- Email: [email protected]
Measuring Egg Shell Strength by Beta Backscatter Technique
Measuring Egg Shell Strength by Beta Backscatter Technique PAUL E. JAMES AND HENRY J. RETZER1 (Received for publication March 6, 1967)
B
1 Agricultural Engineers, Agricultural Engineering Research Division, USDA-ARS, Beltsville, Maryland 20705. The work reported in this paper was cooperative with the Poultry Research Branch, Animal Husbandry Research Division, USDA-ARS, and Technical Services, Isotope Development Center, Oak Ridge National Laboratory, AEC.
have thinner shells as the bird gets older. (5) The environmental temperature— high temperatures tend to produce thin shells. The numerous methods which have been attempted to measure shell strength indicate the need for an improved method. Some which have been tried are: (1) Eggs have been placed in an arbor press and the pressure required to break the shell recorded (Rehkugler, 1964). (2) The thickness of shells has been estimated from measuring the specific gravity of eggs by placing them in various salt solutions and determining where they float. (3) By dropping one egg on another and calculating the energy at failure (Rehkugler, 1964). (4) By twisting the egg and measuring the deformation. (5) By the impact method of increasing drop heights of a 2-gram aluminum cylinder until the egg cracked (Tyler and Geake, 1963). (6) By the impact method of increasing the drop height of a % 2 " m ch diameter, 0.7-gram steel ball until the egg cracked. All of these methods are inadequate. Some require an excessive amount of time; others probably change the structure of the eggs by repeated impacts, and several even crack the egg shell. Because the poultry scientists of the Agricultural Research Service desired a quick, nondestructive method for measuring shell strength, U.S.D.A. agricultural engineers in cooperation with research scientists at Oak Ridge National
1200
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
ECAUSE of the increased use of mechanical techniques for handling eggs during the past few years, a greater loss due to egg shell breakage is occurring. Previously, many of the fragile eggs broke when the producer collected them in wire baskets, but now papier-mache trays which have replaced wire baskets protect the eggs during the mechanical handling process, and more fragile eggs leave the producer for supermarkets and consumers. Breakage of fragile eggs amounted to approximately 3 percent of the total eggs produced during 196S (Anonymous, 1966) which resulted in a $25 million loss. In addition to this economic loss, a public health hazard is associated with bacterial contamination of broken egg shells. Marketers are also concerned about the annoyance customers experience from broken eggs. Improvements in shell quality are not occurring fast enough to meet the need. According to Peterson (1965) the following factors have been identified as affecting shell quality: (1) Genetic strain—some genetic strains produce thin-shelled eggs. (2) Rate of egg production—as the production rate increases the shells become thinner. (3) The diet of the hen—calcium is required. (4) The age of the bird—eggs produced
MEASURING EGG SHELL STRENGTH
Laboratory began investigating a nuclear method of measuring egg shell strength. X-RAY TECHNIQUE TESTED
PRINCIPLES INVOLVED IN BETA BACKSCATTER TECHNIQUE
The nucleus of the atom is considered to be composed of protons and neutrons. The neutron is composed of a proton and an electron tightly bound together. Upon sufficient excitation, the neutron divides. The heavy proton stays in the nucleus and the light electron leaves the atom. This freed electron is called a beta particle. Material which is losing electrons in this manner is radioactive. When a beta particle leaves the atom it collides and interacts with other atoms in its path. Each collision changes the direction of travel and slows the particle. If the particle reverses its initial direction away from the atom and approaches it, the beta particle is said to backscatter. If an egg shell placed in front of a beta emitter is thick and/or dense, it turns the beta particle back. If it offers little resistance, the particle continues to travel forward. Since both thickness and density turn the beta particle in its flight, measuring the amount of backscatter indicates more nearly what we call the strength rather than either thickness or density of the shell.
