Lecture 12: Food Irradiation

Question 1

when irradiation is discussed, it is done mainly with respect to what?

Answer 1

ionizing radiations: X-rays and gamma-rays

Question 2

when wavelength decreases, what increases?

Answer 2

frequency

Question 3

rank the folowing from smallest to largest wavelength

x ray
UV
visible
infrared
gamma rays
microwave
radio

Answer 3

gamma (smallest wavelenght)
x ray
UV
visible
infrared
microwave
radio (largest wavelength)

Question 4

X rays and gamma rays are v short wavelength radiations htat have very high ____

Answer 4

associated energy levels

Question 5

how can X rays and gamma rays cause ionization?

Answer 5

b/c they are high energy, they can knock off an electron from an atom

Question 6

what are 3 imp components of EMR?

Answer 6

frequency
wavelength
energy

Question 7

what is the variable and unit of frequency?

Answer 7

v (cycles/s)

Question 8

what is the variable and unit of wavelength?

Answer 8

lambda (cm)

Question 9

what is the variable and unit of energy?

Answer 9

E (eV)

Question 10

h represents what?

Answer 10

plank’s constant = 4 x 10^-15 eVs

Question 11

c represents what?

Answer 11

velocity of light = x x 10^10 cm/s

Question 12

what are the pioneering scientists of radiation processing?

Answer 12

roetgen
Becquerel
Curie

Question 13

what are the 3 types of rays (rutherford)? describe each

Answer 13

alpha rays

• positive
• low energy, can be stopped by a sheet of paper

gamma

• neutral
• high energy

beta (neg) rays

• negative
• medium energy

Question 14

outline the history of radiation applications

Answer 14

1920-40: X ray tube, medical application, therapeutic trt of cancer
40-50: radiology equipment, med research
50-60: medical and dental applications, sterilization of non-food items
60-70: major food research, wider applications
70-current: widespread application, food processing

Question 15

what is the main source of ionizing radiation?

Answer 15

1 source of gamma rays: cobalt 60 (a radioactive isotope produced from cobalt 59)

Question 16

why do beta rays need to be accelerated to have enough energy?

how is this done?

Answer 16

b/c associated E levels is too low to be practical

uses cyclotron or linear accelerators

Question 17

what are 2 types of units of ionizing radiation?

Answer 17

1. unit for radiation intensity

2. unit for radiation dose

Question 18

describe radiation intensity

what is the unit used?

Answer 18

rate at which a dose can be given; a measure of dose-rate (power of the source)

Ci (curie)

Question 19

describe radiation dose

Answer 19

the amount of radiation given to the product or absorbed by the product

Question 20

1 curie = what?

Answer 20

1 curie = 3.7 x 10^10 disintegration/s

Question 21

how are radioisotopes diff from conventional E sources?

Answer 21

1. they emit radiation continuously

2. they lose their intensity as they emit radiation (radioactive decay)

Question 22

rate of decay is proportional to what?

Answer 22

intensity

Question 23

what is:
No
N
a
gamma

Answer 23

No = initial intensity
N = intensity at time t
a = decay constant
gamma = half life of radioisotope (time during which the intensity is reduced by 50%)

Question 24

what determines current intensity?

Answer 24

initial intensity
half life
length of time since inception

Question 25

describe radiation dose

Answer 25

radiation E absorbed while the food is exposed to the radiation field

Question 26

one rad = ?

Answer 26

amount of radiation that results in the absorption of 10^-5J/g or 10^-2J/kg of radiation E at the point of interest

Question 27

what is Gy?

Answer 27

international unit Gray for radiation dose

1 Gy = 100 Rad = absorption of 1J/Kg

Question 28

how do you achieve the desired dose of radiation?

Answer 28

by the combination of exposure time and dose rate at product location

Question 29

as a product moves away from the source, dose rate intensity _____

Answer 29

decreases

Question 30

amount of energy absorbed also depends on what?

Answer 30

dose rate
mass
bulk density
thickness of food

Question 31

what are 3 categories of radiation dose?

Answer 31

1. low (up to 1kGy): inhibits sprouting, disinfects F&V from insects, delays physiological processes
2. medium (1-10kGy): eliminates spoilage MOs, extends shelf life of F&V
3. high (10-50 kGy): decontaminates herbs, spices, food ingredients

Question 32

what are 3 imp facts about radiation intensity?

Answer 32

1. radio active intensity decreases w/ time (describe in terms of half life)
2. radio active intensity decreases w/ distance from radio active source (described w/ respect to absorption coefficient)
3. radio active intensity decreases w/ penetration into a body (described w/ penetration

Question 33

absorption is proportional to what?

Answer 33

intensity

Question 34

decrease in absorption = ____ in intensity

Answer 34

decrease

Question 35

intensity and absorption ___ with distance or penetration depth

Answer 35

decreases

Question 36

what is irradiation sterilization based on?

Answer 36

destruction of C. botulinum

Question 37

define the D value

Answer 37

dose required to kill 90% of population

results in one decimal reduction in population or one log cycle reduction

Question 38

sterilization is based on what?

Answer 38

12 log reductions or 12 decimal reductions

Question 39

dose required for sterilization is what?

Answer 39

12x dose for one log or one decimal reduction

eg. if D = 1 min; 12D = 12 min