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Every living cell is an awe-inspiring system of chemical compounds and processes. These processes not only enable the cell to perform its function, it also enables the cell to divide and multiply itself. This cell division is why kids can grow, old or damaged cells are being replaced by new cells and cell division also produces reproductive cells enabling the creation of a brand new lifeform. As you’ve learned in the previous chapter, ionising radiation can change the chemical properties of the atom it hits and with chemical processes as complex as those in a living cell, that carries some risk.
Doses
The damage a living cell sustains depends on the dose, the amount of particles that hit the cell.
A small dose
Your cells contain DNA, the complete instructions on how to build and operate a human being. Every time the cell divides, the entire DNA is copied. When the DNA has been damaged by (a low dose of) ionising radiation, the copying stops and that particular cell won’t divide anymore. The cell will eventually die of old age and be replaced by the division its neighbour undergoes.
Even if the cell is really unfortunate and dies sooner, it will be replaced without problem.
A large dose
When a living being absorbs a large dose of radiation, a lot of cells will die. This means that a dead cell will no longer be replaced because all its neighbours are dead as well. A lot of organs, including your skin, depend on the constant renewal of cells. When that stops on a large enough portion of the organ, the organ will stop functioning and quite likely, that person (or animal) will die.
Between a large and small dose
The most well know effect of radiation is actually caused by moderate doses of radiation. The cell will be damaged but won’t die. Instead of dying or stopping to divide itself, the process that governs the division might go out of control and the cell will start to multiply itself at an increased rate. The cell has become cancerous. Every new cell that this cell makes will also be out of control because it’s a copy of the first defective cell. The growing mass of these cancerous cells is called a tumour.
The higher the dose, the higher the change of the cell becoming cancerous unless the dose is so high that the cell dies off.
Alpha, beta and gamma radiation
The degree to which each different type of radiation is dangerous to the body depends on whether the source is outside or inside the body.
If the radioactive source is inside the body (perhaps after being swallowed or breathed in), then:
Alpha radiation is the most dangerous because it is easily absorbed by cells
Beta and gamma radiation are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it
If the radioactive source is outside the body:
Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body
Beta and gamma radiation are the most dangerous sources because they can penetrate the skin and damage the cells inside
Precautions are taken in hospitals to limit the doses received by patients and staff when repeatedly exposed to radiation.
External tumour treatment
The fact that high doses of radiation can kill cells isn’t always a bad thing, it can be used to kill cancerous cells. If all the cancerous cells are dead, they can’t divide themselves anymore to create new cancerous cells. This method is often used if the tumour is located in a part of the body that is not easily operated on, in the brain for example.
If the tumour is located deep inside the body, a form of radiation with great penetration has to be used, gamma rays. Because gamma rays are strong enough to kill cancer cells, they would also kill healthy cells around the tumour. To avoid this, several weaker sources are used and arranged so the gamma rays are focused on the tumour. This concentrates the gamma rays on the cells that need to be killed.
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