# Exorbitant number of counts per sec. in the Rutherford Experiment

May someone kindly advise on the Rutherford experiment? I have created a Gaussian of dP$_0$/$\Delta$$\theta(\theta), where P_0 is the number of counts of alpha particles through a 1.05X19.86 mm slit divided by the time elapsed and \Delta$$\theta$($\theta$) is the angular width of the detector. At this stage the Au foil was not used, as this was merely the "background" measurement. I have integrated that Gaussian wrt $\theta$ between $-\infty$ and $+\infty$ to obtain the total P$_0$. However, this yielded a total P$_0$ equal to 24,000 counts/sec, which seems exorbitant and wrong. I'd be indebted for any help trying to figure out where the mistake is!

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There isn't really much to go on here. How did you get your result? What is the known strength of the beam? Large numbers are everywhere in physics - what seems so wrong about this one? – Chris White Jan 9 '14 at 7:18
Well, first of all, when used further in the experiment it seems to yield a wrong value for the expected $d\sigma$/d$\Omega$. Moreover, it is unlikely that without the Au leaf and at very small angles the number of counts/second would be that high! Let's examine for instance the readings I obtained for the angle $\theta$=0: number of counts - 1072; time elapsed - 14.1 sec; P0=1072/14.1=76.028 [1/sec]; Δθ = width of slit/distance between source and detector = 1.05mm/44mm = 0.02386; P0/Δθ = 3186.436 [1/sec]. There seems to be something wrong here. Possibly with the evaluation of $\Delta$$\theta$ – peripatein Jan 9 '14 at 7:22
But I am not sure exactly what's erroneous. I'd appreciate some help figuring out the source of the error. – peripatein Jan 9 '14 at 7:24
Couple of questions. First, do you know how strong the source is in absolute activity? Remember that $1 \,\mathrm{\mu Cu}$ is still $4 \times 10^4\,\mathrm{Bq}$ and that if you want to measure the rate are high scattering angles you are going to need a considerable rate or a long counting time. Second, how much rate does your data acquisition system register in the absence of the source? That is, are you sure you have your thresholds high enough? – dmckee Jan 9 '14 at 15:59
And as I commented on your previous question about the experiment you are not giving enough detail. Experimental question often turn on the little things. Don't draw a fuzzy word picture, give us a diagram. – dmckee Jan 9 '14 at 16:02