Radioactivity and Rariopharmaceuticals

Radioactive decay

•Radioactive decay, also known as nuclear decay or radioactivity, is the process by which a nucleus of an unstable atom loses energy by emitting alpha particles, beta particles, and gamma rays . Radiation is the energy or particles that are released during radioactive decay.

Radioactive substance

•A material that spontaneously emits this kind of radiation is considered as radioactive substance.

Radioactive decay particles

•an alpha particle

•a beta particle

•a gamma ray

Atom

An atom is the smallest unit of ordinary matter that forms a chemical element

Alpha particles

•Alpha particle, positively charged particle, identical to the nucleus of the helium atom, spontaneously emitted by some radioactive substances, consisting of two protons and two neutrons bound together, thus having a mass of four units and a positive charge of two.

•Alpha radiation is emitted only from elements having atomic number greater than 82.

Properties of alpha particles

•Alpha particles are by far the heaviest and slowest of all radioactive emissions.
•It is the most highly charged nuclear species with a charge of +2.
•Alpha particles move at a relatively low speed.
•Their  penetrating  power  is  inversely  proportional  to  their ionizing power. They have less penetration power.
•Due to the high mass of the alpha particles, they can’t penetrate the outer layer of the skin when the body exposed to it and not cause a hazard's effect. While when the alpha particle emitters are inhaled, ingested or injected, the alpha particles cause a serious hazard effect on the internal organs due to the high charge of the alpha particles.

Beta particles or beta ray

•Beta particles (β) are high energy, high speed electrons (β-) or positrons (β+) that are ejected from the nucleus by some radionuclides during a form of radioactive decay called beta-decay.

•Beta decay occurs when the atomic nucleus has an “imbalance” between the number of protons and neutrons required for optimal stability.

beta plus decay

•If there are too many protons, there is excess positive charge, and the nucleus attempts to attain greater stability by emitting a positron through beta plus decay.

beta minus decay

•When there is a deficiency of protons (i.e., not enough positive charge), the nucleus can gain greater stability by emitting an electron via beta minus decay.

Properties of beta particles

•Due to the low mass of the beta particles, they have penetration power higher than the alpha particle which allows them to penetrate the sheet of paper but stopped by an aluminum sheet. Can penetrate large thickness of matter, eg. they can easily pass through 1 cm thickness of Aluminium foil sheet.

Gamma ray

•Gamma rays are electromagnetic radiation (Electromagnetic radiation can be defined as a form of energy that is produced by the movement of electrically charged particles.)

•When atoms decay by emitting alpha or beta particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. This excess energy is emitted as gamma rays. The original element doesn’t change here.

Properties of gamma ray

•Their ionizing power is 1/10000 times of alpha particles.

•Their  penetrating power is very high e.g. can easily penetrate through 30 cm thickness of iron.

•Produces fluorescence.

Effects of radiation

1. Not all living cells are equally sensitive to radiation. Those cells which are actively reproducing are more sensitive than those which are not. This is because dividing cells require correct DNA information in order for the cell’s offspring to survive.

This means that different cell systems have different sensitivities. Lymphocytes (white blood cells) and cells which produce blood are constantly regenerating, and are, therefore, the most sensitive.

Reproductive  and  gastrointestinal  cells  are  not  regenerating  as quickly and are less sensitive. The nerve and muscle cells are the slowest to regenerate and are the least sensitive cell.

2. Cells of the human body, have a tremendous ability to repair damage on exposure to radiation. As a result, not all radiation effects are irreversible. In many instances, the cells are able to completely repair any damage and function normally.

If  the  damage  is  severe  enough,  the  affected  cell  dies.  In  some instances, the cell is damaged but is still able to reproduce. The daughter cells, however, may lack in some critical life-sustaining component, and they die.

3. The other possible result of radiation exposure is that the cell is affected in such a way that it does not die but is simply mutated. The mutated cell reproduces  and  thus  perpetuates  the  mutation.  This could be the beginning of a malignant tumor.

Biological effects of radiation

•Biological effects of radiation are typically divided into two categories:

•ACUTE : The first category consists of exposure to high doses of radiation over short periods of time producing acute or short term effects.

