init_annulus_dect Function

    function init_annulus_dect(pos, dir, layer, r1, r2, nbins, maxval, trackHistory) result(out)
        !! Initalise Annular detector

        !> Centre of detector
        type(vector),  intent(in) :: pos
        !> Normal of the detector
        type(vector),  intent(in) :: dir
        !> Layer ID
        integer,       intent(in) :: layer
        !> Inner radius
        real(kind=wp), intent(IN) :: r1
        !> Outer radius
        real(kind=wp), intent(IN) :: r2
        !> Number of bins in the detector
        integer,       intent(in) :: nbins
        !> Maximum value to store in bins
        real(kind=wp), intent(in) :: maxval
        !> Boolean on if to store photon's history prior to hitting the detector.
        logical,       intent(in) :: trackHistory

        type(annulus_dect) :: out

        out%pos = pos
        out%dir = dir
        out%layer = layer
        !extra bin for data beyond end of array
        out%nbins = nbins + 1
        out%r1 = r1
        out%r2 = r2
        allocate(out%data(out%nbins))
        out%data = 0.0_wp
        if(nbins == 0)then
            out%bin_wid = 1._wp
        else
            out%bin_wid = maxval / real(nbins, kind=wp)
        end if
        out%trackHistory = trackHistory

    end function init_annulus_dect