RADIOACTIVE SOURCES USED
Different radiation sources, i.e., radioactive isotopes, emit beta particles of different speeds. Since beta particles traveling at high speed penetrate further than those traveling slowly, high-velocity beta sources are more useful in measuring egg shell strength because an egg shell is comparatively dense. Strontium 90 was originally selected as a source for these tests because it emits high-velocity particles, is inexpensive, and lasts a long time. It was found inadequate, however, because it was unsafe to use enough of this material to give an adequate sampling. The next source considered was ruthenium 106-rhodium 106. This emits particles at various speeds which give high backscatter counts. The variation, however, of successive readings measured at a given location was as great as the variation between weak and strong egg shells. To minimize this variation, more radiation material was used to obtain a better sample. Although the amount needed for this was well within safety regulations, the Geiger-Mueller tube used for counting the backscatter could not function efficiently with this high counting rate (U. S. Department of Health, Education, and Welfare, 1960). Finally, a technique was evolved by scattering back three times as many particles as could be observed by the counter. This proved satisfactory both from a safety and sampling point of view. Remaining objections to the use of this material are that it has a relatively short life, reducing to one-half its original rate of emission after one year, and that it is difficult to concentrate the material. MEASURING PROCEDURE
Research indicates that the best distance from the source of radiation to the egg shell is 0.07S inches, with the window of the Geiger-Mueller tube 0.75 of an inch below
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
The first method attempted on this project for measuring shell strength by radiation consisted of sending an X-ray through the egg and measuring how much of it was stopped. The X-ray, chosen because it was easily stopped by the egg shell, was found to be slowed down by the interior of the egg as well, and a large-diameter egg had the same effect as a thick shell. This technique was discarded after 18 months of experimenting and investigation of the beta backscatter technique was undertaken.
1201
1202
P. E. JAMES AND H. J. RETZER
this might weaken the egg, backscatter counts were made first to estimate the fracture distance. With this technique, two or three drops were usually sufficient.
EGG APERTURE BETA EMITTER
RESULTS
WINDOW OF G. M. TUBE HALOGEN GAS ANODE OF 3.M. TUBE ANNULAR
HOLDER
FIG. 1. System for measurement by backscatter.
the egg shell. A 0.75-inch diameter opening for the egg also proved best. See Figures 1 and 2 for details. In order to correlate beta backscatter measurements with actual egg shell strength, a measuring device was developed which drops a steel ball from a height great enough to fracture the egg. This ball weighed 0.7 grams and was 7/32 inches in diameter. The egg was placed under a plastic tube which contained an adjustable pin to hold the ball at various heights above the egg. Starting low enough so the egg was not expected to break, the pin was released allowing the ball to drop freely on the egg. This test was repeated at increasing drop distances until the egg broke. See Figure 3. Early tests with this equipment required as many as 10 ball drops on the egg. Since
CONCLUSIONS
We have an extremely sensitive tool which is capable of measuring variations in the shell of an individual egg without damaging the egg in any way. The egg is still viable and edible. This technique should be extremely valuable to the geneticists and those making nutritional and environmental studies. Thus
7/32" DIA STEEL BALL BALL RELEASE KEY TUBE GRADUATIONS
ADJUSTABLE PLASTIC TUBE
<
LEVELING SCREW
FIG. 2. Backscatter gauge with egg.
FIG. 3. Impact tester.
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
SOURCE
G M. TUBE
A better correlation was obtained with impact resistance than with the thickness of the shell as measured with a micrometer. See Figure 4. Ten microcuries of activity with counts for 5 seconds allow identification of six categories of strength.
MEASURING EGG SHELL STRENGTH 8ACKSCATTER CO U N T 5/15 sec. 90.000
0 /
/ ' o
80-
co
60-
v
A o V
o 7 0
50-
/
/
*
<3 •7
O
v-impacf O-thickntjs 40
v
30
/
o
22 24 26 28 30 EGGSHELL THICKNESS. 12
32 34 » . • I0" 2
36
38
14 16 18 20 IMPACT DISTANCE, cm. FIG. 4
FIG. 4. Backscatter versus egg shell thickness and backscatter versus impact strength.
