1. Environmental Physics
Chapter 15: Effects and Uses of Radiation
Copyright © 2008 by DBS

2. Introduction Radiation is present everywhere
Can have both positive and negative effects on living things
Earth has been subject to cosmic rays since it was formed

4. Question Calculate the energy (in eV) of visible light and Gamma rays
E = hν = hc/λ
= (6.626 x Js x 3.00 x 108 m/s)/ 10-6 m = 2 x J x (1 eV/1.6 x 10-19J) = 1 eV
= (6.626 x Js x 3.00 x 108 m/s)/ m = 2 x J x (1 eV/1.6 x 10-19J) = 1 MeV

5. Introduction
We will study radiation that produces harmful biological effects - ionizing radiation
Radiowaves, microwaves, visible light etc are of too low energy to cause damage
Energy around 12 eV is required to ionize water

6. Nuclear Physics Heavy particles less penetrating Type Description
Penetration
Shielding
Charge α
He nucleus
Low
Skin
+ve β
Electrons
Medium
1-5 mm metal
-ve
γ-ray, x-ray
EM radiation
High
10 mm + lead, 1 m concrete

7. Radiation Dose Ionizing Radiation: Gamma rays X-Rays Beta particles
Alpha particles
Gamma and X-Rays are not charged, do not ionize through electrical interaction Produce e- indirectly via the Compton effect
Compton scattering or the Compton effect is the decrease in energy (increase in wavelength) of a gamma ray photon when it interacts with matter.

8. Radiation Dose
Activity (A) – measures the no. of decays per second (Ci or Bq)
Absorbed dose (D) – energy absorbed per gram of tissue (rads or Grays, 1 Gy = 100 rads)
Dose equivalent (H) – absorbed dose multiplied by a biological effectiveness factor (rems or Sieverts, 1 Sv = 100 rems
Quality factor (QF) (see table)
H = D x QF

9. Radiation Dose
Absorbed Dose, D. is the energy deposited in an organ or a mass of tissue per unit mass of irradiated tissue. A common unit for absorbed dose is the rad, which is 100 ergs (100 x 10-7 J) per gram of material.
To calculate D you usually calculate the total absorbed energy first
You use the activity (Bq), the energy (eV) of the radiation and exposure time to calculate the total amount of energy that arrives at the surface of your body
Tissue absorption coefficients are then used to calculate the total energy absorbed by the body
The last step is to calculate the absorbed energy per unit mass, which requires a decision on what mass of tissue to use—the mass of the whole body or just the mass of the irradiated tissue
(by taking into account such factors as the fraction of the radiation from the source that’s moving in the right direction, the distance between the source and your body, the length of time for the exposure, and attenuation from any shielding or the air)

10. H (rem, Sv) = QF x D (rad, Gy)
Radiation Dose
Dose-equivalent, H. A key factor that the absorbed dose doesn’t take into account is the density of the ionization created by the radiation
e.g. α leaves an ion track that’s several hundred times more dense than that of β
Generally, one rad of α ~20 x as effective at causing cellular damage—and thus cancer—than one rad of γ or β radiation.
We account for these differences using a radiation-weighting factor, QF, that represents the effectiveness of each type of radiation to cause biological damage. The factors are determined by measuring the occurrence of various biological effects for equal absorbed doses of different radiations
H (rem, Sv) = QF x D (rad, Gy)
Why does gamma radiation have the same weighting factor as beta particles?
γ-radiation is more diffuse but does the same amount of damage
The idea is that equal dose-equivalents generate equivalent amounts of biological damage.
Less than half the energy of 5-MeV γ-ray photons is absorbed as they pass horizontally through your torso. However, the energy that’s deposited is from electrons that have been knocked loose. The ionization tracks generated at these points by the ejected electrons have the same ion density as beta particles, despite the fact the regions are scattered throughout the material. Thus, beta and gamma radiation delivering the same dose-equivalent create the same density of ionization in the cells per gram of tissue.

