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RADIATION SAFETY MANUAL
Section 2: General Information

INDEX
2.1 Objectives of Radiation Protection
2.2 Nature of Radiation Units
2.3 Sources of Ionising Radiation
2.4 Ionising Radiation - The Risks Involved
2.5 Organisation of Radiation Safety
2.6 Responsibilities
2.7 Continuing Education
2.8 NSW Legislation
2.9 Licenses

2.1 OBJECTIVES OF RADIATION PROTECTION
Radiation effects are divided into two groups:

• stochastic effects
• non-stochastic effects.

These terms are rather academic, but are not too difficult to understand.

In stochastic effects, the probability (but not the severity) of occurrence is related to the magnitude of the dose, without threshold. An example is cancer induction. A small dose will give you a small probability of getting cancer, and a larger dose, a larger probability - however, the severity of the cancer is the same in both cases. Genetic effects are also stochastic.

With non-stochastic effects, there is a threshold and the severity of the effect is related to the dose. An example is a radiation burn - a small dose will not produce a burn, a very large dose will, and the larger the dose the worse the burn. The object of the radiation protection is to prevent detrimental non-stochastic effects, and to limit the occurrence of stochastic effects to acceptable levels.

This is achieved by setting annual limits to the radiation dose equivalent (not including natural or medical radiation) which can be received by workers and the general public. Also, there is a requirement that all uses of ionising radiation result in doses to patients, workers and public that is "As Low as Reasonably Achievable" - the ALARA principle. This means that we are to regard limits as just that, and aim for the lowest possible dose.

The dose limits and radiation protection are set by the International Commission on Radiological Protection (ICRP, 1990) (Refer Appendix) and are generally adopted by all countries.

2.2 NATURE OF RADIATION UNITS
In this manual, reference will be made to the various types of radiation, and the units used for their measurement. SI units will be used throughout, however, in some areas old units will be given as well. A conversion table can be found in Appendix 3.

Ionising Radiation
Ionisation may be simply defined as any process by which an atom or molecule gains an electric charge. Any radiation which is capable of causing this effect is known as ionising radiation (see Glossary, Appendix 2). These are not to be confused with non-ionising radiations such as light and microwaves. Ionising radiations emitted from radioactive atoms or produced by devices such as x-ray machines include:

Due to the identity of waves and particles on a microscopic level some types of radiation (alpha and beta) are particles, while others (gamma and x-rays) would be commonly classified as waves or rays. These are the only directed ionising radiations with which we will be concerned.

Alpha particles are identical with helium nuclei, having two protons and two neutrons. Alpha particles thus carry a positive charge and are usually emitted by heavy radioactive atoms such as uranium and radium. Being large and relatively slow, they quickly dissipate their energy by colliding with the atoms of the material through which they travel causing heavy ionisation to take place. Alpha particles thus have very little power of penetration and are stopped completely by a sheet of paper, the outer layer of human skin, or a few centimetres of air. Alpha emitters are most damaging when incorporated into the body, and are not used at the University except under exceptional circumstances..

Beta particles are high speed electrons (ie negatively charged)emitted from the nuclei of radioactive atoms. Being light (almost no mass), and emitted with a speed close to that of light, beta particles have greater penetrating ability than alpha particles of the same energy, but still will be stopped by a few millimetres of aluminium, a centimetre or so of human tissue or a few metres of air, dependent on their energy.

In practice, the most commonly used shielding for beta particles is aluminium or perspex. Lead is not an effective shielding as absorption of beta particles gives rise to secondary radiation by the bremsstrahlung process in the form of x-rays. Aluminium and perspex do not give rise to secondary radiation of any significance.

Beta emitters are also most hazardous when ingested, but can also be hazardous, externally, especially to the cornea. Beta emitters are often administered as therapeutic agents.

Gamma rays are electromagnetic radiations of the same family as visible light, and travel at the same speed. They have a high penetrating power and can pass through several hundreds of metres of air or many centimetres of dense materials such as iron or lead. Gamma emitters are hazardous internally and externally, although less damaging than the particle sources.