•CHRONIC : The second category represents exposure to low doses of radiation over an extended period of time producing chronic or long term effects.

•High doses can kill so many cells that tissues and organs are damaged.

•Low doses spreading out over an extended period of time don’t cause an immediate problem to any body organ but the damage accumulates over time and produce long term effects.

Main organs affected by radioactivity

⮚Blood Forming Organs

⮚Reproductive and Gastrointestinal Tract Organs

⮚Skin

⮚Muscle and Brain

Summarized effects of radiation

❖Damage to the organism itself resulting in either sickness or death.

❖Effects may appear immediately or years later, usually in the form of cancer

❖DNA damage in male or female reproductive cells. That damage can be transmitted to the next generation

Units of radioactivity

•The activity of a radioactive source is defined as the number of transformations per unit time.

•The old traditional unit of radiation is curie (Ci). One curie is defined as 3.7 × 10¹⁰ disintegrations per second (dps).

•Nevertheless, the SI unit is becquerel (Bq), which is equal to 1 dps and is a metric unit

Radiopharmaceuticals

•Radiopharmaceuticals (radionuclides) are radioactive substances used in the fields of diagnosis (95%) and therapy (almost 5%)

Diagnostic radiopharmaceuticals

•Diagnostic radiopharmaceuticals can be used to track the movement of drugs in the  body;  identification  of  cancer  cells  in  the  bones,  brain tumors; to monitor the function of liver, lungs, heart or kidneys; monitor blood flow; heart muscle activity.

•Doctors and chemists have identified a number of chemicals which are absorbed by specific organs.

•Those  radioisotopes  can  be  attached  to  non-radioactive  element  or biologically active molecules to reach the target tissues.

•One common diagnostic test use is the Thallium-201  scan  for  the  cardiovascular  system, which reveals blockages in the coronary arteries and examines heart activity. The radioactive isotope thallium 201 behaves physiologically as a potassium analog, and when injected intravenously accumulates rapidly within the cells of many organs. In contrast to normally perfused myocardial cells, ischemic cells show delayed uptake.

•Radionuclide scans can detect abnormalities such as fractures, bone infections, arthritis, rickets, and tumors that have spread, among other diseases.

•Glucose is an important molecule for metabolism. It is more actively taken up in tumor cells than in normal cells, thus making it possible to detect the tumor. Radiolabeled glucose derivates have been successfully employed for tumor imaging for several decades.

Therapeutic radiopharmaceuticals

▪For some medical conditions like cancer, it is useful to destroy or weaken malfunctioning cells using radiation. The  radioisotope  that  generates  the  radiation  can  be localized  in  the  required  organ.  This  is  radionuclide therapy (RNT) or radiotherapy.

▪Iodine-131 is used to treat the thyroid cancers and other abnormal conditions such as hyperthyroidism (over-active thyroid).

▪In a disease called Polycythemia vera, an excess of red blood cells is produced in the bone marrow. Phosphorus-32 is used to control this excess.

▪A new and still experimental procedure uses boron-10, which concentrates in the tumor.

Sterilization

•Radioisotopes are used for sterilizing pharmaceuticals in their final packed containers and surgical instruments in hospitals. E.g. Cobalt 60 is a source of gamma radiation and is used for the sterilization of surgical instruments.

•No heat or chemical gets involved.

•Thermolabile (heat sensitive) substances like vitamins, hormones antibiotics can be safely sterilized.

PRECAUTIONS  FOR  HANDLING RADIOACTIVE SUBSTANCES

•Always separate radioactive activities from non-radioactive activities.

•As far as possible, limit the area where radioactive substances are used and mark the area

•Apply a radiation symbol to any containers and items that have come into contact with radioactive substances

•When handling radioactive materials, always wear the appropriate protective clothing

•Radioactive materials should never be touched with hand but handled with forceps or suitable instrument.

•Do not eat, drink and smoke in areas where unsealed radionuclides are stored.

•Regularly check the radiation level of your working area and all objects used.

•Dispose of all radioactive waste in the appropriate containers.