P6.5.5.4 Atomic and nuclear physics Nuclear physics γ spectroscopy Identifying and determining the activity of radioactive samples Description from CASSY Lab 2 For loading examples and settings, please use the CASSY Lab 2 help. CASSY Lab 2 (2012-09-27) by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved

CASSY Lab 2 Identifying and determining the activity of weakly radioactive samples can also be carried out with Pocket-CASSY Safety note When handling radioactive preparations, in addition to the radiation protection regulations, state-specific requirements and the regulations of the educational authorities are also to be observed, e.g. in the Federal Republic of Germany at the very least the radiation protection regulations (StrlSchV - Strahlenschutzverordnung) and the directives on safety during school lessons. This applies even in cases where the preparation used in this experiment in itself does not require the nomination of a trained radiation officer. Since the used preparations produce ionizing radiation, the following safety rules must nevertheless be kept to: Prevent access to the preparations by unauthorized persons. Before using the reparations make sure that they are intact. For the purpose of shielding, keep the preparations in their safety container. To ensure minimum exposure time and minimum activity, take the preparations out of the safety container only as long as is necessary for carrying out the experiment. To ensure maximum distance, hold the preparations only at the upper end of the metal holder. Experiment description The detection probability of the scintillation counter is determined at several γ energies with calibrating preparations. The γ spectrum of a weakly radioactive sample is recorded, and its radioactive components are determined. Equipment list 1 Sensor-CASSY 524 010 or 524 013 1 CASSY Lab 2 524 220 1 MCA box 524 058 2 Marinelli beakers 559 88 1 Calibrating preparation Cs-137, 5 kbq 559 885 by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved 329

CASSY Lab 2 4 Potassium chloride, 250 g 672 5210 1 Scintillation counter 559 901 1 Detector output stage 559 912 1 High-voltage power supply 1.5 kv 521 68 1 Scintillator screening 559 89 1 Socket for scintillator screening 559 891 1 PC with Windows XP/Vista/7 Experiment setup (see drawing) The output stage of the scintillation counter is connected to the MCA box and to the high-voltage power supply. The scintillation counter is mounted in the socket from above with the lead screening. The preparation in the Marinelli beaker is placed above the scintillation counter. Carrying out the experiment Load settings Fill 1 kg of potassium chloride into a Marinelli beaker and place it above the scintillation counter. Record the spectrum with varying the high voltage until the full range of measurement is covered. Remove the Marinelli beaker and insert the calibrating preparation Cs-137 Record the spectrum Make an energy calibration using the lines at 1460 kev and 662 kev in the two spectra. Remove the preparation Equally distribute the test substance in a Marinelli beaker, place the beaker above the scintillation counter, and record the spectrum of the sample. Make a background measurement without preparation. The measuring time should be equal to that with the sample. Evaluation The activities of potassium chloride (17 kbq/kg) and the Cs-137 calibrating preparation (approx. 5 kbq, see calibration certificate, mind the half-life) are known. From the integrated counting rate below the lines of the two spectra the detection probability of the scintillation counter at 1460 kev and 662 kev can be determined for this particular geometry. The background spectrum is subtracted from the spectrum of the sample. From the resulting spectrum and the previously determined detection probability the radioactive contamination of the sample can be determined. The observed energies enable the radiating isotope in the sample to be determined, and with the detection probabilities just determined, the quantity can be estimated. Remarks The NaI(Tl) crystal at the end of the scintillation counter is sensitive to mechanical damage. Be careful when inserting the Marinelli beakers and when setting up the lead screen. When making measurements with strongly radiating samples heed the display of the dead time and, if necessary, dilute the sample. by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved 330

P6.5.5.5 Atomic and nuclear physics Nuclear physics γ spectroscopy Recording a β spectrum with a scintillation counter Description from CASSY Lab 2 For loading examples and settings, please use the CASSY Lab 2 help. CASSY Lab 2 (2012-09-27) by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved

CASSY Lab 2 Recording a β spectrum using a scintillation counter can also be carried out with Pocket-CASSY Safety note When handling radioactive preparations, in addition to the radiation protection regulations, state-specific requirements and the regulations of the educational authorities are also to be observed, e.g. in the Federal Republic of Germany at the very least the radiation protection regulations (StrlSchV - Strahlenschutzverordnung) and the directives on safety during school lessons. The preparations used in this experiment are type approved according to StrlSchV (2001) or they are below the exemption limit and do not require approval. For this reason handling without express permission is possible. Since the used preparations produce ionizing radiation, the following safety rules must nevertheless be kept to: Prevent access to the preparations by unauthorized persons. Before using the reparations make sure that they are intact. For the purpose of shielding, keep the preparations in their safety container. To ensure minimum exposure time and minimum activity, take the preparations out of the safety container only as long as is necessary for carrying out the experiment. To ensure maximum distance, hold the preparations only at the upper end of the metal holder. Experiment description The β spectrum of Sr-90 is recorded with a scintillation counter. The energy loss per path length de/dx of the β particles in aluminum is measured. Equipment list 1 Sensor-CASSY 524 010 or 524 013 1 CASSY Lab 2 524 220 1 MCA box 524 058 1 Set of radioactive preparations 559 835 1 Na-22 preparation 559 865 by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved 331

CASSY Lab 2 1 Set of absorbers and targets 559 94 1 Scintillation counter 559 901 1 Detector output stage 559 912 1 High-voltage power supply 1.5 kv 521 68 1 Scintillator screening 559 89 1 Socket for scintillator screening 559 891 1 Stand rod, 47 cm 300 42 1 Leybold multiclamp 301 01 1 Universal clamp, 0...80 mm 666 555 1 PC with Windows XP/Vista/7 Experiment setup (see drawing) The output stage of the scintillation counter is connected to the MCA box and to the high-voltage power supply. The scintillation counter is mounted in the socket from above with the lead screening. The acrylic glass tube is put over the scintillation counter within the lead screening. The preparation is place a few centimeters above the scintillation counter with stand material. The absorber plates are laid on the acrylic glass tube so that they are located between the detector and the preparation. Carrying out the experiment Load settings Mount the Sr-90 preparation, and record the spectrum with. Set the high voltage so that the spectrum is not cut off on the right side. For the energy calibration, mount the Na-22 preparation, and calibrate the energy axis with the 511 kev and the 1275 kev line. The Sr-90 spectrum extends to approx. 2000 kev. It is recommendable to determine the background without preparation. Mount the Sr-90 preparation once more, and see to it that there is enough space for the absorbers. One after another record the spectra without absorber, with a 0.5 mm thick aluminum absorber, 1 mm aluminum, and so on up to 3 mm aluminum. Evaluation The aluminum absorber reduces the maximum energy of the electron reaching the detector. The highest energy of each Sr-90 spectrum at which electrons are detected is determined. These energies are compiled in a table together with the corresponding thickness of the absorber. The slope of the regression line gives the energy loss per path length de/dx, which, in this case, amounts to about 400 450 kev/mm. by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved 332

P6.5.5.6 Atomic and nuclear physics Nuclear physics γ spectroscopy Coincidence and γ-γ angular correlation in positron decay Description from CASSY Lab 2 For loading examples and settings, please use the CASSY Lab 2 help. CASSY Lab 2 (2012-09-27) by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved

CASSY Lab 2 Coincidence and γ-γ angular correlation in positron decay Safety note When handling radioactive preparations, in addition to the radiation protection regulations, state-specific requirements and the regulations of the educational authorities are also to be observed, e.g. in the Federal Republic of Germany at the very least the radiation protection regulations (StrlSchV - Strahlenschutzverordnung) and the directives on safety during school lessons. The preparations used in this experiment are type approved according to StrlSchV (2001) or they are below the exemption limit and do not require approval. For this reason handling without express permission is possible. Since the used preparations produce ionizing radiation, the following safety rules must nevertheless be kept to: Prevent access to the preparations by unauthorized persons. Before using the reparations make sure that they are intact. For the purpose of shielding, keep the preparations in their safety container. To ensure minimum exposure time and minimum activity, take the preparations out of the safety container only as long as is necessary for carrying out the experiment. To ensure maximum distance, hold the preparations only at the upper end of the metal holder. Experiment description The spatial coincidence of the two γ quanta in electron-positron pair annihilation is demonstrated. The conservation of momentum requires emission of the two quanta at an angle of 180, which is visualized in the experiment. Selective measurement of a coincidence spectrum leads to the suppression of non-correlated lines. Equipment list 1 Sensor-CASSY 524 010 or 524 013 by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved 337