X-rays are physically identical to gamma rays and differ only in their means of production, which is usually by means of electrons striking a dense material as occurs in a common diagnostic x-ray machine.

Radiation Units
Energy
The energy of particles or rays is expressed in electron volts (eV). An electron volt is the energy acquired by an electron when accelerated by a potential difference of one volt. Since this is a very small amount of energy, we usually talk in terms of keV and MeV, is, kilo or million electron volts.

Radiation Exposure (C/kg)
This unit measures the amount of Ionisation produced in air by a given radiation source. It is measured in coulombs per kilogram of air at normal temperature and pressure and is directly related to the number of radioactive particles or gamma rays per unit area incident on a given body. This unit is not often used and the old unit was the Roentgen (R).

Radiation Absorbed Dose (Gray)
This unit measures the amount of energy deposited per unit mass of material by ionising radiation. One Gray is the amount of radiation which will deposit one Joule per Kilogram of energy in a specified material. The Gray is a very large unit and most radiation doses usually encountered are likely to lie in the milligray (mGry) or microgray (mGy) region. For example, a chest x-ray gives about 200 microGray to the Chest wall, while a radiotherapy treatment may involve 60 Gy (300,000 times as much as the chest x-ray).

Note that the tissue or material involved must also be specified along with the absorbed dose. The old unit of absorbed dose is the rad, which is equal to 0.01 Gray.

Equivalent Dose (Sievert)
This unit is a measure of the biological effect produced, for equal energy absorption, by different types of radiation as well as other effects. The relation between dose equivalent and absorbed dose is given by:

Sieverts = Grays x WR x N
Where WR is the radiation weighting factor depending on the type of radiation, and N is the product of all other modifying factors. Table 2.1 lists the radiation weighting factor according to ICRP.

Table 2.1 Radiation Weighting Factors (1)

(1) All values relate to the radiation incident on the body, or for internal sources, emitted from the source.
(2) Excluding Auger electrons emitted from the nuclei bound to DNA. 

For most radiation encountered in the University environment WR is nearly equal to 1, also N is currently taken to be equal to 1, so that dose equivalent often is numerically equal to absorbed dose. The Sievert is again therefore a rather large unit and most dose equivalents will be in the millisievert (mSv) and microsievert (mSv) range. The old unit of dose equivalent is the Rem which equals 0.01 Sievert.

Activity (Becquerel)
The radioactivity of a given radioactive source is measured in terms of the number of radioactive disintegrations per second occurring in that source. The unit of radioactivity is the Becquerel (Bq) which is the activity of a source giving rise to 1 disintegration per second. Each disintegration is associated with the emission of ionising radiation of some sort. The Becquerel is a very small unit, and the usual activities encountered in the University are in the Kilobecquerel (kBq), Megabecquerel (MBq) or Gigabecquerel (Gbq) range. The old unit of radioactivity is the Curie which equals 3.7 x 1010 Bq.

Half Life (Radioactive Decay)
Radioactive decay is proportional to the total number of atoms in a system. with the result being that radioactive decay is exponential. It may be described by the formula:

The half life ( T1/2 )of a radioactive species is the time taken for half of the material to decay is the disintegration rate to reduce to half its original value. The greater the stability of a species the longer it takes to decay (has a longer half life), the less stable the species the shorter length of time it takes to decay, ie a shorter half life.

The half life of a particular radioactive isotope is constant, the radioactive decay occurring at a characteristic rate for each element. Therefore measurement of the half life can assist in identifying the composition of unknown radioactive samples.

Radiolytic Self Decomposition varies according to the storage, sensitivity of the compound, solvent (type and purity) and affects the usefulness of the compound, eg 3H thymidine.

Biological Half Life
This refers to the time taken for half an administered or ingested amount to be excreted by the body, this value having nothing to do with radiation. Please note that after two half lifes there is still one-quarter of the original activity present. Waiting for 10 half lifes reduces the activity to 0.1% of the original activity.