11. Radiation Dose
0.1 μg Pu-239 in your hand (5 cm diameter area), what dose do you receive from 5-MeV α-particles in one hour?
Assume 50% penetrates the body (50% attenuated by the air), energy of α-particle = 5 MeV, and 1 g Pu-239 emits 2.2 x 109 α –particles/s
Abs. Dose (rads) = (Activity) x (Ave. Energy per particle) x (Fraction Absorbed) x (Time)
Skin absorbs energy of 0.1 x 10-6 g x (2.2 x 109 α –particles/s / 1 g) x 0.5 = 110 α-particles/s
110 α-particles/s x 5 MeV/particle = 550 MeV/s x (1.6 x 10-19J/ 1 eV) x erg/10-7 J = erg/s
Assume α penetrates 30 μm, energy is deposited in a disc of tissue 0.06 cm3, using density of 1 g/cm3, we have erg/s / 0.06 g tissue = erg/s per g
Abs. Dose (rads) = erg/s per g x (1 rad / 100 ergs/g) = 1.5 x 10-4 rads/s
Dose equivalent = 1.5 x 10-4 rads/s x 20 = rem/s x 3600 s/hr = 11 rem
The idea is that equal dose-equivalents generate equivalent amounts of biological damage.
Less than half the energy of 5-MeV γ-ray photons is absorbed as they pass horizontally through your torso. However, the energy that’s deposited is from electrons that have been knocked loose. The ionization tracks generated at these points by the ejected electrons have the same ion density as beta particles, despite the fact the regions are scattered throughout the material. Thus, beta and gamma radiation delivering the same dose-equivalent create the same density of ionization in the cells per gram of tissue.

12. Radiation Dose

13. Biological Effects
Non-ionizing radiation is thought to be essentially harmless below the levels that cause heating.
Ionizing radiation is dangerous in direct exposure, although the degree of danger is a subject of debate
Humans and animals can also be exposed to ionizing radiation internally: if radioactive isotopes are present in the environment, they may be taken into the body

14. Biological Effects Average adult has ~ 50 trillion cells
Nucleus and chromosomes carries DNA with instructions for replication
Ionizing radiation may cause direct DNA damage, inhibiting repair
Cell are made of 70 % water
may be ionized forming highly reactive free radicals
Figure 15.1: Diagram of a cell.

15. alpha particle
Highly energetic α, β particles rip through tissue causing cellular and genetic damage

16. Biological Effects Damage may be: Somatic – affecting the individual
Genetic – affecting offspring
Damaged cells may grow in an uncontrolled manner and invade and destroy surrounding host cells becoming malignant cancer
This is an over simplification… cancer is probably caused by several factors

17. Biological Effects Effects may be acute or chronic
For small doses cancers may not be seen for many years – hard to establish cause and effect
For high doses under short time spans we have data from human and animal experiments
Figure 15.2: Dose-effect distribution curve for mice. The point at which 50% of the population dies is called the lethal dose-50, or LD-50. It is about 1000 rads in this example.

18. Biological Effects
Biological effects depend on what part of the body is irradiated
Hands and feet can take higher doses
Internal organs are more susceptible
Standards governing exposure are determined based on past exposures
Health effects of high doses of radiation are well known, information on low dose effects is difficult to obtain
Two very different sources of data…

19. Biological Effects
Hiroshima and Nagasaki survivors received average exposure of 130 rem (this is still 100 x higher than occupational low-dose exposure)
Created 120 additional cancers over 27 years
Both somatic and genetic studies reported
One example of a radiation effect curve is that for leukemia
2 cases per million people per year per rem
Figure 15.3: Leukemia mortality dose-response curves for Hiroshima and Nagasaki.

