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Ultraviolet radiation and skin cancer

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Introduction

ULTRAVIOLET RADIATION AND SKIN CANCER Skin cancer is the most common malignancy in humans and accounts for one third of newly diagnosed cancers. It is estimated that skin cancer will be diagnosed in around 1 in 5 Americans during their lifetime and more than 1 million cases are diagnosed each year [1]. Ultraviolet light from the Sun is the main cause of skin cancer and plays a major role in the 2-3 million non-melanoma skin cancers and 132,000 malignant melanomas that occur annually. The incidences of skin cancer are becoming more and more common, causing global concern. There could be many reasons for this. For example, people are living longer and so their lifetime sun exposure is increased. They also have more money to spend on outdoor activities and holidays in sunny climates. Many still feel that suntans are healthy and attractive and therefore deliberately expose themselves to the sun and consequently to UV radiation [2]. Due to the causal link between UV light and skin cancer, its prevention and protection against this type of radiation has been at the forefront of a lot of research done by companies such as the World Health Organisation. They have set up a scheme called INTERSUN, a 'global UV project'. This project promotes research activities that aim to fill in gaps in knowledge and quantifies the health risks of UV exposure [3]. ...read more.

Middle

of some minimum size. He proposed that the energy, E, of a single quantum equals a constant times its frequency. That is: E = hf. h is the Planck constant: h = 6.63 x 10-34 and energy is always emitted or absorbed in whole-number multiples of hf. The photoelectric effect refers to the phenomenon in which electrons are emitted from the surface of a substance when light strikes it. We can attempt to explain the photoelectric effect using something called the Bohr Model. In this model an electron in an atom, in a given orbit around a nucleus, can only absorb energy in multiples of a certain definite amount. These multiples are referred to as the different energy levels of the atom. In the same way, the only way the electron can lose energy is by dropping from one energy level to another one. When this happens, the atom emits a photon of radiation corresponding to the difference in energy levels. When all energy levels are filled electrons in higher levels cannot move to lower levels and therefore cannot lose energy. At this point the atom energetically stable and is said to be in its ground state. Atoms can absorb energy from an outside source (such as the Sun), causing one or more of the electrons within the atom to move to higher energy levels. ...read more.

Conclusion

hf is a packet or quanta of energy. Planck formed this equation by looking at how small electric oscillators radiated and absorbed radiation where their collective distribution of energy of the radiation was similar to that of the blackbody spectrum. He found that oscillators with a particular amount of energy only emitted particular frequencies of radiation. At high frequencies (short wavelength radiation) the energy needed to emit one quantum of radiation was very large, and only a few of these oscillators had this much energy (in accordance with statistics) therefore only a few of these high-energy quanta are emitted. At very low frequencies (long wavelength radiation) a lot of low energy quanta were emitted, but as they all have so little energy their sum still wasn't significantly large. It was only in the central range of frequencies that there are enough oscillators to emit a lot of radiation. These electric oscillators are similar to vibrating atoms in the Sun. Planck's findings did provide an explanation for the peak in the blackbody curve and why the Sun emits radiation in the way that it does [11]. Below is a graph showing the curves of three different blackbodies. It was made using Wein's law. We can see from this graph that as the temperature of the blackbody increases the magnitude of the peak increases and shifts towards the shorter wavelengths. This fact is significant for future generations as the Sun's temperature is increasing and as it does, more and more ultraviolet radiation will be emitted. ...read more.

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