2.3 SOURCES OF IONISING RADIATION
There are a number of possible situations:

• exposure may be experienced in the workplace (occupational exposure), by members of the public or due to medical treatment.
• the nature of the exposure may be intentional or accidental.

It is interesting to note that the majority of the average annual radiation dose to the population is from natural sources of radiation. In Australia the background radiation dose equivalent is of the order of 2mSv.

Table 2.2 - Average Annual Radiation dose to the Population (UK Data)

(1) Includes - discharges, occupational, fallout and miscellaneous.

2.4 IONISING RADIATION - THE RISKS INVOLVED
Evaluation of the risks involved due to exposure to ionising radiation is a very complex problem. Most estimates have been extrapolated from data obtained on groups of persons receiving relatively high doses (such as the victims of the Hiroshima and Nagasaki atomic bombs). These estimates assume a linear dose effect relationship (that is, no threshold) which would probably overestimate rather than underestimate the risk. The risks in the table 2.3 represent the overall risk to all age groups over a period of 20 to 25 years. In the case of genetic risk (hereditary effects) the risk estimated is for the next and succeeding generations (ref. ICRP 26).

Radiation at the Cellular Level
The effects of radiation depend greatly on whether the exposure is delivered as a single fractionated or continuous dose. Generally, the fact that several small doses of radiation cause less damage than a single dose of the same magnitude indicates that mammalian cells have a capacity to repair damage caused by radiation. This damage repaired within a few hours of exposure, means that something like 90% or more of lesions to DNA, chromosomes, etc, are efficiently repaired when radiation doses are smaller and cells have time to repair themselves.

Differentiating cells and cells undergoing division are much more sensitive to radiation e.g. the radiation hazard is 100 times greater for the fetus during the 3rd-7th week than for the pregnant mother.

Organs and tissues in which the cells are replaced slowly also exhibit high radiation sensitivity. The human tissues which exhibit higher than normal sensitivity to radiation damage are:

• reproductive organs
• skin
• organs of the abdominal cavity
• eyes
• blood forming organs in the spleen and bone marrow
• tissues of the nervous system

In general, the more differentiated the cells of an organ are the greater the sensitivity to radiation.

Alpha-radiation is more hazardous to the cell as the dense ionisation column of alpha-radiation leads to disruption of the DNA molecule. On the other hand, a gamma-ray photon may pass even a whole chromosome without causing a chromosome disruption or structural charge. However, any radiation whether a, b or g causes radiolysis of the water in the cell and the products may react with the DNA or RNA to such an extent that the cell dies.

Table 2.3 Radiation Risks

The actual risk per annum due to a given radiation dose is difficult to compute since it will vary with the latent period after irradiation and any subsequent radiation received in the interim. However, this risk per annum from an individual dose will certainly be a lot smaller than the overall risk quoted above. In order to put the above risk in perspective the risks from various other causes of death are compared below with the risk per year of death for:

• a hospital radiation worker receiving around 2mSv per annum (a typical figure) over a working period of many years.
• a patient receiving 20mSv bone marrow dose as a result of some diagnostic procedure involving radiation.

The risk of death each year from lung cancer is 1 in 4000; from murder is 1 in 100,000; from a car accident is 1 in 5000; from leukaemia as a result of radiation worker receiving 3mSv per year for many years is 1 in 130,000; and from leukaemia as a result of receiving significantly less than a single exposure of 20mSv to bone marrow is 1 in 25,000.

It can be seen from the above table that, under normal circumstances, the risk is relatively small compared with the risk of death from other causes. However, it cannot be described as being negligible and current policy is to keep the radiation exposure of workers as low as is practicably feasible. In the case of patients irradiated during some diagnostic or therapeutic procedure involving ionising radiation there are definite risk versus benefit considerations. Often the benefit of the diagnostic information far outweighs the radiation hazard, and for older patients the associated hereditary portion of the risk will obviously be negligible.

Also, the risk associated with a patient's illness may be such that any additional hazard due to radiation will be insignificant. In spite of this, a policy should be maintained that no examination involving ionising radiation should be performed if little or no additional information is likely to be obtained from this examination. Multiple tests involving ionising radiation are also to be discouraged, bearing in mind the cumulative nature of the risk.