20. Biological Effects Uranium miners High incidence of lung cancer
X-ray technicians
Radium dial painters
Studies generally assume a linear dose-response relationship
Curve can be extrapolated back from high-dose data to the low dose region
Assumes no threshold, any radiation exposure produces a harmful effect
Considerable debate as to the validity of this argument
Figure 15.4: (a) No threshold dose-response curve—that is, that the data from high doses (solid curve) can be extrapolated back to low doses, (b) threshold curve

21. Adverse Health Effects
Atomic Bomb Survivors
Observed Effects
Underground Miners
Medical Patients
Adverse Health Effects
? ? ?
Linear
No threshold
Dose (rem)

22. End
Review

24. Background Radiation Natural sources Man-made sources
See Eckhardt, R. (1995) Radiation is Everywhere. Los Alamos Science, No. 23, pp
Radon and its decay products make up 55% of background
Eckhardt, R. (1995)

25. What is Radon? Natural Radioactivity
22286Rn
Invisible, odorless, colorless, tasteless
Only gas in 238U decay chain

26. Question
Radon is said to be a daughter of radium-226, polonium-218 is a daughter of radon. Why are these not called sons?
Radon decay products (RDP’s) continue to decay giving birth to new daughters (progeny).
Indeed these RDP are the real culprits in the radon story!

27. What is Radon? Radon Gas
50 minutes
26.8m

28. Health Effects Radon Gas
Source: Turco (2002)
Health Effects Radon Gas
Turco (2002) Earth Under Siege, OUP.
Progenies (‘daughters’) build up in confined space –are breathed in, stick to surface of airways and emit α-particles

30. Background Radiation
Medical studies of uranium miners has shown that long-term exposure causes cancer
Generally agreed that Rn is a major cause of cancer
10-15 % of all lung cancers ?
Second hand smoke
Figure 15.6: Comparable risks from exposure to radon gas.

31. Health Effects How Radon Compares To Other Causes Of Death
estimate
Upper
The comparison above is from the US EPA’s Home Buyer’s and Seller’s Guide to Radon (July 2000). It compares the estimated number of deaths in the U.S. due to radon, with other more widely known causes of death. This comparison provides one reason why the EPA and other health organizations are so concerned about the radon issue. Furthermore, because radon is so easy to detect and also easy to fix, one can see why radon detection and remediation has become a priority.
According to the National Safety Council Radon is estimated to cause between 15,000 and 22,000 lung cancer deaths in the U.S. per year (this is why the radon bar is stacked). The numbers of deaths from other causes are taken from 1999 National Safety Council report: Injury Facts.
Lower estimate
Drunk
Driving
Radon
Drownings
Fires/Burns
Air
Transportation
Source: U.S. EPA’s Home Buyer’s and Seller’s Guide (Radon: National Academy of Sciences, Non-radon: National Safety Council)

32. Question Convert pCi L-1 to Bq m-3
1 pCi L-1 x 1000 L m-3 = 1000 pCi m-3
1000 pCi m-3 x 3.7 x 1010 Bq / Ci
= 1 x 10-9 Ci m-3 x 3.7 x 1010 Bq / Ci
= 37 Bq m-3

33. Background Radiation
How did we discover radon was a problem?

34. Background Radiation Stanley Watras
Limerick Nuclear Power Plant, Christmas 1984
Set off radiation alarm bells
Home basement Rn ~ Bq m-3
Risk equivalent smoking 135 packs of cigarettes per day
Designed to detect radiation on workers leaving…Watras was entering!

35. What is Radon?
1988 EPA orders every home tested

36. What is Radon?

37. Background Radiation Pressure driven air flow
Warm air rises and escapes home
Lower pressure inside than out
Replacement air drawn in from below
Increases with wind speed
Stack effect enhances Rn movement

38. Radon-222 Zone 1: > 4 pCi/L (red) Zone 2: 2-4 pCi/L (orange)
Zone 3: < 2 pCi/L (yellow)
Radon-222
Based on indoor measurements, geology, aerial radioactivity, soil parameters and foundation type

