docs: def calculate_trans(thickness_cm: np.float, miu_per_cm: np.array):
      """calculate the transmission signal using the formula
  
      transmission = exp( - thickness_cm * atoms_per_cm3 * 1e-24 * sigma_b)
  
      Parameters:
      ===========
      thickness: float (in cm)
      atoms_per_cm3: float (number of atoms per cm3 of element/isotope)
      sigma_b: np.array of sigma retrieved from database
  
      Returns:
      ========
      transmission array
      """
      transmission = np.exp(-thickness_cm * miu_per_cm)
      return np.array(transmission)