1. Introduction to Radioisotopes: Measurements and Biological Effects
UW Radiation Safety Training Manual
Chapter 1: 1-3,
Chapter 2: 21 – 30
We will begin this course by discussing the structure of the atom. We will continue discussing some basic concepts of radioactivity and finish with an overview of some of the biological effects of radiation exposure.
This manual is available on the website for the UW-Madison Environmental Health and Safety website.

2. Elements: a review WHAT IS AN ELEMENT?
A substance that can not be broken down into simpler substances by ordinary chemical processes
Protons
Electrons
Neutrons
To understand the basic concepts of radioactivity, we must begin with a review of atomic structure. First, remember that an element is a substance that can not be broken down into simpler substances by ordinary chemical processes. Elements are composed of three types of particles: protons, neutrons and electrons. Protons are positively charged particles, bearing a charge of (+1) and having a mass approximately equal to 1 atomic mass unit, or amu. Electrons are negatively charged particles , bearing a charge of (-1) and having a mass approximately equal to 1/1840 amu. Neutrons are uncharged particles with a mass of approximately equal to 1 amu. Protons and neutrons are particles with very similar mass.

3. The structure of the atom
Nucleus: dense central core formed by neutrons and protons. Electrons orbit in various energy levels.
atomic number (Z) = # protons in atom
The simplest unit that retains the identity of an element is an atom. As shown on this slide, atoms have a dense central core formed by neutrons and protons. This central core is called the nucleus. Surrounding the nucleus, electrons orbit in various energy levels. Each atom has the same number of protons as electrons giving an electrically neutral entity. The number of protons in an atom is called the atomic number. The atomic number is represented by a capital Z..

4. Isotopes
All atoms of an element have the same number of protons but can have different number of neutrons.
Mass number = # neutrons + # protons
All atoms of the same element share the same number of protons. However, atoms of an element may differ in the number of neutrons found in the nucleus. The mass number of an atom is the sum of all the protons and neutrons found in the atom. Therefore, all atoms of the same element share the same atomic number, but may differ in their mass numbers. Or, more simply, you may determine the identity of an element by its atomic number, but atoms may have the same mass number and be different elements.

5. Isotopes
Different nuclear configurations of an element are called isotopes
Isotopes, then, are different nuclear arrangements of the same element. Here you see two different atoms, both of hydrogen. Because both atoms contain a single proton, both atoms have an atomic number of 1, and are hydrogen. However, the two hydrogen atoms differ in mass number, with the lighter atom having a mass number of 1 and the heavier atom having a mass number of two. Now, atoms of an element may be different isotopes without being radioisotopes. We discuss the features that make a given isotope a radioisotope in the next slide.

6. Nuclear Disintegration
The process by which unstable isotopes try to stabilize by rearranging their nuclear configuration and releasing energy
Usually change in atomic number
Some forms of an elements exist in an energetically unstable state. These particular isotopes will undergo rearrangements until the atom has found a more stable state. The process by which unstable isotopes try to stabilize by rearranging their nuclear configuration and releasing energy is called nuclear disintegration. Often this will result in a change in atomic number, or a change in the number of protons present in the atom. Because the atomic number determines the elemental identity of the atom, nuclear disintegration can cause the atom to become a different element than it was originally.
Usually: produces change in atomic number
Neutrons disintegrates to proton + electron
Neutron gives up an electron to become a proton.

7. Radioactive Decay
The process of giving off energy during nuclear rearrangement
Radioisotopes
A part of the stabilization process is called radioactive decay. Radioactive decay is the process of giving off energy during nuclear rearrangement. Those isotopes capable of undergoing decay are called radioisotopes. All radioisotopes share the characteristic that they will undergo a change in nuclear configuration accompanied by a release in energy as the radioisotope seeks a more stable configuration. However, we will discuss three parameters that differ between radioisotopes. An understanding of these parameters is critical to gaining an appreciation of how to work safely in the laboratory with radioactive materials. The three associated parameters that we will consider are: the type of radiation energy emitted, the magnitude of the energy that is released during decay, and the rate of radioactive decay.