39. EPA – Breathing Easy: What Home Buyers and Sellers Should know About Radon. EPA 402-C-03-002.
Based upon current and past studies, the EPA established a guidance for non-occupational exposures to radon. This guidance level was arrived at by analyzing both the health risks and the cost of fixing buildings with elevated levels. That is, the 4.0 pCi/L guidance is BOTH a health and an economic based number.
The 4.0 pCi/L guidance is not a safety standard. Levels below 4.0 pCi/L still represent some risk. Even the outdoor air contains some radon.
So, avoid making comments such as “the house tested safe,” or “there is no radon in the home.” Just because a house is below the EPA’s action level does not mean that there is no risk at all.
The conclusion that radon is a serious health risk is supported not only by the US EPA, but also the American Lung Association, the National Academy of Sciences and the National Council on Radiation Protection, among others.
Basement level

40. Background Radiation
At 4 pCi/L people receive a dose of ~ 7700 mrem to the lung or 1000 mrem whole body equivalent each year (based on 75 % of time spent inside)
National Academy of Sciences BEIR VI Report (1998) stated an average effective dose equivalent for US from radon to be 200 mrem/y (2 mSv/y)
Basis for working out our average background radiation exposure

41. Background Radiation Remediation Seal cracks
Pump air to roof from underneath basement
Figure 15.7: Key to major radon entry routes.

42. Background Radiation Cosmic rays (30 mrem/y)
High energy particles (p+) and gamma rays from outer space
Dose depends on altitude and latitude
Atmosphere attenuates radiation – lower doses at sea-level e.g. 30 mrem/y Al, CA, MA vs. 120 mrem/y CO
Earth’s magnetic field deflects best at equator, least at the poles
Increased exposure on airplane flights ~ 2 mrem for a transcontinental flight
Terrestrial (30 mrem/y)

43. Background Radiation Internal Exposure (40 mrem/y) K-40 in the body
Food and liquid ingested
U-238 and K-40 from phosphate fertilizers
Ra-226 from cereals and Brazil nuts
Cosmogenically produced C-14

44. Background Radiation Artificial sources
Medical and Dental – diagnostic/therapeutic (53 mrem/y)
Typical chest X-ray about 10 mrem
Thyroid scan using radioactive Iodine mrem
Have to do a risk assessment analysis for yourself e.g. for a thyroid scan I-131 is a beta emitter with a 8 day half-life vs. I-123 is a gamma emitter with a 13 hr half-life e.g. breast cancer screening for women – when to start

45. Background Radiation Varies – depends on the person
Average is 4 dental X-rays and 1 medical X-ray every 10 years

46. Background Radiation Consumer Products (9 mrem/y)
Luminous paint on dials
Smoke detectors (Am-241)
Fiestaware
Porcelain teeth and crowns
Rose tinted glasses
Tobacco (leaves absorb Rn) – Po daughter suspected to be major cause of lung cancer

47. Background Radiation

48. End
Review

49. Radiation Standards
Biological Effects of Ionizing Radiation (BEIR) VI report of 1998
Obtained risk estimates from animal studies
Genetic doubling dose (dose to achieve number of mutations equal to natural occurrence) = 100 rem
Somatic (cellular) effects determined from atom bomb survivors and miners
560 excess cancer deaths per million people per extra (above BG) rem of annual whole body dose (all cancers)
Compare with 18,000 cancer deaths per year per million people (all causes)
NRC has public limit of 100 mrem above background (1994)
Radiation workers allowed up to 5 rem/y whole body

50. Radiation Standards f
See Eckhardt, R. (1995) Radiation is Everywhere. Los Alamos Science, No. 23, pp

51. Medical and Industrial Uses
Treatment of cancer
Cobalt-60 treatment
Cancer cells divide rapidly, more sensitive to radiation than normal cells
Patient receives treatment from all sides
10,000 Ci source, dose of ~100 rem
Small doses given periodicaly
Figure 15.8: A cobalt-60 unit for radiation therapy. The machine allows the radioactive source to rotate around the stationary patient. The tumor being treated is placed exactly at the center of rotation, so that damage to good tissue is minimized.

