# Accession Number:

## AD0632284

# Title:

## EFFICIENT DETECTION OF LOW LEVELS OF RADIOACTIVITY IN SEAWATER

# Descriptive Note:

# Corporate Author:

## NAVAL RADIOLOGICAL DEFENSE LAB SAN FRANCISCO CA

# Personal Author(s):

# Report Date:

## 1966-05-20

# Pagination or Media Count:

## 26.0

# Abstract:

The problem of assaying radioactivity in the sea has been under study with a view to designing an optimum detector for gamma radiation spectra, with suitable statistical accuracy. The responses of a series of crystal detector spheres of radii from 0.1 cm to 15 cm, having unit intrinsic efficiency to gamma rays has been calculated for unit gamma emitter per unit volume. The principal result brought out is the large increase in counting rate as the solid angle of acceptance of the spheres for gamma radiation increases. With larger spheres the sample volume increases but gives a negligible increase in counting rate. Graphs are given for the series of spheres for energies between 0.137 Mev and 3. 6 Mev. A formula is given for the maximum counting rate for any size sphere under bombardment with any gamma ray energy. It can be used to estimate the size detector needed to count an emitter with required statistical accuracy, making allowance for intrinsic efficiency of the detector to gamma rays of a particular energy, and for any concentration of emitter. A procedure is outlined for selecting the particular isotope which has been activated by unit neutron fluence to obtain the maximum counting information in the shortest time. Differential counting of two isotopes over two different periods of time should give information on recency of activation.

# Descriptors:

# Subject Categories:

- Physical and Dynamic Oceanography
- Nuclear Instrumentation
- Radioactivity, Radioactive Wastes and Fission Products