8. Types of Radiation:  particles
2 neutrons + 2 protons with total charge = +2
Very short range in air
Usually not a hazard to workers
Internally, dangerous
Let’s begin with a discussion of the types of energy that are released during radioactive decay. It is important to remember that not all radioisotopes emit the same types of energy. Additionally, you should be aware that some radioisotopes give off more than one form of energy. The first type of radiation particles that may be emitted are called alpha particles. Alpha particles are relatively large particles consisting of 2 neutrons and 2 protons. This makes alpha particles identical in configuration to the nucleus of the helium atom. Alpha particles carry an overall charge of +2.
Because alpha particles are so large, they have can only move a very short distance in air before their energy is spent. Alpha particles will travel less than 5 cm through the air before they have lost all of their energy. They can move even less readily through a structure such as skin. In fact, alpha particles will generally go only about mm in tissue before energy is lost. Because skin restricts alpha particle movement so easily, radioisotopes that give off alpha particles, called alpha emitters, are usually not a hazard to workers unless they get into the body. However, if the alpha particles do manage to enter the body, their large size means that they cause more damage than other types of radiation.

9. Types of Radiation:  particles
charge = -1
Energy is emitted at various levels
Low energy beta are only an internal hazard
High energy beta (like 32P) internal and external
A second type of energy that may be released during radioactive decay is the beta particle. Beta particles are essentially electrons, carrying a charge of -1. Like standard electrons, beta particles may hold a variety of different energy levels. Beta emitters can be generally classified as either low energy or high energy. Low energy beta particles do not have enough energy to penetrate far in tissue or to travel far in air. Therefore, low energy beta particles are primarily internal hazards. Therefore, they only pose a danger if they are inhaled, ingested, injected or the like.
Note also, as shown on this slide, that emission of beta particles results in an increase in the number of protons (shown in red) and therefore a change in both atomic number and elemental identity.
In contrast, high energy beta emitters do pose an external hazard. Beta particles are able to travel up to 20 feet in air and about 95%of beta particles carry sufficient energy to penetrate skin. Therefore, exposure to beta particles does present an external hazard which must be managed.

10. Types of Radiation:  and X-rays
Electromagnetic rays
A third type of energy that may be emitted during nuclear decay are electromagnetic rays, such as X-rays and gamma rays. These types of emissions are similar to each other in nature and are very highly penetrating, making them serious external hazards.
Note that the emission of gamma or X-rays does not change the elemental identity of the atom.

11. Half-life Each isotope has a distinct decay rate
Physical half-life = T1/2
the time required for a radioisotope to decrease to one-half its original amount
During radioactive decay, a radioisotope undergoes a nuclear reconfiguration, releases energy and is converted into a more stable isotope. Each radioisotope has its own distinct decay rate, which is expressed by its physical half-life. The physical half-life is defined as the time that is required for the amount of a particular radioisotope to decrease to one-half its original amount. Because radioisotopes decay, the amount of the original radioisotope in a stock vial is always decreasing at a rate unique to that radioisotope. The physical half-life is a parameter that must be carefully considered when assessing the risk associated with a radioisotope.

12. Half-life: the math NOT a linear process
Think of isotope with a half-life of 2 weeks:
Start with 1000 atoms:
Time (weeks elapsed): # atoms remaining:
2 500
4 250
6 125
The progress of the nuclear decay of a radioisotope is not linear as, shown. Consider a radioisotope with a half-life of two weeks. This means that, after each two-week interval, there will be exactly one-half as much of the radioisotope as at the beginning of the two-week interval. So, if we start with 1000 atoms of this radioactive isotope, then there will be exactly one-half as many atoms remaining once the length of time corresponding to the physical half-life has elapsed. Because for this radioisotope the physical half-life is two weeks, there will be 500 atoms of the original 1000 after two weeks. In the next interval, from two to four weeks, the 500 atoms will be reduced to 250 and so forth. Note that, after two half-lives have elapsed, only one-quarter of the original amount of radioisotope remains.

13. “Activity” The # of nuclear decays / second = activity
A measure of the amount of radioactivity is the activity of the sample. The activity is defined as the number of nuclear decays per second. Because, as mentioned previously, the amount of the original radioisotope changes over time, the activity of the sample will decrease over time. In the laboratory, it is important to know how radioactive a chemical stock vial is at any point in time, both to know what volume to use in an experiment, as well as to estimate the risks associated with that vial of radioactivity. An equation exists to calculate the activity of a stock vial, as long as you know how much activity you started with and the physical half-life of the radioisotope.