it may lead to improvement in the production of eggs with tougher shells. The shell-strength tester could also be used for rating eggs in order to help reduce the $25 million loss due to broken eggs. Those having the greatest strength could be used for overseas shipment, whereas weaker eggs could be sold to supermarkets and commercial users of eggs. Different types of
REFERENCES Anonymous, 1966. Poultry and egg situation. Economic and Statistical Information, Office of Management Service, Division of Information, USDA. Overman, R. T., and H. M. Clark, 1960. Radioisotope Techniques. McGraw-Hill Book Co., Inc., New York. Peterson, C. F., 1965. Factors influencing eggshell quality—A review. Worlds Poultry Sci. J. 2 1 : 110-138. Rehkugler, G. E., 1964. Egg-handling equipment design. Trans. A.S.A.E. 4 : 174-187. Tyler, C , and F. H. Geake, 1963. A study of various impact and crushing methods used for measuring shell strength. British Poultry Sci. 4 : 49-61. TJ. S. Department of Health, Education, and Welfare, 1960. Radiological Health Handbook.
NEWS AND NOTES (continued from page 1194) suiting tasks. Last August he received the Borden Award, administered by the Poultry Science Association. He served as an International Officer with the Food and Agricultural Organization, has been a Consultant for the Quartermaster General of the TJ. S. Army, and the Office of Naval Research, all in the field of nutrition relating to food rations. Some of his work in neurological control of food intake stemmed from the problems of service men and others who found the early Krations extremely unpalatable, even when they were very hungry. Born in Poland, November IS, 1899, he earned Bachelor and Master of Science, and Doctor of
Philosophy degrees at the University. After research in anatomy at the University of California, Berkeley campus for six years, he was Research Associate in the Institute of Experimental Biology for seven years. In 1935 he transferred to the Department of Poultry Husbandry on the Berkeley campus, and has been Professor since 1945, and Nutritionist in the University of California Agricultural Experiment Station. Members of the Orange County Farm Bureau presented a desk clock to Donald Bell in recognition of his service to the poultry industry in that County during his service as University of California Farm Advisor, starting in January 19S8 and
(continued on page 1219)
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
egg trays might be designed for fragile eggs. Supermarkets might advertise eggs having shell strength measured. Chicken hatcheries might use this equipment for measuring shell strength and thus be able to discard strains laying thin-shelled eggs. A method for measuring egg shell strength will permit an analysis of how rough various mechanical egg-handling equipment is on eggs, i.e., if eggs with a standardized backscatter count of SO K break in an egg-handling machine, perhaps the machine should be redesigned.
V
70
1203
B
1 Agricultural Engineers, Agricultural Engineering Research Division, USDA-ARS, Beltsville, Maryland 20705. The work reported in this paper was cooperative with the Poultry Research Branch, Animal Husbandry Research Division, USDA-ARS, and Technical Services, Isotope Development Center, Oak Ridge National Laboratory, AEC.
have thinner shells as the bird gets older. (5) The environmental temperature— high temperatures tend to produce thin shells. The numerous methods which have been attempted to measure shell strength indicate the need for an improved method. Some which have been tried are: (1) Eggs have been placed in an arbor press and the pressure required to break the shell recorded (Rehkugler, 1964). (2) The thickness of shells has been estimated from measuring the specific gravity of eggs by placing them in various salt solutions and determining where they float. (3) By dropping one egg on another and calculating the energy at failure (Rehkugler, 1964). (4) By twisting the egg and measuring the deformation. (5) By the impact method of increasing drop heights of a 2-gram aluminum cylinder until the egg cracked (Tyler and Geake, 1963). (6) By the impact method of increasing the drop height of a % 2 " m ch diameter, 0.7-gram steel ball until the egg cracked. All of these methods are inadequate. Some require an excessive amount of time; others probably change the structure of the eggs by repeated impacts, and several even crack the egg shell. Because the poultry scientists of the Agricultural Research Service desired a quick, nondestructive method for measuring shell strength, U.S.D.A. agricultural engineers in cooperation with research scientists at Oak Ridge National
1200
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
