Most of the energy is converted into heat in the anode (which is cooled with water), and a small part is converted into radiation - X-rays. The first was called polonium (after Marie's native Poland), and the second was called radium (which is "that which radiates").
The Curie Family
Marie won the Chemistry Prize in 1911, and finally their daughter Irene won the Chemistry Prize in 1935 with her husband Frederic Joliot.
The Nobel Prize in Physics 1903
Nobel Prize in Chemistry 1911
The Nobel Prize in Chemistry 1935
Chapter 2
Radioactive Elements
The Nature of Radiation
Evidence for the three types of radiation comes from experiments in which the radiation from radioactive compounds was passed through magnetic and/or electric fields.
Some details on the nature of the radiation from radioactive sources
Alpha-radiation
The color of the emitted light confirmed that the glass tube was filled with helium. It was Ernest Rutherford (considered the father of nuclear physics) who was finally able to conclude that the α-particle was the nucleus of the helium atom.
Beta-radiation
Almost all sources of α particles are found among the heavy elements and most of them are natural. Only the energy of the β particle varies from zero to a maximum value - equal to the constant.
The average β -particle energy : rule of thumb
Proton changes into a neutron
Electron capture
Positron decay
What is an isotope ?
These processes take place continuously in the atmosphere and small amounts are always present. However, during the years of nuclear bomb testing in the atmosphere, the level of neutrons increased with the result that more tritium and C-14 were formed.
The Radioactive Series
A series of unstable atoms where one atom changes into another is called a radioactive family or simply a radioactive series. When one half of the atoms has decayed, the source has gone through a so-called “half-life”.
The Energy of the Radiation
All these atoms will sooner or later emit radiation, but these emissions do not occur simultaneously. The intensity of the source depends on the number of atoms disintegrating per second (i.e. the number of becquerels).
Decay scheme
How is a radioactive source described?
The last example would be the potassium isotope decay scheme K-40 – mainly because it is different from the other examples. Thus, in 89.3 % the decay is by ordinary β-decay, with the emission of an electron with a maximum energy of 1.3 MeV.
How radiation is absorbed in matter
This decay mode also includes some characteristic X-rays – because one of the orbital electrons is captured by the nucleus, leaving a hole that is filled with other electrons. M+ is a positively charged molecule (positive ion) and e– is an electron that was knocked out of the molecule.
Ionization
Excitation
The energy that is allocated per length unit of the track, is called "Linear Energy Transfer" (abbreviated LET). The range of almost all α-particles from radioactive sources is shorter, as the initial energy of the α-particle is below 10 MeV.
Absorption mechanisms for the different types of radiation Alpha-radiation
The goal is to maximize damage to the tumor while minimizing damage to healthy tissue. As a rule of thumb, one can say that a β-particle with an energy of 1 MeV will have a range in water or soft tissue of 0.5 cm.
Gamma-radiation
If these particles hit the skin, the penetration into the body will be less than 1 mm.
Compton scattering
During the war, Compton, together with Vannevar Bush and Ernest Lawrence, started the Manhattan Project with the aim of making an atomic bomb. In December 1942, a team of Met Lab scientists led by Enrico Fermi in Chicago achieved a sustained chain reaction in the world's first nuclear reactor.
The Nobel Prize in Physics 1927
Pair production
The Penetration of Radiation
Summing up
Radioactive Decay Laws
Half-life
The Physical Half-life
Definition
The Laws of Radioactive Decay
Biological Half-life
If tp is large compared to tb, the effective half-life is approximately the same as tb (see example below). The biological half-life is quite uncertain compared to the exact value of the physical half-life.
Radio-ecological Half-life
Cesium is eliminated from the body quite quickly and the biological half-life for sheep is 2-3 weeks. Some other radioactive species, such as radium and strontium, are bone scavengers and have quite long biological half-lives.
C-14 used as a biological clock
This is shorter than the value we use today - and is known as Libby's "half-life". An important requirement was that the C-14 content at the point of death be constant.
Artificial Radioactive Isotopes
The Discovery
They announced this discovery at the Academy of Sciences in January 1934 - and received the Nobel Prize a year later. It may be mentioned that Marie Curie died in July 1934 and thus was able to follow this exciting research almost to the third Nobel Prize in the family.
Radioactive isotopes are made!
Noble prize in physics 1938
Enrico Fermi
Fission
A short history
She and Otto Hahn had many discussions in the summer of 1938 – when the political situation in Germany became increasingly difficult for Lise Meitner. This research resulted in the conclusion that uranium can split into two large fragments when bombarded with neutrons (see illustration below).
