# Exposure rate from thermal neutrons through water

• Phillyfan321
In summary, the task is to find the exposure rate 100cm beyond a 1cm thick water target that is being struck by a beam of thermal neutrons. The target is a round disk with a diameter of 20cm. The only relevant equation for this calculation is D(n,gamma) = 1.6e-13 (J/MeV) * Flux * Number of atoms * cross section of hydrogen * Energy gamma * AF. However, since the task is to find exposure rate, not dose rate, it would be necessary to create a secondary equation with the water disk as a disk source of radiation. To convert the dose rate value (in Gy/s) to something usable for calculating exposure rate, the energy value
Phillyfan321

## Homework Statement

A beam of thermal neutrons (10^12 neutrons per cm^2 second) strikes a 1cm thick water target normal to its surface. The target is a round disk with diameter 20cm. Find the exposure rate (R/second) 100cm beyond the water target (the middle of the disk) from only the 1H(n,gamma)2H reaction. Ignore attenuation in water and air. Atomic density is 6e23 atoms/gram.

## Homework Equations

The only real equation I know if for dose calculation, not exposure.

D(n,gamma) = 1.6e-13 (J/MeV) * Flux * Number atoms (given) * cross section of hydrogen * Energy gamma * AF

## The Attempt at a Solution

I can get a value for the dose rate created from the (n, gamma) reaction, but am unsure how to get exposure 100cm past that point. The above formula gives a Dose rate absorbed in the water shield (we often used water as a substitute for tissue anyway). Would it be logical to create a secondary equation with the water disk as a disk source of radiation that is irradiating the point 100 cm away from its center? If so, how would a number in Gy/s be converted back to something usable to calculate exposure.

Last edited:
Phillyfan321 said:
Would it be logical to create a secondary equation with the water disk as a disk source of radiation that is irradiating the point 100 cm away from its center?
I guess so. A point-like source might be a good approximation as 100 cm >> 10 cm.
Phillyfan321 said:
If so, how would a number in Gy/s be converted back to something usable to calculate exposure.
Don't calculate energy values - the formula you posted multiplies gamma photons per time with their energy, you can remove the energy part to get photons per time. Then you just have to take the distance into account.

## 1. What is the definition of exposure rate from thermal neutrons through water?

Exposure rate from thermal neutrons through water refers to the measure of the amount of radiation exposure a person receives when exposed to thermal neutrons that have passed through water. This is typically measured in units of milliroentgens per hour (mR/hr) or microsieverts per hour (μSv/hr).

## 2. How is exposure rate from thermal neutrons through water calculated?

The exposure rate from thermal neutrons through water is calculated by measuring the number of thermal neutrons that pass through a specific area in a given period of time. This measurement is then converted into units of radiation exposure (mR/hr or μSv/hr) using conversion factors specific to the type and energy of the radiation.

## 3. What factors can affect the exposure rate from thermal neutrons through water?

The exposure rate from thermal neutrons through water can be influenced by various factors such as the distance from the radiation source, the type and energy of the radiation, the thickness and composition of the water, and the shielding materials present in the surrounding environment.

## 4. How does exposure rate from thermal neutrons through water impact human health?

The exposure rate from thermal neutrons through water can potentially have harmful effects on human health. Exposure to high levels of radiation can damage cells and tissues, leading to acute or chronic health effects such as radiation sickness, increased risk of cancer, and genetic mutations.

## 5. Are there safety regulations in place for exposure rate from thermal neutrons through water?

Yes, there are safety regulations and guidelines set by organizations such as the International Commission on Radiological Protection and the Nuclear Regulatory Commission to limit the exposure rate from thermal neutrons through water to levels that are considered safe for human health. These regulations also require proper monitoring and control measures to be implemented in environments where exposure to thermal neutrons through water may occur.

Replies
5
Views
2K
Replies
12
Views
3K
Replies
1
Views
2K
Replies
1
Views
2K
Replies
1
Views
2K
Replies
4
Views
3K
Replies
2
Views
5K
Replies
3
Views
2K
Replies
5
Views
930
Replies
2
Views
3K