with is equal to 100 rem.
See Table 9.4 on page 333.
What is a FILM BADGE?
People who work radiology labs wear film badges to determine their exposure to radiation. It contains a piece of photographic film in a container that is attached to clothing.
Periodically, the film badges are collected and developed to determine the level of exposure to radiation.
Exposure to Radiation:
Every day we are exposed to low levels of radiation from naturally occurring radioactive isotopes, cosmic radiation produced by the sun and manmade sources. This is called _________ radiation.
Background
Radiation Sickness:
Exposure to radiation less than ___ rem is usually not detected.
Whole body exposure of _____ rem produces a temporary decrease in the number of while blood cells.
If the exposure to radiation is great than ____ rem, a person may experience symptoms of radiation sickness, which are ______, _____, _______ and _______.
A whole body dosage greater than _____ rem can decrease the WBC to zero.
25
100
100; nausea, vomiting, fatigue, reduction in white-cell count
300
What is the LETHAL DOSE FOR ONE-HALF THE POPULATION (LD50)?
Radiation dosages of _____ rem or greater would be fatal to all humans within a few weeks.
Exposure to radiation of 500 rem is expected to cause death in 50% of the people receiving the dose.
600
What is the HALF-LIFE of a RADIOISOTOPE?
What is a DECAY CURVE?
The amount of time it takes for 1/2 a sample to decay.
A decay curve is a diagram that shows the decay of a radioactive isotope for each half-life.
See page 335 for the explanation and calculations and DECAY CURVE
Naturally occurring isotopes of the elements usually have _______ half-lives.
Many of the radioisotopes used in nuclear medicine have _______ half-lives
long
short
What are 2 medical applications using radioactivity?
- determining the condition of an organ in the body (scans)
2. treatment of disease
A common method of determining THYROID FUNCTION is the use of _______ _____ _____.
Radioactive iodine uptake
What is POSITRON EMISSION TOMOGRAPHY (PET)?
Positron emitters with short half-lives are used in this imaging method.
As positrons are emitted, they combine with electrons to produce gamma rays that are detected by computerized equipment to create a 3-dimensional image of the organ.
What is NUCLEAR FISSION?
Give an example using uranium-235
The total mass is slightly less than the mass of the starting materials because _______.
Bombarding an element with neutrons splits the atom and generates ATOMIC ENERGY.
For example, when uranium-235 absorbs a neutron, it breaks apart to form 2 smaller nuclei, several neutrons and a great amount of energy. See page 343 for the equation
…the missing mass has been converted into energy, consistent with the famous equation by Einstein E= mc^2
CHAIN REACTION:
Fission begins when ___________. The resulting nucleus is __________ and splits into smaller nuclei.
This fission process also releases several ______ and large amounts of ______ radiation and ______.
The neutrons emitted have high energies and bombard more nuclei and there is a rapid increase in the number of high-energy neutrons capable of splitting more atoms- this is call a CHAIN REACTION.
To sustain this, sufficient quantities of uranium-235 must be brought together to provide a ________ __________ in which almost all the neutrons immediately collide with more nuclei.
a neutron collides with the nucleus of a uranium atom; unstable
neutrons; gamma; energy
critical mass
What is NUCLEAR FUSION?
Is mass lost or gained?
This requires a temperature of _________ degrees Celsius to overcome the repulsion of the hydrogen nuclei and cause them to undergo fusion.
Fusion reactions occur continuously in the ______ and ________, providing us with heat and light.
Two small nuclei combine to form a larger nucleus. A tremendous amount of energy is released, even more than from nuclear fission.
Mass is lost.
100 000 000 degrees C
Sun and other stars