Thursday, 14 November 2019, 2:33 PM
Site: The Science Portal: 21C Science with Style
Course: The Science Portal: 21C Science with Style (21CScience)
Glossary: IB Physics Glossary
B

#### Bacquerel

, Bq, is the SI unit of activity for radioactive sources. It is equivalent to a count or disintegration per second. The activity is measured, typically, with a Geiger-Muller (GM) tube.

#### Beta decay

$^A_ZX \rightarrow~{}^{A}_{Z+1}Y + ^{0}_{-1}\beta + ^{0}_{0}\bar{\nu}$

or

$^A_ZX \rightarrow~{}^{A}_{Z+1}Y + ^{0}_{-1}e + ^{0}_{0}\bar{\nu}$.

Where X is the parent nucleus, Y is the daughter nucleus, A is the number of nucleons and Z is the number of protons.
An example decay is
$^{90}_{38}Sr \rightarrow~{}^{90}_{39}Y + ^{0}_{-1}\beta + ^{0}_{0}\bar{\nu}$.

Properties of beta particles include
• continuous energy spectrum
• -1 charge
• relatively light
• moderately ionizing
• moderate range in air (cm to m)/medium penetration
• can be blocked by a few mm of aluminum or thin lead sheets
• deflected by magnetic-fields and electric-fields (in direction opposite to alpha particles)

#### Binary to decimal conversion

for a five bit-number
$b_4 b_3 b_2 b_1 b_0$

the decimal equivalent is

$b_4 \times 2^4 + b_3 \times 2^3 + b_2 \times 2^2 + b_1 \times 2^1 + b_0 \times 2^0$.

An example is the binary number $10101$ which in decimal is

$1 \times 2^4 + 0 \times 2^3 + 1 \times 2^2 + 0 \times 2^1 + 1 \times 2^0 = 21$.

#### Binding energy

is the energy required to assemble a nucleus or to separate the nucleus into its individual components/nucleons. (d)

The binding energy per nucleon is the total binding energy for a particular nucleus divided by the number of nucleons contained in the nucleus.

For energy to be released in a nuclear reaction, fusion or fission, the binding energy must increase.

Image taken from http://www.smsec.com/en/nucl/07_1.htm

#### Blind spot

is a region where the optical nerve leaves the retina which does not contain rods or cones.

#### Brewster's law

When the angle of incidence equals Brewster's angle, the reflected and the refracted rays are perpendicular to each other. The reflected ray becomes completely horizontally plane-polarized.

$n=\tan \phi$