CASSY Lab 2 1 CASSY Lab 2 524 220 2 MCA boxes 524 058 1 Na-22 preparation 559 865 1 Set of 3 radioactive preparations 559 835 or 559 845 2 Scintillation counters 559 901 2 Detector output stages 559 912 2 High-voltage power supplies 1.5 kv 521 68 2 Sockets for scintillator screening 559 891 1 Stand rod, 47 cm 300 42 1 Leybold multiclamp 301 01 1 Universal clamp, 0...80 mm 666 555 1 PC with Windows XP/Vista/7 Experiment setup (see drawing) The output stages of the scintillation counters are connected to the MCA boxes and to the high-voltage power supplies. Both MCA boxes must be plugged in the same CASSY. The preparation is placed near one scintillation counter with the stand material so that the other detector can be moved around the setup, in order that the angle detector 1 - preparation - detector 2 can be varied. Carrying out the experiment Load settings Select the display Energy calibration Use the two detectors to record the normal Na-22 spectrum each with In the Settings NA calibrate input A, and in the Settings NB calibrate the detector at input B Select the display 511 kev In the Settings NA set the measurement to the Coincidence trigger for the other box and adjust the coincidence window to the 511 kev line (mark with two vertical lines) Place the movable detector so that the preparation is located between the detectors. Record the coincidence spectrum with. Place the movable detector so that it is located perpendicularly to the connecting line preparation - other detector. Record the coincidence spectrum with. Select the display 1275 kev In the Settings NA set the coincidence window to the 1275 kev line (reset the old window by pressing 0 and mark the new window by means of two vertical lines) Record the coincidence spectrum at 180 and at 90 each with. Select the display Cs-137 and Na-22 In the Settings NA set the coincidence window to the 511 kev line (reset the old window by pressing 0 and mark the new window by means of two vertical lines) Fix the Cs-137 preparation together with the Na-22 preparation between the detectors, place the movable detector so that the preparations are located between the detectors. Record the coincidence spectrum with. Record the normal MCA spectrum of this arrangement. Evaluation The normal Na-22 spectrum consists of a line at 1275 kev and the pair annihilation radiation at 511 kev. The two 511 kev quanta are correlated in time and space (emission under 180 ). The 1275 kev quanta are correlated with the 511 kev quanta in time as the delay of 3.7 ps cannot be detected with this setup. This emission is not correlated in space. In the normal MCA spectrum both lines are visible. At 180 coincidence, the 511 kev line clearly stands out because the other components of the spectrum (1275 kev line, Compton distribution) are correlated in time only and not in space so they are weakened by the solid angle of the second detector relative to the 511 kev line, which is correlated in space. Thereby the absolute counting rate of the 511 kev line drop according to the detection probability of the second detector. If the detector is swivelled out of the 180 direction, the 511 kev line disappears, whereas those components that are not correlated in space remain unchanged. If the measurement is made in coincidence to the 1275 kev line, there is no correlation in space. Therefore the spectra look the same at different angles. Since there is only one 1275 kev quantum per decay, no 1275 kev line is observed in coincidence. In order to show the suppression of quanta that are not correlated in time, two preparations are used at the same time. Cs-137 provides a non-correlated background, which is only visible in the coincidence measurement because of accidental coincidence, whereas it is clearly visible without coincidence measurement. by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved 338

CASSY Lab 2 Remark The time window for coincidences has a fixed default value of 4 μs. by LD DIDACTIC GmbH Leyboldstrasse 1 D-50354 Huerth www.ld-didactic.com Phone: +49-2233-604-0 Fax: +49-2233-604-222 E-mail: info@ld-didactic.de Technical alterations reserved 339