ECAUSE of the increased use of mechanical techniques for handling eggs during the past few years, a greater loss due to egg shell breakage is occurring. Previously, many of the fragile eggs broke when the producer collected them in wire baskets, but now papier-mache trays which have replaced wire baskets protect the eggs during the mechanical handling process, and more fragile eggs leave the producer for supermarkets and consumers. Breakage of fragile eggs amounted to approximately 3 percent of the total eggs produced during 196S (Anonymous, 1966) which resulted in a $25 million loss. In addition to this economic loss, a public health hazard is associated with bacterial contamination of broken egg shells. Marketers are also concerned about the annoyance customers experience from broken eggs. Improvements in shell quality are not occurring fast enough to meet the need. According to Peterson (1965) the following factors have been identified as affecting shell quality: (1) Genetic strain—some genetic strains produce thin-shelled eggs. (2) Rate of egg production—as the production rate increases the shells become thinner. (3) The diet of the hen—calcium is required. (4) The age of the bird—eggs produced
MEASURING EGG SHELL STRENGTH
Laboratory began investigating a nuclear method of measuring egg shell strength. X-RAY TECHNIQUE TESTED
PRINCIPLES INVOLVED IN BETA BACKSCATTER TECHNIQUE
The nucleus of the atom is considered to be composed of protons and neutrons. The neutron is composed of a proton and an electron tightly bound together. Upon sufficient excitation, the neutron divides. The heavy proton stays in the nucleus and the light electron leaves the atom. This freed electron is called a beta particle. Material which is losing electrons in this manner is radioactive. When a beta particle leaves the atom it collides and interacts with other atoms in its path. Each collision changes the direction of travel and slows the particle. If the particle reverses its initial direction away from the atom and approaches it, the beta particle is said to backscatter. If an egg shell placed in front of a beta emitter is thick and/or dense, it turns the beta particle back. If it offers little resistance, the particle continues to travel forward. Since both thickness and density turn the beta particle in its flight, measuring the amount of backscatter indicates more nearly what we call the strength rather than either thickness or density of the shell.
RADIOACTIVE SOURCES USED
Different radiation sources, i.e., radioactive isotopes, emit beta particles of different speeds. Since beta particles traveling at high speed penetrate further than those traveling slowly, high-velocity beta sources are more useful in measuring egg shell strength because an egg shell is comparatively dense. Strontium 90 was originally selected as a source for these tests because it emits high-velocity particles, is inexpensive, and lasts a long time. It was found inadequate, however, because it was unsafe to use enough of this material to give an adequate sampling. The next source considered was ruthenium 106-rhodium 106. This emits particles at various speeds which give high backscatter counts. The variation, however, of successive readings measured at a given location was as great as the variation between weak and strong egg shells. To minimize this variation, more radiation material was used to obtain a better sample. Although the amount needed for this was well within safety regulations, the Geiger-Mueller tube used for counting the backscatter could not function efficiently with this high counting rate (U. S. Department of Health, Education, and Welfare, 1960). Finally, a technique was evolved by scattering back three times as many particles as could be observed by the counter. This proved satisfactory both from a safety and sampling point of view. Remaining objections to the use of this material are that it has a relatively short life, reducing to one-half its original rate of emission after one year, and that it is difficult to concentrate the material. MEASURING PROCEDURE
Research indicates that the best distance from the source of radiation to the egg shell is 0.07S inches, with the window of the Geiger-Mueller tube 0.75 of an inch below
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
The first method attempted on this project for measuring shell strength by radiation consisted of sending an X-ray through the egg and measuring how much of it was stopped. The X-ray, chosen because it was easily stopped by the egg shell, was found to be slowed down by the interior of the egg as well, and a large-diameter egg had the same effect as a thick shell. This technique was discarded after 18 months of experimenting and investigation of the beta backscatter technique was undertaken.
1201
1202
P. E. JAMES AND H. J. RETZER
this might weaken the egg, backscatter counts were made first to estimate the fracture distance. With this technique, two or three drops were usually sufficient.
EGG APERTURE BETA EMITTER
RESULTS
WINDOW OF G. M. TUBE HALOGEN GAS ANODE OF 3.M. TUBE ANNULAR
HOLDER
FIG. 1. System for measurement by backscatter.
