Teaching Resources - Nuclear Physics

Videos

1.  The Most Radioactive Places on Earth

 

 

 

Published on Dec 17, 2014 by Veritasium

Who on Earth is exposed to the most ionizing radiation?
[Check out Audible: http://bit.ly/AudibleVe]
A documentary for TV about how Uranium and radioactivity have shaped the modern world to be ll be broadcast in mid-2015, details to come. The film goes to the most radioactive places on Earth (and some places, which surprisingly aren't as radioactive as you'd think). Chernobyl and Fukushima were incredible to see as they present post-apocalyptic landscapes. It also visits nuclear power plants, research reactors, Marie Curie's institute, Einstein's apartment, nuclear medicine areas of hospitals, uranium mines, nuclear bomb sites, and interviewed numerous experts.

Notes about measuring radiation:
Sieverts are a measure of 'effective dose' - that means they measure the biological impact of the energy transferred to tissues from radiation.

On Nuclear Radiation Part 3: Effects of Different Radiation

This is a third part to a series of FAQs which I received from my friends and family after the Nuclear Accident in Japan Fukushima.  Note that most of the notes came from a set of lecture notes that I compiled 2 years ago.  The lecture notes were integrated from various sources which was used for lecturing Nuclear Physics for A-levels. 

(Picture from Reuters:  The No.3 nuclear reactor of the Fukushima Daiichi nuclear plant is seen burning, March 14, 2011. REUTERS/Digital Globe.)

Question:  Of the Types of Ionising Radiation, which is the most harmful?  How do they affect the human body?

This is a complex question, as each type of ionising radiation impacts the body differently. In general, the effect of ionizing radiation on the human body or any other living things depend on three things:

1. The type of ionizing radiation which was absorbed,
2. The number of cells affected, the number and
3. The amount and the rate at which ionizing radiation was absorbed.

  Let us look at the effect of each type of ionizing radiation

• Alpha-particles:

Even though alpha-particles have a short range in air and can be stopped by the skin or a sheet of paper, it will still pose a danger if it gets into the body through ingestion and inhalation.

Alpha particles are the largest of the radiation and carry a charge of (+2e) - hence possessing the greatest ionization power, the particles will deposit their energy over a smaller volume (possibly only a few cells) if they enter the body and cause more damage to these few cells.

Radon gas (one of the key sources of lung cancer in US) is an example of an isotope that radiates alpha particles during of its course of decay and hence, there has been suggestions for buildings to be tested for Radon gas.

•   Beta Particles:

Beta-particles have a longer range than alpha-particles, but ionise much less strongly. Therefore, they do around 1/20 th of the damage done by the same dose of alpha particles.  But with greater penetrating power, affect a greater number of cells.

•   Gamma Rays, X-rays :

Gamma and x-ray are pure energy (photons) and have no mass.  They are however very penetrating and can easily pass through the whole body, and hence will still interact with many atoms in the body as they pass through.  Both X-rays and gamma rays spread their energy over a large volume, which causes less damage per collision. Of course at very high levels of exposure, they can still cause a great deal of tissue damage. Furthermore, because of their penetrating ability, they can easily reach internal organs and bones which is why large doses can be used to damage cancer tissue.

Interaction of Radiation and Cells
So how do the radiation affect the cells and human body?
The effects of the radiation can be characterised as:

• Direct effects
• Indirect effects

Direct Effects
For direct effects, the radiation interacts with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell.

Such an interaction may affect the ability of the cell to reproduce and, thus, survive. If enough atoms are affected such that the chromosomes do not replicate properly, or if there is significant alteration in the information carried by the DNA molecule, then the cell may be destroyed by “direct” interference with its life-sustaining system.

Indirect Effects
However, the probability of the radiation interacting with the DNA molecule is very small since these critical components make up such a small part of the cell. The radiation has a higher probability interacting with the water that makes up most of the cell’s volume.

When radiation interacts with water, it may break the bonds that hold the water molecule together, producing fragments such as hydrogen (H) and hydroxyls (OH). These fragments may recombine or may interact with other fragments to form toxic substances, such as hydrogen peroxide (H2O2), which can contribute to the destruction of the cell.


In general, the following are possible effects of radiation on the cells:
1. Cells are undamaged.
Ionisation may form chemically active substances which in some cases alter the structure of the cells. These alterations may be the same as those changes that occur naturally in the cell and may have no negative effect.


2. Cells are damaged, but the damage is repaired and they continue to operate normally.
Some ionizing events produce substances not normally found in the cell. These can lead to a breakdown of the cell structure and its components. Cells can repair themselves if the damage is limited. Even damage to chromosomes is usually repaired.


3. Cells are damaged, repaired but is mutated.
When cells divide to reproduce, an exact copy of the cell's chromosomes are created for the new cell. If the DNA of the chromosome is damaged, the instructions that control the function of the cells and reproduction are also damaged.

If the cells reproduce instead of die, a new mutated cell may be produced. In many cancers, the instruction that turns off cell growth are somehow damaged causing cells to reproduce out of control, creating tumours.

