KJM-FYS 5920 Lab Exercise 2 - Student Report

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KJM-FYS 5920 Lab Exercise 2 report (Autumn 2010):

Setting up a HPGe gamma-spectroscopy system

Participating students (authors): Tomas Kvalheim Eriksen, Alexander Mauring, Therese Renstrøm, Inger Eli Ruud, Pejman Mansouri Samani, Martin Ytre-Eide, Sindre Øvergaard.

Teachers: Prof. Jon Petter Omtvedt and Hilde-Therese Nyhus (lab assistant) 

University of Oslo 1st October 2010


(Written by: Jon Petter Omtvedt)

Detector and Preamplifier Signals

(Written by: Pejman)

Spectroscopy Amplifier Setup & Signals

(Written by: Martin)

ADC and MCA Setup

(Written by: Thomas)


([File:Oscilloscopy_01Oct2010-1-.jpg]) Bilde av 2 energitopper til Co-60

The electrical signal from the Ge-detector has now propagated through many components that has both shaped and enhanced the pulse. The energy of interest is of course that deposited by the gamma in the detector. The Gaussian-like pulse produced in the main amplifier will have an amplitude proportional to the gamma-energy.

The signals from the main amplifier are analysed by the ADC/MCA unit. Information from the MCA is received by the lab-computer in the form of a histogram; number of counts pr energy bin. We use the spectrum analysis program MAESTRO to look at the resulting spectra. Since the detector has a linear response, we have that:

E_gamma = a * ch + b                                    (1)

To determine the two unknowns, a and b, in (1) we need two equations. So we need two known gamma energies and their corresponding channel number. Co-60 has two prominent peaks, one at 1173 keV and one at 1332 keV. This radioactive isotope provides excellent calibration for energies in this region. In the spectrum we observed three strong peaks. The unknown peak appeared to come from the considerable concentration of K-40 in the concrete walls of the lab. Table of Isotopes gives one gamma energy for K-40, E_gamma = 1460 keV. This peak would correspond to the highest of the three detected peaks. We also tested this theory by removing the Co-60 source. The two peaks with the lower energy disappeared as expected. The reason why the background line was so strong, was that we did not shield the source with lead blocks. A rough calibration was performed with Co-60.( KLADD: bad at low E. one peak from Co-57(122keV). good sep in E. zero in zero. adjust energy pr channel. )

(Written by: Therese and Inger Eli )

Detector Performance

(Written by: Alexander and Sindre)


(Written by: )

Teachers Remarks