Isotopes formed by fission
Meitner and Frisch published their theoretical calculations in the British Journal Nature, and Bohr let the news break at a conference in the United States in January 1939.
Nobel prize in chemistry 1944
Fission products
There are a large number of fission products, and some of the most important are listed in the table above.
Transuranic elements
Activation products
Plutonium
Activation Analysis
Women in nuclear chemistry
The activity of a radioactive source
Cork containers are used for the vaginal sources and a cylindrical tube for the uterine sources. In some cases, the needles were melted with radium to form solid paraffin and placed directly on the patient's skin.
An example of brachytherapy
Intensity of radioactive sources
Some examples
An example of teletherapy
This drawing from 1931 shows the treatment of cervical cancer using small needles containing radium. The treatment time was quite long for the patients, as they could not move from their position during the treatment.
Smoke detectors
For treatment, the source was placed in the position of exposure - approximately 10 cm from the skin.
Specific Activity
Radiation Dose
This unit was quite uncertain as the redness of the skin varied from person to person. The smallest UV dose that results in reddening of the skin is called MED, which is short for minimum erythema dose.
Dose Units and Their History
Over the 100 years of ionizing radiation treatment, several different dose units have been used. To calculate the radiation dose (in Gy) from an exposure of 1 R depends on the x- or g-radiation energy and the composition of the irradiated material.
Equivalent Dose
The biological effect depends on the LET of the radiation, i.e. the distribution of the absorbed energy. The dose unit sievert (Sv) is introduced to take into account the LET dependence Sv = wR.
Relative Biological Efficiency (RBE)
Even if the number of ionized molecules, and consequently the energy deposition, within the two circles is the same (the absorbed dose, measured in Gy is the same), the biological result can be different. This fact introduced a new dose unit sievert (Sv), named after the Swedish scientist Rolf M.
How to arrive at the w R factor?
RBE D
Since the equivalent dose includes the wR factor, it cannot be measured - and cannot be given in joules per kilogram. He served for several years as director of the Swedish National Institute for Radiation Protection.
Effective Equivalent Dose
In addition to the units already defined, there are some other terms used in radiation protection, such as "collective dose" and "committed equivalent dose". Radiation biologists are interested in the mechanisms that result in the observable macroscopic effects on biological systems, while radiation protection authorities are interested in guidelines for large groups of the population.
Collective dose
Based on the collective dose, risk analyzes were (unfortunately) carried out both by people from state protection authorities and journalists. Thus, he assumes that radiation would cause harmful effects even at the smallest dose.
The Measurement of Radiation
Introduction
How to count Bq and measure Gy ?
The simplest type of measurement is to observe the amount of radiation hitting the sensitive volume or counter detector. If the sensitive volume is covered with plates of different thickness and composition, information on the type of radiation can be obtained.
Detection methods and instruments
How little radioactivity can be observed ?
Film
Thermoluminescence-dosimeter (TLD)
Detectors Based on Ionization
The voltage is high enough that each electron attracted to the central electrode can form a cascade of new ions. The requirement that the radiation must reach the sensitive gas volume can be difficult for α-particles.
The Scintillation Counter
This results in a pulse that is detected by a counting system and can also be sent to a speaker that produces an audible click.
Semiconductor Counters
The Energy of the Radiation – Isotope Identification
The consequences of the accident in Chernobyl in April 1986 were observed in several places around the world. Such methods made it possible to identify the isotopes present in the fallout from nuclear tests in the 1960s.
Dose Measurements
In order to use radiation for the treatment of cancer, it is important to have knowledge of these depth dose curves. The goal is to deliver a high lethal dose to the tumor while minimizing the dose to surrounding healthy tissue.
Fricke dosimetry
For tumors positioned deeper than 6 cm in the tissue, x-rays with energy greater than 20 MeV should be used.
Free Radical Dosimetry
A radiation accident
What was the radiation dose?
With a calibration curve in hand, the tablets that were irradiated together with the victim could be determined, as shown in the figure below. A number of TLD dosimeters were used and it was determined that a dose of 38.5 Gy at the location of the nitroglycerol tablet box (in his pocket) provided an average whole body dose of 22.5 Gy.
ESR - dosimetry
UNSCEAR (United Nations Committee on the Effects of Atomic Radiation) collected information on the distribution of the radiation sources around the world and doses to the public. We are exposed to natural radiation from cradle to grave - and the accumulated lifetime dose depends on the four different radiation sources.
