Chapter 7 Radiation: risks and uses
Radiation is emitted by a source and travels in a straight line until it hits another object. When it is absorbed, it no longer exists as radiation but heats up the absorber and may also cause chemical changes.
Radiation is emitted by a source and travels in a straight line until it hits another object. When it is absorbed, it no longer exists as radiation but heats up the absorber and may also cause chemical changes.
Some substances: radioactive. They emit ionising radiation(radiation with enough energy to break up which can cause changes within living cells, changes which can make them grow ou of control and cause cancer. The health risks of ionising radiation increase with the dose a person receives.
Electromagnetic radiation and its effects
The light we can see is a very narrow band in the broad spectrum of electromagnetic radiation from the Sun and other sources. Our eyes can see because this visible light produces chemcial changes in the cells of our retinas. Other types of electr. magn. radiation with different wavelengths can also bring about physical and chemical changes, but our eyes cannot see them.
The light we can see is a very narrow band in the broad spectrum of electromagnetic radiation from the Sun and other sources. Our eyes can see because this visible light produces chemcial changes in the cells of our retinas. Other types of electr. magn. radiation with different wavelengths can also bring about physical and chemical changes, but our eyes cannot see them.
For life on Earth the most important chemical effect of the Sun’s visible radiation is photosynthesis, which harnesses the energy from the sun to make foods that are energy stores. Other effects of radiation are harmful and can kill. When UV, X-rays or gamma radiation is absorbed by cells, the energy carried by the radiation does not just heat up the cells; it can also break up molecules into fragments.
High-intensoity radiation can damage so many molecules so many molecules in cells that it destroys them. Cells may be able to repair lesser amounts of damage done by lower levels of radiation. If the DNA in cells is damaged even a small amount of damage can have serious consequences.
If vital genes are damaged, cells can be crippled or killed. If radiation damages the genes that control growth and replication, cells can start to divide uncontrollably to produce tumours of rogue cells -> cancer.
Scientists are confident in claiming that ionising radiation causes cancer.
Are mobile phoes a health risk?
1999: UK government set up an expert group to review the evidence if mobile phones are a health risk
2000: Report was published (Mobile Phones and Health). The scientists said that the public was not harmed by the microwave radiation from mobile phones and base stations. However, they accepted that there was evidence that there could be biological effects from the radiation even at exposure levels below those permitted inter- and nationally.
2000: Report was published (Mobile Phones and Health). The scientists said that the public was not harmed by the microwave radiation from mobile phones and base stations. However, they accepted that there was evidence that there could be biological effects from the radiation even at exposure levels below those permitted inter- and nationally.
2007: Researchers collected data from 678 people with acoustic neuroma. In this condition, benign tumours grow in the nerve that connects the ear to the brain. The tumours are not cancers but they cause loss of hearing. They grow slowly and do not spread to other parts of the body.
Looking at the whole group, scientists found no link between phone use and brain cancer.
Possible explanations
Scientists have been looking for evidence of how microwaves might damage cells. Various claims have been made, eg (microwaves make cells hotter; microwaves disrupt the mechanism in cells).
Scientists have been looking for evidence of how microwaves might damage cells. Various claims have been made, eg (microwaves make cells hotter; microwaves disrupt the mechanism in cells).
Living close to a high-voltage power line
Pylon lines are a feature of our landscape, both in cities and in the country. They carry electricity form power stations to consumers. Mains electricity in the UK is an alternating 50 Hz supply so that the current changes direction and back again 50x p/s. This means that the eletrical and magnetic fields around cables and power lines are also alternating with the same frequency. As a result the cables emit electromagnetic radiation.
Pylon lines are a feature of our landscape, both in cities and in the country. They carry electricity form power stations to consumers. Mains electricity in the UK is an alternating 50 Hz supply so that the current changes direction and back again 50x p/s. This means that the eletrical and magnetic fields around cables and power lines are also alternating with the same frequency. As a result the cables emit electromagnetic radiation.
ELF Radiation = radiation from wires and cables carrying mains electricity with a very low frequency compared to other types. ELF is non-ionising.
In 1996 and 1999 Denis Henshaw and his colleagues at the University of Bristol published a theory to explain the health effects of power lines. The idea is that the ions in the air join up with small particles of air pollution so that these particles become electrically charged. The electric charge on these particles means that they are more likely to stick in the lungs. So, in this theory, the rise in cancers is caused by the increased effect of air pollutants. In 2004 a group of the National Radiological Protection Board decided that this was not a plausible explanation.
What do we mean by ‘ risk’?
Risk estimates like these are never exact. One reason is that someone might be diagnosed as having influenza when they only have a heavy cold. For this reason, the risk of death from different causes is easier to measure as the outcome can be detected with certainty. All statements about risk are estimates. Often it is difficult to measure the size of a risk. This may be because the outcome is hard to detect with certainty, or because the risk is low and only a few people are affected, even when data is collected from a large population.
Risk estimates like these are never exact. One reason is that someone might be diagnosed as having influenza when they only have a heavy cold. For this reason, the risk of death from different causes is easier to measure as the outcome can be detected with certainty. All statements about risk are estimates. Often it is difficult to measure the size of a risk. This may be because the outcome is hard to detect with certainty, or because the risk is low and only a few people are affected, even when data is collected from a large population.
Sometimes a risk is expressed in terms of the number of people likely to experience the event in question. The size of risk may also depend on exposure to the hazard.