Ionizing radiation, along with many other substances such as some chemicals, heavy metals and intense e.m. waves can damage cells in this manner.

Radio-Sensitivity of Cells:
Not all cells in the human body respond in the same way to radiation.  The most radiosensitive cells are those which :

*have a high division rate

*have a high metabolic rate

*are of a non-specialized type, and

*are well-nourished.

Examples of radio-sensitive cells :

*reproductive cells

*Blood forming tissues

* Epithidium of skin

*Epithidium of gastrointestinal tract.

This is why when people go on radiotherapy, their alocepia (hair loss) tends to occur as hair is a fast growing cell.  This also why young children/babies and foetuses carried by pregnant mothers are especially susceptible to radiation. This is because children/babies are growing rapidly, with more cells dividing and thus a greater opportunity for radiation to disrupt the process.

Related Links  and Previous Related Posts:

1)  On Nuclear Physics Part I :  What is Radiation?  Does a person continue to radiate radiation after he has been irradiated?

2) Can we therefore make the radioactive isotopes non-radioactive by chemical reactions etc.?

3)  Japan's Nuclear Concerns Explained by CNN

4)  Why do the Spent Fuel Rods Need to Be Cooled Down?  What happens If they are Not?  - External Blog :  Fukushima's Spent Fuel Rods Pose Great Dangers.

5) Scientific American Article : Radiation's Complications: Pinning Health Problems on a Nuclear Disaster Isn't So Easy

Japan's Nuclear Concerns Explained by CNN

A CNN Link that explains the concerns of Japan's Fukushima Nuclear Concerns.

On Nuclear Radiation_Part 2

This is a continuation from a previous blog on nuclear radiation.


I hear that Radioactivty is both a Spontaneous and Random Process, what do the two terms mean?  Is there a difference?  Can we therefore make the radioactive isotopes non-radioactive by chemical reactions etc.?

Yes, radioactivity is both a random and spontaneous process.  Let us explain what it first means to say that it is a "random" process and then talk about the "spontaneous part.

Random Process:

By random, we mean that for a sample of radioactive isotopes, we do not know at an instant of time which one will decay.  It also means that when we select a particular atom, we do not know when it will precisely decay.

What is however associated with this process is a probability of decay and that is manifested as what is known as half-life of the sample.

Beyond the scientific community, it is a common misconception that the half-life of a sample determines the time it takes for it to become non-radioactive.

This is not true, it is only the time taken for it to decay to half its initial activity.  (by layman terms that may be the amount of radiation emitted per unit time.)

In the case of nuclear waste from nuclear fission power plants, it becomes rather complicated, as the waste product consists of many radioactive isotopes, some ranging to short half lives ( e.g. Iodine-131 ~ 8days) to extremely long half lives ( Tc-99 ~ 220,000 years and I-129 ~ 17 million years).

There are problems in dealing with the shorter half lives radioactive isotopes and longer radioactive isotopes.  In general, the short-lived ones though having a short half live decays rapidly, also emits alot of radiation and that tends to generate alot of energy.  This is why in the case of the nuclear accident at Japan, though there are some spent (used fuel ) continuous cooling is needed to bring the temperature down.

For the case of the isotopes with long half-lives, the activity is smaller but the impact is for a longer period of time, with half lives of 220, 00 years and even million years, this means the radioactive substance will still be emitting radiation many, many years after we have gone.   Proper disposal and storage of these waste will therefore be needed as well.

Spontaneous Process:

Understanding the spontaneity part will also help understand why we cannot just destroy or hasten or slow down the radioactivity of the radioactive isotopes.  Radioactivity comes about because the isotopes are energetically unstable and they try to achieve stability by emitting radiation.  It is termed a spontaneous process, as its activity (decay) is unaffected by external pressures, temperatures or any chemical processes.  You need time to just let it decay and to come to a stable state.

This is why we also cannot just add chemicals, heat the spent fuel and to treat it to make it safe.  You need proper containment procedures to keep it away from possible risks of contamination.

Officials in protective gear check for signs of radiation on children who are from the evacuation area near the Fukushima Daini nuclear plant in Koriyama, March 13, 2011. Japanese Chief Cabinet Secretary Yukio Edano confirmed on Saturday there has been an explosion and radiation leakage at Tokyo Electric Power Co's (TEPCO) Fukushima Daiichi nuclear power plant. The biggest earthquake to hit Japan on record struck the northeast coast on Friday, triggering a 10-metre tsunami that swept away everything in its path, including houses, ships, cars and farm buildings on fire. (Kim Kyung-Hoon/REUTERS)

Other Relevant Links:

(1)  On Nuclear Physics Part I :  What is Radiation?  Does a person continue to radiate radiation after he has been irradiated?

On Nuclear Radiation_Part 1

The Japan's Friday Earthquake and Tsunami has caused Japan's nuclear reactors to malfunction and meltdown, many people may be wondering on the effects of radiation and what harm it may cause and what are the immediate and long term effects.

I was talking to my husband and a few friends and was surprised to find that they did not know what was radioactivity and the possible health effects (which left me quite frustrated, as I had gone through radiotherapy before and so was very sure that at least my husband should have known the risk that I was exposed to.)   Anyway, I took for granted that most people should know, so I was also quite shock when I heard some of questions asked. 