It is generally accepted that the tissues and organs of children are more radiosensitive to those of adults. Also, the foetus is particularly sensitive to radiation, especially during the 3-7 week period. Risks of the order of 4 in 10,000 (per mSv) have been quoted for irradiation of the foetus in utero. For the above reasons the irradiation of pregnant women or children needs special consideration. If an examination involving radiation is considered absolutely necessary, then steps must be taken to keep the radiation dose at a minimum (see Section 13).

2.5 ORGANISATION OF RADIATION SAFETY
The overall responsibility for Radiation Safety and Protection at The University of Newcastle rests with the Vice-Chancellor. An employer is required to protect employees, (and in this case, students), members of the public and the environment from unnecessary exposure to radiation arising from their operations which may use radiation apparatus and/or radioactive substances.. The Vice Chancellor has chosen to appoint a Radiation Safety Officer for the University (URSO) to assist the institution to fulfil its obligations under the Act. A Radiation Safety Committee (RSC) has also been appointed to act as an administrative and consultative body that reviews the radiation safety of all uses of ionising and non-ionising radiation and radioactive substances within the institution and to recommend implementation of radiation safety policies within the organization. The University Radiation Safety Officer is the Chair of the Radiation Safety Committee which can report directly to the Vice Chancellor but normally works through the University’s Occupational Health and Safety Committee. The RSC through the OH&SC is thus able to give direction, stop procedures or impose conditions when in its considered opinion the safety of staff, students or general public is being significantly compromised. The RSC will normally act through the Manager, Health and Safety Team however the URSO may also act without direction of the Committee if and when safety of staff, students or general public is being significantly compromised.

The Radiation Safety Committee covers matters relating to ionising and non-ionising radiation safety and its activities include receiving regular reports from the Radiation Safety Officer, consideration of research proposals involving radiation or radioactive material, investigations of incidents involving radiation, approval of procedures for uses of radiation and inspection of areas where these procedures are carried out.

Within each relevant school or building where members of the University staff or students carry out activities, a local Radiation Safety Officer (usually the representative to the Radiation Safety Committee) is appointed.

2.6 RESPONSIBILITIES

2.7 CONTINUING EDUCATION
All staff commencing work with or in areas where ionising radiation is used has to be introduced to the particular problems arising from the radiation by the Chief Investigator for the laboratory in which the assistance of the local Radiation Safety Officer may be sought. This induction should be as early as possible after commencement of the position.

The Regulation (2003) of the Radiation Control Act of NSW (1990) indicates that a certain level of training will be required of applicants for a licence. The Laboratory and Research Safety Officer in Human Resource Services, Health and Safety Team, will provide information on training courses from time to time and if necessary provide the requisite training. All costs of such training will be borne by the applicants or their supervisors. Provision of training for licence qualification is not the responsibility of the University.

From time to time there will be training and updating seminars on radiation protection provided by the Health and Safety Team. Information on these seminars will be circulated to all licence holders.

2.8 NSW REGULATIONS
The NSW Radiation Control Act 1990 in the Regulation (2003) sets down regulations governing the use of "irradiating apparatus" and radioactive substances. This Act is administered by the Environmental Protection Authority (EPA), Radiation Information Services Centre (Radiation Control Section), phone: 02 9995 5959, fax: 02 9995 6603, email: radiation@epa.nsw.gov.au) with the overall responsibility resting with the NSW Radiological Advisory Council. Officers from the EPA may inspect institutions from time to time to ensure compliance with the regulations. They are also available for consultation on various forms of radiation protection.

The Regulations are based on recommendations made by the International Commission on Radiological Protection (ICRP), World Health Organisation and the National Health and Medical Research Council. It is impossible here to cover all aspects of the Act; some of the important points to note, however, are as follows:

Further details on the above, and other subjects such as packaging, contamination, labelling and transportation of radioactive substances, etc, may be obtained from the Radiation Safety Officer.

2.9 LICENCES