Radioactivity Practical (Group 1)

Introduction
Radioactivity is a physical phenomenon discovered in the late 19th century by Henri Becquerel. During this physical process a nucleus of an unstable atom loses energy by shedding some of its particles, or excess energy, in the form of γ rays

Radioactive decay can proceed in 3 ways. Either by emitting α, β or γ particles. An α particle resembles nucleus of helium, therefore having 2 protons and 2 neutrons. There are 2 subtypes of β decay; β- and β+. β- decay occurs when a neutron transmutes into a proton, which releases an electron and an electron antineutrino. Whereas β+ decay occurs when a proton transmutes into a neutron, which releases a positron and an electron neutrino. β+ decay can also be called positron emission (Nave N.D.). Lastly, γ decay is a form of dissipation of excess energy by using photons. All the above mentioned processes are completely spontaneous (Nave N.D.)

Fig. 1.1 - Examples of α,β, γ radiation











Clinical importance
Discovery of radioactivity allowed for important breakthroughs in clinical medicine, especially in the fields of medical imaging and cancer treatments, making it important for medical diagnoses and therapies.

The most common types of medical imaging using radioactivity are X-ray photographs. X-rays are able to penetrate through materials, but depending on the material are absorbed to certain degree. Thanks to this, images of the inner structures the body can be created, such as of bones, which have much higher absorbance than soft tissue. Other types of medical imaging that use radioactivity are computerised tomography (CT scan), which uses X-ray images taken from various angles that are processed by a computer and cross sectional images are created. Positron emission tomography (PET scan), uses positron emitting radionuclide and is used to follow metabolic processes of the body.

Cancer treatment involving radioactivity are based on irradiating a tumour in the body. The high energy radiation then interferes with the tumour cells, damaging its DNA, which should stop the cells from proliferating further. Unfortunately this method has proven to be quite dangerous for the patients as cells around the tumour were also irreversibly damaged, so new methods of tumour therapy are currently being investigated, such as proton therapy.

Literature review
Radioactivity is crucial for medical imaging, otherwise we wouldn’t be able to screen patients without using intervening methods such as exploratory surgery. Medical imaging also allows us to monitor metabolical processes, circulatory system or our immune system, which provides another view into patient’s body, and allows for early treatment of pathological conditions, such as arteriosclerosis. Using radioactivity to visualise patient’s body means exposure to ionising radiation (David J. Brenner 2004), but thanks to modern technology it is possible to decrease the amount of radiation emitted by using more sensitive detectors.

Method by which imaging methods such as X-ray photography, CT scan or PET scan work is by utilising radioactive substances or radioactivity in a variety of ways. X-rays use X-ray tube that accelerates electrons in order to generate X-rays which can then penetrate patient’s tissue, get absorbed depending on the makeup of the tissue and its thickness and the resulting image is then gathered on a cassette which contains a metal sensitive to X-rays and finally the image is rendered. PET scan works by either having the patient ingest or inject the patient with a tracer substance, which contains a γ ray emitting radioactive isotope. The patient is then screened using a circular sensor that detects the incoming γ radiation and its direction and finally a 3D image of the patient’s body can be created by using a computer.

Regarding tumour treatment, use of gamma rays has been successful, but the treatment doesn’t have high success rate, and the possibility of side effects is substantial. Especially dangerous is irradiation of neighbouring cells which gets damaged by the ionising beams. This can cause mutations of DNA of the cells, and begin to proliferate uncontrollably, thus creating another tumour. Therefore the disadvantages of tumour therapy seem to outweigh the advantages, but it is important to nota that other treatment methods are jut being investigated, but some have already gone into clinical trial. Therefore for the time being we have to settle with radiation therapy as other method are either very limited or non-existent whatsoever (CancerResearchUK N.D.).

Regarding ethics, it is required to have the patient’s voluntary consent before using imaging methods or tumour treatment based on radioactivity as some people do feel threatened when faced with radioactivity. Therefore the amount of radiation a patient is exposed to must not exceed the amount routinely required for scan or tumour treatment as that could harm the patient’s body (Vetter 2014).

Apparatus

 * Radiation source
 * Radiation source holder
 * γ/β radiation indicator
 * Digital pulse counter
 * Copper plate shield (50 x 100 x 2 mm)
 * Aluminium plate shield (50 x 100 x 2 mm)
 * Iron plate shield (50 x 100 x 2 mm)

Methodology

 * 1) Connect the digital pulse counter with the γ/β radiation indicator using the provided lead and turn both pieces of equipment on
 * 2) Set the γ/β radiation indicator into the biggest hole of the radiation source holder, so that it is at 90° degrees to the long axis of the radiation source holder
 * 3) Make sure that the radiation source is closed by its outer ring and take it to a different room in order to prevent systematic error in radiation background reading
 * 4) Press the 100s button on the digital pulse counter to gather background radiation data. Repeat 10 times.
 * 5) Bring the radiation source back, secure it in the hole closest to the γ/β radiation indicator in the holder, and open it so that β radiation is being emitted.
 * 6) Press the 10s button on the digital pulse counter and note down the values. Repeat 5 times
 * 7) Repeat step 6 for the rest of the holes present in the holder.
 * 8) Repeat step 6 & 7, but instead using γ radiation
 * 9) Secure aluminium plate shield in the holder, and take five 10s measurements from each distance of the holder using β radiation, then γ radiation
 * 10) Repeat step 9 for copper plate shield and then iron plate shield
 * 11) Note down all the measurements taken, take an average of each of the repeated measurements, and construct a graph showing fluence versus distance of the radioactivity source for both γ and β radiation

Conclusion
Nowadays cancer treatment is moving away from using using γ radiation as proton therapy is staring to become more common. The advantages of proton therapy is the ability to focus protons more precisely onto the tumour by using magnetic field, so that surrounding tissue isn’t damaged as it would be with conventional γ rays.

Another highly beneficial addition is medical imaging, which allows early diagnosis of pathological conditions. Screenings are safer for the patient than exploratory surgery even with the use of radioactive substances. Early diagnosis significantly increases chances of successfully treating patient as well as increasing the patient’s wellbeing by eliminating severe signs of pathological conditions that would be otherwise present if the patient didn’t undergo early screening.