Lecture 12: Food Irradiation Flashcards
when irradiation is discussed, it is done mainly with respect to what?
ionizing radiations: X-rays and gamma-rays
when wavelength decreases, what increases?
frequency
rank the folowing from smallest to largest wavelength
x ray UV visible infrared gamma rays microwave radio
gamma (smallest wavelenght) x ray UV visible infrared microwave radio (largest wavelength)
X rays and gamma rays are v short wavelength radiations htat have very high ____
associated energy levels
how can X rays and gamma rays cause ionization?
b/c they are high energy, they can knock off an electron from an atom
what are 3 imp components of EMR?
frequency
wavelength
energy
what is the variable and unit of frequency?
v (cycles/s)
what is the variable and unit of wavelength?
lambda (cm)
what is the variable and unit of energy?
E (eV)
h represents what?
plank’s constant = 4 x 10^-15 eVs
c represents what?
velocity of light = x x 10^10 cm/s
what are the pioneering scientists of radiation processing?
roetgen
Becquerel
Curie
what are the 3 types of rays (rutherford)? describe each
alpha rays
- positive
- low energy, can be stopped by a sheet of paper
gamma
- neutral
- high energy
beta (neg) rays
- negative
- medium energy
outline the history of radiation applications
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
what is the main source of ionizing radiation?
1 source of gamma rays: cobalt 60 (a radioactive isotope produced from cobalt 59)
why do beta rays need to be accelerated to have enough energy?
how is this done?
b/c associated E levels is too low to be practical
uses cyclotron or linear accelerators
what are 2 types of units of ionizing radiation?
- unit for radiation intensity
2. unit for radiation dose
describe radiation intensity
what is the unit used?
rate at which a dose can be given; a measure of dose-rate (power of the source)
Ci (curie)
describe radiation dose
the amount of radiation given to the product or absorbed by the product
1 curie = what?
1 curie = 3.7 x 10^10 disintegration/s
how are radioisotopes diff from conventional E sources?
- they emit radiation continuously
2. they lose their intensity as they emit radiation (radioactive decay)
rate of decay is proportional to what?
intensity
what is: No N a gamma
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%)
what determines current intensity?
initial intensity
half life
length of time since inception
describe radiation dose
radiation E absorbed while the food is exposed to the radiation field
one rad = ?
amount of radiation that results in the absorption of 10^-5J/g or 10^-2J/kg of radiation E at the point of interest
what is Gy?
international unit Gray for radiation dose
1 Gy = 100 Rad = absorption of 1J/Kg
how do you achieve the desired dose of radiation?
by the combination of exposure time and dose rate at product location
as a product moves away from the source, dose rate intensity _____
decreases
amount of energy absorbed also depends on what?
dose rate
mass
bulk density
thickness of food
what are 3 categories of radiation dose?
- low (up to 1kGy): inhibits sprouting, disinfects F&V from insects, delays physiological processes
- medium (1-10kGy): eliminates spoilage MOs, extends shelf life of F&V
- high (10-50 kGy): decontaminates herbs, spices, food ingredients
what are 3 imp facts about radiation intensity?
- radio active intensity decreases w/ time (describe in terms of half life)
- radio active intensity decreases w/ distance from radio active source (described w/ respect to absorption coefficient)
- radio active intensity decreases w/ penetration into a body (described w/ penetration
absorption is proportional to what?
intensity
decrease in absorption = ____ in intensity
decrease
intensity and absorption ___ with distance or penetration depth
decreases
what is irradiation sterilization based on?
destruction of C. botulinum
define the D value
dose required to kill 90% of population
results in one decimal reduction in population or one log cycle reduction
sterilization is based on what?
12 log reductions or 12 decimal reductions
dose required for sterilization is what?
12x dose for one log or one decimal reduction
eg. if D = 1 min; 12D = 12 min
