Low energy neutrons produce harmful biological effect in human body, although applying a neutron dosimeter can’t determine the absolute received dose but it can be useful in warning at infected situation. Designing a device to approximate the received dose is the purpose of this research. 3He used as a sphere thermal neutron detector with a radius of 5 cm encircled by a 10 cm radius of paraffin sphere. In order to estimate the received dose, after measuring the detector counts, the paraffin sphere replaced with ICRU one which contains soft tissues and dose equivalent determined as a desired output. The quantity that is measurable for neutron dosimeter is counts, so the necessity of finding an appropriate relation between counts and equivalent dose is obvious. Results on the energies below 1 MeV demonstrated the similarity of changing process of these two quantities, so they could be related to each other with an adequate factor. To find the best fit different factors considered and the smallest χ2 (goodness of fit) was 162533 due to a factor of about 7.5e8. To improve χ2 two covers of cadmium and gadolinium, separately, put around the detector and χ2 resulted from the new simulations were 32568 for cadmium cover and 4238 for gadolinium due to factors of 136388900 and 1.75e7, respectively. Then, gadolinium cover fits the curves of counts and equivalent dose in best way, so applying a simple detector lead us to estimate whole body equivalent dose.

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