þ7#  F˜ Beeeees ÓÓÓ ß é óó&x“@‘ ±*/3eÇ>b616-Oct-87 R.S. Galik revised June '92 E. Cassel Physics 310 Gamma Ray Absorption Guidance and Direction This is not meant to be a substitute for the handout written by R.H. Siemann: however, the available apparatus and goals of the experiment have changed since its inception and this supplement is designed to give an updated overview of the experiment's capabilities and provide direction for the student. Plateau and Background How much data should be taken to obtain an adequate plateau curve? Should the duration of runs be measured in time or in events? What are the conditions under which background runs are taken? Are there background conditions you can't simulate? What accuracy do you need for the subtraction? How do you determine this? Will differing geometry's require different background determination? Measurements of Absorptive Coefficients For the initial measurements of m, the strongest of the 60Co sources is best. Using the 2" diameter disks measure m for lead, copper, and aluminum. Using the 1" diameter disks measure m for carbon, using the lead as a cross check. The f(1,2)" diameter disks allow a determination of m for tin, zinc, and nickel, with cross checks on lead and carbon. Armed with the values of m, what dependence is observed for the absorption cross section as a function of Z? How well do your m values match those from reference tables and what is the dominant interaction between gamma ray and target nucleus? How "good" are your least squares fits? What are the confidence levels? Dependence on Photon Energy Does a source with different photon energy (137Cs) yield a value of absorptive coefficient in lead which agrees with i) the "accepted" values and ii) your value from before? What is your estimate of the size of the effect on the fit for the coefficient due to the two different energies in the cobalt source? Is the same background subtraction adequate for both sources? How can you tell? Geometric Considerations Try another geometry's. Are the systematic uncertainties the same? Are the lead coefficients different? Why or why not? Spend no more than one lab session investigating this aspect of the experiment. Other Considerations What is the overall dead time of the experiment? how large a correction is that at your highest counting rate point? Does the counting rate with no absorber scale with the square of the distance from source to detector? Why or why not? What are two permanent improvements that can be made to this experiment, not to make it a necessarily easier experiment, but a more useful, educational experiment? -- u€ering geometries en gamma ray and target nucleus? Try another geometrieabsorption dead time of the experiment? H tn carbon. Armed with the values of š°?fˆ‰ ¢ÛÝ"$VZ[\]_‡‰äåJK %SV¯Ç • © ? @ A E F K [ \ { | } “ ž ¾ À Á Âûûøòøøììòøøøûòûûæà @ @  1 &0<Qhš±5?gÊÀ &Õ]¯È • ª ! š ? C D E F } ÂùùùùïææÜÒÉÀÒ·À®ÒÉÉ®ÒÀÒÉÉɤŸŸÉŸŸ óý0!À!Àý0h ÿ!ÀMý0h!Àý0h!Àý0h !Àý0hð !Àý0hð!Àý0h !Àý0hð!À ý0 ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿóôöÞ I@ F¦ Iÿÿ@ÿÿ&+À¿¬ œ I!À!À!À!À!À  Â!"‚‘’å ÓHHÚ(ÿáÿâùFG(üHHÚ(d'@=à/ÐÐ ØÐR@H -:LaserWriter ChicagoNew YorkGenevaMonacoVenice San FranciscoN Helvetica NarrowTimes HelveticaCourierSymbol! Avant Garde"New Century Schlbk‚SantiagoI New Century Schlbk Italic‘B New Century Schlbk Bold’BI New Century Schlbk BoldItåcmmi8 ÓMT Extra„  €€ (Kþ(µ0&ö,-Wv´µ¶¿ÕÀà ê õ ÷   A B H I0€ K€ [€u€ \€6€ {€t¿€ }€Þ€ “ € ž Þ€ õ€ ¾€ é€ À€  Á ? E6310Department of PhysicsDepartment of Physics