52. Medical and Industrial Uses

53. Medical and Industrial Uses
Technitium-99

54. Figure 15. 9: Radioisotope use in industry
Figure 15.9: Radioisotope use in industry. An increase or reduction in the intensity of gamma rays transmitted through the sheet metal indicates a thinner or thicker sheet, respectively. This is used as a thickness gauge.
Figure 15.9: Radioisotope use in industry. An increase or reduction in the intensity of gamma rays transmitted through the sheet metal indicates a thinner or thicker sheet, respectively. This is used as a thickness gauge.
Fig. 15-9, p. 518

55. p. 519

56. Figure 15.10: Computed Tomography (CT- or CAT-scan) equipment.
Fig , p. 520

57. Figure 15.11: MRI image of a head. A tumor appears as a white spot.
Fig , p. 521

58. Radiation Protection Best dose is zero!
Distance – intensity of radiation is inversely proportional to square of the distance from source
Shielding – concrete, lead etc. Intensity reduces exponentionally
Exposure Time – dose is cumulative
Figure 15.12: Radiation detection devices. The film badge in the center consists of photographic film, which darkens as a function of the amount of ionizing radiation received. The pocket dosimeter on the left can be read at any time to see how much radiation has been accumulated. The Geiger tube on the right is used with a counter to measure radiation intensity, while the large device in the background is a detector to monitor neutron activity.

59. Being checked for contamination by whole-body scan (using NaI detectors), upon exiting nuclear power plant.
Being checked for contamination by whole-body scan (using NaI detectors), upon exiting nuclear power plant.
p. 521

60. Table 15-7a, p. 526

61. Radiation Standards Eckhardt, R. (1995)
Eckhardt, R. (1995) Radiation is Everywhere. Los Alamos Science, No. 23, pp
Eckhardt, R. (1995)

62. Radiation Detection
Instruments for monitoring radiation exposure or determining type and energy of radiation
Detect ions produced by radiation
Gas-Filled Detectors
Scintillators
Solid-state detectors

63. Figure 15.13: A gas-filled radiation detector.
A common radiation detector is the Geiger-Müller counter, which has a long, narrow tube containing a gas that’s easily ionized. The tube has a wire down its center, and a voltage drop is created between the wire and the sides of the tube. Whenever radiation penetrates the tube and ionizes some of the gas, the voltage causes positive ions to be pulled toward the walls and negative electrons to accelerate toward the wire, creating an electrical discharge—a miniature lightning bolt. The resulting current pulse in the circuit is registered by the counter.
Sometimes radiation may not be counted by the detector because it’s blocked by the wall of the tube or it passes through the tube without ionizing any of the gas. So to understand your measurements fully, you need to know the type of radiation you’re trying to measure and the efficiency of the counter for detecting that radiation.
Still, a Geiger-Müller counter with a thin mica window on one end of the tube (to let some of the weakly penetrating radiations into the gas) is a good all-around tool for detecting most types of ionizing radiation. You can learn a lot about your environment and your own exposures taking measurements with a simple hand-held Geiger-Müller counter. There are several such counters available today in the $250 to $350 price range.
Figure 15.13: A gas-filled radiation detector.
Fig , p. 528

64. Radiation Detection Scintillation Counters
Sodium iodide crystal
Emits light when exposed to gamma radiation
Photomultiplier uses photoelectric effect to produce a current
Figure 15.14: Analysis of γ rays from a radioactive source, using a NaI scintillation detector. The NaI crystal is coupled to a photomultiplier tube, whose output is amplified and directed to an analyzer. The analyzer determines the number of γ rays as a function of their energy, and the results are displayed on the monitor.

65. Radiation Detection Semiconductor Detectors
Similar in principle to a GM tube
Gas is replaced by Si or Ge
Current is proportional to the energy of the radiation
Figure 15.15: Gamma-ray spectrum of Eu-152, obtained with a germanium detector. The spectrum shows the number of counts (on the y-axis) as a function of γ-ray energy.

66. End
Review

67. Summary
As you can see, we live in a sea of ionizing radiation, most of which has been here from the birth of the planet. Man’s ability to manipulate radioactive materials and to create new sources of radiation is adding to the amount of ionizing radiation we receive each year.