Cosmic Radiation
The nature of the cosmic radiation
The Earth's magnetic field partially reduces the intensity of cosmic rays that reach the top of the atmosphere. The high-energy particles that hit the atmosphere interact with atoms and molecules in the air.
Cosmic rays – a laboratory for high energy physics
We have tried to outline some of the difficulties in arriving at an average public dose due to cosmic rays. The majority of the world's population does not fly, but aircrew members average 500 hours in the air.
Other results and effects of the cosmic radiation
External Gamma-radiation from natural sources
This is because most of the radiation comes from the wall materials in the basement and the ground just outside. Examples of the radiation level inside different types of houses in the same area are given in the figure below.
Dose level inside homes
Internal Radioactivity (sources inside the body)
Muscular young people get a higher dose than older people, and men get a higher dose than women.
A simple calculation of the K-40 dose
Body concentrations were calculated based on radioisotope concentrations in foods and consumption for infants, children and adults. In the following, we will try to give you some information about the radon families - physical aspects, measurements in residences and estimates of annual doses for the population.
The Radon Family – physical aspects
Radon
Depending on the radiation dose, it can be understood that the most important a-particles are from the daughters of radon (i.e. isotopes of polonium) with energies from 5.49 MeV to 8.78 MeV. For entry into the atmosphere, radon concentrations in the soil within a few meters from the surface are important.
Radon measurements around the world
Radon measurements are carried out in all countries worldwide, and UNSCEAR presents tables of the values. In the table below we have quoted the values for some selected countries – the values may change when more measurements are carried out.
Radon Doses
Only a small fraction of radon atoms decays within the respiratory system, and most of the dose comes from the inhalation of short-lived girls. Furthermore, no estimates have been made to account for the effect of damaged cilia in the bronchi due to smoking - unless this would increase the effective dose.
Radon and lung cancer
If the damage is not repaired or if the cell is not killed by apoptosis - there is a possibility for. There have been few attempts to investigate the relationship between radon levels in homes and the occurrence of lung cancer.
Summary
Other data from Finland have been presented which show no correlation between the incidence of lung cancer and radon in Finnish homes. All the Finnish results can be explained by smoking – and the changes in smoking habits.
Nuclear Weapons – Reactor Accidents and Pollution
Reactors and Nuclear Bombs
The fission reactor
The type of waste causing the problems consists of long-lived radioisotopes and comes from used fuel that is not reprocessed or from components that are separated during reprocessing. The waste can be in liquid or vitrified form and the activity is high enough to produce heat.
The energy involved in fission and fusion
The size of the critical mass depends on shape, density and even the objects surrounding the nuclear fuel. During the war, the "Manhatten Project" included the most skilled physicists in the world with the goal of constructing a fission bomb.
Some of the details for the two bombs in Japan in 1945
The first man-made fusion explosion occurred in November 1952 at Enewetak Atoll in the Pacific. In the Soviet Union, Andrei Sakharov developed the hydrogen bomb – and the first one was tested in November 1955.
The men behind the projects leading to the atomic bombs
Scientists such as Edvard Teller worked for the development of fusion bombs with much higher power. The first wave of radioactive products took 4 days to travel the distance from Novaya Zemlja to Oslo – 2000 km.
Nuclear bomb tests
March 1954
October 1961
August 1945
November 195216. July 1945
Nuclear weapon tests sites
A particular US test – Castle Bravo
Due to the extreme temperature of a nuclear explosion, the radioactive material is finely distributed in the atmosphere. This part of the radioactive release will gradually fall out, the average time in the atmosphere is about a month.
Carbon-14 (C-14), although not a direct product of fission, is formed in the atmosphere as an indirect product. The fission process releases neutrons that interact with nitrogen in the atmosphere and, under the right conditions, C-14 is formed as an activation product.
The "Tzar Bomba"
Fallout
Measurements in Oslo
The measurements presented here serve as an example of airborne radioactivity in combination with nuclear tests in the atmosphere. As can be seen, the October 30 "Tzar Bomba" did not yield a peak value in early November – confirming that it was a fairly clean bomb.
Radioactivity in food and people
The content of Cs-137 in reindeer meat and in the people who own the animals. The activity is assumed to be evenly distributed in the body and is therefore given as Bq/kg.