14. Activity units Curie = 3.7 X 10 10 dps Becquerel = 1 dps
While we mentioned that activity is defined as the number of nuclear decays per second, you should be aware that there are units of measurement associated with radioactivity. A common unit to express radioactivity is the Becquerel. 1 Becquerel is equal to 1 nuclear disintegration per second, or 1 dps. Another common unit used to express radioactivity is the Curie. 1 Curie is equal to 3.7 X 10^10 nuclear disintegrations per second.

15. Ionizing Radiation
Radiation with sufficient energy to directly or indirectly cause electron ejection
If radiation is simply defined as the energy released during the process of nuclear decay, it should be recognized that not all radiation is harmful. We are concerned with what is called ionizing radiation, which is radiation with sufficient energy to directly or indirectly cause another atom to release an electron. The reason that ionizing radiation is a concern is that this release electron can cause nuclear transformations of other atoms with which the radiation comes in contact.
another atom to release an electron.edu/ehs/images/ionizing%20radiation.jpg

16. Radiation safety goal
Deposit energy other places than in the worker’s tissues
Because the radioactive sources used in the laboratory release energy with ionizing potential, the goal of safety programs is to get the energy deposited other places than in the worker’s tissues to avoid the possibility of damaging biological molecules such as DNA in the worker’s cells. Effective radiation safety programs must consider both the range of the radiation and the energy released.

17. Types of Hazards: External
Radiation with energy to penetrate the outer layer of skin and deposit energy deep inside body tissues
3 major types
Gamma and X-rays
Neutrons
High energy beta particles
Radiation safety programs must be designed to minimize the effects of external radiation hazards. External hazards are those types of radiation that have sufficient energy to pass through the outer layers of the worker’s skin to deposit ionizing radiation deep within the worker’s body tissues. The types of radiation that contain sufficient energy to be external hazards are gamma and x-rays, neutrons and high energy beta particles. These types of radiation are called external hazards because they can exert their harmful effects from a position external to the worker’s body. For instance, a radioactive source emitting gamma rays or high energy beta particles can harm the worker while sitting on a lab bench next to the worker. The worker does not even need to be in contact with the source to be harmed.

18. Types of Hazards: Internal
Inhalation, ingestion, absorption through the skin
Metabolized and stored in body depending upon where element is needed
Radiation safety programs must also be designed to protect the worker from internal hazards. These types of radioactivity are hazardous only when the radioactive material enters the body by inhalation, ingestion, absorption through the skin. They will not harm the worker when they are located externally to the worker’s body. One of the major concerns with internal hazards is that many of these radioactive chemicals will be incorporated into biological molecules such as DNA and will remain in the body for long periods of time and continue to exert their harmful effects. The particular isotope is metabolized and stored in body depending upon where the element is needed. All radiation poses this hazard, but larger particles (like alpha particles) are the most dangerous.

19. Measuring radiation: Roentgen vs. Rad
Roentgen (refers to gamma and x-rays)
Rad: radiation absorbed dose
The amount of damage done by 1 rad of alpha particles is much greater than the amount of damage by 1 rad of high energy beta particles.
We mentioned that units of activity include the Becquerel and the Curie. But these units only express the number of nuclear decays per second. They do not differentiate between external and internal hazards, or between particularly hazardous radioisotopes and those that are less so. We do have several units that measure radiation that do differentiate between the different hazards posed by particular radioisotopes. The Roentgen refers to gamma and x-rays in particular. More generally, we are interested in the rad, or radiation absorbed dose. 1 rad is equal to the amount of a radioisotope that will deposit 100 ergs of energy per gram of matter. 1 Roentgen is approximately equal to 0.96 rad. The rad corrects for the different levels of energy that are associated with different types of ionizing radiation. However, it is also important to remember that the type of radiation also affects the damage that will be sustained by the worker. So, for instance, the amount of damage done by 1 rad of alpha particles is much greater than the amount of damage by 1 rad of high energy beta particles.

20. Dose equivalence Rem = unit of dose equivalence Rem = rad X Q
Q ranges from 1 to 20
The unit of measurement for radioactivity that reflects the biological harm that will be sustained by a laboratory worker is the Rem. The rem is a unit of dose equivalence. Therefore, radiation safety programs are designed to control the number of rem to which a worker is exposed during the course of his laboratory work. The rem is related to the radiation absorbed dose, or the rad by the equation:
Rem = rad X Q
Q is a quality factor which corrects for damaging effects of different types of radiation. Q ranges from 1 to 20, with gamma, x-rays and electrons having the lowest quality factor and alpha particles having a Q value of 20. When you consider the relationship between rads and rem, you can see that 1 rad of alpha particles exert 20 times the does of 1 rad of electrons.

