# Fundamental-mode sources in approach-to-critical experiments

## Abstract

The 1/M method is commonly used in approach-to-critical experiments to ensure criticality safety. Ideally, a plot of 1/M versus amount of nuclear material or separation distance will be linear. However, the result is usually a curve. If the curve is concave up it is said to be conservative, since the critical mass is underestimated. However, it is possible for the curve to be non-conservative and overestimate the critical mass. This paper discusses one of the factors contributing to the shape of the 1/M curve and how it can be predicted and measured. Two source distributions, producing the same number of spontaneous fission neutrons, will not necessarily contribute equally towards the multiplication of a given system. For this reason equally sized units added during an approach-to-critical will have different effects on the multiplication of the system. A method of denoting the relative importance of source distributions is needed. One method is to compare any given source distribution to its equivalent fundamental-mode source distribution. An equivalent fundamental-mode source is an imaginary source distributed identically in space, energy, and angle to the fundamental-mode fission source that would produce the same neutron multiplication as the given source distribution. A factor, denoted as g* andmore »

- Authors:

- Publication Date:

- Research Org.:
- Los Alamos National Lab., NM (US)

- Sponsoring Org.:
- US Department of Energy (US)

- OSTI Identifier:
- 769001

- Report Number(s):
- LA-UR-00-2423

TRN: US0100684

- DOE Contract Number:
- W-7405-ENG-36

- Resource Type:
- Conference

- Resource Relation:
- Conference: ANS2000 Annual Meeting, San Diego, CA (US), 06/04/2000--06/08/2000; Other Information: PBD: 1 May 2000

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CRITICAL MASS; CRITICALITY; DISTRIBUTION; FISSION; NEUTRONS; SAFETY; SHAPE; SPONTANEOUS FISSION

### Citation Formats

```
Goda, J., and Busch, R.
```*Fundamental-mode sources in approach-to-critical experiments*. United States: N. p., 2000.
Web.

```
Goda, J., & Busch, R.
```*Fundamental-mode sources in approach-to-critical experiments*. United States.

```
Goda, J., and Busch, R. Mon .
"Fundamental-mode sources in approach-to-critical experiments". United States. https://www.osti.gov/servlets/purl/769001.
```

```
@article{osti_769001,
```

title = {Fundamental-mode sources in approach-to-critical experiments},

author = {Goda, J. and Busch, R.},

abstractNote = {The 1/M method is commonly used in approach-to-critical experiments to ensure criticality safety. Ideally, a plot of 1/M versus amount of nuclear material or separation distance will be linear. However, the result is usually a curve. If the curve is concave up it is said to be conservative, since the critical mass is underestimated. However, it is possible for the curve to be non-conservative and overestimate the critical mass. This paper discusses one of the factors contributing to the shape of the 1/M curve and how it can be predicted and measured. Two source distributions, producing the same number of spontaneous fission neutrons, will not necessarily contribute equally towards the multiplication of a given system. For this reason equally sized units added during an approach-to-critical will have different effects on the multiplication of the system. A method of denoting the relative importance of source distributions is needed. One method is to compare any given source distribution to its equivalent fundamental-mode source distribution. An equivalent fundamental-mode source is an imaginary source distributed identically in space, energy, and angle to the fundamental-mode fission source that would produce the same neutron multiplication as the given source distribution. A factor, denoted as g* and defined as the ratio of the fixed-source multiplication to the fundamental-mode multiplication, is used to relate a given source strength to its equivalent fundamental-mode source strength (Spriggs, et al., 1999).},

doi = {},

journal = {},

number = ,

volume = ,

place = {United States},

year = {2000},

month = {5}

}