2- Radiation Exposure and Relative Risk

Radiation Safety Training – Sealed sources
2- Radiation Exposure and Relative Risk
Originally created: February 18th, 2011
Last revised: March 9, 2011
For more information, refer to the Radiation Safety Manual, 2005, Section 300
What are the potential outcomes of exposure to ionizing radiation?
Damage to cells can lead to a transformed cell or to the cell death. Or
the cell gets successfully repaired.
When too many cells die, we see cataracts developing, radiation burns,
radiation illness or death.
When the cell is not successfully repaired then the transformation can
lead to cancer or negative reproductive effects.
In addition, exposure to radiation is cumulative and additive throughout your whole life.
What are the effects of over-exposure to Ionizing Radiation?
Radiation Exposure is measured in milisieverts (mSv).
Acute effects (short term effects):
 Cataracts
 Burns
 Radiation illness
 Death
Threshold:
100mSv
>100mSv
>1000mSv
>10 000mSv
Long term effects:
 Cancer
 Reproductive effects
No threshold
However, let’s put the long term effects in perspective:
Lets say, you consider a control group of 1000 people exposed to background
radiation only - about 250 are likely to develop cancer over their lifetime.
Now, if you consider a hypothetical group of people exposed to 10 mSv
occupationally – statistically, 250.3 persons are likely to develop cancer in their
lifetime.
How can radiation risks be compared to other risks?
Another perspective:
This graph shows you how many years these factors will shorten on average person’s life:
Alcoholic
10.96
Poverty
10.00
6.16
Sm oking-Male
4.50
No Friends
Heart Disease
4.40
Cancer
3.42
3.15
High Risk Job
20% Overw eight
2.85
H.S. Drop-Out
2.33
Orphan
2.20
0.57
Car Accidents
0
2
4
6
Years
8
10
12
And this graph how many days:
207
Car Accidents
130
Alcohol
115
Suicide
93
Murder
77
Air Pollution
55
AIDS
Energy Conservation
50
Spouse Smoking
50
30
Radon
Drowning
24
Radiation Worker
23
Drinking Water
22
20
Fire, Burns
9.3
Natural Radiation
7
Natural Hazards
0
50
100
150
200
Days
Note the Radiation worker – and you are not a Radiation worker!
When do I become a Radiation Worker or the new term Nuclear Energy Worker (NEW)?
You only become a NEW if you can anticipate, based on the history or type of experiment, that your annual
exposure will exceed the limit for a member of public.
250
Here are the criteria:
Regulatory Limits for whole body exposure:
Members of the public: 1mSv/yr, whole body
(You and me)
15mSv/yr, lens of eye
(All U of M employees) 50mSv/yr, skin
50mSv/yr, hands and feet
Nuclear Energy Workers (NEW): max 50mSv/yr, whole body
Average 100mSv/5 yr
150mSv/yr, lens of eye
500mSv/yr, skin
50mSv/yr, hands and feet
Background radiation: 3-4 mSv/yr for Winnipeg
Restricted access to
UofM NEW or accompanied by NEW: exposure rate over 25uSv/h
Nuclear Energy Workers are, for instance, radiopharmacy workers, people working with a cyclotron, nuclear
power employees, industrial radiographers, operators of the cyclotron or Nuclear Medicine Technicians,
researchers working on certain research projects.
Please note the Background Radiation in the Table above. What is Background
Radiation?
Background Radiation in Winnipeg contributes 3.60 mSv per year. Background radiation comes from different
sources:
0.28 mSv from cosmic radiation
0.4 mSv from your diet:
More sources of Background Radiation:
0.28 mSv from terrestrial sources:
0.1 mSv from consumer products:
And most of it (2mSv) from radioactive gas Radon:
Your real Personal Exposure consists of exposure from medical procedures, background radiation and your
occupational exposure.
+
Medical
+
Background
Occupational
How is the occupational exposure measured at the U of M?
By:
 Dosimeter
 TLD – badge (whole body and skin dose)
 Ring dosimeter (extremity dose)
How should you take care of your TLD badge?
You must take good care for your badge. These are the rules:
 Wear the badge on your chest or waist
 Do not wear the badge when undergoing medical procedures involving radioisotopes or X-ray
 Name Facing Outward
 Check for contamination often
 Report if the foil is not light tight
 Store badge away from radiation source
The results of you dosimeter readings will be mailed to the Radiation Safety Officer and
you will be informed about any positive reading on personal basis.
At The University of Manitoba:
What are your occupational radiation risks while working at the
University?
History indicates that they are extremely low.
Those are the highest exposures recorded at the U of M:
Year
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Maximum Individual Exposure at U of M
1 mSv
0.4
0.5
1
0.6
0.4
0.4
0.4
0.2
0.15
0.12
0.3
0.0
0.0
Are some radioisotopes safer than others?
It depends on several factors, for example:
Radiation hazards depend on the energy and type of radiation and on the shielding material of the sealed source.
How can you control your exposure?
 Minimize the exposure time
 Increase the distance (inverse square law)
 Use effective shielding
!ALARA!
As low as reasonably achievable! (You dose of course)
Also avoid restricted areas when exposure rate higher than
25uSv/h.
This will be determined by the Radiation Safety Officer.
Can you get the radioactive material from sealed sources inside your body?
There is always a chance that the radioactive sealed source can start to leak
and when not handled properly, it can get inside your body.
That is why sealed sources are tested for leakage every year when
imbedded in an instrument and every 6 months when handled
manually. Only sealed sources containing more that 50 MBq must me leak tested.
The leak test kit will be mailed to the permit holder on a timely basis along with further
instructions. The swipes will be analyzed by the Radiation Safety Offices and the
certificates will be mailed to the permit holder.
Sample:
* * * LEAK
TEST CERTIFICATE * * *
DATE REPORTED: March 28, 2010
LEAK TEST SAMPLE # : 841
NAME OF MEASURER:
Environmental Health & Safety Office
University of Manitoba
ADDRESS OF MEASURER:
T248 Old Basic Science Building
770 Bannatyne, R3E 0W3
TELEPHONE # OF MEASURER:
(204) 789 3359
NAME OF LICENCEE / Permit Holder:
*******/****
ADDRESS OF LICENCEE / Permit Holder:
******* Bldg.
University of Manitoba
TELEPHONE # OF LICENCEE / Permit
Holder:
204-***-****
Permit Number:
*********
SAMPLE METHOD:
Swab
DATE SWABBED:
March 11, 2010
MEASURING METHOD:
Liquid Scintillation Counter
MEASURING INSTRUMENT:
Beckman LS 6500
CALIBRATIONS & VERIFICATIONS
DATE OF MEASURING EQUIPMENT:
Calibrated with <1uCi unquenched C-14
source
GAUGE OR SOURCE
MANUFACTURERS:
********
SOURCE SERIAL #:
******
RADIONUCLIDE:
Co-57
ACTIVITY:
420 MBq (decay corrected)
BACKGROUND MEASUREMENT:
19.4 cpm
SAMPLE MEASUREMENT:
22.8 cpm
CONCLUSION:
* < than 200 Bq
MEASURER:
Eva Sailerova
*CNSC sealed source leak test criterion < 200 Bq./> 200 Bq, then the licencee shall be notified
For more details refer to the Radiation Safety Manual, RSP-500.