21. Biological Effects of Radiation
Free radical formation
Can also directly interact with cellular components like DNA and damage them
So we have considered the magnitude of the biological effects of various forms of ionizing radiation. But what are the biological effects that are seen as a result of exposure to ionizing radiation? Ionizing radiation acts essentially as oxidizing or reducing agents through the process of free radical formation. The free radicals that are formed can inactivate cellular events or damage DNA. The formation of free radicals is an indirect way in which ionizing radiation can cause biological harm. However, alpha particles, for instance can directly damage DNA through contact between the DNA and the alpha particle. Radiation safety programs are especially concerned with radiation damage done to chromosomes because this form of damage results in mutations that are passed on during future cell divisions, so the damage is amplified beyond the original incident.

22. Possible outcomes of radiation-induced cell damage
repair
damaged cell repairs itself
cell death
mutations
change in DNA which can eventually lead to cancer
Fortunately for all us, exposure to radiation does not automatically mean that we will suffer heritable genetic defects. In fact, ionizing radiation, having interacted with DNA can result in one of three different consequences. Most commonly, the DNA repair mechanisms in our cells will fix the damage inflicted by the radiation before the DNA is replicated and passed on to daughter cells. Sometimes, the radiation damage will be severe enough that the cell will die. Again, in this case, the damage will not be passed on to future generations of cells. Occasionally, however, the ionizing radiation will result in a mutation in the DNA, and, sometimes, this mutation will be in a position in the chromosome that will result in uncontrolled cell proliferation, or cancer.

23. Cells most susceptible to radiation damage
Cells that are:
rapidly dividing
have many future divisions
undifferentiated
Not all cells are equally susceptible to the damage inflicted by ionizing radiation. Those cells that suffer the most acute damage are those that are
rapidly dividing, those that have many future divisions, and immature cells. Immature cells are also called undifferentiated and are cells that have not yet developed into specialized cells. Cells are most sensitive to the effects of ionizing radiation when they are reproducing. Those cells with a good supply of oxygen and blood are at particular risk. Muscle and nerve cells, however, are relatively insensitive to radiation-induced damage.

24. Biological Effects of Radiation
Somatic: Arise directly from radiation damage and only occur in irradiated person
Hereditary: Arise in reproductive cells so damage can be passed on to future generations
There are two categories of biological effects that can result from radiation exposure. The first category is somatic effects. Somatic effects are those that are the direct consequence of radiation exposure. Somatic effects affect only the individual who has been exposed to the radiation. In contrast, hereditary effects are those that arise in reproductive cells. Hereditary effects are passed on to offspring.

25. Symptoms of Radiation Exposure
Acute exposure
200 rad = more than most lifetime exposures
blood changes
nausea, vomiting, hair loss
diarrhea, dizziness, nervous disorders, hemorrhage
When we consider the individual who has been exposed to radiation, we can predict some of the biological effects that that individual will experience. For some symptoms of radiation exposure, the severity of symptoms will increase with radiation dose. Let us consider the effects observed following acute exposure, which we will define as a one-time exposure to 200 rad. This radiation absorbed dose is greater than the cumulative dose that most individuals will experience over the course of their entire lives. Immediate effects include blood changes, nausea, vomiting, hair loss, diarrhea, dizziness, nervous disorders, and hemorrhage. Higher exposures can lead to sterility and certain death. It is important to note that these levels of exposure are extremely rare and not the types of exposure associated with work in a radioisotopes laboratory. These exposures reflect the doses received in a severe nuclear accident.

26. Stochastic vs. Non-stochastic Effects
stochastic effect arises from injury to one or a few cells
all or none event
non-stochastic effects are somatic effects
increasing severity with increasing radiation dose
Workers in radioisotopes laboratories are more likely to be concerned with the differences between stochastic and non-stochastic effects. Stochastic effects arise from injury to one or a few cells and can be considered to be all or none events. Increased radiation dose increases the probability of stochastic effects occurring, but not the severity. Cancer is an example of a stochastic effect.
Non-stochastic effects are somatic effects, in which increasing severity of the effect is observed with increasing radiation dose. Examples of non-stochastic effects are radiation burns, skin reddening, and cataracts.
Although it can be scary to consider the biological effects that radioisotopes can induce, it is important to remember that a well-trained worker following a well-thought out radiation safety program can work safely with radioisotopes.