Swedish groups 1959 – 2000
According to the figure on page 116, in 1965 the Lapps had a whole-body activity of about 600 Bq/kg for men and 300 for women, which corresponds to an equivalent dose of 1.5 mSv for men and 0.7 mSv for women that year. The bomb tests over a ten-year period showed that the dose to the Laplanders was about 8.8 mSv, while the dose to the Stockholm group was about 0.14 mSv.
How to perform simple calculations of radiation doses ?
The internal doses resulting from Cs-137 in the Lapps of northern Norway were among the highest for any group of people, and much higher than those for other members of the public. For comparison; the dose of the natural background was approximately 30 mSv during the same period.
Radiation Doses from Cs-137 in the body
Dose
Accumulated doses
Reactor accidents – Chernobyl
Kyshtym
Windscale
A number of estimates of thyroid doses have been made in connection with the Chernobyl accident. Let's start with the conclusion reached by UNSCEAR based on the 2000 report of the Chernobyl Forum.
The Chernobyl accident – April 1986
Although those exposed such as children and emergency workers are at increased risk of radiation-induced effects, the vast majority of the population does not have to live in fear of serious health consequences due to the radiation from the Chernobyl accident. The safety systems had been turned off and improper, unstable operation of the reactor allowed an uncontrollable current surge, resulting in successive steam explosions that severely damaged the reactor building and completely destroyed the reactor.
Release of radioactivity
All the plutonium and most of the strontium fallout (Sr-89 and Sr-90) were confined to an area within 30 km of the reactor. In the table below we present some of the most important data on the release of isotopes.
Cs-137 fallout after Chernobyl
In the Nordic countries, more than 20 laboratories are involved in measurements of the fallout from Chernobyl. During the first days, Cs-137 and I-131 activity was observed in the air as well as deposits on the ground.
Plutonium pollution Strontium pollution
The dose rates on the roof and in the chambers of the reactor block reached hundreds of gray values per hour. It is reasonable to assume that most workers were well aware of the radiation.
Doses and health effects
Emergency workers
Failure of the bone marrow is the cause of death for whole body doses in the range of 3 to 10 Gy. A total of 13 allogeneic bone marrow transplants and six embryonic liver cell transplants were performed.
Recovery operation workers
The average effective dose of external gamma radiation for recovery operations personnel (approximately 200,000) over the years was approximately 100 mSv, with individual effective doses ranging from less than 10 mSv to more than 500 mSv. Some of the recovery staff used stable iodine prophylaxis, but this was not mandatory and was not suggested to everyone.
Biological dosimetry
Evacuated groups
This level was not too alarming, but they considered the situation to be serious. They considered the possibility that the burning reactor core could melt the concrete floor and fall into basements, below which they can be filled with water.
Dose level and evacuation
In the case of the evacuees from the territory of Belarus, the estimated average dose was 31 mSv. Average effective doses from external radiation received during the first 10 years after the accident are estimated to vary from 5 mSv in urban areas of the Russian Federation to 11 mSv in rural Ukraine.
Another scenario with I-131 and thyroid dose
Due to the cases of thyroid cancer observed in children exposed to the Chernobyl accident, it was of great importance to estimate thyroid doses. The main route of exposure for the thyroid dose was the route from pasture to cow's milk, with a secondary component via inhalation.
Comment on Cs-137 doses
Doses to people in Scandinavia
Considerations with regard to max-values in food products
Thyroid cancer after Chernobyl
Chernobyl – Summery
- The Chernobyl accident was the largest and most severe reactor accident ever. The accident
- An increase of childhood thyroid cancer has been observed in the most contaminated areas in
- There is no evidence of other radiation-in-
- The most severe effect of the Chernobyl reactor accident is the psychological effects and mental disorders. It is a fact that a large amount of Post-Traumatic Stress Disorders (PTSD) have appeared
- One important factor to the psychological effects was the evacuation of large groups of people. It would have been wise to evacuate those near the reactor (Pripyat) – but they should have been brought
Radiation used for diagnostic purposes
History of x-ray pictures
Nikola Tesla and his pictures – shadowgraphs
Some of the highlights for x-ray diagnostic
He succeeded in showing that a narrow catheter could be advanced from a vein in the arm into the right atrium of the heart for a distance of almost two-thirds of a meter. In connection with this "breakthrough" in medical imaging, we must mention the predecessor of the technique called "planography".
The physical basis for an x-ray picture
The x-ray source
When high-energy electrons collide at the "anticathode" - a small part of the energy is converted into radiation. This means that most of the energy is dissipated as heat, and therefore the anode must be cooled.