People often don’t know the actual risk for many of the activities they choose. They have to use their own perception of risk to decide whether it is safe to do something. People tend to overestimate the risk of unfamiliar events, and underestimate the risks of familiar ones. If there has recently been an accident or a health-scare story in the news, people are likely to see the risk of this as larger than it really is.
Risk factors
There are often claims that something is believed to pose a risk to health, or to improve our health. For instance, living under high-voltage power lines has been claimed to increase the risk of some types of cancer. On the positive side, it has been claimed that drinking a glass of red iwne a day reduces the risk of heart disease. Claims like these, however, are often contested.
If a factor causes a major effect, it is easy to spot - and people quickly recognise that it is important. But often a factor causes a very small effect; for example, worries about the effect of low levels of ionising radiation or about the use of mobile phones. The number of cases is very small. So if a study compares a group that is exposed to the factor with a control group, the numbers of individuals affected will be small in both groups. And if the numers are small it is hard to be sure if any difference is real or just due to random variation.
One way to tackle this is to use large samples. The bigger the samples, the more cases there will be in both groups and the bigger any difference will be. The larger the difference, the less likely it is that it is just due to chance.
Another option is to use a case-control study. This type of study has the advantage that it guarantees that there are enough cases of the ill effects in the data set to reveal a pattern if there really is one. But it is harder to avoid bias.
Media reports - genuine concern or just hype?
Media reports sometimes sensationalise new scientific claims. Reports can make them appear to be quite certain even when thye are in fact provisional, based on limited evidence, and not yet confirmed by other scientists. Conflicting findings reported by other scientists may be ignored. This can lead other scientists to enter the discussion, to counter the claims being made. The result is a public disagreement between scientists.
Media reports sometimes sensationalise new scientific claims. Reports can make them appear to be quite certain even when thye are in fact provisional, based on limited evidence, and not yet confirmed by other scientists. Conflicting findings reported by other scientists may be ignored. This can lead other scientists to enter the discussion, to counter the claims being made. The result is a public disagreement between scientists.
Media reports also have a tendency to give undue weight to case histories of individual people. This may be done to add human interest to the story. But it can be very misleading, as it usually implies that there is little or no doubt that the indiviudal’s ill health was caused by whatever the ‘scare’ story is about.
Three types of ionising radiation
- Alpha radiation: particles have a positive electrical charge and are several 1000x more massive than beta particles. They are much more easily absorbed.
- Beta radiation: particles are electrons, so they have a negative electrical charge and only a very small mass. They pass reasonably well through many materials.
- Gamma radiation: Electromagnetic radiation from the short-wavelength end of the electromagnetic spectrum.
- Alpha radiation: particles have a positive electrical charge and are several 1000x more massive than beta particles. They are much more easily absorbed.
- Beta radiation: particles are electrons, so they have a negative electrical charge and only a very small mass. They pass reasonably well through many materials.
- Gamma radiation: Electromagnetic radiation from the short-wavelength end of the electromagnetic spectrum.
Alpha particles are very easily absorbed -> cause a lot of ionisation in a short distance. It might seem that they are more likely to damage cells than beta particles or gamma rays. This is true if unstable atoms are close up against liveing cells or even inside them. But for sources of radiation outside the body, alpha is least dangerous because alpha radiation will not even reach the body.
Effective dose is an important quantity becuase it is related directly to the risk of dying from cancer.
A source of radiation that is outside a person’s body can harm that person’s body by the radiation it emits: it can irradiate the body. This irradiation can be reduced by screening the source or moving the source and the person apart. The source of radiation may be actually on the body. We then say that te person is contaminated by the radioactive substances that is the source of the radiation. It may then be difficult to remove the source.
Radon is a radioactive gas that is produced in a series of radioactive decays that begin with unstable uranium and thorium atoms. There are small quantities of these elements in almost all types of rock and soil, so radon is produced nearly everywhere.
Scienteist believe that there is a risk of cancer form ionising radiation, no matter how small the dose is. Even a single alpha or beta particle or gamma ray can damage the DNA in a cell in such a way as to make it cancerous. Others bleive that there may well be a threshold level of radiation below which there is little/no risk of cancer.
The seascale leukaemia cluster
1990: Martin Gardner claimed that he had evidence indicating that children of workers at Sellafield were 6-8x as likely to develop leukaemia if their fathers had received cumulative radiation doses exceeding 100mSv. Possible explanation: radiation damage to the fathers’ sperm.
1990: Martin Gardner claimed that he had evidence indicating that children of workers at Sellafield were 6-8x as likely to develop leukaemia if their fathers had received cumulative radiation doses exceeding 100mSv. Possible explanation: radiation damage to the fathers’ sperm.
1999: Report was published concluding that children of fathers who had been exposed to radiation before their conception were more likely to have leukaemia.
Later 1999: new twist in the story. Evidence was found supporting the virus theory; suggesting that leukaemia clusters are triggered by infections that occur in populations where many of the people are new to the area.
Radiation and health
Radiologists use X-ray machines to obtain images of bones and ohter parts of the body. A CT scan is a more sophisticated way to use X-rays.
Nuclear medicine uses radioactive substances introduced into patient for diagnosis or treatment. The radioactive atoms are part of a chemical known to be taken up by the tissues or organ to be examined.
An example of radiotherapy with radioactive isotopes is the use of iodine-131 to kill cancer cells in the thyroid gland. The patient swallows a capsule containing the radioactive isotope.
Radiotherapy aims to treat or cure cancers with a powerful beam of radiation from X-ray machines/radioactive sources. The doses of radiation are many 1000x higher than those used for diagnosis. The aim is to cure cancer or at least to alleviate the most distressing symptoms.
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