the egg shell. A 0.75-inch diameter opening for the egg also proved best. See Figures 1 and 2 for details. In order to correlate beta backscatter measurements with actual egg shell strength, a measuring device was developed which drops a steel ball from a height great enough to fracture the egg. This ball weighed 0.7 grams and was 7/32 inches in diameter. The egg was placed under a plastic tube which contained an adjustable pin to hold the ball at various heights above the egg. Starting low enough so the egg was not expected to break, the pin was released allowing the ball to drop freely on the egg. This test was repeated at increasing drop distances until the egg broke. See Figure 3. Early tests with this equipment required as many as 10 ball drops on the egg. Since
CONCLUSIONS
We have an extremely sensitive tool which is capable of measuring variations in the shell of an individual egg without damaging the egg in any way. The egg is still viable and edible. This technique should be extremely valuable to the geneticists and those making nutritional and environmental studies. Thus
7/32" DIA STEEL BALL BALL RELEASE KEY TUBE GRADUATIONS
ADJUSTABLE PLASTIC TUBE
<
LEVELING SCREW
FIG. 2. Backscatter gauge with egg.
FIG. 3. Impact tester.
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
SOURCE
G M. TUBE
A better correlation was obtained with impact resistance than with the thickness of the shell as measured with a micrometer. See Figure 4. Ten microcuries of activity with counts for 5 seconds allow identification of six categories of strength.
MEASURING EGG SHELL STRENGTH 8ACKSCATTER CO U N T 5/15 sec. 90.000
0 /
/ ' o
80-
co
60-
v
A o V
o 7 0
50-
/
/
*
<3 •7
O
v-impacf O-thickntjs 40
v
30
/
o
22 24 26 28 30 EGGSHELL THICKNESS. 12
32 34 » . • I0" 2
36
38
14 16 18 20 IMPACT DISTANCE, cm. FIG. 4
FIG. 4. Backscatter versus egg shell thickness and backscatter versus impact strength.
it may lead to improvement in the production of eggs with tougher shells. The shell-strength tester could also be used for rating eggs in order to help reduce the $25 million loss due to broken eggs. Those having the greatest strength could be used for overseas shipment, whereas weaker eggs could be sold to supermarkets and commercial users of eggs. Different types of
REFERENCES Anonymous, 1966. Poultry and egg situation. Economic and Statistical Information, Office of Management Service, Division of Information, USDA. Overman, R. T., and H. M. Clark, 1960. Radioisotope Techniques. McGraw-Hill Book Co., Inc., New York. Peterson, C. F., 1965. Factors influencing eggshell quality—A review. Worlds Poultry Sci. J. 2 1 : 110-138. Rehkugler, G. E., 1964. Egg-handling equipment design. Trans. A.S.A.E. 4 : 174-187. Tyler, C , and F. H. Geake, 1963. A study of various impact and crushing methods used for measuring shell strength. British Poultry Sci. 4 : 49-61. TJ. S. Department of Health, Education, and Welfare, 1960. Radiological Health Handbook.
NEWS AND NOTES (continued from page 1194) suiting tasks. Last August he received the Borden Award, administered by the Poultry Science Association. He served as an International Officer with the Food and Agricultural Organization, has been a Consultant for the Quartermaster General of the TJ. S. Army, and the Office of Naval Research, all in the field of nutrition relating to food rations. Some of his work in neurological control of food intake stemmed from the problems of service men and others who found the early Krations extremely unpalatable, even when they were very hungry. Born in Poland, November IS, 1899, he earned Bachelor and Master of Science, and Doctor of
Philosophy degrees at the University. After research in anatomy at the University of California, Berkeley campus for six years, he was Research Associate in the Institute of Experimental Biology for seven years. In 1935 he transferred to the Department of Poultry Husbandry on the Berkeley campus, and has been Professor since 1945, and Nutritionist in the University of California Agricultural Experiment Station. Members of the Orange County Farm Bureau presented a desk clock to Donald Bell in recognition of his service to the poultry industry in that County during his service as University of California Farm Advisor, starting in January 19S8 and
(continued on page 1219)
Downloaded from http://ps.oxfordjournals.org/ at Temple University Law School Library on April 22, 2015
egg trays might be designed for fragile eggs. Supermarkets might advertise eggs having shell strength measured. Chicken hatcheries might use this equipment for measuring shell strength and thus be able to discard strains laying thin-shelled eggs. A method for measuring egg shell strength will permit an analysis of how rough various mechanical egg-handling equipment is on eggs, i.e., if eggs with a standardized backscatter count of SO K break in an egg-handling machine, perhaps the machine should be redesigned.
V
70
1203