Absorption and scattering in the body
Many technological improvements have been made to the X-ray source – probably William Coolidge's most important – resulting in stronger (more brilliant) and stable sources. We are not going to describe all technological developments regarding the control of exposure time and equipment for the different types of examinations.
Conclusion
The detector system
The X-ray image was created when the radiation was absorbed in the film emulsion consisting of silver halides (AgBr as well as AgCl and AgI). We do not intend to go through the technical details of strengthening screens – nor the many technological details of X-ray diagnostics.
Mammography
In the usual morning meeting, the doctors were often gathered in front of the "light box" to discuss the patients (see illustration). Energies lower than 30 kV are used for mammography – which is very effective at seeing details in soft tissue.
Implants
Tumor
Fluoroscopy
Shoe-fitting fluoroscopy
When you placed your feet in the opening, you stood on top of the X-ray tube. Measurements in recent years show that the doses to the feet were in the Gy range with an exposure of 20 seconds.
Digital imaging
CT – Computer tomography
Compton scattering
The X-ray tube and detector system are now on the same side of the object. The picture is formed by a pencil-shaped beam of rays that is sweeping the object. The technique is excellent for observing objects hidden in people or cargo in containers – objects that cannot be observed with conventional metal detectors.
The use of radioactive isotopes Nuclear medicine
Diagnosis
Isotopes for diagnosis
Some of the highlights in the history of nuclear medicine
Berkeley – the birthplace of nuclear medicine
University Of California
He used a radioactive isotope for the first time in the treatment of a human disease (leukemia). In recent years, a hybrid PET/MR has been developed and an expanded combination of images with PET/CT images, which enable a functional understanding of the underlying causes of disease in the body by combining functional and anatomical information in the same image. .
Some of the isotopes used in nuclear medicine
Isotopes used as tracers
Isotopes in radiation therapy
Isotopes for diagnostic purposes
In the figure above we have outlined how to make the isotope, as well as its physical properties. In the example shown (right), Tc-99m has been added to methylene diphosphonate, which is absorbed by the bone-forming cells (the osteoblasts).
SPECT
PET – Positron Emission Tomography
Para-positronium decays into two photons, both with energy 511 keV, while ortho-positronium decays into three photons (combined energy is 1.022 MeV). Ore published the work in two articles; "Annihilation of Positions in Gases" and "Ortho-Parapositronium Conversion".
Positron emitters
In connection with positron emission – PET – and positronium, it should be mentioned that the first theoretical work with positronium was carried out by Aadne Ore in 1949. Para-positronium has a lifetime of about 0.1 nanosecond, whereas ortho-positronium has a lifetime. in about 140 nanoseconds.
An example: PET in combination with CT
Magnetic resonance – MR (MRI)
The pioneers of magnetic resonance
The physics of magnetic resonance
The reonance phenomenon
However, in a magnetic field, the magnets will be oriented “with” or “against” the magnetic field. This means that we try to increase the magnetic field and for NMR it is normal to use fields of the order of 1.5 tesla (and even up to 7 tesla).
Nobel prize for MR – 2003
MR pictures and use in medicine
Diagnostic ultrasound
A short description of the technique
A new pulse is produced and sent in a slightly different direction (pulse repetition frequency is in the range 2 – 10 kHz). By changing the angle of the wavefront, a three-dimensional image can be built up over a large area.
Radiation doses in medicine
How to observe annual doses ?
Will this dose give deleterious effects ?
Second, no information exists about the doses received in the time since the last examination - ie. this is done to check the collapse of the lung - as shown in the illustration.
Radiation used for therapy – radiation therapy
The early history
Radium teletherapy
Radium brachytherapy
Fractionation therapy
1950s and high energy radiation therapy machines
Depthdose curves
High energy accelerators – Betatrons and Linear accelerators
Betatron
Linear accelerator
Guidelines for treatment
The radiation dose
Radiation quality and heavy ion therapy
In the photo on the right, Cornelius Tobias performs a strange experiment at the Berkeley cyclotron in 1970. Photo on the left shows the entrance to the Lawrence Radiation Laboratory with the 184 inch cyclotron in the background.
Radiation therapy for the future
He saw the same display of lights and then they identified the source of the lights witnessed by the astronauts as cosmic rays, a phenomenon that Tobias had predicted almost 20 years earlier.
Modern brachytherapy