My husband remarked that this was because the biological effects was in the A-level syllabus and I had taught it and so I knew, but I should "enlighten" those who did not take Physics through my blog....anyway I will try my best and present the following as a FAQ in parts.  (so that it can be slowly published).

[I have to note that much of these were taken from a set of lecture notes I prepared for A-levels two years ago and takes references from many websites, so not all the work are my original work, though I consolidated most.]

(Picture Taken from stock.xchng at http://www.sxc.hu/.  H-Bomb by Sergey Lebedev.)

What is radiation?
The main danger from radiation is the damage it does to the cells in your body.


Most of this damage is due to ionization when the radiation passes, although if levels of radiation are high there can also be damage due to heating effects as your body absorbs the energy from the radiation.

Types of ionizing radiation includes :

• alpha particles  (Helium nucleus)
• beta particles (electrons and positrons)
• gamma rays
• X-rays, and
• neutrons

Alpha and Beta particles are further known as direct radiation as they transfer energy directly to their target materials.

Gamma rays, x-rays, as well as neutrons are known as indirect radiation, as they affect the cells in the body by transferring energy to neighbouring atoms. This causes the atoms to become excited and they can produce secondary electrons and photons that can continue to transfer the energy to nearby atoms.


So what are the harms associated with exposure to these radiation?  Does a person continue to radiate radiation after he has been irradiated?

To understand this, we need to make distinction between internal exposure vs. external exposure as well as irradiation and contamination.

Internal Exposure vs. External Exposure

There are two ways in which people can get exposed to radiation exposure :

• Internal Exposure,
• External Exposure

o Internal Exposure is exposure of radioactive material taken into the body by inhalation, ingestion absorption through skin, or through an open wound.

o External Exposure is exposure of radiation sources outside the body.

 Internal exposure can continue if the radioactive material remains in the body. In contrast, external exposure will not occur again once the radiation has penetrated the body.

Outside the nuclear and scientific community, there is a general misunderstanding that everything exposed to ionizing radiation is contaminated and dangerous forever. This is not the case, and there is a big difference between something being irradiated and something being contaminated.

Contamination vs. Irradiation

o Irradiation:

When something has been irradiated, the irradiation stops as soon as the source of ionizing radiation has been removed. The same can be said about the energy of ionizing radiation.
However even the irradiation has stopped, the biological effects of the irradiation may still occur if un-repaired cell damage has been inflicted.

o Contamination:

When contamination occurs, the source of the ionizing radiation itself is transfered, such as when radioactive isotopes in solid, liquid or gaseous forms are introduced into the environment.
When something has been contaminated with radioactive isotopes, it will remain radioactive until the radioactive isotope has decayed to a safe level.

Hence, from above we see that although one is irradiated by radiation, you do not become radioactive after that and become the source of radiation.  This is why food exposed to microwaves do not emit microwave or food that has been treated with X-rays to lengthen their shelf lives are not sources of X-rays themselves.

However, for the case of Japan, as the nuclear reactors are spewing out particles that are radioactive, the particles can be inhaled by people or get attached to the clothes, the bodies or the vehicles that are passing through.  Furthermore, the fall out will land in the water, on the soil etc.  Those people and objects that have particles attached to them or have inhaled the particles, consumed the particles or "drank the particles" would therefore continue to emit radiation.  This is why people are advised to wear mask and stay indoors. And food from the sources needs to be scanned as the fishes and subsequently the produce may contain high amount of radiation. 

This is the principle we use for carbon dating.  Carbon-14 is a radioactive isotope that is continually ingested and inhaled by animals and plants.  Due to biological decays and its radioactive decay, the proportion in a living material is more or less fixed and hence there is a stable amount of radiation we emit.  When however a living thing die, we stop taking in Carbon-14.  That is why the radioactivity reduces and by looking at the reduction, we can date back the once living artifacts to the year it "died".


I hear that the winds are blowing the steam, the fallout of the explosions into the sea?  So is the problem solved?

That depends on how you see it,  if the fallout goes towards the sea, the radioactive particles will deposit into the ocean, this means that marine life will get a greater exposure to the radiation and will also ingest a greater amount of radioactive particles.  This goes for the same if the steam and smoke gets carried by the winds into the atmosphere, this means the area that is exposed to the radioactive particles are greater but will also mean more distributed and evened out.

Some people are actually hoping for rain, as the precipitation will keep the affected area more confined, but this means the distribution is also more concentrated.


Coming up next
(1)  Can we therefore make the radioactive isotopes non-radioactive by chemical reactions etc.?
(2)  You mentioned alpha particles, but I also know that alpha particle can be stopped by paper,so out of the radiation which is less harmful, and what are the impacts of each type of radiation?
(3)  Some people say swarthing iodine the bodies will help prevent the radiation from harming the body, is it true?  If it is not true, then why are the governments buying iodine pills?
(4)  How do we know that a person has been irradiated, are there visible signs e.g. glowing etc? 
(5)  What are the short term and long term biological effects of exposure to radiation?